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Nano-Optics and Biophotonics

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Detection of a plasmon-polariton quantum wave packet. Pres, Sebastian; Huber, Bernhard; Hensen, Matthias; Fersch, Daniel; Schatz, Enno; Friedrich, Daniel; Lisinetskii, Victor; Pompe, Ruben; Hecht, Bert; Pfeiffer, Walter; Brixner, Tobias. In Nature Physics. Springer Science and Business Media {LLC}, 2023.
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Plasmon polaritons (plasmons, for simplicity) have become paramount for tailored nanoscale light–matter interaction, and extensive research has been conducted to monitor and manipulate their spatial3 and spatio-temporal dynamics. These dynamics result from the superposition of various plasmon modes, which are classical wave packets. Beyond this classical picture, plasmon modes are treated as quasiparticles and they are considered essential for the realization of future nanoscale quantum functionality. Implementing and demonstrating such functionality requires access to the quasiparticle’s quantum state to monitor and manipulate its corresponding quantum wave packet dynamics in Hilbert space. Here we report the local detection of nanoscale plasmon quantum wave packets using plasmon-assisted electron emission as a signal in coherent two-dimensional nanoscopy. The observation of a quantum coherence oscillating at the third harmonic of the plasmon frequency is traced back to the superposition of energetically non-adjacent plasmon occupation number states and is therefore a direct fingerprint of the quantum wave packet. Beyond demonstrating the existence of a plasmon quantum wave packet via the coherence between certain occupation number states and providing an improved model for plasmon-assisted electron emission processes, the results may enable time-dependent probing and manipulation of coupled quantum states and dynamics on the nanoscale.

@article{Pres_2023, abstract = {Plasmon polaritons (plasmons, for simplicity) have become paramount for tailored nanoscale light–matter interaction, and extensive research has been conducted to monitor and manipulate their spatial3 and spatio-temporal dynamics. These dynamics result from the superposition of various plasmon modes, which are classical wave packets. Beyond this classical picture, plasmon modes are treated as quasiparticles and they are considered essential for the realization of future nanoscale quantum functionality. Implementing and demonstrating such functionality requires access to the quasiparticle’s quantum state to monitor and manipulate its corresponding quantum wave packet dynamics in Hilbert space. Here we report the local detection of nanoscale plasmon quantum wave packets using plasmon-assisted electron emission as a signal in coherent two-dimensional nanoscopy. The observation of a quantum coherence oscillating at the third harmonic of the plasmon frequency is traced back to the superposition of energetically non-adjacent plasmon occupation number states and is therefore a direct fingerprint of the quantum wave packet. Beyond demonstrating the existence of a plasmon quantum wave packet via the coherence between certain occupation number states and providing an improved model for plasmon-assisted electron emission processes, the results may enable time-dependent probing and manipulation of coupled quantum states and dynamics on the nanoscale.}, author = {Pres, Sebastian and Huber, Bernhard and Hensen, Matthias and Fersch, Daniel and Schatz, Enno and Friedrich, Daniel and Lisinetskii, Victor and Pompe, Ruben and Hecht, Bert and Pfeiffer, Walter and Brixner, Tobias}, journal = {Nature Physics}, keywords = {wave}, month = {02}, publisher = {Springer Science and Business Media {LLC}}, title = {Detection of a plasmon-polariton quantum wave packet}, year = 2023 }

%0 Journal Article %1 Pres_2023 %A Pres, Sebastian %A Huber, Bernhard %A Hensen, Matthias %A Fersch, Daniel %A Schatz, Enno %A Friedrich, Daniel %A Lisinetskii, Victor %A Pompe, Ruben %A Hecht, Bert %A Pfeiffer, Walter %A Brixner, Tobias %D 2023 %I Springer Science and Business Media {LLC} %J Nature Physics %R 10.1038/s41567-022-01912-5 %T Detection of a plasmon-polariton quantum wave packet %U https://doi.org/10.1038%2Fs41567-022-01912-5 %X Plasmon polaritons (plasmons, for simplicity) have become paramount for tailored nanoscale light–matter interaction, and extensive research has been conducted to monitor and manipulate their spatial3 and spatio-temporal dynamics. These dynamics result from the superposition of various plasmon modes, which are classical wave packets. Beyond this classical picture, plasmon modes are treated as quasiparticles and they are considered essential for the realization of future nanoscale quantum functionality. Implementing and demonstrating such functionality requires access to the quasiparticle’s quantum state to monitor and manipulate its corresponding quantum wave packet dynamics in Hilbert space. Here we report the local detection of nanoscale plasmon quantum wave packets using plasmon-assisted electron emission as a signal in coherent two-dimensional nanoscopy. The observation of a quantum coherence oscillating at the third harmonic of the plasmon frequency is traced back to the superposition of energetically non-adjacent plasmon occupation number states and is therefore a direct fingerprint of the quantum wave packet. Beyond demonstrating the existence of a plasmon quantum wave packet via the coherence between certain occupation number states and providing an improved model for plasmon-assisted electron emission processes, the results may enable time-dependent probing and manipulation of coupled quantum states and dynamics on the nanoscale.
Anticrossing of a plasmonic nanoresonator mode and a single quantum dot at room temperature. Friedrich, Daniel; Qin, Jin; Schurr, Benedikt; Tufarelli, Tommaso; Groß, Heiko; Hecht, Bert. 2023.

cite arxiv:2305.06909
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Room-temperature strong coupling of a single quantum emitter and a single resonant plasmonic mode is a key resource for quantum information processing and quantum sensing at ambient conditions. To beat dephasing, ultrafast energy transfer is achieved by coupling single emitters to a plasmonic nanoresonator with an extremely small mode volume and optimal spectral overlap. Typically, normal mode splittings in luminescence spectra of single-emitter strongly-coupled systems are provided as evidence for strong coupling and to obtain rough estimates of the light-matter coupling strength g. However, a complete anticrossing of a single emitter and a cavity mode as well as the characterization of the uncoupled constituents is usually hard to achieve. Here, we exploit the light-induced oxygen-dependent blue-shift of individual CdSe/ZnS semiconductor quantum dots to tune their transition energy across the resonance of a scanning plasmonic slit resonator after characterizing both single emitter and nano resonator in their uncoupled states. Our results provide clear proof of single-emitter strong light-matter coupling at ambient condition as well as a value for the Rabi splitting at zero detuning 100 meV, consistent with modeling, thereby opening the path towards plexitonic devices that exploit single-photon nonlinearities at ambient conditions.

@article{friedrich2023anticrossing, abstract = {Room-temperature strong coupling of a single quantum emitter and a single resonant plasmonic mode is a key resource for quantum information processing and quantum sensing at ambient conditions. To beat dephasing, ultrafast energy transfer is achieved by coupling single emitters to a plasmonic nanoresonator with an extremely small mode volume and optimal spectral overlap. Typically, normal mode splittings in luminescence spectra of single-emitter strongly-coupled systems are provided as evidence for strong coupling and to obtain rough estimates of the light-matter coupling strength g. However, a complete anticrossing of a single emitter and a cavity mode as well as the characterization of the uncoupled constituents is usually hard to achieve. Here, we exploit the light-induced oxygen-dependent blue-shift of individual CdSe/ZnS semiconductor quantum dots to tune their transition energy across the resonance of a scanning plasmonic slit resonator after characterizing both single emitter and nano resonator in their uncoupled states. Our results provide clear proof of single-emitter strong light-matter coupling at ambient condition as well as a value for the Rabi splitting at zero detuning 100 meV, consistent with modeling, thereby opening the path towards plexitonic devices that exploit single-photon nonlinearities at ambient conditions.}, author = {Friedrich, Daniel and Qin, Jin and Schurr, Benedikt and Tufarelli, Tommaso and Groß, Heiko and Hecht, Bert}, keywords = {plasmon}, note = {cite arxiv:2305.06909}, title = {Anticrossing of a plasmonic nanoresonator mode and a single quantum dot at room temperature}, year = 2023 }

%0 Journal Article %1 friedrich2023anticrossing %A Friedrich, Daniel %A Qin, Jin %A Schurr, Benedikt %A Tufarelli, Tommaso %A Groß, Heiko %A Hecht, Bert %D 2023 %T Anticrossing of a plasmonic nanoresonator mode and a single quantum dot at room temperature %U http://arxiv.org/abs/2305.06909 %X Room-temperature strong coupling of a single quantum emitter and a single resonant plasmonic mode is a key resource for quantum information processing and quantum sensing at ambient conditions. To beat dephasing, ultrafast energy transfer is achieved by coupling single emitters to a plasmonic nanoresonator with an extremely small mode volume and optimal spectral overlap. Typically, normal mode splittings in luminescence spectra of single-emitter strongly-coupled systems are provided as evidence for strong coupling and to obtain rough estimates of the light-matter coupling strength g. However, a complete anticrossing of a single emitter and a cavity mode as well as the characterization of the uncoupled constituents is usually hard to achieve. Here, we exploit the light-induced oxygen-dependent blue-shift of individual CdSe/ZnS semiconductor quantum dots to tune their transition energy across the resonance of a scanning plasmonic slit resonator after characterizing both single emitter and nano resonator in their uncoupled states. Our results provide clear proof of single-emitter strong light-matter coupling at ambient condition as well as a value for the Rabi splitting at zero detuning 100 meV, consistent with modeling, thereby opening the path towards plexitonic devices that exploit single-photon nonlinearities at ambient conditions.
Direct electrical modulation of surface response in a single plasmonic nanoresonator. Zurak, Luka; Wolff, Christian; Meier, Jessica; Kullock, René; Mortensen, N. Asger; Hecht, Bert; Feichtner, Thorsten. 2023.

cite arxiv:2307.01423Comment: 10 pages, 3 figures, 15 pages Supplementary
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Classical electrodynamics describes the optical response of macroscopic systems, where the boundaries between materials is treated as infinitesimally thin. However, due to the quantum nature of electrons, interfaces acquires a finite thickness. To include non-classical surface effects in the framework of Maxwell's equations, surface-response functions can be introduced, also known as Feibelman $d$-parameters. Surface response impacts systems with strong field localization at interfaces, which is encountered in noble metal nanoparticles supporting surface plasmon polaritons. However, studying surface response is challenging as it necessitates sub-nanometer control of geometric features, e.g. the gap size in a dimer antenna, while minimizing uncertainties in morphology. In contrast, electrical gating is convenient since the static screening charges are confined exclusively to the surface, which alleviates the need for precise control over the morphology. Here, we study the perturbation of Feibelman $d$-parameters by direct electric charging of a single plasmonic nanoresonator and investigate the resulting changes of the resonance in experiment and theory. The measured change of the resonance frequency matches the theory by assuming a perturbation of the tangential surface current. However, we also observe an unforeseen narrowing in the resonance width when adding electrons to the surface of a plasmonic nanoresonator. These reduced losses cannot be explained by electron spill-out within the local-response approximation (LRA). Such an effect is likely caused by nonlocality and the anisotropy of the perturbed local permittivity. Our findings open up possibilities to reduce losses in plasmonic resonators and to develop ultrafast and extremely small electrically driven plasmonic modulators and metasurfaces by leveraging electrical control over non-classical surface effects.

@misc{zurak2023direct, abstract = {Classical electrodynamics describes the optical response of macroscopic systems, where the boundaries between materials is treated as infinitesimally thin. However, due to the quantum nature of electrons, interfaces acquires a finite thickness. To include non-classical surface effects in the framework of Maxwell's equations, surface-response functions can be introduced, also known as Feibelman $d$-parameters. Surface response impacts systems with strong field localization at interfaces, which is encountered in noble metal nanoparticles supporting surface plasmon polaritons. However, studying surface response is challenging as it necessitates sub-nanometer control of geometric features, e.g. the gap size in a dimer antenna, while minimizing uncertainties in morphology. In contrast, electrical gating is convenient since the static screening charges are confined exclusively to the surface, which alleviates the need for precise control over the morphology. Here, we study the perturbation of Feibelman $d$-parameters by direct electric charging of a single plasmonic nanoresonator and investigate the resulting changes of the resonance in experiment and theory. The measured change of the resonance frequency matches the theory by assuming a perturbation of the tangential surface current. However, we also observe an unforeseen narrowing in the resonance width when adding electrons to the surface of a plasmonic nanoresonator. These reduced losses cannot be explained by electron spill-out within the local-response approximation (LRA). Such an effect is likely caused by nonlocality and the anisotropy of the perturbed local permittivity. Our findings open up possibilities to reduce losses in plasmonic resonators and to develop ultrafast and extremely small electrically driven plasmonic modulators and metasurfaces by leveraging electrical control over non-classical surface effects.}, author = {Zurak, Luka and Wolff, Christian and Meier, Jessica and Kullock, René and Mortensen, N. Asger and Hecht, Bert and Feichtner, Thorsten}, keywords = {plasmon}, note = {cite arxiv:2307.01423Comment: 10 pages, 3 figures, 15 pages Supplementary}, title = {Direct electrical modulation of surface response in a single plasmonic nanoresonator}, year = 2023 }

%0 Generic %1 zurak2023direct %A Zurak, Luka %A Wolff, Christian %A Meier, Jessica %A Kullock, René %A Mortensen, N. Asger %A Hecht, Bert %A Feichtner, Thorsten %D 2023 %T Direct electrical modulation of surface response in a single plasmonic nanoresonator %U http://arxiv.org/abs/2307.01423 %X Classical electrodynamics describes the optical response of macroscopic systems, where the boundaries between materials is treated as infinitesimally thin. However, due to the quantum nature of electrons, interfaces acquires a finite thickness. To include non-classical surface effects in the framework of Maxwell's equations, surface-response functions can be introduced, also known as Feibelman $d$-parameters. Surface response impacts systems with strong field localization at interfaces, which is encountered in noble metal nanoparticles supporting surface plasmon polaritons. However, studying surface response is challenging as it necessitates sub-nanometer control of geometric features, e.g. the gap size in a dimer antenna, while minimizing uncertainties in morphology. In contrast, electrical gating is convenient since the static screening charges are confined exclusively to the surface, which alleviates the need for precise control over the morphology. Here, we study the perturbation of Feibelman $d$-parameters by direct electric charging of a single plasmonic nanoresonator and investigate the resulting changes of the resonance in experiment and theory. The measured change of the resonance frequency matches the theory by assuming a perturbation of the tangential surface current. However, we also observe an unforeseen narrowing in the resonance width when adding electrons to the surface of a plasmonic nanoresonator. These reduced losses cannot be explained by electron spill-out within the local-response approximation (LRA). Such an effect is likely caused by nonlocality and the anisotropy of the perturbed local permittivity. Our findings open up possibilities to reduce losses in plasmonic resonators and to develop ultrafast and extremely small electrically driven plasmonic modulators and metasurfaces by leveraging electrical control over non-classical surface effects.
Site-selective functionalization of in-plane nanoelectrode-antennas. Ochs, Maximilian; Jucker, Laurent; Rödel, Maximilian; Emmerling, Monika; Kullock, René; Pflaum, Jens; Mayor, Marcel; Hecht, Bert. In Nanoscale, 15(11), pp. 5249–5256. The Royal Society of Chemistry, 2023.
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Stacked organic optoelectronic devices make use of electrode materials with different work functions{,} leading to efficient large area light emission. In contrast{,} lateral electrode arrangements offer the possibility to be shaped as resonant optical antennas{,} radiating light from subwavelength volumes. However{,} tailoring electronic interface properties of laterally arranged electrodes with nanoscale gaps - to e.g. optimize charge-carrier injection - is rather challenging{,} yet crucial for further development of highly efficient nanolight sources. Here{,} we demonstrate site-selective functionalization of laterally arranged micro- and nanoelectrodes by means of different self-assembled monolayers. Upon applying an electric potential across nanoscale gaps{,} surface-bound molecules are removed selectively from specific electrodes by oxidative desorption. Kelvin-probe force microscopy as well as photoluminescence measurements are employed to verify the success of our approach. Moreover{,} we obtain asymmetric current–voltage characteristics for metal–organic devices in which just one of the electrodes is coated with 1-octadecanethiol; further demonstrating the potential to tune interface properties of nanoscale objects. Our technique paves the way for laterally arranged optoelectronic devices based on selectively engineered nanoscale interfaces and in principle enables molecular assembly with defined orientation in metallic nano-gaps.

@article{D2NR06343C, abstract = {Stacked organic optoelectronic devices make use of electrode materials with different work functions{,} leading to efficient large area light emission. In contrast{,} lateral electrode arrangements offer the possibility to be shaped as resonant optical antennas{,} radiating light from subwavelength volumes. However{,} tailoring electronic interface properties of laterally arranged electrodes with nanoscale gaps - to e.g. optimize charge-carrier injection - is rather challenging{,} yet crucial for further development of highly efficient nanolight sources. Here{,} we demonstrate site-selective functionalization of laterally arranged micro- and nanoelectrodes by means of different self-assembled monolayers. Upon applying an electric potential across nanoscale gaps{,} surface-bound molecules are removed selectively from specific electrodes by oxidative desorption. Kelvin-probe force microscopy as well as photoluminescence measurements are employed to verify the success of our approach. Moreover{,} we obtain asymmetric current–voltage characteristics for metal–organic devices in which just one of the electrodes is coated with 1-octadecanethiol; further demonstrating the potential to tune interface properties of nanoscale objects. Our technique paves the way for laterally arranged optoelectronic devices based on selectively engineered nanoscale interfaces and in principle enables molecular assembly with defined orientation in metallic nano-gaps.}, author = {Ochs, Maximilian and Jucker, Laurent and Rödel, Maximilian and Emmerling, Monika and Kullock, René and Pflaum, Jens and Mayor, Marcel and Hecht, Bert}, journal = {Nanoscale}, keywords = {plasmon}, number = 11, pages = {5249-5256}, publisher = {The Royal Society of Chemistry}, title = {Site-selective functionalization of in-plane nanoelectrode-antennas}, volume = 15, year = 2023 }

%0 Journal Article %1 D2NR06343C %A Ochs, Maximilian %A Jucker, Laurent %A Rödel, Maximilian %A Emmerling, Monika %A Kullock, René %A Pflaum, Jens %A Mayor, Marcel %A Hecht, Bert %D 2023 %I The Royal Society of Chemistry %J Nanoscale %N 11 %P 5249-5256 %R 10.1039/D2NR06343C %T Site-selective functionalization of in-plane nanoelectrode-antennas %U http://dx.doi.org/10.1039/D2NR06343C %V 15 %X Stacked organic optoelectronic devices make use of electrode materials with different work functions{,} leading to efficient large area light emission. In contrast{,} lateral electrode arrangements offer the possibility to be shaped as resonant optical antennas{,} radiating light from subwavelength volumes. However{,} tailoring electronic interface properties of laterally arranged electrodes with nanoscale gaps - to e.g. optimize charge-carrier injection - is rather challenging{,} yet crucial for further development of highly efficient nanolight sources. Here{,} we demonstrate site-selective functionalization of laterally arranged micro- and nanoelectrodes by means of different self-assembled monolayers. Upon applying an electric potential across nanoscale gaps{,} surface-bound molecules are removed selectively from specific electrodes by oxidative desorption. Kelvin-probe force microscopy as well as photoluminescence measurements are employed to verify the success of our approach. Moreover{,} we obtain asymmetric current–voltage characteristics for metal–organic devices in which just one of the electrodes is coated with 1-octadecanethiol; further demonstrating the potential to tune interface properties of nanoscale objects. Our technique paves the way for laterally arranged optoelectronic devices based on selectively engineered nanoscale interfaces and in principle enables molecular assembly with defined orientation in metallic nano-gaps.
Evolutionary Optimized, Monocrystalline Gold Double Wire Gratings as a SERS Sensing Platform. Sweedan, Amro; Pavan, Mariela J.; Schatz, Enno; Maaß, Henriette; Tsega, Ashageru; Tzin, Vered; Höflich, Katja; Mörk, Paul; Feichtner, Thorsten; Bashouti, Muhammad Y. 2023.

cite arxiv:2308.01395Comment: 22 pages, 6 Figures, 12 pages Supplementary
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Achieving reliable and quantifiable performance in large-area surface-enhanced Raman spectroscopy (SERS) substrates has long been a formidable challenge. It requires substantial signal enhancement while maintaining a reproducible and uniform response. Conventional SERS substrates are typically made of inhomogeneous materials with random resonator geometries and distributions. As a result, they exhibit several or broadened plasmonic resonances, undesired absorptive losses, and inhomogeneous field enhancement. These limitations diminish the signal strength and hamper reproducibility, making it difficult to conduct comparative studies with high sensitivity. In this study, we propose an approach that utilizes monocrystalline gold flakes to fabricate well-defined gratings composed of plasmonic double-wire resonators, which are fabricated through focused ion-beam lithography. The geometry of the double wire grating substrate (DWGS) was evolutionary optimized to achieve efficient enhancement for both excitation and emission processes. The use of monocrystalline material minimizes absorption losses while enhancing the shape fidelity during the nanofabrication process. The DWGS shows notable reproducibility (RSD=6.6%), repeatability (RSD=5.6%), and large-area homogeneity over areas $>10^4\,\mu$m$^2$. Moreover, it provides a SERS enhancement factor of $\approx 10^6$ for 4-Aminothiophenol (4-ATP) analyte and detection capability for sub-monolayer coverage. The DWGS demonstrates reusability, as well as long-term stability on the shelf. Experimental validation with various analytes, in different states of matter, including biological macromolecules, confirms the sensitive and reproducible nature of DWGSs, thereby establishing them as a promising SERS substrate design for future sensing applications.

@misc{sweedan2023evolutionary, abstract = {Achieving reliable and quantifiable performance in large-area surface-enhanced Raman spectroscopy (SERS) substrates has long been a formidable challenge. It requires substantial signal enhancement while maintaining a reproducible and uniform response. Conventional SERS substrates are typically made of inhomogeneous materials with random resonator geometries and distributions. As a result, they exhibit several or broadened plasmonic resonances, undesired absorptive losses, and inhomogeneous field enhancement. These limitations diminish the signal strength and hamper reproducibility, making it difficult to conduct comparative studies with high sensitivity. In this study, we propose an approach that utilizes monocrystalline gold flakes to fabricate well-defined gratings composed of plasmonic double-wire resonators, which are fabricated through focused ion-beam lithography. The geometry of the double wire grating substrate (DWGS) was evolutionary optimized to achieve efficient enhancement for both excitation and emission processes. The use of monocrystalline material minimizes absorption losses while enhancing the shape fidelity during the nanofabrication process. The DWGS shows notable reproducibility (RSD=6.6%), repeatability (RSD=5.6%), and large-area homogeneity over areas $>10^4\,\mu$m$^2$. Moreover, it provides a SERS enhancement factor of $\approx 10^6$ for 4-Aminothiophenol (4-ATP) analyte and detection capability for sub-monolayer coverage. The DWGS demonstrates reusability, as well as long-term stability on the shelf. Experimental validation with various analytes, in different states of matter, including biological macromolecules, confirms the sensitive and reproducible nature of DWGSs, thereby establishing them as a promising SERS substrate design for future sensing applications.}, author = {Sweedan, Amro and Pavan, Mariela J. and Schatz, Enno and Maaß, Henriette and Tsega, Ashageru and Tzin, Vered and Höflich, Katja and Mörk, Paul and Feichtner, Thorsten and Bashouti, Muhammad Y.}, keywords = {plasmon}, note = {cite arxiv:2308.01395Comment: 22 pages, 6 Figures, 12 pages Supplementary}, title = {Evolutionary Optimized, Monocrystalline Gold Double Wire Gratings as a SERS Sensing Platform}, year = 2023 }

%0 Generic %1 sweedan2023evolutionary %A Sweedan, Amro %A Pavan, Mariela J. %A Schatz, Enno %A Maaß, Henriette %A Tsega, Ashageru %A Tzin, Vered %A Höflich, Katja %A Mörk, Paul %A Feichtner, Thorsten %A Bashouti, Muhammad Y. %D 2023 %T Evolutionary Optimized, Monocrystalline Gold Double Wire Gratings as a SERS Sensing Platform %U http://arxiv.org/abs/2308.01395 %X Achieving reliable and quantifiable performance in large-area surface-enhanced Raman spectroscopy (SERS) substrates has long been a formidable challenge. It requires substantial signal enhancement while maintaining a reproducible and uniform response. Conventional SERS substrates are typically made of inhomogeneous materials with random resonator geometries and distributions. As a result, they exhibit several or broadened plasmonic resonances, undesired absorptive losses, and inhomogeneous field enhancement. These limitations diminish the signal strength and hamper reproducibility, making it difficult to conduct comparative studies with high sensitivity. In this study, we propose an approach that utilizes monocrystalline gold flakes to fabricate well-defined gratings composed of plasmonic double-wire resonators, which are fabricated through focused ion-beam lithography. The geometry of the double wire grating substrate (DWGS) was evolutionary optimized to achieve efficient enhancement for both excitation and emission processes. The use of monocrystalline material minimizes absorption losses while enhancing the shape fidelity during the nanofabrication process. The DWGS shows notable reproducibility (RSD=6.6%), repeatability (RSD=5.6%), and large-area homogeneity over areas $>10^4\,\mu$m$^2$. Moreover, it provides a SERS enhancement factor of $\approx 10^6$ for 4-Aminothiophenol (4-ATP) analyte and detection capability for sub-monolayer coverage. The DWGS demonstrates reusability, as well as long-term stability on the shelf. Experimental validation with various analytes, in different states of matter, including biological macromolecules, confirms the sensitive and reproducible nature of DWGSs, thereby establishing them as a promising SERS substrate design for future sensing applications.

Coherent Control of the Nonlinear Emission of Single Plasmonic Nanoantennas by Dual-Beam Pumping. Francescantonio, Agostino Di; Locatelli, Andrea; Wu, Xiaofei; Zilli, Attilio; Feichtner, Thorsten; Biagioni, Paolo; Du{\`{o}}, Lamberto; Rocco, Davide; Angelis, Costantino De; Celebrano, Michele; Hecht, Bert; Finazzi, Marco. In Advanced Optical Materials, p. 2200757. Wiley, 2022.
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@article{Di_Francescantonio_2022, author = {Francescantonio, Agostino Di and Locatelli, Andrea and Wu, Xiaofei and Zilli, Attilio and Feichtner, Thorsten and Biagioni, Paolo and Du{\`{o}}, Lamberto and Rocco, Davide and Angelis, Costantino De and Celebrano, Michele and Hecht, Bert and Finazzi, Marco}, journal = {Advanced Optical Materials}, keywords = {plasmon}, month = {08}, pages = 2200757, publisher = {Wiley}, title = {Coherent Control of the Nonlinear Emission of Single Plasmonic Nanoantennas by Dual-Beam Pumping}, year = 2022 }

%0 Journal Article %1 Di_Francescantonio_2022 %A Francescantonio, Agostino Di %A Locatelli, Andrea %A Wu, Xiaofei %A Zilli, Attilio %A Feichtner, Thorsten %A Biagioni, Paolo %A Du{\`{o}}, Lamberto %A Rocco, Davide %A Angelis, Costantino De %A Celebrano, Michele %A Hecht, Bert %A Finazzi, Marco %D 2022 %I Wiley %J Advanced Optical Materials %P 2200757 %R 10.1002/adom.202200757 %T Coherent Control of the Nonlinear Emission of Single Plasmonic Nanoantennas by Dual-Beam Pumping %U https://doi.org/10.1002%2Fadom.202200757
Light-driven microdrones. Wu, Xiaofei; Ehehalt, Raphael; Razinskas, Gary; Feichtner, Thorsten; Qin, Jin; Hecht, Bert. In Nature Nanotechnology. 2022.

Shared Link

further coverage:
Nature Research Highlight, Nature Community blog post
- [ Abstract ]
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When photons interact with matter, forces and torques occur due to the transfer of linear and angular momentum, respectively. The resulting accelerations are small for macroscopic objects but become substantial for microscopic objects with small masses and moments of inertia, rendering photon recoil very attractive to propel micro- and nano-objects. However, until now, using light to control object motion in two or three dimensions in all three or six degrees of freedom has remained an unsolved challenge. Here we demonstrate light-driven microdrones (size roughly 2 μm and mass roughly 2 pg) in an aqueous environment that can be manoeuvred in two dimensions in all three independent degrees of freedom (two translational and one rotational) using two overlapping unfocused light fields of 830 and 980 nm wavelength. To actuate the microdrones independent of their orientation, we use up to four individually addressable chiral plasmonic nanoantennas acting as nanomotors that resonantly scatter the circular polarization components of the driving light into well-defined directions. The microdrones are manoeuvred by only adjusting the optical power for each motor (the power of each circular polarization component of each wavelength). The actuation concept is therefore similar to that of macroscopic multirotor drones. As a result, we demonstrate manual steering of the microdrones along complex paths. Since all degrees of freedom can be addressed independently and directly, feedback control loops may be used to counteract Brownian motion. We posit that the microdrones can find applications in transport and release of cargos, nanomanipulation, and local probing and sensing of nano and mesoscale objects.

@article{wu2022lightdriven, abstract = {When photons interact with matter, forces and torques occur due to the transfer of linear and angular momentum, respectively. The resulting accelerations are small for macroscopic objects but become substantial for microscopic objects with small masses and moments of inertia, rendering photon recoil very attractive to propel micro- and nano-objects. However, until now, using light to control object motion in two or three dimensions in all three or six degrees of freedom has remained an unsolved challenge. Here we demonstrate light-driven microdrones (size roughly 2 μm and mass roughly 2 pg) in an aqueous environment that can be manoeuvred in two dimensions in all three independent degrees of freedom (two translational and one rotational) using two overlapping unfocused light fields of 830 and 980 nm wavelength. To actuate the microdrones independent of their orientation, we use up to four individually addressable chiral plasmonic nanoantennas acting as nanomotors that resonantly scatter the circular polarization components of the driving light into well-defined directions. The microdrones are manoeuvred by only adjusting the optical power for each motor (the power of each circular polarization component of each wavelength). The actuation concept is therefore similar to that of macroscopic multirotor drones. As a result, we demonstrate manual steering of the microdrones along complex paths. Since all degrees of freedom can be addressed independently and directly, feedback control loops may be used to counteract Brownian motion. We posit that the microdrones can find applications in transport and release of cargos, nanomanipulation, and local probing and sensing of nano and mesoscale objects.}, author = {Wu, Xiaofei and Ehehalt, Raphael and Razinskas, Gary and Feichtner, Thorsten and Qin, Jin and Hecht, Bert}, journal = {Nature Nanotechnology}, keywords = {plasmon}, month = {04}, note = {<a href="https://rdcu.be/cLP6O">Shared Link</a> further coverage: <a href="https://www.nature.com/articles/d41586-022-01132-0">Nature Research Highlight</a>, <a href="https://engineeringcommunity.nature.com/posts/light-driven-microdrones-a-new-level-of-optical-manipulation">Nature Community blog post</a>}, title = {Light-driven microdrones}, year = 2022 }

%0 Journal Article %1 wu2022lightdriven %A Wu, Xiaofei %A Ehehalt, Raphael %A Razinskas, Gary %A Feichtner, Thorsten %A Qin, Jin %A Hecht, Bert %D 2022 %J Nature Nanotechnology %R https://doi.org/10.1038/s41565-022-01099-z %T Light-driven microdrones %U https://www.nature.com/articles/s41565-022-01099-z %X When photons interact with matter, forces and torques occur due to the transfer of linear and angular momentum, respectively. The resulting accelerations are small for macroscopic objects but become substantial for microscopic objects with small masses and moments of inertia, rendering photon recoil very attractive to propel micro- and nano-objects. However, until now, using light to control object motion in two or three dimensions in all three or six degrees of freedom has remained an unsolved challenge. Here we demonstrate light-driven microdrones (size roughly 2 μm and mass roughly 2 pg) in an aqueous environment that can be manoeuvred in two dimensions in all three independent degrees of freedom (two translational and one rotational) using two overlapping unfocused light fields of 830 and 980 nm wavelength. To actuate the microdrones independent of their orientation, we use up to four individually addressable chiral plasmonic nanoantennas acting as nanomotors that resonantly scatter the circular polarization components of the driving light into well-defined directions. The microdrones are manoeuvred by only adjusting the optical power for each motor (the power of each circular polarization component of each wavelength). The actuation concept is therefore similar to that of macroscopic multirotor drones. As a result, we demonstrate manual steering of the microdrones along complex paths. Since all degrees of freedom can be addressed independently and directly, feedback control loops may be used to counteract Brownian motion. We posit that the microdrones can find applications in transport and release of cargos, nanomanipulation, and local probing and sensing of nano and mesoscale objects.
Color-Switchable Subwavelength Organic Light-Emitting Antennas. Grimm, Philipp; Zeißner, Stefan; Rödel, Maximilian; Wiegand, Simon; Hammer, Sebastian; Emmerling, Monika; Schatz, Enno; Kullock, René; Pflaum, Jens; Hecht, Bert. In Nano Lett. 2022.
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Future photonic devices require efficient, multifunctional, electrically driven light sources with directional emission properties and subwavelength dimensions. Electrically driven plasmonic nanoantennas have been demonstrated as enabling technology. Here, we present the concept of a nanoscale organic light-emitting antenna (OLEA) as a color- and directionality-switchable point source. The device consists of laterally arranged electrically contacted gold nanoantennas with their gap filled by the organic semiconductor zinc phthalocyanine (ZnPc). Since ZnPc shows preferred hole conduction in combination with gold, the recombination zone relocates depending on the polarity of the applied voltage and couples selectively to either of the two antennas. Thereby, the emission characteristics of the device also depend on polarity. Contrary to large-area OLEDs where recombination at metal contacts significantly contributes to losses, our ultracompact OLEA structures facilitate efficient radiation into the far-field rendering transparent electrodes obsolete. We envision OLEA structures to serve as wavelength-scale pixels with tunable color and directionality for advanced display applications.

@article{noauthororeditor, abstract = {Future photonic devices require efficient, multifunctional, electrically driven light sources with directional emission properties and subwavelength dimensions. Electrically driven plasmonic nanoantennas have been demonstrated as enabling technology. Here, we present the concept of a nanoscale organic light-emitting antenna (OLEA) as a color- and directionality-switchable point source. The device consists of laterally arranged electrically contacted gold nanoantennas with their gap filled by the organic semiconductor zinc phthalocyanine (ZnPc). Since ZnPc shows preferred hole conduction in combination with gold, the recombination zone relocates depending on the polarity of the applied voltage and couples selectively to either of the two antennas. Thereby, the emission characteristics of the device also depend on polarity. Contrary to large-area OLEDs where recombination at metal contacts significantly contributes to losses, our ultracompact OLEA structures facilitate efficient radiation into the far-field rendering transparent electrodes obsolete. We envision OLEA structures to serve as wavelength-scale pixels with tunable color and directionality for advanced display applications.}, author = {Grimm, Philipp and Zeißner, Stefan and Rödel, Maximilian and Wiegand, Simon and Hammer, Sebastian and Emmerling, Monika and Schatz, Enno and Kullock, René and Pflaum, Jens and Hecht, Bert}, journal = {Nano Lett.}, keywords = {switchable}, month = {01}, title = {Color-Switchable Subwavelength Organic Light-Emitting Antennas}, year = 2022 }

%0 Journal Article %1 noauthororeditor %A Grimm, Philipp %A Zeißner, Stefan %A Rödel, Maximilian %A Wiegand, Simon %A Hammer, Sebastian %A Emmerling, Monika %A Schatz, Enno %A Kullock, René %A Pflaum, Jens %A Hecht, Bert %D 2022 %J Nano Lett. %R 10.1021 %T Color-Switchable Subwavelength Organic Light-Emitting Antennas %U https://doi.org/10.1021/acs.nanolett.1c03994 %X Future photonic devices require efficient, multifunctional, electrically driven light sources with directional emission properties and subwavelength dimensions. Electrically driven plasmonic nanoantennas have been demonstrated as enabling technology. Here, we present the concept of a nanoscale organic light-emitting antenna (OLEA) as a color- and directionality-switchable point source. The device consists of laterally arranged electrically contacted gold nanoantennas with their gap filled by the organic semiconductor zinc phthalocyanine (ZnPc). Since ZnPc shows preferred hole conduction in combination with gold, the recombination zone relocates depending on the polarity of the applied voltage and couples selectively to either of the two antennas. Thereby, the emission characteristics of the device also depend on polarity. Contrary to large-area OLEDs where recombination at metal contacts significantly contributes to losses, our ultracompact OLEA structures facilitate efficient radiation into the far-field rendering transparent electrodes obsolete. We envision OLEA structures to serve as wavelength-scale pixels with tunable color and directionality for advanced display applications.
Development of Rotaxanes as E-Field-Sensitive Superstructures in Plasmonic Nano-Antennas. Jucker, Laurent; Ochs, Maximilian; Kullock, René; Aeschi, Yves; Hecht, Bert; Mayor, Marcel. In Organic Materials, 4(03), pp. 127–136. 2022.
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@article{jucker2022development, author = {Jucker, Laurent and Ochs, Maximilian and Kullock, René and Aeschi, Yves and Hecht, Bert and Mayor, Marcel}, journal = {Organic Materials}, keywords = {plasmon}, number = {03}, pages = {127-136–}, title = {Development of Rotaxanes as E-Field-Sensitive Superstructures in Plasmonic Nano-Antennas}, volume = 4, year = 2022 }

%0 Journal Article %1 jucker2022development %A Jucker, Laurent %A Ochs, Maximilian %A Kullock, René %A Aeschi, Yves %A Hecht, Bert %A Mayor, Marcel %D 2022 %J Organic Materials %N 03 %P 127-136-- %R 10.1055/a-1927-8947 %T Development of Rotaxanes as E-Field-Sensitive Superstructures in Plasmonic Nano-Antennas %V 4
Tunable nano-plasmonic photodetectors. Pertsch, Patrick; Kullock, René; Gabriel, Vinzenz; Zurak, Luka; Emmerling, Monika; Hecht, Bert. In arxiv, 2204(13978). 2022.
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Visible and infrared photons can be detected with a broadband response via the internal photoeffect. By using plasmonic nanostructures, i.e. nanoantennas, wavelength selectivity can be introduced to such detectors through geometry-dependent resonances. Also, additional functionality, like electronic responsivity switching and polarization detection have been realized. However, previous devices consisted of large arrays of nanostructures to achieve detectable photocurrents. Here we show that this concept can be scaled down to a single antenna level, resulting in detector dimensions well below the resonance wavelength of the device. Our design consists of a single electrically-connected plasmonic nanoantenna covered with a wide-bandgap semiconductor allowing broadband photodetection in the VIS/NIR via injection of hot carriers. We demonstrate electrical switching of the color sensitivity as well as polarization detection. Our results hold promise for the realization of ultra small, highly integratable photodetectors with advanced functionality.

@article{noauthororeditor, abstract = {Visible and infrared photons can be detected with a broadband response via the internal photoeffect. By using plasmonic nanostructures, i.e. nanoantennas, wavelength selectivity can be introduced to such detectors through geometry-dependent resonances. Also, additional functionality, like electronic responsivity switching and polarization detection have been realized. However, previous devices consisted of large arrays of nanostructures to achieve detectable photocurrents. Here we show that this concept can be scaled down to a single antenna level, resulting in detector dimensions well below the resonance wavelength of the device. Our design consists of a single electrically-connected plasmonic nanoantenna covered with a wide-bandgap semiconductor allowing broadband photodetection in the VIS/NIR via injection of hot carriers. We demonstrate electrical switching of the color sensitivity as well as polarization detection. Our results hold promise for the realization of ultra small, highly integratable photodetectors with advanced functionality.}, author = {Pertsch, Patrick and Kullock, René and Gabriel, Vinzenz and Zurak, Luka and Emmerling, Monika and Hecht, Bert}, journal = {arxiv}, keywords = {plasmon}, number = 13978, title = {Tunable nano-plasmonic photodetectors}, volume = 2204, year = 2022 }

%0 Journal Article %1 noauthororeditor %A Pertsch, Patrick %A Kullock, René %A Gabriel, Vinzenz %A Zurak, Luka %A Emmerling, Monika %A Hecht, Bert %D 2022 %J arxiv %N 13978 %R https://doi.org/10.48550/arXiv.2204.13978 %T Tunable nano-plasmonic photodetectors %V 2204 %X Visible and infrared photons can be detected with a broadband response via the internal photoeffect. By using plasmonic nanostructures, i.e. nanoantennas, wavelength selectivity can be introduced to such detectors through geometry-dependent resonances. Also, additional functionality, like electronic responsivity switching and polarization detection have been realized. However, previous devices consisted of large arrays of nanostructures to achieve detectable photocurrents. Here we show that this concept can be scaled down to a single antenna level, resulting in detector dimensions well below the resonance wavelength of the device. Our design consists of a single electrically-connected plasmonic nanoantenna covered with a wide-bandgap semiconductor allowing broadband photodetection in the VIS/NIR via injection of hot carriers. We demonstrate electrical switching of the color sensitivity as well as polarization detection. Our results hold promise for the realization of ultra small, highly integratable photodetectors with advanced functionality.
Atomically Smooth Single-Crystalline Platform for Low-Loss Plasmonic Nanocavities. Liu, Lufang; Krasavin, Alexey V.; Zheng, Junsheng; Tong, Yuanbiao; Wang, Pan; Wu, Xiaofei; Hecht, Bert; Pan, Chenxinyu; Li, Jialin; Li, Linjun; Guo, Xin; Zayats, Anatoly V.; Tong, Limin. In Nano Letters. 2022.
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Nanoparticle-on-mirror plasmonic nanocavities, capable of extreme optical confinement and enhancement, have triggered state-of-the-art progress in nanophotonics and development of applications in enhanced spectroscopies. However, the optical quality factor and thus performance of these nanoconstructs are undermined by the granular polycrystalline metal films (especially when they are optically thin) used as a mirror. Here, we report an atomically smooth single-crystalline platform for lowloss nanocavities using chemically synthesized gold microflakes as a mirror. Nanocavities constructed using gold nanorods on such microflakes exhibit a rich structure of plasmonic modes, which are highly sensitive to the thickness of optically thin (down to ∼15 nm) microflakes. The microflakes endow nanocavities with significantly improved quality factor (∼2 times) and scattering intensity (∼3 times) compared with their counterparts based on deposited films. The developed low-loss nanocavities further allow for the integration with a mature platform of fiber optics, opening opportunities for realizing nanocavity-based miniaturized photonic devices for practical applications.

@article{noauthororeditor, abstract = {Nanoparticle-on-mirror plasmonic nanocavities, capable of extreme optical confinement and enhancement, have triggered state-of-the-art progress in nanophotonics and development of applications in enhanced spectroscopies. However, the optical quality factor and thus performance of these nanoconstructs are undermined by the granular polycrystalline metal films (especially when they are optically thin) used as a mirror. Here, we report an atomically smooth single-crystalline platform for lowloss nanocavities using chemically synthesized gold microflakes as a mirror. Nanocavities constructed using gold nanorods on such microflakes exhibit a rich structure of plasmonic modes, which are highly sensitive to the thickness of optically thin (down to ∼15 nm) microflakes. The microflakes endow nanocavities with significantly improved quality factor (∼2 times) and scattering intensity (∼3 times) compared with their counterparts based on deposited films. The developed low-loss nanocavities further allow for the integration with a mature platform of fiber optics, opening opportunities for realizing nanocavity-based miniaturized photonic devices for practical applications.}, author = {Liu, Lufang and Krasavin, Alexey V. and Zheng, Junsheng and Tong, Yuanbiao and Wang, Pan and Wu, Xiaofei and Hecht, Bert and Pan, Chenxinyu and Li, Jialin and Li, Linjun and Guo, Xin and Zayats, Anatoly V. and Tong, Limin}, journal = {Nano Letters}, keywords = {platform}, title = {Atomically Smooth Single-Crystalline Platform for Low-Loss Plasmonic Nanocavities}, year = 2022 }

%0 Journal Article %1 noauthororeditor %A Liu, Lufang %A Krasavin, Alexey V. %A Zheng, Junsheng %A Tong, Yuanbiao %A Wang, Pan %A Wu, Xiaofei %A Hecht, Bert %A Pan, Chenxinyu %A Li, Jialin %A Li, Linjun %A Guo, Xin %A Zayats, Anatoly V. %A Tong, Limin %D 2022 %J Nano Letters %T Atomically Smooth Single-Crystalline Platform for Low-Loss Plasmonic Nanocavities %X Nanoparticle-on-mirror plasmonic nanocavities, capable of extreme optical confinement and enhancement, have triggered state-of-the-art progress in nanophotonics and development of applications in enhanced spectroscopies. However, the optical quality factor and thus performance of these nanoconstructs are undermined by the granular polycrystalline metal films (especially when they are optically thin) used as a mirror. Here, we report an atomically smooth single-crystalline platform for lowloss nanocavities using chemically synthesized gold microflakes as a mirror. Nanocavities constructed using gold nanorods on such microflakes exhibit a rich structure of plasmonic modes, which are highly sensitive to the thickness of optically thin (down to ∼15 nm) microflakes. The microflakes endow nanocavities with significantly improved quality factor (∼2 times) and scattering intensity (∼3 times) compared with their counterparts based on deposited films. The developed low-loss nanocavities further allow for the integration with a mature platform of fiber optics, opening opportunities for realizing nanocavity-based miniaturized photonic devices for practical applications.
Controlling field asymmetry in nanoscale gaps for second harmonic generation. Meier, Jessica; Zurak, Luka; Locatelli, Andrea; Feichtner, Thorsten; Kullock, René; Hecht, Bert. 2022.
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Plasmonic dimer antennas create strong field enhancement by squeezing light into a nanoscale gap. These optical hotspots are highly attractive for boosting nonlinear processes, such as harmonic generation, photoelectron emission, and ultrafast electron transport. Alongside large field enhancement, such phenomena often require control over the field asymmetry in the hotspot, which is challenging considering the nanometer length scales. Here, by means of strongly enhanced second harmonic generation, we demonstrate unprecedented control over the field distribution in a hotspot by systematically introducing geometrical asymmetry to the antenna gap. We use focused helium ion beam milling of mono-crystalline gold to realize asymmetric-gap dimer antennas in which an ultra-sharp tip with 3 nm apex radius faces a flat counterpart, conserving the bonding antenna mode and the concomitant field enhancement at the fundamental frequency. By decreasing the tip opening angle, we are able to systematically increase both field enhancement and asymmetry, thus enhancing second harmonic radiation to the far-field, which is nearly completely suppressed for equivalent symmetric dimer antennas. Combining these findings with second harmonic radiation patterns as well as quantitative nonlinear simulations, we further obtain remarkably detailed insights into the mechanism of second harmonic generation at the nanoscale. Our results open new opportunities for the realization of novel nonlinear nanoscale systems, where the control over local field asymmetry in combination with large field enhancement is essential to create nonreciprocal functionalities.

@misc{meier2022controlling, abstract = {Plasmonic dimer antennas create strong field enhancement by squeezing light into a nanoscale gap. These optical hotspots are highly attractive for boosting nonlinear processes, such as harmonic generation, photoelectron emission, and ultrafast electron transport. Alongside large field enhancement, such phenomena often require control over the field asymmetry in the hotspot, which is challenging considering the nanometer length scales. Here, by means of strongly enhanced second harmonic generation, we demonstrate unprecedented control over the field distribution in a hotspot by systematically introducing geometrical asymmetry to the antenna gap. We use focused helium ion beam milling of mono-crystalline gold to realize asymmetric-gap dimer antennas in which an ultra-sharp tip with 3 nm apex radius faces a flat counterpart, conserving the bonding antenna mode and the concomitant field enhancement at the fundamental frequency. By decreasing the tip opening angle, we are able to systematically increase both field enhancement and asymmetry, thus enhancing second harmonic radiation to the far-field, which is nearly completely suppressed for equivalent symmetric dimer antennas. Combining these findings with second harmonic radiation patterns as well as quantitative nonlinear simulations, we further obtain remarkably detailed insights into the mechanism of second harmonic generation at the nanoscale. Our results open new opportunities for the realization of novel nonlinear nanoscale systems, where the control over local field asymmetry in combination with large field enhancement is essential to create nonreciprocal functionalities.}, author = {Meier, Jessica and Zurak, Luka and Locatelli, Andrea and Feichtner, Thorsten and Kullock, René and Hecht, Bert}, keywords = {plasmon}, title = {Controlling field asymmetry in nanoscale gaps for second harmonic generation}, year = 2022 }

%0 Generic %1 meier2022controlling %A Meier, Jessica %A Zurak, Luka %A Locatelli, Andrea %A Feichtner, Thorsten %A Kullock, René %A Hecht, Bert %D 2022 %R 10.1002/adom.202300731 %T Controlling field asymmetry in nanoscale gaps for second harmonic generation %U https://doi.org/10.1002/adom.202300731 %X Plasmonic dimer antennas create strong field enhancement by squeezing light into a nanoscale gap. These optical hotspots are highly attractive for boosting nonlinear processes, such as harmonic generation, photoelectron emission, and ultrafast electron transport. Alongside large field enhancement, such phenomena often require control over the field asymmetry in the hotspot, which is challenging considering the nanometer length scales. Here, by means of strongly enhanced second harmonic generation, we demonstrate unprecedented control over the field distribution in a hotspot by systematically introducing geometrical asymmetry to the antenna gap. We use focused helium ion beam milling of mono-crystalline gold to realize asymmetric-gap dimer antennas in which an ultra-sharp tip with 3 nm apex radius faces a flat counterpart, conserving the bonding antenna mode and the concomitant field enhancement at the fundamental frequency. By decreasing the tip opening angle, we are able to systematically increase both field enhancement and asymmetry, thus enhancing second harmonic radiation to the far-field, which is nearly completely suppressed for equivalent symmetric dimer antennas. Combining these findings with second harmonic radiation patterns as well as quantitative nonlinear simulations, we further obtain remarkably detailed insights into the mechanism of second harmonic generation at the nanoscale. Our results open new opportunities for the realization of novel nonlinear nanoscale systems, where the control over local field asymmetry in combination with large field enhancement is essential to create nonreciprocal functionalities.

Single quantum emitter Dicke enhancement. Tufarelli, Tommaso; Friedrich, Daniel; Groß, Heiko; Hamm, Joachim; Hess, Ortwin; Hecht, Bert. In Phys. Rev. Research. 2021.

» arXiv: 2010.12585v2 (2021).
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Coupling N identical emitters to the same field mode is a well-established method to enhance light-matter interaction. However, the resulting √N boost of the coupling strength comes at the cost of a “linearized” (effectively semiclassical) dynamics. Here, we instead demonstrate a new approach for enhancing the coupling constant of a single quantum emitter, while retaining the nonlinear character of the light-matter interaction. We consider a single quantum emitter with N nearly degenerate transitions that are collectively coupled to the same field mode. We show that in such conditions an effective Jaynes-Cummings model emerges with a boosted coupling constant of order √N. The validity and consequences of our general conclusions are analytically demonstrated for the instructive case N=2. We further observe that our system can closely match the spectral line shapes and photon autocorrelation functions typical of Jaynes-Cummings physics, proving that quantum optical nonlinearities are retained. Our findings match up very well with recent broadband plasmonic nanoresonator strong-coupling experiments and will, therefore, facilitate the control and detection of single-photon nonlinearities at ambient conditions.

@article{tufarelli2020dicke, abstract = {Coupling N identical emitters to the same field mode is a well-established method to enhance light-matter interaction. However, the resulting √N boost of the coupling strength comes at the cost of a “linearized” (effectively semiclassical) dynamics. Here, we instead demonstrate a new approach for enhancing the coupling constant of a single quantum emitter, while retaining the nonlinear character of the light-matter interaction. We consider a single quantum emitter with N nearly degenerate transitions that are collectively coupled to the same field mode. We show that in such conditions an effective Jaynes-Cummings model emerges with a boosted coupling constant of order √N. The validity and consequences of our general conclusions are analytically demonstrated for the instructive case N=2. We further observe that our system can closely match the spectral line shapes and photon autocorrelation functions typical of Jaynes-Cummings physics, proving that quantum optical nonlinearities are retained. Our findings match up very well with recent broadband plasmonic nanoresonator strong-coupling experiments and will, therefore, facilitate the control and detection of single-photon nonlinearities at ambient conditions.}, author = {Tufarelli, Tommaso and Friedrich, Daniel and Groß, Heiko and Hamm, Joachim and Hess, Ortwin and Hecht, Bert}, journal = {Phys. Rev. Research}, keywords = {theory}, month = {07}, note = {<a href="https://arxiv.org/abs/2010.12585v2" style="font-style: normal;">» arXiv: 2010.12585v2 (2021)</a>.}, title = {Single quantum emitter Dicke enhancement}, year = 2021 }

%0 Journal Article %1 tufarelli2020dicke %A Tufarelli, Tommaso %A Friedrich, Daniel %A Groß, Heiko %A Hamm, Joachim %A Hess, Ortwin %A Hecht, Bert %D 2021 %J Phys. Rev. Research %R 10.1103/PhysRevResearch.3.033103 %T Single quantum emitter Dicke enhancement %U https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.3.033103 %X Coupling N identical emitters to the same field mode is a well-established method to enhance light-matter interaction. However, the resulting √N boost of the coupling strength comes at the cost of a “linearized” (effectively semiclassical) dynamics. Here, we instead demonstrate a new approach for enhancing the coupling constant of a single quantum emitter, while retaining the nonlinear character of the light-matter interaction. We consider a single quantum emitter with N nearly degenerate transitions that are collectively coupled to the same field mode. We show that in such conditions an effective Jaynes-Cummings model emerges with a boosted coupling constant of order √N. The validity and consequences of our general conclusions are analytically demonstrated for the instructive case N=2. We further observe that our system can closely match the spectral line shapes and photon autocorrelation functions typical of Jaynes-Cummings physics, proving that quantum optical nonlinearities are retained. Our findings match up very well with recent broadband plasmonic nanoresonator strong-coupling experiments and will, therefore, facilitate the control and detection of single-photon nonlinearities at ambient conditions.
Near-infrared nanospectroscopy using a low-noise supercontinuum source. Kaltenecker, Korbinian J.; S., Shreesha Rao D.; Rasmussen, Mattias; Lassen, Henrik B.; Kelleher, Edmund J. R.; Krauss, Enno; Hecht, Bert; Mortensen, N. Asger; Grüner-Nielsen, Lars; Markos, Christos; Bang, Ole; Stenger, Nicolas; Jepsen, Peter Uhd. In {APL} Photonics, 6(6), p. 066106. {AIP} Publishing, 2021.
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Unlocking the true potential of optical spectroscopy on the nanoscale requires development of stable and low-noise laser sources. Here, we have developed a low-noise supercontinuum (SC) source based on an all-normal dispersion fiber pumped by a femtosecond fiber laser and demonstrate high resolution, spectrally resolved near-field measurements in the near-infrared (NIR) region. Specifically, we explore the reduced-noise requirements for aperture-less scattering-type scanning near-field optical microscopy (s-SNOM), including inherent pulse-to-pulse fluctuation of the SC. We use our SC light source to demonstrate the first NIR, spectrally resolved s-SNOM measurement, a situation where state-of-the-art commercial SC sources are too noisy to be useful. We map the propagation of surface plasmon polariton (SPP) waves on monocrystalline gold platelets in the wavelength region of 1.34–1.75 μm in a single measurement, thereby characterizing experimentally the dispersion curve of the SPP in the NIR. Our results represent a technological breakthrough that has the potential to enable a wide range of new applications of low-noise SC sources in near-field studies.

@article{Kaltenecker_2021, abstract = {Unlocking the true potential of optical spectroscopy on the nanoscale requires development of stable and low-noise laser sources. Here, we have developed a low-noise supercontinuum (SC) source based on an all-normal dispersion fiber pumped by a femtosecond fiber laser and demonstrate high resolution, spectrally resolved near-field measurements in the near-infrared (NIR) region. Specifically, we explore the reduced-noise requirements for aperture-less scattering-type scanning near-field optical microscopy (s-SNOM), including inherent pulse-to-pulse fluctuation of the SC. We use our SC light source to demonstrate the first NIR, spectrally resolved s-SNOM measurement, a situation where state-of-the-art commercial SC sources are too noisy to be useful. We map the propagation of surface plasmon polariton (SPP) waves on monocrystalline gold platelets in the wavelength region of 1.34–1.75 μm in a single measurement, thereby characterizing experimentally the dispersion curve of the SPP in the NIR. Our results represent a technological breakthrough that has the potential to enable a wide range of new applications of low-noise SC sources in near-field studies.}, author = {Kaltenecker, Korbinian J. and S., Shreesha Rao D. and Rasmussen, Mattias and Lassen, Henrik B. and Kelleher, Edmund J. R. and Krauss, Enno and Hecht, Bert and Mortensen, N. Asger and Grüner-Nielsen, Lars and Markos, Christos and Bang, Ole and Stenger, Nicolas and Jepsen, Peter Uhd}, journal = {{APL} Photonics}, keywords = {plasmon}, month = {06}, number = 6, pages = {066106}, publisher = {{AIP} Publishing}, title = {Near-infrared nanospectroscopy using a low-noise supercontinuum source}, volume = 6, year = 2021 }

%0 Journal Article %1 Kaltenecker_2021 %A Kaltenecker, Korbinian J. %A S., Shreesha Rao D. %A Rasmussen, Mattias %A Lassen, Henrik B. %A Kelleher, Edmund J. R. %A Krauss, Enno %A Hecht, Bert %A Mortensen, N. Asger %A Grüner-Nielsen, Lars %A Markos, Christos %A Bang, Ole %A Stenger, Nicolas %A Jepsen, Peter Uhd %D 2021 %I {AIP} Publishing %J {APL} Photonics %N 6 %P 066106 %R 10.1063/5.0050446 %T Near-infrared nanospectroscopy using a low-noise supercontinuum source %U https://doi.org/10.1063%2F5.0050446 %V 6 %X Unlocking the true potential of optical spectroscopy on the nanoscale requires development of stable and low-noise laser sources. Here, we have developed a low-noise supercontinuum (SC) source based on an all-normal dispersion fiber pumped by a femtosecond fiber laser and demonstrate high resolution, spectrally resolved near-field measurements in the near-infrared (NIR) region. Specifically, we explore the reduced-noise requirements for aperture-less scattering-type scanning near-field optical microscopy (s-SNOM), including inherent pulse-to-pulse fluctuation of the SC. We use our SC light source to demonstrate the first NIR, spectrally resolved s-SNOM measurement, a situation where state-of-the-art commercial SC sources are too noisy to be useful. We map the propagation of surface plasmon polariton (SPP) waves on monocrystalline gold platelets in the wavelength region of 1.34–1.75 μm in a single measurement, thereby characterizing experimentally the dispersion curve of the SPP in the NIR. Our results represent a technological breakthrough that has the potential to enable a wide range of new applications of low-noise SC sources in near-field studies.
Driving plasmonic nanoantennas at perfect impedance matching using generalized coherent perfect absorption. Grimm, Philipp; Razinskas, Gary; Huang, Jer-Shing; Hecht, Bert. In nanoph-2021-0048. 2021.

» arXiv: 1907.08174 (2020)
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Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g., plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are suppressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a single nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both radiant and subradiant characteristics are considered. We further demonstrate potential applications in background-free sensing.

@article{grimm2020driving, abstract = {Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g., plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are suppressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a single nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both radiant and subradiant characteristics are considered. We further demonstrate potential applications in background-free sensing.}, author = {Grimm, Philipp and Razinskas, Gary and Huang, Jer-Shing and Hecht, Bert}, journal = {nanoph-2021-0048}, keywords = {resonance}, month = {04}, note = {<a href="https://arxiv.org/abs/1907.08174" style="font-style: normal;">» arXiv: 1907.08174 (2020)</a>}, title = {Driving plasmonic nanoantennas at perfect impedance matching using generalized coherent perfect absorption}, year = 2021 }

%0 Journal Article %1 grimm2020driving %A Grimm, Philipp %A Razinskas, Gary %A Huang, Jer-Shing %A Hecht, Bert %D 2021 %J nanoph-2021-0048 %R 10.1515/nanoph-2021-0048 %T Driving plasmonic nanoantennas at perfect impedance matching using generalized coherent perfect absorption %U https://www.degruyter.com/document/doi/10.1515/nanoph-2021-0048/html %X Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g., plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are suppressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a single nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both radiant and subradiant characteristics are considered. We further demonstrate potential applications in background-free sensing.
Nanoscale Electrical Excitation of Distinct Modes in Plasmonic Waveguides. Ochs, Maximilian; Zurak, Luka; Krauss, Enno; Meier, Jessica; Emmerling, Monika; Kullock, René; Hecht, Bert. In Nano Letters. 2021.
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The electrical excitation of guided plasmonic modes at the nanoscale enables integration of optical nanocircuitry into nanoelectronics. In this context, exciting plasmons with a distinct modal field profile constitutes a key advantage over conventional single-mode integrated photonics. Here, we demonstrate the selective electrical excitation of the lowest-order symmetric and antisymmetric plasmonic modes in a two-wire transmission line. We achieve mode selectivity by precisely positioning nanoscale excitation sources, i.e., junctions for inelastic electron tunneling, within the respective modal field distribution. By using advanced fabrication that combines focused He-ion beam milling and dielectrophoresis, we control the location of tunnel junctions with sub-10 nm accuracy. At the far end of the two-wire transmission line, the guided plasmonic modes are converted into far-field radiation at separate spatial positions showing two distinct orthogonal polarizations. Hence, the resulting device represents the smallest electrically driven light source with directly switchable polarization states with possible applications in display technology.

@article{ochs2021nanoscale, abstract = {The electrical excitation of guided plasmonic modes at the nanoscale enables integration of optical nanocircuitry into nanoelectronics. In this context, exciting plasmons with a distinct modal field profile constitutes a key advantage over conventional single-mode integrated photonics. Here, we demonstrate the selective electrical excitation of the lowest-order symmetric and antisymmetric plasmonic modes in a two-wire transmission line. We achieve mode selectivity by precisely positioning nanoscale excitation sources, i.e., junctions for inelastic electron tunneling, within the respective modal field distribution. By using advanced fabrication that combines focused He-ion beam milling and dielectrophoresis, we control the location of tunnel junctions with sub-10 nm accuracy. At the far end of the two-wire transmission line, the guided plasmonic modes are converted into far-field radiation at separate spatial positions showing two distinct orthogonal polarizations. Hence, the resulting device represents the smallest electrically driven light source with directly switchable polarization states with possible applications in display technology.}, author = {Ochs, Maximilian and Zurak, Luka and Krauss, Enno and Meier, Jessica and Emmerling, Monika and Kullock, René and Hecht, Bert}, journal = {Nano Letters}, keywords = {plasmon}, month = {04}, title = {Nanoscale Electrical Excitation of Distinct Modes in Plasmonic Waveguides}, year = 2021 }

%0 Journal Article %1 ochs2021nanoscale %A Ochs, Maximilian %A Zurak, Luka %A Krauss, Enno %A Meier, Jessica %A Emmerling, Monika %A Kullock, René %A Hecht, Bert %D 2021 %J Nano Letters %R 10.1021/acs.nanolett.1c00182 %T Nanoscale Electrical Excitation of Distinct Modes in Plasmonic Waveguides %U https://pubs.acs.org/doi/10.1021/acs.nanolett.1c00182 %X The electrical excitation of guided plasmonic modes at the nanoscale enables integration of optical nanocircuitry into nanoelectronics. In this context, exciting plasmons with a distinct modal field profile constitutes a key advantage over conventional single-mode integrated photonics. Here, we demonstrate the selective electrical excitation of the lowest-order symmetric and antisymmetric plasmonic modes in a two-wire transmission line. We achieve mode selectivity by precisely positioning nanoscale excitation sources, i.e., junctions for inelastic electron tunneling, within the respective modal field distribution. By using advanced fabrication that combines focused He-ion beam milling and dielectrophoresis, we control the location of tunnel junctions with sub-10 nm accuracy. At the far end of the two-wire transmission line, the guided plasmonic modes are converted into far-field radiation at separate spatial positions showing two distinct orthogonal polarizations. Hence, the resulting device represents the smallest electrically driven light source with directly switchable polarization states with possible applications in display technology.
The patterning toolbox FIB-o-mat: Exploiting the full potential of focused helium ions for nanofabrication. Deinhart, Victor; Kern, Lisa-Marie; Kirchhof, Jan N; Juergensen, Sabrina; Sturm, Joris; Krauss, Enno; Feichtner, Thorsten; Kovalchuk, Sviatoslav; Schneider, Michael; Engel, Dieter; Pfau, Bastian; Hecht, Bert; Bolotin, Kirill I; Reich, Stephanie; Höflich, Katja. In Beilstein Journal of Nanotechnology, 12, pp. 304–318. Beilstein Institut, 2021.
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Focused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.

@article{Deinhart_2021, abstract = {Focused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.}, author = {Deinhart, Victor and Kern, Lisa-Marie and Kirchhof, Jan N and Juergensen, Sabrina and Sturm, Joris and Krauss, Enno and Feichtner, Thorsten and Kovalchuk, Sviatoslav and Schneider, Michael and Engel, Dieter and Pfau, Bastian and Hecht, Bert and Bolotin, Kirill I and Reich, Stephanie and Höflich, Katja}, journal = {Beilstein Journal of Nanotechnology}, keywords = {fib}, month = {04}, pages = {304–318}, publisher = {Beilstein Institut}, title = {The patterning toolbox FIB-o-mat: Exploiting the full potential of focused helium ions for nanofabrication}, volume = 12, year = 2021 }

%0 Journal Article %1 Deinhart_2021 %A Deinhart, Victor %A Kern, Lisa-Marie %A Kirchhof, Jan N %A Juergensen, Sabrina %A Sturm, Joris %A Krauss, Enno %A Feichtner, Thorsten %A Kovalchuk, Sviatoslav %A Schneider, Michael %A Engel, Dieter %A Pfau, Bastian %A Hecht, Bert %A Bolotin, Kirill I %A Reich, Stephanie %A Höflich, Katja %D 2021 %I Beilstein Institut %J Beilstein Journal of Nanotechnology %P 304--318 %R 10.3762/bjnano.12.25 %T The patterning toolbox FIB-o-mat: Exploiting the full potential of focused helium ions for nanofabrication %U https://doi.org/10.3762%2Fbjnano.12.25 %V 12 %X Focused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.

Electrically-driven Yagi-Uda antennas for light. Kullock, René; Ochs, Maximilian; Grimm, Philipp; Emmerling, Monika; Hecht, Bert. In Nat Commun, 11(1), pp. 1–7. 2020.

press:
pro-physik.de, elektronik-informationen.de, photonics.com, sciencedaily.com, laboratory-journal.com, phys.org, nanowerk.com, Gold Nanoparticles (nanopartz), innovations-report.com, bestresearchreports.com, trendintech.com, electronicsonline.net, idw-online.de, scitechdaily.com, advancedsciencenews.com
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Yagi-Uda antennas are a key technology for efficiently transmitting information from point to point using radio waves. Since higher frequencies allow higher bandwidths and smaller footprints, a strong incentive exists to shrink Yagi-Uda antennas down to the optical regime. Here we demonstrate electrically-driven Yagi-Uda antennas for light with wavelength-scale footprints that exhibit large directionalities with forward-to-backward ratios of up to 9.1 dB. Light generation is achieved via antenna-enhanced inelastic tunneling of electrons over the antenna feed gap. We obtain reproducible tunnel gaps by means of feedback-controlled dielectrophoresis, which precisely places single surface-passivated gold nanoparticles in the antenna gap. The resulting antennas perform equivalent to radio-frequency antennas and combined with waveguiding layers even outperform RF designs. This work paves the way for optical on-chip data communication that is not restricted by Joule heating but also for advanced light management in nanoscale sensing and metrology as well as light emitting devices.

@article{kullock2020electricallydriven, abstract = {Yagi-Uda antennas are a key technology for efficiently transmitting information from point to point using radio waves. Since higher frequencies allow higher bandwidths and smaller footprints, a strong incentive exists to shrink Yagi-Uda antennas down to the optical regime. Here we demonstrate electrically-driven Yagi-Uda antennas for light with wavelength-scale footprints that exhibit large directionalities with forward-to-backward ratios of up to 9.1 dB. Light generation is achieved via antenna-enhanced inelastic tunneling of electrons over the antenna feed gap. We obtain reproducible tunnel gaps by means of feedback-controlled dielectrophoresis, which precisely places single surface-passivated gold nanoparticles in the antenna gap. The resulting antennas perform equivalent to radio-frequency antennas and combined with waveguiding layers even outperform RF designs. This work paves the way for optical on-chip data communication that is not restricted by Joule heating but also for advanced light management in nanoscale sensing and metrology as well as light emitting devices.}, author = {Kullock, René and Ochs, Maximilian and Grimm, Philipp and Emmerling, Monika and Hecht, Bert}, journal = {Nat Commun}, keywords = {nano-optics}, month = {01}, note = {press: <a href="https://www.pro-physik.de/nachrichten/nano-antennen-fuer-den-datentransfer">pro-physik.de</a>, <a href="https://www.elektronik-informationen.de/nanoantennen-fuer-den-datentransfer/150/23202/398077">elektronik-informationen.de</a>, <a href="https://www.photonics.com/Articles/Nanoantennas_for_Data_Transfer/a65445">photonics.com</a>, <a href="https://www.sciencedaily.com/releases/2020/01/200108074755.htm">sciencedaily.com</a>, <a href="https://www.laboratory-journal.com/news/scientific-news/nano-antennas-data-transfer">laboratory-journal.com</a>, <a href="https://phys.org/news/2020-01-nano-antennas.html">phys.org</a>, <a href="https://www.nanowerk.com/nanotechnology-news2/newsid=54323.php">nanowerk.com</a>, <a href="https://www.nanopartz.com/Customer-Spotlight/Wuerzburg-Antennas.asp">Gold Nanoparticles (nanopartz)</a>, <a href="https://www.innovations-report.com/html/reports/energy-engineering/nano-antennas-for-data-transfer.html">innovations-report.com</a>, <a href="https://bestresearchreports.com/2020/01/30/nano-antennas-for-data-transfer/">bestresearchreports.com</a>, <a href="http://trendintech.com/2020/01/25/wurzburg-physicists-develop-the-worlds-first-directional-antenna-for-light/">trendintech.com</a>, <a href="https://www.electronicsonline.net.au/content/components/news/nano-antennas-enable-data-transfer-1514775135#axzz6Cba5BvX6">electronicsonline.net</a>, <a href="https://idw-online.de/de/news729582">idw-online.de</a>, <a href="https://scitechdaily.com/nano-antennas-for-data-transfer-could-allow-processor-cores-to-exchange-data-at-speed-of-light/">scitechdaily.com</a>, <a href="https://www.advancedsciencenews.com/nano-scale-antennas-for-optical-data-communication/">advancedsciencenews.com</a>}, number = 1, pages = {1-7}, title = {Electrically-driven Yagi-Uda antennas for light}, volume = 11, year = 2020 }

%0 Journal Article %1 kullock2020electricallydriven %A Kullock, René %A Ochs, Maximilian %A Grimm, Philipp %A Emmerling, Monika %A Hecht, Bert %D 2020 %J Nat Commun %N 1 %P 1-7 %R 10.1038/s41467-019-14011-6 %T Electrically-driven Yagi-Uda antennas for light %V 11 %X Yagi-Uda antennas are a key technology for efficiently transmitting information from point to point using radio waves. Since higher frequencies allow higher bandwidths and smaller footprints, a strong incentive exists to shrink Yagi-Uda antennas down to the optical regime. Here we demonstrate electrically-driven Yagi-Uda antennas for light with wavelength-scale footprints that exhibit large directionalities with forward-to-backward ratios of up to 9.1 dB. Light generation is achieved via antenna-enhanced inelastic tunneling of electrons over the antenna feed gap. We obtain reproducible tunnel gaps by means of feedback-controlled dielectrophoresis, which precisely places single surface-passivated gold nanoparticles in the antenna gap. The resulting antennas perform equivalent to radio-frequency antennas and combined with waveguiding layers even outperform RF designs. This work paves the way for optical on-chip data communication that is not restricted by Joule heating but also for advanced light management in nanoscale sensing and metrology as well as light emitting devices.
Mono-crystalline gold platelets: a high-quality platform for surface plasmon polaritons. Kaltenecker, Korbinian J.; Krauss, Enno; Casses, Laura; Geisler, Mathias; Hecht, Bert; Mortensen, N. Asger; Jepsen, Peter Uhd; Stenger, Nicolas. In Nanophotonics, 9(2), pp. 509–522. 2020.

» arxiv:1909.08321 (2020)
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We use mono-crystalline gold platelets with ultra-smooth surfaces and superior plasmonic properties to investigate the formation of interference patterns caused by surface plasmon polaritons (SPPs) with scattering-type scanning near-field microscopy at 521 and 633 nm. By applying a Fourier analysis approach, we can identify and separate several signal channels related to SPPs launched and scattered by the atomic force microscopy tip and the edges of the platelet. Especially at the excitation wavelength of 633 nm, we can isolate a region in the center of the platelets where we find only contributions of SPPs which are launched by the tip and reflected at the edges. These signatures are used to determine the SPP wavelength of λSPP = 606 nm in good agreement with theoretical predictions. Furthermore, we were still able to measure SPP signals after 20 µm propagation, which demonstrates impressively the superior plasmonic quality of these mono-crystalline gold platelets.

@article{kaltenecker2020monocrystalline, abstract = {We use mono-crystalline gold platelets with ultra-smooth surfaces and superior plasmonic properties to investigate the formation of interference patterns caused by surface plasmon polaritons (SPPs) with scattering-type scanning near-field microscopy at 521 and 633 nm. By applying a Fourier analysis approach, we can identify and separate several signal channels related to SPPs launched and scattered by the atomic force microscopy tip and the edges of the platelet. Especially at the excitation wavelength of 633 nm, we can isolate a region in the center of the platelets where we find only contributions of SPPs which are launched by the tip and reflected at the edges. These signatures are used to determine the SPP wavelength of λSPP = 606 nm in good agreement with theoretical predictions. Furthermore, we were still able to measure SPP signals after 20 µm propagation, which demonstrates impressively the superior plasmonic quality of these mono-crystalline gold platelets.}, author = {Kaltenecker, Korbinian J. and Krauss, Enno and Casses, Laura and Geisler, Mathias and Hecht, Bert and Mortensen, N. Asger and Jepsen, Peter Uhd and Stenger, Nicolas}, journal = {Nanophotonics}, keywords = {plasmon}, month = {01}, note = {<a href="https://arxiv.org/abs/1909.08321" style="font-style: normal;">» arxiv:1909.08321 (2020)</a>}, number = 2, pages = {509-522}, title = {Mono-crystalline gold platelets: a high-quality platform for surface plasmon polaritons}, volume = 9, year = 2020 }

%0 Journal Article %1 kaltenecker2020monocrystalline %A Kaltenecker, Korbinian J. %A Krauss, Enno %A Casses, Laura %A Geisler, Mathias %A Hecht, Bert %A Mortensen, N. Asger %A Jepsen, Peter Uhd %A Stenger, Nicolas %D 2020 %J Nanophotonics %N 2 %P 509-522 %R 10.1515/nanoph-2019-0362 %T Mono-crystalline gold platelets: a high-quality platform for surface plasmon polaritons %V 9 %X We use mono-crystalline gold platelets with ultra-smooth surfaces and superior plasmonic properties to investigate the formation of interference patterns caused by surface plasmon polaritons (SPPs) with scattering-type scanning near-field microscopy at 521 and 633 nm. By applying a Fourier analysis approach, we can identify and separate several signal channels related to SPPs launched and scattered by the atomic force microscopy tip and the edges of the platelet. Especially at the excitation wavelength of 633 nm, we can isolate a region in the center of the platelets where we find only contributions of SPPs which are launched by the tip and reflected at the edges. These signatures are used to determine the SPP wavelength of λSPP = 606 nm in good agreement with theoretical predictions. Furthermore, we were still able to measure SPP signals after 20 µm propagation, which demonstrates impressively the superior plasmonic quality of these mono-crystalline gold platelets.

Space- and time-resolved UV-to-NIR surface spectroscopy and 2D nanoscopy at 1 MHz repetition rate. Huber, Bernhard; Pres, Sebastian; Wittmann, Emanuel; Dietrich, Lysanne; Lüttig, Julian; Fersch, Daniel; Krauss, Enno; Friedrich, Daniel; Kern, Johannes; Lisinetskii, Victor; Hensen, Matthias; Hecht, Bert; Bratschitsch, Rudolf; Riedle, Eberhard; Brixner, Tobias. In Rev. Sci. Instrum., 90(11), p. 113103. 2019.
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We describe a setup for time-resolved photoemission electron microscopy with aberration correction enabling 3 nm spatial resolution and sub-20 fs temporal resolution. The latter is realized by our development of a widely tunable (215–970 nm) noncollinear optical parametric amplifier (NOPA) at 1 MHz repetition rate. We discuss several exemplary applications. Efficient photoemission from plasmonic Au nanoresonators is investigated with phase-coherent pulse pairs from an actively stabilized interferometer. More complex excitation fields are created with a liquid-crystal-based pulse shaper enabling amplitude and phase shaping of NOPA pulses with spectral components from 600 to 800 nm. With this system we demonstrate spectroscopy within a single plasmonic nanoslit resonator by spectral amplitude shaping and investigate the local field dynamics with coherent two-dimensional (2D) spectroscopy at the nanometer length scale (“2D nanoscopy”). We show that the local response varies across a distance as small as 33 nm in our sample. Further, we report two-color pump–probe experiments using two independent NOPA beamlines. We extract local variations of the excited-state dynamics of a monolayered 2D material (WSe2) that we correlate with low-energy electron microscopy (LEEM) and reflectivity measurements. Finally, we demonstrate the in situ sample preparation capabilities for organic thin films and their characterization via spatially resolved electron diffraction and dark-field LEEM.

@article{huber2019space, abstract = {We describe a setup for time-resolved photoemission electron microscopy with aberration correction enabling 3 nm spatial resolution and sub-20 fs temporal resolution. The latter is realized by our development of a widely tunable (215–970 nm) noncollinear optical parametric amplifier (NOPA) at 1 MHz repetition rate. We discuss several exemplary applications. Efficient photoemission from plasmonic Au nanoresonators is investigated with phase-coherent pulse pairs from an actively stabilized interferometer. More complex excitation fields are created with a liquid-crystal-based pulse shaper enabling amplitude and phase shaping of NOPA pulses with spectral components from 600 to 800 nm. With this system we demonstrate spectroscopy within a single plasmonic nanoslit resonator by spectral amplitude shaping and investigate the local field dynamics with coherent two-dimensional (2D) spectroscopy at the nanometer length scale (“2D nanoscopy”). We show that the local response varies across a distance as small as 33 nm in our sample. Further, we report two-color pump–probe experiments using two independent NOPA beamlines. We extract local variations of the excited-state dynamics of a monolayered 2D material (WSe2) that we correlate with low-energy electron microscopy (LEEM) and reflectivity measurements. Finally, we demonstrate the in situ sample preparation capabilities for organic thin films and their characterization via spatially resolved electron diffraction and dark-field LEEM.}, author = {Huber, Bernhard and Pres, Sebastian and Wittmann, Emanuel and Dietrich, Lysanne and Lüttig, Julian and Fersch, Daniel and Krauss, Enno and Friedrich, Daniel and Kern, Johannes and Lisinetskii, Victor and Hensen, Matthias and Hecht, Bert and Bratschitsch, Rudolf and Riedle, Eberhard and Brixner, Tobias}, journal = {Rev. Sci. Instrum.}, keywords = {plasmon}, month = 11, number = 11, pages = 113103, title = {Space- and time-resolved UV-to-NIR surface spectroscopy and 2D nanoscopy at 1 MHz repetition rate}, volume = 90, year = 2019 }

%0 Journal Article %1 huber2019space %A Huber, Bernhard %A Pres, Sebastian %A Wittmann, Emanuel %A Dietrich, Lysanne %A Lüttig, Julian %A Fersch, Daniel %A Krauss, Enno %A Friedrich, Daniel %A Kern, Johannes %A Lisinetskii, Victor %A Hensen, Matthias %A Hecht, Bert %A Bratschitsch, Rudolf %A Riedle, Eberhard %A Brixner, Tobias %D 2019 %J Rev. Sci. Instrum. %N 11 %P 113103 %R 10.1063/1.5115322 %T Space- and time-resolved UV-to-NIR surface spectroscopy and 2D nanoscopy at 1 MHz repetition rate %V 90 %X We describe a setup for time-resolved photoemission electron microscopy with aberration correction enabling 3 nm spatial resolution and sub-20 fs temporal resolution. The latter is realized by our development of a widely tunable (215–970 nm) noncollinear optical parametric amplifier (NOPA) at 1 MHz repetition rate. We discuss several exemplary applications. Efficient photoemission from plasmonic Au nanoresonators is investigated with phase-coherent pulse pairs from an actively stabilized interferometer. More complex excitation fields are created with a liquid-crystal-based pulse shaper enabling amplitude and phase shaping of NOPA pulses with spectral components from 600 to 800 nm. With this system we demonstrate spectroscopy within a single plasmonic nanoslit resonator by spectral amplitude shaping and investigate the local field dynamics with coherent two-dimensional (2D) spectroscopy at the nanometer length scale (“2D nanoscopy”). We show that the local response varies across a distance as small as 33 nm in our sample. Further, we report two-color pump–probe experiments using two independent NOPA beamlines. We extract local variations of the excited-state dynamics of a monolayered 2D material (WSe2) that we correlate with low-energy electron microscopy (LEEM) and reflectivity measurements. Finally, we demonstrate the in situ sample preparation capabilities for organic thin films and their characterization via spatially resolved electron diffraction and dark-field LEEM.
Evidence for cascaded third harmonic generation in non-centrosymmetric gold nanoantennas. Celebrano, Michele; Locatelli, Andrea; Ghirardini, Lavinia; Pellegrini, Giovanni; Biagioni, Paolo; Zilli, Attilio; Wu, Xiaofei; Grossmann, Swen; Carletti, Luca; De Angelis, Costantino; Duò, Lamberto; Hecht, Bert; Finazzi, Marco. In Nano Lett., 19(10), pp. 7013–7020. 2019.

» arXiv:1803.03617 (2018)
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The optimization of nonlinear optical processes on the nanoscale is a crucial step for the integration of complex functionalities into compact photonic devices and metasurfaces. In such systems, photon upconversion can be achieved with higher efficiencies via third-order processes, such as third-harmonic generation (THG), thanks to the resonantly enhanced volume currents. Conversely, second-order processes, such as second-harmonic generation (SHG), are often inhibited by the symmetry of metal lattices and of common nanoantenna geometries. SHG and THG processes in plasmonic nanostructures are generally treated independently because they typically represent small perturbations in the light–matter interaction mechanisms. In this work, we demonstrate that this paradigm does not hold for plasmon-enhanced nonlinear optics by providing evidence of a sum-frequency generation (SFG) process seeded by SHG, which sizably contributes to the overall THG yield. We address this mechanism by unveiling a characteristic fingerprint in the polarization state of the THG emission from gold noncentrosymmetric nanoantennas, which directly reflects the asymmetric distribution of second-harmonic fields within the structure and does not depend on the model one employs to describe photon upconversion. We suggest that such cascaded processes may also appear for structures that exhibit only moderate SHG yields. The presence of this peculiar mechanism in THG from plasmonic nanoantennas at telecommunication wavelengths allows us to gain further insight into the physics of plasmon-enhanced nonlinear optical processes. This could be crucial in the realization of nanoscale elements for photon conversion and manipulation operating at room temperature.

@article{celebrano2019evidence, abstract = {The optimization of nonlinear optical processes on the nanoscale is a crucial step for the integration of complex functionalities into compact photonic devices and metasurfaces. In such systems, photon upconversion can be achieved with higher efficiencies via third-order processes, such as third-harmonic generation (THG), thanks to the resonantly enhanced volume currents. Conversely, second-order processes, such as second-harmonic generation (SHG), are often inhibited by the symmetry of metal lattices and of common nanoantenna geometries. SHG and THG processes in plasmonic nanostructures are generally treated independently because they typically represent small perturbations in the light–matter interaction mechanisms. In this work, we demonstrate that this paradigm does not hold for plasmon-enhanced nonlinear optics by providing evidence of a sum-frequency generation (SFG) process seeded by SHG, which sizably contributes to the overall THG yield. We address this mechanism by unveiling a characteristic fingerprint in the polarization state of the THG emission from gold noncentrosymmetric nanoantennas, which directly reflects the asymmetric distribution of second-harmonic fields within the structure and does not depend on the model one employs to describe photon upconversion. We suggest that such cascaded processes may also appear for structures that exhibit only moderate SHG yields. The presence of this peculiar mechanism in THG from plasmonic nanoantennas at telecommunication wavelengths allows us to gain further insight into the physics of plasmon-enhanced nonlinear optical processes. This could be crucial in the realization of nanoscale elements for photon conversion and manipulation operating at room temperature.}, author = {Celebrano, Michele and Locatelli, Andrea and Ghirardini, Lavinia and Pellegrini, Giovanni and Biagioni, Paolo and Zilli, Attilio and Wu, Xiaofei and Grossmann, Swen and Carletti, Luca and De Angelis, Costantino and Duò, Lamberto and Hecht, Bert and Finazzi, Marco}, journal = {Nano Lett.}, keywords = {plasmon}, month = 10, note = {<a href="https://arxiv.org/abs/1803.03617" style="font-style: normal;">» arXiv:1803.03617 (2018)</a>}, number = 10, pages = {7013-7020}, title = {Evidence for cascaded third harmonic generation in non-centrosymmetric gold nanoantennas}, volume = 19, year = 2019 }

%0 Journal Article %1 celebrano2019evidence %A Celebrano, Michele %A Locatelli, Andrea %A Ghirardini, Lavinia %A Pellegrini, Giovanni %A Biagioni, Paolo %A Zilli, Attilio %A Wu, Xiaofei %A Grossmann, Swen %A Carletti, Luca %A De Angelis, Costantino %A Duò, Lamberto %A Hecht, Bert %A Finazzi, Marco %D 2019 %J Nano Lett. %N 10 %P 7013-7020 %R 10.1021/acs.nanolett.9b02427 %T Evidence for cascaded third harmonic generation in non-centrosymmetric gold nanoantennas %V 19 %X The optimization of nonlinear optical processes on the nanoscale is a crucial step for the integration of complex functionalities into compact photonic devices and metasurfaces. In such systems, photon upconversion can be achieved with higher efficiencies via third-order processes, such as third-harmonic generation (THG), thanks to the resonantly enhanced volume currents. Conversely, second-order processes, such as second-harmonic generation (SHG), are often inhibited by the symmetry of metal lattices and of common nanoantenna geometries. SHG and THG processes in plasmonic nanostructures are generally treated independently because they typically represent small perturbations in the light–matter interaction mechanisms. In this work, we demonstrate that this paradigm does not hold for plasmon-enhanced nonlinear optics by providing evidence of a sum-frequency generation (SFG) process seeded by SHG, which sizably contributes to the overall THG yield. We address this mechanism by unveiling a characteristic fingerprint in the polarization state of the THG emission from gold noncentrosymmetric nanoantennas, which directly reflects the asymmetric distribution of second-harmonic fields within the structure and does not depend on the model one employs to describe photon upconversion. We suggest that such cascaded processes may also appear for structures that exhibit only moderate SHG yields. The presence of this peculiar mechanism in THG from plasmonic nanoantennas at telecommunication wavelengths allows us to gain further insight into the physics of plasmon-enhanced nonlinear optical processes. This could be crucial in the realization of nanoscale elements for photon conversion and manipulation operating at room temperature.
Spatial Variations in Femtosecond Field Dynamics within a Plasmonic Nanoresonator Mode. Hensen, Matthias; Huber, Bernhard; Friedrich, Daniel; Krauss, Enno; Pres, Sebastian; Grimm, Philipp; Fersch, Daniel; Lüttig, Julian; Lisinetskii, Victor; Hecht, Bert; Brixner, Tobias. In Nano Lett., 19(7), pp. 4651–4658. 2019.
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Plasmonic resonators can be designed to support spectrally well-separated discrete modes. The associated characteristic spatial patterns of intense electromagnetic hot-spots can be exploited to enhance light–matter interaction. Here, we study the local field dynamics of individual hot-spots within a nanoslit resonator by detecting characteristic changes of the photoelectron emission signal on a scale of ∼12 nm using time-resolved photoemission electron microscopy (TR-PEEM) and by excitation with the output from a 20 fs, 1 MHz noncollinear optical parametric amplifier (NOPA). Surprisingly, we detect apparent spatial variations of the Q-factor and resonance frequency that are commonly considered to be global properties for a single mode. By using the concept of quasinormal modes we explain these local differences by crosstalk of adjacent resonator modes. Our findings are important in view of time-domain studies of plasmon-mediated strong light–matter coupling at ambient conditions.

@article{hensen2019spatial, abstract = {Plasmonic resonators can be designed to support spectrally well-separated discrete modes. The associated characteristic spatial patterns of intense electromagnetic hot-spots can be exploited to enhance light–matter interaction. Here, we study the local field dynamics of individual hot-spots within a nanoslit resonator by detecting characteristic changes of the photoelectron emission signal on a scale of ∼12 nm using time-resolved photoemission electron microscopy (TR-PEEM) and by excitation with the output from a 20 fs, 1 MHz noncollinear optical parametric amplifier (NOPA). Surprisingly, we detect apparent spatial variations of the Q-factor and resonance frequency that are commonly considered to be global properties for a single mode. By using the concept of quasinormal modes we explain these local differences by crosstalk of adjacent resonator modes. Our findings are important in view of time-domain studies of plasmon-mediated strong light–matter coupling at ambient conditions.}, author = {Hensen, Matthias and Huber, Bernhard and Friedrich, Daniel and Krauss, Enno and Pres, Sebastian and Grimm, Philipp and Fersch, Daniel and Lüttig, Julian and Lisinetskii, Victor and Hecht, Bert and Brixner, Tobias}, journal = {Nano Lett.}, keywords = {plasmon}, month = {07}, number = 7, pages = {4651-4658}, title = {Spatial Variations in Femtosecond Field Dynamics within a Plasmonic Nanoresonator Mode}, volume = 19, year = 2019 }

%0 Journal Article %1 hensen2019spatial %A Hensen, Matthias %A Huber, Bernhard %A Friedrich, Daniel %A Krauss, Enno %A Pres, Sebastian %A Grimm, Philipp %A Fersch, Daniel %A Lüttig, Julian %A Lisinetskii, Victor %A Hecht, Bert %A Brixner, Tobias %D 2019 %J Nano Lett. %N 7 %P 4651-4658 %R 10.1021/acs.nanolett.9b01672 %T Spatial Variations in Femtosecond Field Dynamics within a Plasmonic Nanoresonator Mode %V 19 %X Plasmonic resonators can be designed to support spectrally well-separated discrete modes. The associated characteristic spatial patterns of intense electromagnetic hot-spots can be exploited to enhance light–matter interaction. Here, we study the local field dynamics of individual hot-spots within a nanoslit resonator by detecting characteristic changes of the photoelectron emission signal on a scale of ∼12 nm using time-resolved photoemission electron microscopy (TR-PEEM) and by excitation with the output from a 20 fs, 1 MHz noncollinear optical parametric amplifier (NOPA). Surprisingly, we detect apparent spatial variations of the Q-factor and resonance frequency that are commonly considered to be global properties for a single mode. By using the concept of quasinormal modes we explain these local differences by crosstalk of adjacent resonator modes. Our findings are important in view of time-domain studies of plasmon-mediated strong light–matter coupling at ambient conditions.
Nonclassical Optical Properties of Mesoscopic Gold. Großmann, Swen; Friedrich, Daniel; Karolak, Michael; Kullock, René; Krauss, Enno; Emmerling, Monika; Sangiovanni, Giorgio; Hecht, Bert. In Phys. Rev. Lett., 122(24), p. 246802. 2019.

» arxiv:1905.09942 (2019)
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Gold nanostructures have important applications in nanoelectronics, nano-optics, and in precision metrology due to their intriguing optoelectronic properties. These properties are governed by the bulk band structure but to some extent are tunable via geometrical resonances. Here we show that the band structure of gold itself exhibits significant size-dependent changes already for mesoscopic critical dimensions below 30 nm. To suppress the effects of geometrical resonances and grain boundaries, we prepared atomically flat ultrathin films of various thicknesses by utilizing large chemically grown single-crystalline gold platelets. We experimentally probe thickness-dependent changes of the band structure by means of two-photon photoluminescence and observe a surprising 100-fold increase of the nonlinear signal when the gold film thickness is reduced below 30 nm allowing us to optically resolve single-unit-cell steps. The effect is well explained by density functional calculations of the thickness-dependent 2D band structure of gold.

@article{gromann2019nonclassical, abstract = {Gold nanostructures have important applications in nanoelectronics, nano-optics, and in precision metrology due to their intriguing optoelectronic properties. These properties are governed by the bulk band structure but to some extent are tunable via geometrical resonances. Here we show that the band structure of gold itself exhibits significant size-dependent changes already for mesoscopic critical dimensions below 30 nm. To suppress the effects of geometrical resonances and grain boundaries, we prepared atomically flat ultrathin films of various thicknesses by utilizing large chemically grown single-crystalline gold platelets. We experimentally probe thickness-dependent changes of the band structure by means of two-photon photoluminescence and observe a surprising 100-fold increase of the nonlinear signal when the gold film thickness is reduced below 30 nm allowing us to optically resolve single-unit-cell steps. The effect is well explained by density functional calculations of the thickness-dependent 2D band structure of gold.}, author = {Großmann, Swen and Friedrich, Daniel and Karolak, Michael and Kullock, René and Krauss, Enno and Emmerling, Monika and Sangiovanni, Giorgio and Hecht, Bert}, journal = {Phys. Rev. Lett.}, keywords = {gold}, month = {06}, note = {<a href="https://arxiv.org/abs/1905.09942"style="font-style: normal;">» arxiv:1905.09942 (2019)</a>}, number = 24, pages = 246802, title = {Nonclassical Optical Properties of Mesoscopic Gold}, volume = 122, year = 2019 }

%0 Journal Article %1 gromann2019nonclassical %A Großmann, Swen %A Friedrich, Daniel %A Karolak, Michael %A Kullock, René %A Krauss, Enno %A Emmerling, Monika %A Sangiovanni, Giorgio %A Hecht, Bert %D 2019 %J Phys. Rev. Lett. %N 24 %P 246802 %R 10.1103/PhysRevLett.122.246802 %T Nonclassical Optical Properties of Mesoscopic Gold %V 122 %X Gold nanostructures have important applications in nanoelectronics, nano-optics, and in precision metrology due to their intriguing optoelectronic properties. These properties are governed by the bulk band structure but to some extent are tunable via geometrical resonances. Here we show that the band structure of gold itself exhibits significant size-dependent changes already for mesoscopic critical dimensions below 30 nm. To suppress the effects of geometrical resonances and grain boundaries, we prepared atomically flat ultrathin films of various thicknesses by utilizing large chemically grown single-crystalline gold platelets. We experimentally probe thickness-dependent changes of the band structure by means of two-photon photoluminescence and observe a surprising 100-fold increase of the nonlinear signal when the gold film thickness is reduced below 30 nm allowing us to optically resolve single-unit-cell steps. The effect is well explained by density functional calculations of the thickness-dependent 2D band structure of gold.
Reversible Mapping and Sorting the Spin of Photons on the Nanoscale: A Spin-Optical Nanodevice. Krauss, Enno; Razinskas, Gary; Köck, Dominik; Grossmann, Swen; Hecht, Bert. In Nano Lett., 19(5), pp. 3364–3369. 2019.

» arxiv:1812.03721 (2018)
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The photon spin is an important resource for quantum information processing as is the electron spin in spintronics. However, for subwavelength confined optical excitations, polarization as a global property of a mode cannot be defined. Here, we show that any polarization state of a plane-wave photon can reversibly be mapped to a pseudospin embodied by the two fundamental modes of a subwavelength plasmonic two-wire transmission line. We design a device in which this pseudospin evolves in a well-defined fashion throughout the device reminiscent of the evolution of photon polarization in a birefringent medium and the behavior of electron spins in the channel of a spin field-effect transistor. The significance of this pseudospin is enriched by the fact that it is subject to spin–orbit locking. Combined with optically active materials to exert external control over the pseudospin precession, our findings could enable spin-optical transistors, that is, the routing and processing of quantum information with light on a subwavelength scale.

@article{krauss2019reversible, abstract = {The photon spin is an important resource for quantum information processing as is the electron spin in spintronics. However, for subwavelength confined optical excitations, polarization as a global property of a mode cannot be defined. Here, we show that any polarization state of a plane-wave photon can reversibly be mapped to a pseudospin embodied by the two fundamental modes of a subwavelength plasmonic two-wire transmission line. We design a device in which this pseudospin evolves in a well-defined fashion throughout the device reminiscent of the evolution of photon polarization in a birefringent medium and the behavior of electron spins in the channel of a spin field-effect transistor. The significance of this pseudospin is enriched by the fact that it is subject to spin–orbit locking. Combined with optically active materials to exert external control over the pseudospin precession, our findings could enable spin-optical transistors, that is, the routing and processing of quantum information with light on a subwavelength scale.}, author = {Krauss, Enno and Razinskas, Gary and Köck, Dominik and Grossmann, Swen and Hecht, Bert}, journal = {Nano Lett.}, keywords = {plasmon}, month = {05}, note = {<a href="https://arxiv.org/abs/1812.03721"style="font-style: normal;">» arxiv:1812.03721 (2018)</a>}, number = 5, pages = {3364-3369}, title = {Reversible Mapping and Sorting the Spin of Photons on the Nanoscale: A Spin-Optical Nanodevice}, volume = 19, year = 2019 }

%0 Journal Article %1 krauss2019reversible %A Krauss, Enno %A Razinskas, Gary %A Köck, Dominik %A Grossmann, Swen %A Hecht, Bert %D 2019 %J Nano Lett. %N 5 %P 3364-3369 %R 10.1021/acs.nanolett.9b01162 %T Reversible Mapping and Sorting the Spin of Photons on the Nanoscale: A Spin-Optical Nanodevice %V 19 %X The photon spin is an important resource for quantum information processing as is the electron spin in spintronics. However, for subwavelength confined optical excitations, polarization as a global property of a mode cannot be defined. Here, we show that any polarization state of a plane-wave photon can reversibly be mapped to a pseudospin embodied by the two fundamental modes of a subwavelength plasmonic two-wire transmission line. We design a device in which this pseudospin evolves in a well-defined fashion throughout the device reminiscent of the evolution of photon polarization in a birefringent medium and the behavior of electron spins in the channel of a spin field-effect transistor. The significance of this pseudospin is enriched by the fact that it is subject to spin–orbit locking. Combined with optically active materials to exert external control over the pseudospin precession, our findings could enable spin-optical transistors, that is, the routing and processing of quantum information with light on a subwavelength scale.

Interference in edge-scattering from monocrystalline gold flakes [Invited]. Boroviks, Sergejs; Wolff, Christian; Linnet, Jes; Yang, Yuanqing; Todisco, Francesco; Roberts, Alexander S.; Bozhevolnyi, Sergey I.; Hecht, Bert; Mortensen, N. Asger. In Opt. Mater. Express, 8(12), pp. 3688–3697. 2018.
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We observe strongly dissimilar scattering from the two types of sidewall configurations (here referred to as “edges”) in hexagonal quasi-monocrystalline gold flakes with thicknesses around 1 micron. As the origin of the phenomena, we identify the interference between a direct, quasi-specular scattering and an indirect scattering process involving an intermediate surface-plasmon state. The dissimilarity between the two types of edges is a direct consequence of the three-fold symmetry around the [111]-axis and the intrinsic chirality of a face-centered cubic lattice. We propose that this effect can be potentially used to estimate dielectric function of the monocrystalline gold.

@article{boroviks2018interference, abstract = {We observe strongly dissimilar scattering from the two types of sidewall configurations (here referred to as “edges”) in hexagonal quasi-monocrystalline gold flakes with thicknesses around 1 micron. As the origin of the phenomena, we identify the interference between a direct, quasi-specular scattering and an indirect scattering process involving an intermediate surface-plasmon state. The dissimilarity between the two types of edges is a direct consequence of the three-fold symmetry around the [111]-axis and the intrinsic chirality of a face-centered cubic lattice. We propose that this effect can be potentially used to estimate dielectric function of the monocrystalline gold.}, author = {Boroviks, Sergejs and Wolff, Christian and Linnet, Jes and Yang, Yuanqing and Todisco, Francesco and Roberts, Alexander S. and Bozhevolnyi, Sergey I. and Hecht, Bert and Mortensen, N. Asger}, journal = {Opt. Mater. Express}, keywords = {gold}, month = 12, number = 12, pages = {3688-3697}, title = {Interference in edge-scattering from monocrystalline gold flakes [Invited]}, volume = 8, year = 2018 }

%0 Journal Article %1 boroviks2018interference %A Boroviks, Sergejs %A Wolff, Christian %A Linnet, Jes %A Yang, Yuanqing %A Todisco, Francesco %A Roberts, Alexander S. %A Bozhevolnyi, Sergey I. %A Hecht, Bert %A Mortensen, N. Asger %D 2018 %J Opt. Mater. Express %N 12 %P 3688-3697 %R 10.1364/OME.8.003688 %T Interference in edge-scattering from monocrystalline gold flakes [Invited] %V 8 %X We observe strongly dissimilar scattering from the two types of sidewall configurations (here referred to as “edges”) in hexagonal quasi-monocrystalline gold flakes with thicknesses around 1 micron. As the origin of the phenomena, we identify the interference between a direct, quasi-specular scattering and an indirect scattering process involving an intermediate surface-plasmon state. The dissimilarity between the two types of edges is a direct consequence of the three-fold symmetry around the [111]-axis and the intrinsic chirality of a face-centered cubic lattice. We propose that this effect can be potentially used to estimate dielectric function of the monocrystalline gold.
High-Q, low-mode-volume and multiresonant plasmonic nanoslit cavities fabricated by helium ion milling. Chen, Kai; Razinskas, Gary; Vieker, Henning; Gross, Heiko; Wu, Xiaofei; Beyer, André; Gölzhäuser, Armin; Hecht, Bert. In Nanoscale, 10(36), pp. 17148–17155. 2018.
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Helium ion milling of chemically-synthesized micron-sized gold flakes is performed to fabricate ultra-narrow nanoslit cavities with a varying length and width down to 5 nm. Their plasmon resonances are characterized by one-photon photoluminescence spectroscopy. The combination of fabrication based on single-crystalline gold and resonant modes with low radiative losses leads to remarkably high quality factors of up to 24. Multiple Fabry–Pérot-type resonances in the visible/near infrared spectral range are observed due to the achieved narrow slit widths and the resulting short effective wavelengths of nanoslit plasmons. These features make nanoslit cavities attractive for a range of applications such as surface-enhanced spectroscopy, ultrafast nano-optics and strong light–matter coupling.

@article{chen2018highq, abstract = {Helium ion milling of chemically-synthesized micron-sized gold flakes is performed to fabricate ultra-narrow nanoslit cavities with a varying length and width down to 5 nm. Their plasmon resonances are characterized by one-photon photoluminescence spectroscopy. The combination of fabrication based on single-crystalline gold and resonant modes with low radiative losses leads to remarkably high quality factors of up to 24. Multiple Fabry–Pérot-type resonances in the visible/near infrared spectral range are observed due to the achieved narrow slit widths and the resulting short effective wavelengths of nanoslit plasmons. These features make nanoslit cavities attractive for a range of applications such as surface-enhanced spectroscopy, ultrafast nano-optics and strong light–matter coupling.}, author = {Chen, Kai and Razinskas, Gary and Vieker, Henning and Gross, Heiko and Wu, Xiaofei and Beyer, André and Gölzhäuser, Armin and Hecht, Bert}, journal = {Nanoscale}, keywords = {resonance}, month = {09}, number = 36, pages = {17148-17155}, title = {High-Q, low-mode-volume and multiresonant plasmonic nanoslit cavities fabricated by helium ion milling}, volume = 10, year = 2018 }

%0 Journal Article %1 chen2018highq %A Chen, Kai %A Razinskas, Gary %A Vieker, Henning %A Gross, Heiko %A Wu, Xiaofei %A Beyer, André %A Gölzhäuser, Armin %A Hecht, Bert %D 2018 %J Nanoscale %N 36 %P 17148-17155 %R 10.1039/C8NR02160K %T High-Q, low-mode-volume and multiresonant plasmonic nanoslit cavities fabricated by helium ion milling %V 10 %X Helium ion milling of chemically-synthesized micron-sized gold flakes is performed to fabricate ultra-narrow nanoslit cavities with a varying length and width down to 5 nm. Their plasmon resonances are characterized by one-photon photoluminescence spectroscopy. The combination of fabrication based on single-crystalline gold and resonant modes with low radiative losses leads to remarkably high quality factors of up to 24. Multiple Fabry–Pérot-type resonances in the visible/near infrared spectral range are observed due to the achieved narrow slit widths and the resulting short effective wavelengths of nanoslit plasmons. These features make nanoslit cavities attractive for a range of applications such as surface-enhanced spectroscopy, ultrafast nano-optics and strong light–matter coupling.
Gap-mode-assisted light-induced switching of sub-wavelength magnetic domains. Scheunert, G.; McCarron, R.; Kullock, R.; Cohen, S. R.; Rechav, K.; Kaplan-Ashiri, I.; Bitton, O.; Hecht, B.; Oron, D. In J. Appl. Phys., 123(14), p. 143102. 2018.
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Creating sub-micron hotspots for applications such as heat-assisted magnetic recording (HAMR) is a challenging task. The most common approach relies on a surface-plasmon resonator (SPR), whose design dictates the size of the hotspot to always be larger than its critical dimension. Here, we present an approach which circumvents known geometrica restrictions by resorting to electric field confinement via excitation of a gap-mode (GM) between a comparatively large Gold (Au) nano-sphere (radius of 100 nm) and the magnetic medium in a grazing-incidence configuration. Operating a λ=785 nm laser, sub-200 nm hot spots have been generated and successfully used for GM-assisted magnetic switching on commercial CoCrPt perpendicular magnetic recording media at laser powers and pulse durations comparable to SPR-based HAMR. Lumerical electric field modelling confirmed that operating in the near-infrared regime presents a suitable working point where most of the light's energy is deposited in the magnetic layer, rather than in the nano-particle. Further, modelling is used for predicting the limits of our method which, in theory, can yield sub-30 nm hotspots for Au nano-sphere radii of 25–50 nm for efficient heating of FePt recording media with a gap of 5 nm.

@article{scheunert2018gapmodeassisted, abstract = {Creating sub-micron hotspots for applications such as heat-assisted magnetic recording (HAMR) is a challenging task. The most common approach relies on a surface-plasmon resonator (SPR), whose design dictates the size of the hotspot to always be larger than its critical dimension. Here, we present an approach which circumvents known geometrica restrictions by resorting to electric field confinement via excitation of a gap-mode (GM) between a comparatively large Gold (Au) nano-sphere (radius of 100 nm) and the magnetic medium in a grazing-incidence configuration. Operating a λ=785 nm laser, sub-200 nm hot spots have been generated and successfully used for GM-assisted magnetic switching on commercial CoCrPt perpendicular magnetic recording media at laser powers and pulse durations comparable to SPR-based HAMR. Lumerical electric field modelling confirmed that operating in the near-infrared regime presents a suitable working point where most of the light's energy is deposited in the magnetic layer, rather than in the nano-particle. Further, modelling is used for predicting the limits of our method which, in theory, can yield sub-30 nm hotspots for Au nano-sphere radii of 25–50 nm for efficient heating of FePt recording media with a gap of 5 nm.}, author = {Scheunert, G. and McCarron, R. and Kullock, R. and Cohen, S. R. and Rechav, K. and Kaplan-Ashiri, I. and Bitton, O. and Hecht, B. and Oron, D.}, journal = {J. Appl. Phys.}, keywords = {plasmon}, month = {04}, number = 14, pages = 143102, title = {Gap-mode-assisted light-induced switching of sub-wavelength magnetic domains}, volume = 123, year = 2018 }

%0 Journal Article %1 scheunert2018gapmodeassisted %A Scheunert, G. %A McCarron, R. %A Kullock, R. %A Cohen, S. R. %A Rechav, K. %A Kaplan-Ashiri, I. %A Bitton, O. %A Hecht, B. %A Oron, D. %D 2018 %J J. Appl. Phys. %N 14 %P 143102 %R 10.1063/1.5016970 %T Gap-mode-assisted light-induced switching of sub-wavelength magnetic domains %V 123 %X Creating sub-micron hotspots for applications such as heat-assisted magnetic recording (HAMR) is a challenging task. The most common approach relies on a surface-plasmon resonator (SPR), whose design dictates the size of the hotspot to always be larger than its critical dimension. Here, we present an approach which circumvents known geometrica restrictions by resorting to electric field confinement via excitation of a gap-mode (GM) between a comparatively large Gold (Au) nano-sphere (radius of 100 nm) and the magnetic medium in a grazing-incidence configuration. Operating a λ=785 nm laser, sub-200 nm hot spots have been generated and successfully used for GM-assisted magnetic switching on commercial CoCrPt perpendicular magnetic recording media at laser powers and pulse durations comparable to SPR-based HAMR. Lumerical electric field modelling confirmed that operating in the near-infrared regime presents a suitable working point where most of the light's energy is deposited in the magnetic layer, rather than in the nano-particle. Further, modelling is used for predicting the limits of our method which, in theory, can yield sub-30 nm hotspots for Au nano-sphere radii of 25–50 nm for efficient heating of FePt recording media with a gap of 5 nm.
Parallel mapping of optical near-field interactions by molecular motor-driven quantum dots. Groß, Heiko; Heil, Hannah S.; Ehrig, Jens; Schwarz, Friedrich W.; Hecht, Bert; Diez, Stefan. In Nature Nanotech., 13(8), pp. 691–695. 2018.
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In the vicinity of metallic nanostructures, absorption and emission rates of optical emitters can be modulated by several orders of magnitude. Control of such near-field light–matter interaction is essential for applications in biosensing, light harvesting and quantum communication and requires precise mapping of optical near-field interactions, for which single-emitter probes are promising candidates. However, currently available techniques are limited in terms of throughput, resolution and/or non-invasiveness. Here, we present an approach for the parallel mapping of optical near-field interactions with a resolution of {\textless}5 nm using surface-bound motor proteins to transport microtubules carrying single emitters (quantum dots). The deterministic motion of the quantum dots allows for the interpolation of their tracked positions, resulting in an increased spatial resolution and a suppression of localization artefacts. We apply this method to map the near-field distribution of nanoslits engraved into gold layers and find an excellent agreement with finite-difference time-domain simulations. Our technique can be readily applied to a variety of surfaces for scalable, nanometre-resolved and artefact-free near-field mapping using conventional wide-field microscopes.

@article{gro2018parallel, abstract = {In the vicinity of metallic nanostructures, absorption and emission rates of optical emitters can be modulated by several orders of magnitude. Control of such near-field light–matter interaction is essential for applications in biosensing, light harvesting and quantum communication and requires precise mapping of optical near-field interactions, for which single-emitter probes are promising candidates. However, currently available techniques are limited in terms of throughput, resolution and/or non-invasiveness. Here, we present an approach for the parallel mapping of optical near-field interactions with a resolution of {\textless}5 nm using surface-bound motor proteins to transport microtubules carrying single emitters (quantum dots). The deterministic motion of the quantum dots allows for the interpolation of their tracked positions, resulting in an increased spatial resolution and a suppression of localization artefacts. We apply this method to map the near-field distribution of nanoslits engraved into gold layers and find an excellent agreement with finite-difference time-domain simulations. Our technique can be readily applied to a variety of surfaces for scalable, nanometre-resolved and artefact-free near-field mapping using conventional wide-field microscopes.}, author = {Groß, Heiko and Heil, Hannah S. and Ehrig, Jens and Schwarz, Friedrich W. and Hecht, Bert and Diez, Stefan}, journal = {Nature Nanotech.}, keywords = {near-field}, month = {04}, number = 8, pages = {691-695}, title = {Parallel mapping of optical near-field interactions by molecular motor-driven quantum dots}, volume = 13, year = 2018 }

%0 Journal Article %1 gro2018parallel %A Groß, Heiko %A Heil, Hannah S. %A Ehrig, Jens %A Schwarz, Friedrich W. %A Hecht, Bert %A Diez, Stefan %D 2018 %J Nature Nanotech. %N 8 %P 691-695 %R 10.1038/s41565-018-0123-1 %T Parallel mapping of optical near-field interactions by molecular motor-driven quantum dots %V 13 %X In the vicinity of metallic nanostructures, absorption and emission rates of optical emitters can be modulated by several orders of magnitude. Control of such near-field light–matter interaction is essential for applications in biosensing, light harvesting and quantum communication and requires precise mapping of optical near-field interactions, for which single-emitter probes are promising candidates. However, currently available techniques are limited in terms of throughput, resolution and/or non-invasiveness. Here, we present an approach for the parallel mapping of optical near-field interactions with a resolution of {\textless}5 nm using surface-bound motor proteins to transport microtubules carrying single emitters (quantum dots). The deterministic motion of the quantum dots allows for the interpolation of their tracked positions, resulting in an increased spatial resolution and a suppression of localization artefacts. We apply this method to map the near-field distribution of nanoslits engraved into gold layers and find an excellent agreement with finite-difference time-domain simulations. Our technique can be readily applied to a variety of surfaces for scalable, nanometre-resolved and artefact-free near-field mapping using conventional wide-field microscopes.
Near-field strong coupling of single quantum dots. Groß, Heiko; Hamm, Joachim M.; Tufarelli, Tommaso; Hess, Ortwin; Hecht, Bert. In Science Advances, 4(3), p. eaar4906. 2018.

» BR2 - IQ Wissenschaft und Forschung - Magazin (min 19:51)
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Strong coupling and the resultant mixing of light and matter states is an important asset for future quantum technologies. We demonstrate deterministic room temperature strong coupling of a mesoscopic colloidal quantum dot to a plasmonic nanoresonator at the apex of a scanning probe. Enormous Rabi splittings of up to 110 meV are accomplished by nanometer-precise positioning of the quantum dot with respect to the nanoresonator probe. We find that, in addition to a small mode volume of the nanoresonator, collective coherent coupling of quantum dot band-edge states and near-field proximity interaction are vital ingredients for the realization of near-field strong coupling of mesoscopic quantum dots. The broadband nature of the interaction paves the road toward ultrafast coherent manipulation of the coupled quantum dot-plasmon system under ambient conditions.

@article{gro2018nearfield, abstract = {Strong coupling and the resultant mixing of light and matter states is an important asset for future quantum technologies. We demonstrate deterministic room temperature strong coupling of a mesoscopic colloidal quantum dot to a plasmonic nanoresonator at the apex of a scanning probe. Enormous Rabi splittings of up to 110 meV are accomplished by nanometer-precise positioning of the quantum dot with respect to the nanoresonator probe. We find that, in addition to a small mode volume of the nanoresonator, collective coherent coupling of quantum dot band-edge states and near-field proximity interaction are vital ingredients for the realization of near-field strong coupling of mesoscopic quantum dots. The broadband nature of the interaction paves the road toward ultrafast coherent manipulation of the coupled quantum dot-plasmon system under ambient conditions.}, author = {Groß, Heiko and Hamm, Joachim M. and Tufarelli, Tommaso and Hess, Ortwin and Hecht, Bert}, journal = {Science Advances}, keywords = {autocorrelation}, month = {03}, note = {<a href="https://www.br.de/radio/bayern2/programmkalender/ausstrahlung-1369978.html"style="font-style: normal;">» BR2 - IQ Wissenschaft und Forschung - Magazin (min 19:51)</a>}, number = 3, pages = {eaar4906}, title = {Near-field strong coupling of single quantum dots}, volume = 4, year = 2018 }

%0 Journal Article %1 gro2018nearfield %A Groß, Heiko %A Hamm, Joachim M. %A Tufarelli, Tommaso %A Hess, Ortwin %A Hecht, Bert %D 2018 %J Science Advances %N 3 %P eaar4906 %R 10.1126/sciadv.aar4906 %T Near-field strong coupling of single quantum dots %V 4 %X Strong coupling and the resultant mixing of light and matter states is an important asset for future quantum technologies. We demonstrate deterministic room temperature strong coupling of a mesoscopic colloidal quantum dot to a plasmonic nanoresonator at the apex of a scanning probe. Enormous Rabi splittings of up to 110 meV are accomplished by nanometer-precise positioning of the quantum dot with respect to the nanoresonator probe. We find that, in addition to a small mode volume of the nanoresonator, collective coherent coupling of quantum dot band-edge states and near-field proximity interaction are vital ingredients for the realization of near-field strong coupling of mesoscopic quantum dots. The broadband nature of the interaction paves the road toward ultrafast coherent manipulation of the coupled quantum dot-plasmon system under ambient conditions.
Controlled Growth of High-Aspect-Ratio Single-Crystalline Gold Platelets. Krauss, Enno; Kullock, René; Wu, Xiaofei; Geisler, Peter; Lundt, Nils; Kamp, Martin; Hecht, Bert. In Cryst. Growth Des., 18(3), pp. 1297–1302. 2018.
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We describe the wet-chemical synthesis of high-aspect-ratio single-crystalline gold platelets with thicknesses down to 20 nm and edge lengths up to 0.2 mm. By employing statistical analysis of a large number of platelets, we investigate the effect of temperature on the growth velocities of the top and side facets for constant concentrations of the three common ingredients: ethylene glycol, chloroauric acid, and water. We further show that by varying the chemical environment during growth, the ratio between the growth velocities can be adjusted, and thus thickness and lateral size can be tuned independently. Very large but ultrathin single-crystalline gold platelets represent an important starting material for top-down nanofabrication and may also find applications as transparent conducting substrates as well as substrates for high-end scanning probe and electron microscopy.

@article{krauss2018controlled, abstract = {We describe the wet-chemical synthesis of high-aspect-ratio single-crystalline gold platelets with thicknesses down to 20 nm and edge lengths up to 0.2 mm. By employing statistical analysis of a large number of platelets, we investigate the effect of temperature on the growth velocities of the top and side facets for constant concentrations of the three common ingredients: ethylene glycol, chloroauric acid, and water. We further show that by varying the chemical environment during growth, the ratio between the growth velocities can be adjusted, and thus thickness and lateral size can be tuned independently. Very large but ultrathin single-crystalline gold platelets represent an important starting material for top-down nanofabrication and may also find applications as transparent conducting substrates as well as substrates for high-end scanning probe and electron microscopy.}, author = {Krauss, Enno and Kullock, René and Wu, Xiaofei and Geisler, Peter and Lundt, Nils and Kamp, Martin and Hecht, Bert}, journal = {Cryst. Growth Des.}, keywords = {gold}, month = {03}, number = 3, pages = {1297-1302}, title = {Controlled Growth of High-Aspect-Ratio Single-Crystalline Gold Platelets}, volume = 18, year = 2018 }

%0 Journal Article %1 krauss2018controlled %A Krauss, Enno %A Kullock, René %A Wu, Xiaofei %A Geisler, Peter %A Lundt, Nils %A Kamp, Martin %A Hecht, Bert %D 2018 %J Cryst. Growth Des. %N 3 %P 1297-1302 %R 10.1021/acs.cgd.7b00849 %T Controlled Growth of High-Aspect-Ratio Single-Crystalline Gold Platelets %V 18 %X We describe the wet-chemical synthesis of high-aspect-ratio single-crystalline gold platelets with thicknesses down to 20 nm and edge lengths up to 0.2 mm. By employing statistical analysis of a large number of platelets, we investigate the effect of temperature on the growth velocities of the top and side facets for constant concentrations of the three common ingredients: ethylene glycol, chloroauric acid, and water. We further show that by varying the chemical environment during growth, the ratio between the growth velocities can be adjusted, and thus thickness and lateral size can be tuned independently. Very large but ultrathin single-crystalline gold platelets represent an important starting material for top-down nanofabrication and may also find applications as transparent conducting substrates as well as substrates for high-end scanning probe and electron microscopy.
Limits of Kirchhoff’s Laws in Plasmonics. Razinskas, Gary; Biagioni, Paolo; Hecht, Bert. In Sci Rep, 8(1), pp. 1–9. 2018.
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The validity of Kirchhoff’s laws in plasmonic nanocircuitry is investigated by studying a junction of plasmonic two-wire transmission lines. We find that Kirchhoff’s laws are valid for sufficiently small values of a phenomenological parameter κ relating the geometrical parameters of the transmission line with the effective wavelength of the guided mode. Beyond such regime, for large values of the phenomenological parameter, increasing deviations occur and the equivalent impedance description (Kirchhoff’s laws) can only provide rough, but nevertheless useful, guidelines for the design of more complex plasmonic circuitry. As an example we investigate a system composed of a two-wire transmission line and a nanoantenna as the load. By addition of a parallel stub designed according to Kirchhoff’s laws we achieve maximum signal transfer to the nanoantenna.

@article{razinskas2018limits, abstract = {The validity of Kirchhoff’s laws in plasmonic nanocircuitry is investigated by studying a junction of plasmonic two-wire transmission lines. We find that Kirchhoff’s laws are valid for sufficiently small values of a phenomenological parameter κ relating the geometrical parameters of the transmission line with the effective wavelength of the guided mode. Beyond such regime, for large values of the phenomenological parameter, increasing deviations occur and the equivalent impedance description (Kirchhoff’s laws) can only provide rough, but nevertheless useful, guidelines for the design of more complex plasmonic circuitry. As an example we investigate a system composed of a two-wire transmission line and a nanoantenna as the load. By addition of a parallel stub designed according to Kirchhoff’s laws we achieve maximum signal transfer to the nanoantenna.}, author = {Razinskas, Gary and Biagioni, Paolo and Hecht, Bert}, journal = {Sci Rep}, keywords = {plasmon}, month = {01}, number = 1, pages = {1-9}, title = {Limits of Kirchhoff’s Laws in Plasmonics}, volume = 8, year = 2018 }

%0 Journal Article %1 razinskas2018limits %A Razinskas, Gary %A Biagioni, Paolo %A Hecht, Bert %D 2018 %J Sci Rep %N 1 %P 1-9 %R 10.1038/s41598-018-20239-x %T Limits of Kirchhoff’s Laws in Plasmonics %V 8 %X The validity of Kirchhoff’s laws in plasmonic nanocircuitry is investigated by studying a junction of plasmonic two-wire transmission lines. We find that Kirchhoff’s laws are valid for sufficiently small values of a phenomenological parameter κ relating the geometrical parameters of the transmission line with the effective wavelength of the guided mode. Beyond such regime, for large values of the phenomenological parameter, increasing deviations occur and the equivalent impedance description (Kirchhoff’s laws) can only provide rough, but nevertheless useful, guidelines for the design of more complex plasmonic circuitry. As an example we investigate a system composed of a two-wire transmission line and a nanoantenna as the load. By addition of a parallel stub designed according to Kirchhoff’s laws we achieve maximum signal transfer to the nanoantenna.
Directed emission by electrically driven optical antennas. Kullock, René; Grimm, Philipp; Ochs, Maximilian; Hecht, Bert. In SPIE OPTO, 10540, p. 1054012. International Society for Optics and Photonics, 2018.
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Antennas play a key role in today’s wireless communication networks and it would be hugely beneficial to extent their use into the optical regime. However, classical signal generators do not work at those frequencies and therefore new concepts are needed. Here, we demonstrate how to electrically drive an optical nanoantenna using an atomic-scale feed gap provided by a gold-particle pushed into a precisely tailored interstice between two antenna arms. Upon applying a voltage, inelastic electron tunneling leads to current fluctuations in the optical regime and, hence, light emission. We show how the antennas spectrally shape the emission, how the exact particle position influences these properties and how to increase the directivity via Yagi-Uda arrangements or plasmonic waveguides structures in order to make electricallydriven optical nanoantennas more suitable for on-chip data communication.

@article{kullock2018directed, abstract = {Antennas play a key role in today’s wireless communication networks and it would be hugely beneficial to extent their use into the optical regime. However, classical signal generators do not work at those frequencies and therefore new concepts are needed. Here, we demonstrate how to electrically drive an optical nanoantenna using an atomic-scale feed gap provided by a gold-particle pushed into a precisely tailored interstice between two antenna arms. Upon applying a voltage, inelastic electron tunneling leads to current fluctuations in the optical regime and, hence, light emission. We show how the antennas spectrally shape the emission, how the exact particle position influences these properties and how to increase the directivity via Yagi-Uda arrangements or plasmonic waveguides structures in order to make electricallydriven optical nanoantennas more suitable for on-chip data communication.}, author = {Kullock, René and Grimm, Philipp and Ochs, Maximilian and Hecht, Bert}, booktitle = {Quantum Sensing and Nano Electronics and Photonics XV}, journal = {SPIE OPTO}, keywords = {gold}, month = {01}, pages = 1054012, publisher = {International Society for Optics and Photonics}, title = {Directed emission by electrically driven optical antennas}, volume = 10540, year = 2018 }

%0 Journal Article %1 kullock2018directed %A Kullock, René %A Grimm, Philipp %A Ochs, Maximilian %A Hecht, Bert %B Quantum Sensing and Nano Electronics and Photonics XV %D 2018 %I International Society for Optics and Photonics %J SPIE OPTO %P 1054012 %R 10.1117/12.2289647 %T Directed emission by electrically driven optical antennas %V 10540 %X Antennas play a key role in today’s wireless communication networks and it would be hugely beneficial to extent their use into the optical regime. However, classical signal generators do not work at those frequencies and therefore new concepts are needed. Here, we demonstrate how to electrically drive an optical nanoantenna using an atomic-scale feed gap provided by a gold-particle pushed into a precisely tailored interstice between two antenna arms. Upon applying a voltage, inelastic electron tunneling leads to current fluctuations in the optical regime and, hence, light emission. We show how the antennas spectrally shape the emission, how the exact particle position influences these properties and how to increase the directivity via Yagi-Uda arrangements or plasmonic waveguides structures in order to make electricallydriven optical nanoantennas more suitable for on-chip data communication.

Cavity-assisted ultrafast long-range periodic energy transfer between plasmonic nanoantennas. Aeschlimann, Martin; Brixner, Tobias; Cinchetti, Mirko; Frisch, Benjamin; Hecht, Bert; Hensen, Matthias; Huber, Bernhard; Kramer, Christian; Krauss, Enno; Loeber, Thomas H.; Pfeiffer, Walter; Piecuch, Martin; Thielen, Philip. In Light Sci Appl, 6(11), p. e17111. 2017.
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Radiationless energy transfer is at the core of diverse phenomena, such as light harvesting in photosynthesis, energy-transfer-based microspectroscopies, nanoscale quantum entanglement and photonic-mode hybridization. Typically, the transfer is efficient only for separations that are much shorter than the diffraction limit. This hampers its application in optical communication and quantum information processing, which require spatially selective addressing. Here, we demonstrate highly efficient radiationless coherent energy transfer over a distance of twice the excitation wavelength by combining localized and delocalized plasmonic modes. Analogous to the Tavis–Cummings model, two whispering-gallery-mode antennas placed in the foci of an elliptical plasmonic cavity fabricated from single-crystal gold plates act as a pair of oscillators coupled to a common cavity mode. Time-resolved two-photon photoemission electron microscopy (TR 2P-PEEM) reveals an ultrafast long-range periodic energy transfer in accordance with the simulations. Our observations open perspectives for the optimization and tailoring of mesoscopic energy transfer and long-range quantum emitter coupling.

@article{aeschlimann2017cavityassisted, abstract = {Radiationless energy transfer is at the core of diverse phenomena, such as light harvesting in photosynthesis, energy-transfer-based microspectroscopies, nanoscale quantum entanglement and photonic-mode hybridization. Typically, the transfer is efficient only for separations that are much shorter than the diffraction limit. This hampers its application in optical communication and quantum information processing, which require spatially selective addressing. Here, we demonstrate highly efficient radiationless coherent energy transfer over a distance of twice the excitation wavelength by combining localized and delocalized plasmonic modes. Analogous to the Tavis–Cummings model, two whispering-gallery-mode antennas placed in the foci of an elliptical plasmonic cavity fabricated from single-crystal gold plates act as a pair of oscillators coupled to a common cavity mode. Time-resolved two-photon photoemission electron microscopy (TR 2P-PEEM) reveals an ultrafast long-range periodic energy transfer in accordance with the simulations. Our observations open perspectives for the optimization and tailoring of mesoscopic energy transfer and long-range quantum emitter coupling.}, author = {Aeschlimann, Martin and Brixner, Tobias and Cinchetti, Mirko and Frisch, Benjamin and Hecht, Bert and Hensen, Matthias and Huber, Bernhard and Kramer, Christian and Krauss, Enno and Loeber, Thomas H. and Pfeiffer, Walter and Piecuch, Martin and Thielen, Philip}, journal = {Light Sci Appl}, keywords = {plasmon}, month = 11, number = 11, pages = {e17111}, title = {Cavity-assisted ultrafast long-range periodic energy transfer between plasmonic nanoantennas}, volume = 6, year = 2017 }

%0 Journal Article %1 aeschlimann2017cavityassisted %A Aeschlimann, Martin %A Brixner, Tobias %A Cinchetti, Mirko %A Frisch, Benjamin %A Hecht, Bert %A Hensen, Matthias %A Huber, Bernhard %A Kramer, Christian %A Krauss, Enno %A Loeber, Thomas H. %A Pfeiffer, Walter %A Piecuch, Martin %A Thielen, Philip %D 2017 %J Light Sci Appl %N 11 %P e17111 %R 10.1038/lsa.2017.111 %T Cavity-assisted ultrafast long-range periodic energy transfer between plasmonic nanoantennas %V 6 %X Radiationless energy transfer is at the core of diverse phenomena, such as light harvesting in photosynthesis, energy-transfer-based microspectroscopies, nanoscale quantum entanglement and photonic-mode hybridization. Typically, the transfer is efficient only for separations that are much shorter than the diffraction limit. This hampers its application in optical communication and quantum information processing, which require spatially selective addressing. Here, we demonstrate highly efficient radiationless coherent energy transfer over a distance of twice the excitation wavelength by combining localized and delocalized plasmonic modes. Analogous to the Tavis–Cummings model, two whispering-gallery-mode antennas placed in the foci of an elliptical plasmonic cavity fabricated from single-crystal gold plates act as a pair of oscillators coupled to a common cavity mode. Time-resolved two-photon photoemission electron microscopy (TR 2P-PEEM) reveals an ultrafast long-range periodic energy transfer in accordance with the simulations. Our observations open perspectives for the optimization and tailoring of mesoscopic energy transfer and long-range quantum emitter coupling.
Mode Matching for Optical Antennas. Feichtner, Thorsten; Christiansen, Silke; Hecht, Bert. In Phys. Rev. Lett., 119(21), p. 217401. 2017.

» arXiv:1611.05399 (2016)
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The emission rate of a point dipole can be strongly increased in the presence of a well-designed optical antenna. Yet, optical antenna design is largely based on radio-frequency rules, ignoring, e.g., Ohmic losses and non-negligible field penetration in metals at optical frequencies. Here, we combine reciprocity and Poynting’s theorem to derive a set of optical-frequency antenna design rules for benchmarking and optimizing the performance of optical antennas driven by single quantum emitters. Based on these findings a novel plasmonic cavity antenna design is presented exhibiting a considerably improved performance compared to a reference two-wire antenna. Our work will be useful for the design of high-performance optical antennas and nanoresonators for diverse applications ranging from quantum optics to antenna-enhanced single-emitter spectroscopy and sensing.

@article{feichtner2017matching, abstract = {The emission rate of a point dipole can be strongly increased in the presence of a well-designed optical antenna. Yet, optical antenna design is largely based on radio-frequency rules, ignoring, e.g., Ohmic losses and non-negligible field penetration in metals at optical frequencies. Here, we combine reciprocity and Poynting’s theorem to derive a set of optical-frequency antenna design rules for benchmarking and optimizing the performance of optical antennas driven by single quantum emitters. Based on these findings a novel plasmonic cavity antenna design is presented exhibiting a considerably improved performance compared to a reference two-wire antenna. Our work will be useful for the design of high-performance optical antennas and nanoresonators for diverse applications ranging from quantum optics to antenna-enhanced single-emitter spectroscopy and sensing.}, author = {Feichtner, Thorsten and Christiansen, Silke and Hecht, Bert}, journal = {Phys. Rev. Lett.}, keywords = {nano-optics}, month = 11, note = {<a href="https://arxiv.org/abs/1611.05399" style="font-style: normal;">» arXiv:1611.05399 (2016)</a>}, number = 21, pages = 217401, title = {Mode Matching for Optical Antennas}, volume = 119, year = 2017 }

%0 Journal Article %1 feichtner2017matching %A Feichtner, Thorsten %A Christiansen, Silke %A Hecht, Bert %D 2017 %J Phys. Rev. Lett. %N 21 %P 217401 %R 10.1103/PhysRevLett.119.217401 %T Mode Matching for Optical Antennas %V 119 %X The emission rate of a point dipole can be strongly increased in the presence of a well-designed optical antenna. Yet, optical antenna design is largely based on radio-frequency rules, ignoring, e.g., Ohmic losses and non-negligible field penetration in metals at optical frequencies. Here, we combine reciprocity and Poynting’s theorem to derive a set of optical-frequency antenna design rules for benchmarking and optimizing the performance of optical antennas driven by single quantum emitters. Based on these findings a novel plasmonic cavity antenna design is presented exhibiting a considerably improved performance compared to a reference two-wire antenna. Our work will be useful for the design of high-performance optical antennas and nanoresonators for diverse applications ranging from quantum optics to antenna-enhanced single-emitter spectroscopy and sensing.
Transmission of Plasmons through a Nanowire. Geisler, Peter; Krauss, Enno; Razinskas, Gary; Hecht, Bert. In ACS Photonics, 4(7), pp. 1615–1620. 2017.

» arXiv:1702.03103 (2017)
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Exact quantitative understanding of plasmon propagation along nanowires is mandatory for designing and creating functional devices. Here we investigate plasmon transmission through top-down-fabricated monocrystalline gold nanowires on a glass substrate. We show that the transmission through finite-length nanowires can be described by Fabry–Pérot oscillations that beat with free-space propagating light launched at the incoupling end. Using an extended Fabry–Pérot model, experimental and simulated length-dependent transmission signals agree quantitatively with a fully analytical model.

@article{geisler2017transmission, abstract = {Exact quantitative understanding of plasmon propagation along nanowires is mandatory for designing and creating functional devices. Here we investigate plasmon transmission through top-down-fabricated monocrystalline gold nanowires on a glass substrate. We show that the transmission through finite-length nanowires can be described by Fabry–Pérot oscillations that beat with free-space propagating light launched at the incoupling end. Using an extended Fabry–Pérot model, experimental and simulated length-dependent transmission signals agree quantitatively with a fully analytical model.}, author = {Geisler, Peter and Krauss, Enno and Razinskas, Gary and Hecht, Bert}, journal = {ACS Photonics}, keywords = {plasmon}, month = {07}, note = {<a href="https://arxiv.org/abs/1702.03103" style="font-style: normal;">» arXiv:1702.03103 (2017)</a>}, number = 7, pages = {1615-1620}, title = {Transmission of Plasmons through a Nanowire}, volume = 4, year = 2017 }

%0 Journal Article %1 geisler2017transmission %A Geisler, Peter %A Krauss, Enno %A Razinskas, Gary %A Hecht, Bert %D 2017 %J ACS Photonics %N 7 %P 1615-1620 %R 10.1021/acsphotonics.7b00292 %T Transmission of Plasmons through a Nanowire %V 4 %X Exact quantitative understanding of plasmon propagation along nanowires is mandatory for designing and creating functional devices. Here we investigate plasmon transmission through top-down-fabricated monocrystalline gold nanowires on a glass substrate. We show that the transmission through finite-length nanowires can be described by Fabry–Pérot oscillations that beat with free-space propagating light launched at the incoupling end. Using an extended Fabry–Pérot model, experimental and simulated length-dependent transmission signals agree quantitatively with a fully analytical model.
On-Chip Single-Plasmon Nanocircuit Driven by a Self-Assembled Quantum Dot. Wu, Xiaofei; Jiang, Ping; Razinskas, Gary; Huo, Yongheng; Zhang, Hongyi; Kamp, Martin; Rastelli, Armando; Schmidt, Oliver G.; Hecht, Bert; Lindfors, Klas; Lippitz, Markus. In Nano Lett., 17(7), pp. 4291–4296. 2017.
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Quantum photonics holds great promise for future technologies such as secure communication, quantum computation, quantum simulation, and quantum metrology. An outstanding challenge for quantum photonics is to develop scalable miniature circuits that integrate single-photon sources, linear optical components, and detectors on a chip. Plasmonic nanocircuits will play essential roles in such developments. However, for quantum plasmonic circuits, integration of stable, bright, and narrow-band single photon sources in the structure has so far not been reported. Here we present a plasmonic nanocircuit driven by a self-assembled GaAs quantum dot. Through a planar dielectric-plasmonic hybrid waveguide, the quantum dot efficiently excites narrow-band single plasmons that are guided in a two-wire transmission line until they are converted into single photons by an optical antenna. Our work demonstrates the feasibility of fully on-chip plasmonic nanocircuits for quantum optical applications.

@article{wu2017onchip, abstract = {Quantum photonics holds great promise for future technologies such as secure communication, quantum computation, quantum simulation, and quantum metrology. An outstanding challenge for quantum photonics is to develop scalable miniature circuits that integrate single-photon sources, linear optical components, and detectors on a chip. Plasmonic nanocircuits will play essential roles in such developments. However, for quantum plasmonic circuits, integration of stable, bright, and narrow-band single photon sources in the structure has so far not been reported. Here we present a plasmonic nanocircuit driven by a self-assembled GaAs quantum dot. Through a planar dielectric-plasmonic hybrid waveguide, the quantum dot efficiently excites narrow-band single plasmons that are guided in a two-wire transmission line until they are converted into single photons by an optical antenna. Our work demonstrates the feasibility of fully on-chip plasmonic nanocircuits for quantum optical applications.}, author = {Wu, Xiaofei and Jiang, Ping and Razinskas, Gary and Huo, Yongheng and Zhang, Hongyi and Kamp, Martin and Rastelli, Armando and Schmidt, Oliver G. and Hecht, Bert and Lindfors, Klas and Lippitz, Markus}, journal = {Nano Lett.}, keywords = {plasmon}, month = {07}, number = 7, pages = {4291-4296}, title = {On-Chip Single-Plasmon Nanocircuit Driven by a Self-Assembled Quantum Dot}, volume = 17, year = 2017 }

%0 Journal Article %1 wu2017onchip %A Wu, Xiaofei %A Jiang, Ping %A Razinskas, Gary %A Huo, Yongheng %A Zhang, Hongyi %A Kamp, Martin %A Rastelli, Armando %A Schmidt, Oliver G. %A Hecht, Bert %A Lindfors, Klas %A Lippitz, Markus %D 2017 %J Nano Lett. %N 7 %P 4291-4296 %R 10.1021/acs.nanolett.7b01284 %T On-Chip Single-Plasmon Nanocircuit Driven by a Self-Assembled Quantum Dot %V 17 %X Quantum photonics holds great promise for future technologies such as secure communication, quantum computation, quantum simulation, and quantum metrology. An outstanding challenge for quantum photonics is to develop scalable miniature circuits that integrate single-photon sources, linear optical components, and detectors on a chip. Plasmonic nanocircuits will play essential roles in such developments. However, for quantum plasmonic circuits, integration of stable, bright, and narrow-band single photon sources in the structure has so far not been reported. Here we present a plasmonic nanocircuit driven by a self-assembled GaAs quantum dot. Through a planar dielectric-plasmonic hybrid waveguide, the quantum dot efficiently excites narrow-band single plasmons that are guided in a two-wire transmission line until they are converted into single photons by an optical antenna. Our work demonstrates the feasibility of fully on-chip plasmonic nanocircuits for quantum optical applications.
Plasmonic nanoantenna design and fabrication based on evolutionary optimization. Feichtner, Thorsten; Selig, Oleg; Hecht, Bert. In Opt. Express, 25(10), pp. 10828–10842. 2017.

» arXiv: 1511.05438 (2016)
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Nanoantennas can tailor light-matter interaction for optical communication, sensing, and spectroscopy. Their design is inspired by radio-frequency rules which partly break down at optical frequencies. Here we find unexpected nanoantenna designs exhibiting strong light localization and enhancement by using a general and scalable evolutionary algorithm based on FDTD simulations that also accounts for geometrical fabrication constraints. The resulting nanoantennas are "printed" directly by focused-ion beam milling and their fitness ranking is validated experimentally by two-photon photoluminescence. We find the best antennas' operation principle deviating from that of classical radio wave-inspired designs. Our work sets the stage for a widespread application of evolutionary optimization in nano photonics.

@article{feichtner2017plasmonic, abstract = {Nanoantennas can tailor light-matter interaction for optical communication, sensing, and spectroscopy. Their design is inspired by radio-frequency rules which partly break down at optical frequencies. Here we find unexpected nanoantenna designs exhibiting strong light localization and enhancement by using a general and scalable evolutionary algorithm based on FDTD simulations that also accounts for geometrical fabrication constraints. The resulting nanoantennas are "printed" directly by focused-ion beam milling and their fitness ranking is validated experimentally by two-photon photoluminescence. We find the best antennas' operation principle deviating from that of classical radio wave-inspired designs. Our work sets the stage for a widespread application of evolutionary optimization in nano photonics.}, author = {Feichtner, Thorsten and Selig, Oleg and Hecht, Bert}, journal = {Opt. Express}, keywords = {FIB}, month = {05}, note = {<a href="https://arxiv.org/abs/1511.05438" style="font-style: normal;">» arXiv: 1511.05438 (2016)</a>}, number = 10, pages = {10828-10842}, title = {Plasmonic nanoantenna design and fabrication based on evolutionary optimization}, volume = 25, year = 2017 }

%0 Journal Article %1 feichtner2017plasmonic %A Feichtner, Thorsten %A Selig, Oleg %A Hecht, Bert %D 2017 %J Opt. Express %N 10 %P 10828-10842 %R 10.1364/OE.25.010828 %T Plasmonic nanoantenna design and fabrication based on evolutionary optimization %V 25 %X Nanoantennas can tailor light-matter interaction for optical communication, sensing, and spectroscopy. Their design is inspired by radio-frequency rules which partly break down at optical frequencies. Here we find unexpected nanoantenna designs exhibiting strong light localization and enhancement by using a general and scalable evolutionary algorithm based on FDTD simulations that also accounts for geometrical fabrication constraints. The resulting nanoantennas are "printed" directly by focused-ion beam milling and their fitness ranking is validated experimentally by two-photon photoluminescence. We find the best antennas' operation principle deviating from that of classical radio wave-inspired designs. Our work sets the stage for a widespread application of evolutionary optimization in nano photonics.
Three-dimensional photonic confinement in imprinted liquid crystalline pillar microcavities. Dusel, Marco; Betzold, Simon; Brodbeck, Sebastian; Herbst, Stefanie; Würthner, Frank; Friedrich, Daniel; Hecht, Bert; Höfling, Sven; Dietrich, Christof P. In Appl. Phys. Lett., 110(20), p. 201113. 2017.
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We demonstrate the feasibility of a thermal imprint technology capable of structuring organic thin films with liquid crystalline properties forming feature sizes on a several micrometer scale. The imprint technique can directly be applied onto a variety of substrates including dielectric mirrors. The so fabricated three-dimensional microcavities have lateral extensions up to 20 μm and heights between 1 and 5 μm. Exemplarily, pillar microcavities were produced wherein three-dimensional photonic confinement is observed by the formation of 0D cavity mode patterns. The imprint technique further favors the formation of hemispherical pillar geometries rather than cylindrical pillars, resulting in equidistant mode spacings of transversal cavity modes.

@article{dusel2017threedimensional, abstract = {We demonstrate the feasibility of a thermal imprint technology capable of structuring organic thin films with liquid crystalline properties forming feature sizes on a several micrometer scale. The imprint technique can directly be applied onto a variety of substrates including dielectric mirrors. The so fabricated three-dimensional microcavities have lateral extensions up to 20 μm and heights between 1 and 5 μm. Exemplarily, pillar microcavities were produced wherein three-dimensional photonic confinement is observed by the formation of 0D cavity mode patterns. The imprint technique further favors the formation of hemispherical pillar geometries rather than cylindrical pillars, resulting in equidistant mode spacings of transversal cavity modes.}, author = {Dusel, Marco and Betzold, Simon and Brodbeck, Sebastian and Herbst, Stefanie and Würthner, Frank and Friedrich, Daniel and Hecht, Bert and Höfling, Sven and Dietrich, Christof P.}, journal = {Appl. Phys. Lett.}, keywords = {nano-optics}, month = {05}, number = 20, pages = 201113, title = {Three-dimensional photonic confinement in imprinted liquid crystalline pillar microcavities}, volume = 110, year = 2017 }

%0 Journal Article %1 dusel2017threedimensional %A Dusel, Marco %A Betzold, Simon %A Brodbeck, Sebastian %A Herbst, Stefanie %A Würthner, Frank %A Friedrich, Daniel %A Hecht, Bert %A Höfling, Sven %A Dietrich, Christof P. %D 2017 %J Appl. Phys. Lett. %N 20 %P 201113 %R 10.1063/1.4983565 %T Three-dimensional photonic confinement in imprinted liquid crystalline pillar microcavities %V 110 %X We demonstrate the feasibility of a thermal imprint technology capable of structuring organic thin films with liquid crystalline properties forming feature sizes on a several micrometer scale. The imprint technique can directly be applied onto a variety of substrates including dielectric mirrors. The so fabricated three-dimensional microcavities have lateral extensions up to 20 μm and heights between 1 and 5 μm. Exemplarily, pillar microcavities were produced wherein three-dimensional photonic confinement is observed by the formation of 0D cavity mode patterns. The imprint technique further favors the formation of hemispherical pillar geometries rather than cylindrical pillars, resulting in equidistant mode spacings of transversal cavity modes.
Grazing-incidence optical magnetic recording with super-resolution. Scheunert, Gunther; Cohen, Sidney R.; Kullock, René; McCarron, Ryan; Rechev, Katya; Kaplan-Ashiri, Ifat; Bitton, Ora; Dawson, Paul; Hecht, Bert; Oron, Dan. In Beilstein J. Nanotechnol., 8(1), pp. 28–37. 2017.
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Heat-assisted magnetic recording (HAMR) is often considered the next major step in the storage industry: it is predicted to increase the storage capacity, the read/write speed and the data lifetime of future hard disk drives. However, despite more than a decade of development work, the reliability is still a prime concern. Featuring an inherently fragile surface-plasmon resonator as a highly localized heat source, as part of a near-field transducer (NFT), the current industry concepts still fail to deliver drives with sufficient lifetime. This study presents a method to aid conventional NFT-designs by additional grazing-incidence laser illumination, which may open an alternative route to high-durability HAMR. Magnetic switching is demonstrated on consumer-grade CoCrPt perpendicular magnetic recording media using a green and a near-infrared diode laser. Sub-500 nm magnetic features are written in the absence of a NFT in a moderate bias field of only μ0H = 0.3 T with individual laser pulses of 40 mW power and 50 ns duration with a laser spot size of 3 μm (short axis) at the sample surface – six times larger than the magnetic features. Herein, the presence of a nanoscopic object, i.e., the tip of an atomic force microscope in the focus of the laser at the sample surface, has no impact on the recorded magnetic features – thus suggesting full compatibility with NFT-HAMR.

@article{scheunert2017grazingincidence, abstract = {Heat-assisted magnetic recording (HAMR) is often considered the next major step in the storage industry: it is predicted to increase the storage capacity, the read/write speed and the data lifetime of future hard disk drives. However, despite more than a decade of development work, the reliability is still a prime concern. Featuring an inherently fragile surface-plasmon resonator as a highly localized heat source, as part of a near-field transducer (NFT), the current industry concepts still fail to deliver drives with sufficient lifetime. This study presents a method to aid conventional NFT-designs by additional grazing-incidence laser illumination, which may open an alternative route to high-durability HAMR. Magnetic switching is demonstrated on consumer-grade CoCrPt perpendicular magnetic recording media using a green and a near-infrared diode laser. Sub-500 nm magnetic features are written in the absence of a NFT in a moderate bias field of only μ0H = 0.3 T with individual laser pulses of 40 mW power and 50 ns duration with a laser spot size of 3 μm (short axis) at the sample surface – six times larger than the magnetic features. Herein, the presence of a nanoscopic object, i.e., the tip of an atomic force microscope in the focus of the laser at the sample surface, has no impact on the recorded magnetic features – thus suggesting full compatibility with NFT-HAMR.}, author = {Scheunert, Gunther and Cohen, Sidney R. and Kullock, René and McCarron, Ryan and Rechev, Katya and Kaplan-Ashiri, Ifat and Bitton, Ora and Dawson, Paul and Hecht, Bert and Oron, Dan}, journal = {Beilstein J. Nanotechnol.}, keywords = {nano-optics}, month = {01}, number = 1, pages = {28-37}, title = {Grazing-incidence optical magnetic recording with super-resolution}, volume = 8, year = 2017 }

%0 Journal Article %1 scheunert2017grazingincidence %A Scheunert, Gunther %A Cohen, Sidney R. %A Kullock, René %A McCarron, Ryan %A Rechev, Katya %A Kaplan-Ashiri, Ifat %A Bitton, Ora %A Dawson, Paul %A Hecht, Bert %A Oron, Dan %D 2017 %J Beilstein J. Nanotechnol. %N 1 %P 28-37 %R 10.3762/bjnano.8.4 %T Grazing-incidence optical magnetic recording with super-resolution %V 8 %X Heat-assisted magnetic recording (HAMR) is often considered the next major step in the storage industry: it is predicted to increase the storage capacity, the read/write speed and the data lifetime of future hard disk drives. However, despite more than a decade of development work, the reliability is still a prime concern. Featuring an inherently fragile surface-plasmon resonator as a highly localized heat source, as part of a near-field transducer (NFT), the current industry concepts still fail to deliver drives with sufficient lifetime. This study presents a method to aid conventional NFT-designs by additional grazing-incidence laser illumination, which may open an alternative route to high-durability HAMR. Magnetic switching is demonstrated on consumer-grade CoCrPt perpendicular magnetic recording media using a green and a near-infrared diode laser. Sub-500 nm magnetic features are written in the absence of a NFT in a moderate bias field of only μ0H = 0.3 T with individual laser pulses of 40 mW power and 50 ns duration with a laser spot size of 3 μm (short axis) at the sample surface – six times larger than the magnetic features. Herein, the presence of a nanoscopic object, i.e., the tip of an atomic force microscope in the focus of the laser at the sample surface, has no impact on the recorded magnetic features – thus suggesting full compatibility with NFT-HAMR.

Normal-Incidence PEEM Imaging of Propagating Modes in a Plasmonic Nanocircuit. Razinskas, Gary; Kilbane, Deirdre; Melchior, Pascal; Geisler, Peter; Krauss, Enno; Mathias, Stefan; Hecht, Bert; Aeschlimann, Martin. In Nano Lett., 16(11), pp. 6832–6837. 2016.
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The design of noble-metal plasmonic devices and nanocircuitry requires a fundamental understanding and control of the interference of plasmonic modes. Here we report the first visualization of the propagation and interference of guided modes in a showcase plasmonic nanocircuit using normal-incidence nonlinear two-photon photoemission electron microscopy (PEEM). We demonstrate that in contrast to the commonly used grazing-incidence illumination scheme, normal-incidence PEEM provides a direct image of the structure’s near-field intensity distribution due to the absence of beating patterns and despite the transverse character of the plasmonic modes. Based on a simple heuristic numerical model for the photoemission yield, we are able to model all experimental findings if global plane wave illumination and coupling to multiple input/output ports, and the resulting interference effects are accounted for.

@article{razinskas2016normalincidence, abstract = {The design of noble-metal plasmonic devices and nanocircuitry requires a fundamental understanding and control of the interference of plasmonic modes. Here we report the first visualization of the propagation and interference of guided modes in a showcase plasmonic nanocircuit using normal-incidence nonlinear two-photon photoemission electron microscopy (PEEM). We demonstrate that in contrast to the commonly used grazing-incidence illumination scheme, normal-incidence PEEM provides a direct image of the structure’s near-field intensity distribution due to the absence of beating patterns and despite the transverse character of the plasmonic modes. Based on a simple heuristic numerical model for the photoemission yield, we are able to model all experimental findings if global plane wave illumination and coupling to multiple input/output ports, and the resulting interference effects are accounted for.}, author = {Razinskas, Gary and Kilbane, Deirdre and Melchior, Pascal and Geisler, Peter and Krauss, Enno and Mathias, Stefan and Hecht, Bert and Aeschlimann, Martin}, journal = {Nano Lett.}, keywords = {plasmon}, month = 11, number = 11, pages = {6832-6837}, title = {Normal-Incidence PEEM Imaging of Propagating Modes in a Plasmonic Nanocircuit}, volume = 16, year = 2016 }

%0 Journal Article %1 razinskas2016normalincidence %A Razinskas, Gary %A Kilbane, Deirdre %A Melchior, Pascal %A Geisler, Peter %A Krauss, Enno %A Mathias, Stefan %A Hecht, Bert %A Aeschlimann, Martin %D 2016 %J Nano Lett. %N 11 %P 6832-6837 %R 10.1021/acs.nanolett.6b02569 %T Normal-Incidence PEEM Imaging of Propagating Modes in a Plasmonic Nanocircuit %V 16 %X The design of noble-metal plasmonic devices and nanocircuitry requires a fundamental understanding and control of the interference of plasmonic modes. Here we report the first visualization of the propagation and interference of guided modes in a showcase plasmonic nanocircuit using normal-incidence nonlinear two-photon photoemission electron microscopy (PEEM). We demonstrate that in contrast to the commonly used grazing-incidence illumination scheme, normal-incidence PEEM provides a direct image of the structure’s near-field intensity distribution due to the absence of beating patterns and despite the transverse character of the plasmonic modes. Based on a simple heuristic numerical model for the photoemission yield, we are able to model all experimental findings if global plane wave illumination and coupling to multiple input/output ports, and the resulting interference effects are accounted for.
Two-photon polymerization setup enables experimental mapping and correction of spherical aberrations for improved macroscopic structure fabrication. Stichel, Thomas; Hecht, Bert; Steenhusen, Sönke; Houbertz, Ruth; Sextl, Gerhard. In Opt. Lett., 41(18), pp. 4269–4272. 2016.
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The two-photon photopolymerization of resins by focused laser light in principle enables the fabrication of structures with details below the diffraction limit. However, the method can be highly susceptible to aberrations, which hinders the fabrication of structures that are larger than, e.g., the working distance of the microscope objective. Here, two-photon polymerization is extended to the fabrication of macroscopic structures by making use of medium numerical-aperture microscope objectives. By introducing a substrate holder movable in the axial direction it is possible to keep the focusing conditions constant and to fabricate very large structures with heights that are not limited by the working distance of the objective. Moreover, the constant focusing conditions enable us to quantify spherical aberrations by experimental mapping of the optical point-spread function, which manifests itself in the shape of singe photo-polymerized voxels. By monitoring such shapes it is possible to minimize aberrations. Effective aberration control enables us to fabricate large but detailed biomedical scaffolds with interconnected pores, e.g., in the shape of a human stirrup bone.

@article{stichel2016twophoton, abstract = {The two-photon photopolymerization of resins by focused laser light in principle enables the fabrication of structures with details below the diffraction limit. However, the method can be highly susceptible to aberrations, which hinders the fabrication of structures that are larger than, e.g., the working distance of the microscope objective. Here, two-photon polymerization is extended to the fabrication of macroscopic structures by making use of medium numerical-aperture microscope objectives. By introducing a substrate holder movable in the axial direction it is possible to keep the focusing conditions constant and to fabricate very large structures with heights that are not limited by the working distance of the objective. Moreover, the constant focusing conditions enable us to quantify spherical aberrations by experimental mapping of the optical point-spread function, which manifests itself in the shape of singe photo-polymerized voxels. By monitoring such shapes it is possible to minimize aberrations. Effective aberration control enables us to fabricate large but detailed biomedical scaffolds with interconnected pores, e.g., in the shape of a human stirrup bone.}, author = {Stichel, Thomas and Hecht, Bert and Steenhusen, Sönke and Houbertz, Ruth and Sextl, Gerhard}, journal = {Opt. Lett.}, keywords = {nano-optics}, month = {09}, number = 18, pages = {4269-4272}, title = {Two-photon polymerization setup enables experimental mapping and correction of spherical aberrations for improved macroscopic structure fabrication}, volume = 41, year = 2016 }

%0 Journal Article %1 stichel2016twophoton %A Stichel, Thomas %A Hecht, Bert %A Steenhusen, Sönke %A Houbertz, Ruth %A Sextl, Gerhard %D 2016 %J Opt. Lett. %N 18 %P 4269-4272 %R 10.1364/OL.41.004269 %T Two-photon polymerization setup enables experimental mapping and correction of spherical aberrations for improved macroscopic structure fabrication %V 41 %X The two-photon photopolymerization of resins by focused laser light in principle enables the fabrication of structures with details below the diffraction limit. However, the method can be highly susceptible to aberrations, which hinders the fabrication of structures that are larger than, e.g., the working distance of the microscope objective. Here, two-photon polymerization is extended to the fabrication of macroscopic structures by making use of medium numerical-aperture microscope objectives. By introducing a substrate holder movable in the axial direction it is possible to keep the focusing conditions constant and to fabricate very large structures with heights that are not limited by the working distance of the objective. Moreover, the constant focusing conditions enable us to quantify spherical aberrations by experimental mapping of the optical point-spread function, which manifests itself in the shape of singe photo-polymerized voxels. By monitoring such shapes it is possible to minimize aberrations. Effective aberration control enables us to fabricate large but detailed biomedical scaffolds with interconnected pores, e.g., in the shape of a human stirrup bone.
Polarization dependence of plasmonic near-field enhanced photoemission from cross antennas. Klaer, P.; Razinskas, G.; Lehr, M.; Wu, X.; Hecht, B.; Schertz, F.; Butt, H.-J.; Schönhense, G.; Elmers, H. J. In Appl. Phys. B, 122(5), p. 136. 2016.
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The field enhancement of individual cross-shaped nanoantennas for normal incident light has been measured by the relative photoemission yield using a photoemission electron microscope. We not only measured the electron yield in dependence on the intensity of infrared light (800 nm, 100 fs), but also the polarization dependence. In the normal incidence geometry, the electrical field vector of the illuminating light lies in the surface plane of the sample, independent of the polarization state. Strong yield variations due to an out-of-plane field component as well as changes in the polarization state described by the Fresnel laws are avoided. The electron yield is related to the near-field enhancement as a function of the polarization state of the incident light. The polarization dependence is well explained by numerical simulations.

@article{klaer2016polarization, abstract = {The field enhancement of individual cross-shaped nanoantennas for normal incident light has been measured by the relative photoemission yield using a photoemission electron microscope. We not only measured the electron yield in dependence on the intensity of infrared light (800 nm, 100 fs), but also the polarization dependence. In the normal incidence geometry, the electrical field vector of the illuminating light lies in the surface plane of the sample, independent of the polarization state. Strong yield variations due to an out-of-plane field component as well as changes in the polarization state described by the Fresnel laws are avoided. The electron yield is related to the near-field enhancement as a function of the polarization state of the incident light. The polarization dependence is well explained by numerical simulations.}, author = {Klaer, P. and Razinskas, G. and Lehr, M. and Wu, X. and Hecht, B. and Schertz, F. and Butt, H.-J. and Schönhense, G. and Elmers, H. J.}, journal = {Appl. Phys. B}, keywords = {plasmon}, month = {05}, number = 5, pages = 136, title = {Polarization dependence of plasmonic near-field enhanced photoemission from cross antennas}, volume = 122, year = 2016 }

%0 Journal Article %1 klaer2016polarization %A Klaer, P. %A Razinskas, G. %A Lehr, M. %A Wu, X. %A Hecht, B. %A Schertz, F. %A Butt, H.-J. %A Schönhense, G. %A Elmers, H. J. %D 2016 %J Appl. Phys. B %N 5 %P 136 %R 10.1007/s00340-016-6410-3 %T Polarization dependence of plasmonic near-field enhanced photoemission from cross antennas %V 122 %X The field enhancement of individual cross-shaped nanoantennas for normal incident light has been measured by the relative photoemission yield using a photoemission electron microscope. We not only measured the electron yield in dependence on the intensity of infrared light (800 nm, 100 fs), but also the polarization dependence. In the normal incidence geometry, the electrical field vector of the illuminating light lies in the surface plane of the sample, independent of the polarization state. Strong yield variations due to an out-of-plane field component as well as changes in the polarization state described by the Fresnel laws are avoided. The electron yield is related to the near-field enhancement as a function of the polarization state of the incident light. The polarization dependence is well explained by numerical simulations.
Electromechanically Tunable Suspended Optical Nanoantenna. Chen, Kai; Razinskas, Gary; Feichtner, Thorsten; Grossmann, Swen; Christiansen, Silke; Hecht, Bert. In Nano Lett., 16(4), pp. 2680–2685. 2016.
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Coupling mechanical degrees of freedom with plasmonic resonances has potential applications in optomechanics, sensing, and active plasmonics. Here we demonstrate a suspended two-wire plasmonic nanoantenna acting like a nanoelectrometer. The antenna wires are supported and electrically connected via thin leads without disturbing the antenna resonance. As a voltage is applied, equal charges are induced on both antenna wires. The resulting equilibrium between the repulsive Coulomb force and the restoring elastic bending force enables us to precisely control the gap size. As a result the resonance wavelength and the field enhancement of the suspended optical nanoantenna can be reversibly tuned. Our experiments highlight the potential to realize large bandwidth optical nanoelectromechanical systems.

@article{chen2016electromechanically, abstract = {Coupling mechanical degrees of freedom with plasmonic resonances has potential applications in optomechanics, sensing, and active plasmonics. Here we demonstrate a suspended two-wire plasmonic nanoantenna acting like a nanoelectrometer. The antenna wires are supported and electrically connected via thin leads without disturbing the antenna resonance. As a voltage is applied, equal charges are induced on both antenna wires. The resulting equilibrium between the repulsive Coulomb force and the restoring elastic bending force enables us to precisely control the gap size. As a result the resonance wavelength and the field enhancement of the suspended optical nanoantenna can be reversibly tuned. Our experiments highlight the potential to realize large bandwidth optical nanoelectromechanical systems.}, author = {Chen, Kai and Razinskas, Gary and Feichtner, Thorsten and Grossmann, Swen and Christiansen, Silke and Hecht, Bert}, journal = {Nano Lett.}, keywords = {plasmon}, month = {04}, number = 4, pages = {2680-2685}, title = {Electromechanically Tunable Suspended Optical Nanoantenna}, volume = 16, year = 2016 }

%0 Journal Article %1 chen2016electromechanically %A Chen, Kai %A Razinskas, Gary %A Feichtner, Thorsten %A Grossmann, Swen %A Christiansen, Silke %A Hecht, Bert %D 2016 %J Nano Lett. %N 4 %P 2680-2685 %R 10.1021/acs.nanolett.6b00323 %T Electromechanically Tunable Suspended Optical Nanoantenna %V 16 %X Coupling mechanical degrees of freedom with plasmonic resonances has potential applications in optomechanics, sensing, and active plasmonics. Here we demonstrate a suspended two-wire plasmonic nanoantenna acting like a nanoelectrometer. The antenna wires are supported and electrically connected via thin leads without disturbing the antenna resonance. As a voltage is applied, equal charges are induced on both antenna wires. The resulting equilibrium between the repulsive Coulomb force and the restoring elastic bending force enables us to precisely control the gap size. As a result the resonance wavelength and the field enhancement of the suspended optical nanoantenna can be reversibly tuned. Our experiments highlight the potential to realize large bandwidth optical nanoelectromechanical systems.
$Investigation of the nonlinear refractive index of single-crystalline thin gold films and plasmonic nanostructures$

Investigation of the nonlinear refractive index of single-crystalline thin gold films and plasmonic nanostructures. Goetz, Sebastian; Razinskas, Gary; Krauss, Enno; Dreher, Christian; Wurdack, Matthias; Geisler, Peter; Pawłowska, Monika; Hecht, Bert; Brixner, Tobias. In Appl. Phys. B, 122(4), p. 94. 2016.
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The nonlinear refractive index of plasmonic materials may be used to obtain nonlinear functionality, e.g., power-dependent switching. Here, we investigate the nonlinear refractive index of single-crystalline gold in thin layers and nanostructures on dielectric substrates. In a first step, we implement a z-scan setup to investigate ~100-µm-sized thin-film samples. We determine the nonlinear refractive index of fused silica, n2(SiO2) = 2.9 × 10^(−20) m^2/W, in agreement with literature values. Subsequent z-scan measurements of single-crystalline gold films reveal a damage threshold of 0.22 TW/cm^2 and approximate upper limits of the real and imaginary parts of the nonlinear refractive index, |n2′(Au)| < 1.2 × 10^(−16) m^2/W and |n2″(Au)| < 0.6 × 10^(−16) m^2/W, respectively. To further determine possible effects of a nonlinear refractive index in plasmonic circuitry, interferometry is proposed as a phase-sensitive probe. In corresponding nanostructures, relative phase changes between two propagating near-field modes are converted to amplitude changes by mode interference. Power-dependent experiments using sub-10-fs near-infrared pulses and diffraction-limited resolution (NA = 1.4) reveal linear behavior up to the damage threshold (0.23 times relative to that of a solid single-crystalline gold film). An upper limit for the nonlinear power-dependent phase change between two propagating near-field modes is determined to Δφ < 0.07 rad.

@article{goetz2016investigation, abstract = {The nonlinear refractive index of plasmonic materials may be used to obtain nonlinear functionality, e.g., power-dependent switching. Here, we investigate the nonlinear refractive index of single-crystalline gold in thin layers and nanostructures on dielectric substrates. In a first step, we implement a z-scan setup to investigate 100-µm-sized thin-film samples. We determine the nonlinear refractive index of fused silica, n2(SiO2) = 2.9 × 10^(−20) m^2/W, in agreement with literature values. Subsequent z-scan measurements of single-crystalline gold films reveal a damage threshold of 0.22 TW/cm^2 and approximate upper limits of the real and imaginary parts of the nonlinear refractive index, |n2′(Au)| < 1.2 × 10^(−16) m^2/W and |n2″(Au)| < 0.6 × 10^(−16) m^2/W, respectively. To further determine possible effects of a nonlinear refractive index in plasmonic circuitry, interferometry is proposed as a phase-sensitive probe. In corresponding nanostructures, relative phase changes between two propagating near-field modes are converted to amplitude changes by mode interference. Power-dependent experiments using sub-10-fs near-infrared pulses and diffraction-limited resolution (NA = 1.4) reveal linear behavior up to the damage threshold (0.23 times relative to that of a solid single-crystalline gold film). An upper limit for the nonlinear power-dependent phase change between two propagating near-field modes is determined to Δφ < 0.07 rad.}, author = {Goetz, Sebastian and Razinskas, Gary and Krauss, Enno and Dreher, Christian and Wurdack, Matthias and Geisler, Peter and Pawłowska, Monika and Hecht, Bert and Brixner, Tobias}, journal = {Appl. Phys. B}, keywords = {plasmon}, month = {04}, number = 4, pages = 94, title = {Investigation of the nonlinear refractive index of single-crystalline thin gold films and plasmonic nanostructures}, volume = 122, year = 2016 }

%0 Journal Article %1 goetz2016investigation %A Goetz, Sebastian %A Razinskas, Gary %A Krauss, Enno %A Dreher, Christian %A Wurdack, Matthias %A Geisler, Peter %A Pawłowska, Monika %A Hecht, Bert %A Brixner, Tobias %D 2016 %J Appl. Phys. B %N 4 %P 94 %R 10.1007/s00340-016-6370-7 %T Investigation of the nonlinear refractive index of single-crystalline thin gold films and plasmonic nanostructures %V 122 %X The nonlinear refractive index of plasmonic materials may be used to obtain nonlinear functionality, e.g., power-dependent switching. Here, we investigate the nonlinear refractive index of single-crystalline gold in thin layers and nanostructures on dielectric substrates. In a first step, we implement a z-scan setup to investigate ~100-µm-sized thin-film samples. We determine the nonlinear refractive index of fused silica, n2(SiO2) = 2.9 × 10^(−20) m^2/W, in agreement with literature values. Subsequent z-scan measurements of single-crystalline gold films reveal a damage threshold of 0.22 TW/cm^2 and approximate upper limits of the real and imaginary parts of the nonlinear refractive index, |n2′(Au)| < 1.2 × 10^(−16) m^2/W and |n2″(Au)| < 0.6 × 10^(−16) m^2/W, respectively. To further determine possible effects of a nonlinear refractive index in plasmonic circuitry, interferometry is proposed as a phase-sensitive probe. In corresponding nanostructures, relative phase changes between two propagating near-field modes are converted to amplitude changes by mode interference. Power-dependent experiments using sub-10-fs near-infrared pulses and diffraction-limited resolution (NA = 1.4) reveal linear behavior up to the damage threshold (0.23 times relative to that of a solid single-crystalline gold film). An upper limit for the nonlinear power-dependent phase change between two propagating near-field modes is determined to Δφ < 0.07 rad.

Nanoscale Confinement of All-Optical Magnetic Switching in TbFeCo - Competition with Nanoscale Heterogeneity. Liu, Tian-Min; Wang, Tianhan; Reid, Alexander H.; Savoini, Matteo; Wu, Xiaofei; Koene, Benny; Granitzka, Patrick; Graves, Catherine E.; Higley, Daniel J.; Chen, Zhao; Razinskas, Gary; Hantschmann, Markus; Scherz, Andreas; Stöhr, Joachim; Tsukamoto, Arata; Hecht, Bert; Kimel, Alexey V.; Kirilyuk, Andrei; Rasing, Theo; Dürr, Hermann A. In Nano Lett., 15(10), pp. 6862–6868. 2015.
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Single femtosecond optical laser pulses, of sufficient intensity, are demonstrated to reverse magnetization in a process known as all-optical switching. Gold two-wire antennas are placed on the all-optical switching film TbFeCo. These structures are resonant with the optical field, and they create a field enhancement in the near-field which confines the area where optical switching can occur. The magnetic switching that occurs around and below the antenna is imaged using resonant X-ray holography and magnetic circular dichroism. The results not only show the feasibility of controllable switching with antenna assistance but also demonstrate the highly inhomogeneous nature of the switching process, which is attributed to the process depending on the material’s heterogeneity.

@article{liu2015nanoscale, abstract = {Single femtosecond optical laser pulses, of sufficient intensity, are demonstrated to reverse magnetization in a process known as all-optical switching. Gold two-wire antennas are placed on the all-optical switching film TbFeCo. These structures are resonant with the optical field, and they create a field enhancement in the near-field which confines the area where optical switching can occur. The magnetic switching that occurs around and below the antenna is imaged using resonant X-ray holography and magnetic circular dichroism. The results not only show the feasibility of controllable switching with antenna assistance but also demonstrate the highly inhomogeneous nature of the switching process, which is attributed to the process depending on the material’s heterogeneity.}, author = {Liu, Tian-Min and Wang, Tianhan and Reid, Alexander H. and Savoini, Matteo and Wu, Xiaofei and Koene, Benny and Granitzka, Patrick and Graves, Catherine E. and Higley, Daniel J. and Chen, Zhao and Razinskas, Gary and Hantschmann, Markus and Scherz, Andreas and Stöhr, Joachim and Tsukamoto, Arata and Hecht, Bert and Kimel, Alexey V. and Kirilyuk, Andrei and Rasing, Theo and Dürr, Hermann A.}, journal = {Nano Lett.}, keywords = {resonance}, month = 10, number = 10, pages = {6862-6868}, title = {Nanoscale Confinement of All-Optical Magnetic Switching in TbFeCo - Competition with Nanoscale Heterogeneity}, volume = 15, year = 2015 }

%0 Journal Article %1 liu2015nanoscale %A Liu, Tian-Min %A Wang, Tianhan %A Reid, Alexander H. %A Savoini, Matteo %A Wu, Xiaofei %A Koene, Benny %A Granitzka, Patrick %A Graves, Catherine E. %A Higley, Daniel J. %A Chen, Zhao %A Razinskas, Gary %A Hantschmann, Markus %A Scherz, Andreas %A Stöhr, Joachim %A Tsukamoto, Arata %A Hecht, Bert %A Kimel, Alexey V. %A Kirilyuk, Andrei %A Rasing, Theo %A Dürr, Hermann A. %D 2015 %J Nano Lett. %N 10 %P 6862-6868 %R 10.1021/acs.nanolett.5b02743 %T Nanoscale Confinement of All-Optical Magnetic Switching in TbFeCo - Competition with Nanoscale Heterogeneity %V 15 %X Single femtosecond optical laser pulses, of sufficient intensity, are demonstrated to reverse magnetization in a process known as all-optical switching. Gold two-wire antennas are placed on the all-optical switching film TbFeCo. These structures are resonant with the optical field, and they create a field enhancement in the near-field which confines the area where optical switching can occur. The magnetic switching that occurs around and below the antenna is imaged using resonant X-ray holography and magnetic circular dichroism. The results not only show the feasibility of controllable switching with antenna assistance but also demonstrate the highly inhomogeneous nature of the switching process, which is attributed to the process depending on the material’s heterogeneity.
Silica–gold bilayer-based transfer of focused ion beam-fabricated nanostructures. Wu, Xiaofei; Geisler, Peter; Krauss, Enno; Kullock, René; Hecht, Bert. In Nanoscale, 7(39), pp. 16427–16433. 2015.
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The demand for using nanostructures fabricated by focused ion beam (FIB) on delicate substrates or as building blocks for complex devices motivates the development of protocols that allow FIB-fabricated nanostructures to be transferred from the original substrate to the desired target. However, transfer of FIB-fabricated nanostructures is severely hindered by FIB-induced welding of structure and substrate. Here we present two (ex and in situ) transfer methods for FIB-fabricated nanostructures based on a silica–gold bilayer evaporated onto a bulk substrate. Utilizing the poor adhesion between silica and gold, the nanostructures can be mechanically separated from the bulk substrate. For the ex situ transfer, a spin-coated poly(methyl methacrylate) film is used to carry the nanostructures so that the bilayer can be etched away after being peeled off. For the in situ transfer, using a micro-manipulator inside the FIB machine, a cut-out piece of silica on which a nanostructure has been fabricated is peeled off from the bulk substrate and thus carries the nanostructure to a target substrate. We demonstrate the performance of both methods by transferring plasmonic nano-antennas fabricated from single-crystalline gold flakes by FIB milling to a silicon wafer and to a scanning probe tip.

@article{wu2015silicagold, abstract = {The demand for using nanostructures fabricated by focused ion beam (FIB) on delicate substrates or as building blocks for complex devices motivates the development of protocols that allow FIB-fabricated nanostructures to be transferred from the original substrate to the desired target. However, transfer of FIB-fabricated nanostructures is severely hindered by FIB-induced welding of structure and substrate. Here we present two (ex and in situ) transfer methods for FIB-fabricated nanostructures based on a silica–gold bilayer evaporated onto a bulk substrate. Utilizing the poor adhesion between silica and gold, the nanostructures can be mechanically separated from the bulk substrate. For the ex situ transfer, a spin-coated poly(methyl methacrylate) film is used to carry the nanostructures so that the bilayer can be etched away after being peeled off. For the in situ transfer, using a micro-manipulator inside the FIB machine, a cut-out piece of silica on which a nanostructure has been fabricated is peeled off from the bulk substrate and thus carries the nanostructure to a target substrate. We demonstrate the performance of both methods by transferring plasmonic nano-antennas fabricated from single-crystalline gold flakes by FIB milling to a silicon wafer and to a scanning probe tip.}, author = {Wu, Xiaofei and Geisler, Peter and Krauss, Enno and Kullock, René and Hecht, Bert}, journal = {Nanoscale}, keywords = {FIB}, month = {09}, number = 39, pages = {16427-16433}, title = {Silica–gold bilayer-based transfer of focused ion beam-fabricated nanostructures}, volume = 7, year = 2015 }

%0 Journal Article %1 wu2015silicagold %A Wu, Xiaofei %A Geisler, Peter %A Krauss, Enno %A Kullock, René %A Hecht, Bert %D 2015 %J Nanoscale %N 39 %P 16427-16433 %R 10.1039/C5NR04262C %T Silica–gold bilayer-based transfer of focused ion beam-fabricated nanostructures %V 7 %X The demand for using nanostructures fabricated by focused ion beam (FIB) on delicate substrates or as building blocks for complex devices motivates the development of protocols that allow FIB-fabricated nanostructures to be transferred from the original substrate to the desired target. However, transfer of FIB-fabricated nanostructures is severely hindered by FIB-induced welding of structure and substrate. Here we present two (ex and in situ) transfer methods for FIB-fabricated nanostructures based on a silica–gold bilayer evaporated onto a bulk substrate. Utilizing the poor adhesion between silica and gold, the nanostructures can be mechanically separated from the bulk substrate. For the ex situ transfer, a spin-coated poly(methyl methacrylate) film is used to carry the nanostructures so that the bilayer can be etched away after being peeled off. For the in situ transfer, using a micro-manipulator inside the FIB machine, a cut-out piece of silica on which a nanostructure has been fabricated is peeled off from the bulk substrate and thus carries the nanostructure to a target substrate. We demonstrate the performance of both methods by transferring plasmonic nano-antennas fabricated from single-crystalline gold flakes by FIB milling to a silicon wafer and to a scanning probe tip.
Electrically driven optical antennas. Kern, Johannes; Kullock, René; Prangsma, Jord; Emmerling, Monika; Kamp, Martin; Hecht, Bert. In Nature Photon, 9(9), pp. 582–586. 2015.

» arxiv:1502.04935
press:
» Die Welt (in german), » spektrum.de (in german), » Physik in unserer Zeit (in german)
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Unlike radiowave antennas, so far optical nanoantennas cannot be fed by electrical generators. Instead, they are driven by light or indirectly via excited discrete states in active materials in their vicinity. Here we demonstrate the direct electrical driving of an in-plane optical antenna by the broadband quantum-shot noise of electrons tunnelling across its feed gap. The spectrum of the emitted photons is determined by the antenna geometry and can be tuned via the applied voltage. Moreover, the direction and polarization of the light emission are controlled by the antenna resonance, which also improves the external quantum efficiency by up to two orders of magnitude. The one-material planar design offers facile integration of electrical and optical circuits and thus represents a new paradigm for interfacing electrons and photons at the nanometre scale, for example for on-chip wireless communication and highly configurable electrically driven subwavelength photon sources.

@article{kern2015electrically, abstract = {Unlike radiowave antennas, so far optical nanoantennas cannot be fed by electrical generators. Instead, they are driven by light or indirectly via excited discrete states in active materials in their vicinity. Here we demonstrate the direct electrical driving of an in-plane optical antenna by the broadband quantum-shot noise of electrons tunnelling across its feed gap. The spectrum of the emitted photons is determined by the antenna geometry and can be tuned via the applied voltage. Moreover, the direction and polarization of the light emission are controlled by the antenna resonance, which also improves the external quantum efficiency by up to two orders of magnitude. The one-material planar design offers facile integration of electrical and optical circuits and thus represents a new paradigm for interfacing electrons and photons at the nanometre scale, for example for on-chip wireless communication and highly configurable electrically driven subwavelength photon sources.}, author = {Kern, Johannes and Kullock, René and Prangsma, Jord and Emmerling, Monika and Kamp, Martin and Hecht, Bert}, journal = {Nature Photon}, keywords = {nano-optics}, month = {08}, note = {<a href="https://arxiv.org/abs/1502.04935">» arxiv:1502.04935</a> press: <a href="https://www.welt.de/print/die_welt/wissen/article146060578/Smartphone-fuer-Adleraugen.html">» Die Welt</a> (in german), <a href="http://www.spektrum.de/news/erste-elektrisch-betriebene-lichtantenne-der-welt/1361113">» spektrum.de</a> (in german), <a href="http://onlinelibrary.wiley.com/doi/10.1002/piuz.201590100/abstract">» Physik in unserer Zeit</a> (in german)}, number = 9, pages = {582-586}, title = {Electrically driven optical antennas}, volume = 9, year = 2015 }

%0 Journal Article %1 kern2015electrically %A Kern, Johannes %A Kullock, René %A Prangsma, Jord %A Emmerling, Monika %A Kamp, Martin %A Hecht, Bert %D 2015 %J Nature Photon %N 9 %P 582-586 %R 10.1038/nphoton.2015.141 %T Electrically driven optical antennas %V 9 %X Unlike radiowave antennas, so far optical nanoantennas cannot be fed by electrical generators. Instead, they are driven by light or indirectly via excited discrete states in active materials in their vicinity. Here we demonstrate the direct electrical driving of an in-plane optical antenna by the broadband quantum-shot noise of electrons tunnelling across its feed gap. The spectrum of the emitted photons is determined by the antenna geometry and can be tuned via the applied voltage. Moreover, the direction and polarization of the light emission are controlled by the antenna resonance, which also improves the external quantum efficiency by up to two orders of magnitude. The one-material planar design offers facile integration of electrical and optical circuits and thus represents a new paradigm for interfacing electrons and photons at the nanometre scale, for example for on-chip wireless communication and highly configurable electrically driven subwavelength photon sources.
Single-crystalline gold microplates grown on substrates by solution-phase synthesis. Wu, Xiaofei; Kullock, René; Krauss, Enno; Hecht, Bert. In Cryst. Res. Technol., 50(8), pp. 595–602. 2015.
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Chemically synthesized single-crystalline gold microplates have been attracting increasing interest because of their potential as high-quality gold films for nanotechnology. We present the growth of tens of nanometers thick and tens of micrometers large single-crystalline gold plates directly on solid substrates by solution-phase synthesis. Compared to microplates deposited on substrates from dispersion phase, substrate-grown plates exhibit significantly higher quality by avoiding severe small-particle contamination and aggregation. Substrate-grown gold plates also open new perspectives to study the growth mechanism via step-growth and observation cycles of a large number of individual plates. Growth models are proposed to interpret the evolution of thickness, area and shape of the plates. It is found that the plate surface remains smooth after regrowth, implying the applicability of regrowth for producing giant plates as well as unique single-crystalline nano-structures.

@article{wu2015singlecrystalline, abstract = {Chemically synthesized single-crystalline gold microplates have been attracting increasing interest because of their potential as high-quality gold films for nanotechnology. We present the growth of tens of nanometers thick and tens of micrometers large single-crystalline gold plates directly on solid substrates by solution-phase synthesis. Compared to microplates deposited on substrates from dispersion phase, substrate-grown plates exhibit significantly higher quality by avoiding severe small-particle contamination and aggregation. Substrate-grown gold plates also open new perspectives to study the growth mechanism via step-growth and observation cycles of a large number of individual plates. Growth models are proposed to interpret the evolution of thickness, area and shape of the plates. It is found that the plate surface remains smooth after regrowth, implying the applicability of regrowth for producing giant plates as well as unique single-crystalline nano-structures.}, author = {Wu, Xiaofei and Kullock, René and Krauss, Enno and Hecht, Bert}, journal = {Cryst. Res. Technol.}, keywords = {gold}, month = {07}, number = 8, pages = {595-602}, title = {Single-crystalline gold microplates grown on substrates by solution-phase synthesis}, volume = 50, year = 2015 }

%0 Journal Article %1 wu2015singlecrystalline %A Wu, Xiaofei %A Kullock, René %A Krauss, Enno %A Hecht, Bert %D 2015 %J Cryst. Res. Technol. %N 8 %P 595-602 %R 10.1002/crat.201400429 %T Single-crystalline gold microplates grown on substrates by solution-phase synthesis %V 50 %X Chemically synthesized single-crystalline gold microplates have been attracting increasing interest because of their potential as high-quality gold films for nanotechnology. We present the growth of tens of nanometers thick and tens of micrometers large single-crystalline gold plates directly on solid substrates by solution-phase synthesis. Compared to microplates deposited on substrates from dispersion phase, substrate-grown plates exhibit significantly higher quality by avoiding severe small-particle contamination and aggregation. Substrate-grown gold plates also open new perspectives to study the growth mechanism via step-growth and observation cycles of a large number of individual plates. Growth models are proposed to interpret the evolution of thickness, area and shape of the plates. It is found that the plate surface remains smooth after regrowth, implying the applicability of regrowth for producing giant plates as well as unique single-crystalline nano-structures.
Robustness of plasmonic angular momentum confinement in cross resonant optical antennas. Klaer, Peter; Razinskas, Gary; Lehr, Martin; Krewer, Keno; Schertz, Florian; Wu, Xiao-Fei; Hecht, Bert; Schönhense, Gerd; Elmers, Hans Joachim. In Appl. Phys. Lett., 106(26), p. 261101. 2015.
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Using a combination of photoemission electron microscopy and numerical simulations, we investigated the angular moment transfer in strongly enhanced optical near-fields of artificially fabricated optical antennas. The polarization dependence of the optical near-field enhancement has been measured in a maximum symmetric geometry, i.e., excitation by a normal incident planar wave. Finite-difference time-domain simulations for the realistic antenna geometries as determined by high-resolution electron microscopy reveal a very good agreement with experimental data. The agreement confirms that the geometrical asymmetries and inhomogeneities due to the nanoscale fabrication process preserve the circular polarization in the gap regions with strong near-field enhancement.

@article{klaer2015robustness, abstract = {Using a combination of photoemission electron microscopy and numerical simulations, we investigated the angular moment transfer in strongly enhanced optical near-fields of artificially fabricated optical antennas. The polarization dependence of the optical near-field enhancement has been measured in a maximum symmetric geometry, i.e., excitation by a normal incident planar wave. Finite-difference time-domain simulations for the realistic antenna geometries as determined by high-resolution electron microscopy reveal a very good agreement with experimental data. The agreement confirms that the geometrical asymmetries and inhomogeneities due to the nanoscale fabrication process preserve the circular polarization in the gap regions with strong near-field enhancement.}, author = {Klaer, Peter and Razinskas, Gary and Lehr, Martin and Krewer, Keno and Schertz, Florian and Wu, Xiao-Fei and Hecht, Bert and Schönhense, Gerd and Elmers, Hans Joachim}, journal = {Appl. Phys. Lett.}, keywords = {resonance}, month = {06}, number = 26, pages = 261101, title = {Robustness of plasmonic angular momentum confinement in cross resonant optical antennas}, volume = 106, year = 2015 }

%0 Journal Article %1 klaer2015robustness %A Klaer, Peter %A Razinskas, Gary %A Lehr, Martin %A Krewer, Keno %A Schertz, Florian %A Wu, Xiao-Fei %A Hecht, Bert %A Schönhense, Gerd %A Elmers, Hans Joachim %D 2015 %J Appl. Phys. Lett. %N 26 %P 261101 %R 10.1063/1.4923242 %T Robustness of plasmonic angular momentum confinement in cross resonant optical antennas %V 106 %X Using a combination of photoemission electron microscopy and numerical simulations, we investigated the angular moment transfer in strongly enhanced optical near-fields of artificially fabricated optical antennas. The polarization dependence of the optical near-field enhancement has been measured in a maximum symmetric geometry, i.e., excitation by a normal incident planar wave. Finite-difference time-domain simulations for the realistic antenna geometries as determined by high-resolution electron microscopy reveal a very good agreement with experimental data. The agreement confirms that the geometrical asymmetries and inhomogeneities due to the nanoscale fabrication process preserve the circular polarization in the gap regions with strong near-field enhancement.
Mode matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation. Celebrano, Michele; Wu, Xiaofei; Baselli, Milena; Großmann, Swen; Biagioni, Paolo; Locatelli, Andrea; Angelis, Costantino De; Cerullo, Giulio; Osellame, Roberto; Hecht, Bert; Duò, Lamberto; Ciccacci, Franco; Finazzi, Marco. In Nature Nanotech., 10(5), pp. 412–417. 2015.

» arxiv:1412.0698
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Boosting nonlinear frequency conversion in extremely confined volumes remains a challenge in nano-optics research, but can enable applications in nanomedicine, photocatalysis and background-free biosensing. To obtain brighter nonlinear nanoscale sources, approaches that enhance the electromagnetic field intensity and counter the lack of phase matching in nanoplasmonic systems are often employed. However, the high degree of symmetry in the crystalline structure of plasmonic materials (metals in particular) and in nanoantenna designs strongly quenches second harmonic generation. Here, we describe doubly-resonant single-crystalline gold nanostructures with no axial symmetry displaying spatial mode overlap at both the excitation and second harmonic wavelengths. The combination of these features allows the attainment of a nonlinear coefficient for second harmonic generation of ∼5 × 10{\textasciicircum}(–10) W{\textasciicircum}(–1), enabling a second harmonic photon yield higher than 3 × 10{\textasciicircum}6 photons per second. Theoretical estimations point toward the use of our nonlinear plasmonic nanoantennas as efficient platforms for label-free molecular sensing.

@article{celebrano2015matching, abstract = {Boosting nonlinear frequency conversion in extremely confined volumes remains a challenge in nano-optics research, but can enable applications in nanomedicine, photocatalysis and background-free biosensing. To obtain brighter nonlinear nanoscale sources, approaches that enhance the electromagnetic field intensity and counter the lack of phase matching in nanoplasmonic systems are often employed. However, the high degree of symmetry in the crystalline structure of plasmonic materials (metals in particular) and in nanoantenna designs strongly quenches second harmonic generation. Here, we describe doubly-resonant single-crystalline gold nanostructures with no axial symmetry displaying spatial mode overlap at both the excitation and second harmonic wavelengths. The combination of these features allows the attainment of a nonlinear coefficient for second harmonic generation of ∼5 × 10{\textasciicircum}(–10) W{\textasciicircum}(–1), enabling a second harmonic photon yield higher than 3 × 10{\textasciicircum}6 photons per second. Theoretical estimations point toward the use of our nonlinear plasmonic nanoantennas as efficient platforms for label-free molecular sensing.}, author = {Celebrano, Michele and Wu, Xiaofei and Baselli, Milena and Großmann, Swen and Biagioni, Paolo and Locatelli, Andrea and Angelis, Costantino De and Cerullo, Giulio and Osellame, Roberto and Hecht, Bert and Duò, Lamberto and Ciccacci, Franco and Finazzi, Marco}, journal = {Nature Nanotech.}, keywords = {resonance}, month = {04}, note = {<a href="https://arxiv.org/abs/1412.0698" style="font-style: normal;">» arxiv:1412.0698</a>}, number = 5, pages = {412-417}, title = {Mode matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation}, volume = 10, year = 2015 }

%0 Journal Article %1 celebrano2015matching %A Celebrano, Michele %A Wu, Xiaofei %A Baselli, Milena %A Großmann, Swen %A Biagioni, Paolo %A Locatelli, Andrea %A Angelis, Costantino De %A Cerullo, Giulio %A Osellame, Roberto %A Hecht, Bert %A Duò, Lamberto %A Ciccacci, Franco %A Finazzi, Marco %D 2015 %J Nature Nanotech. %N 5 %P 412-417 %R 10.1038/nnano.2015.69 %T Mode matching in multiresonant plasmonic nanoantennas for enhanced second harmonic generation %V 10 %X Boosting nonlinear frequency conversion in extremely confined volumes remains a challenge in nano-optics research, but can enable applications in nanomedicine, photocatalysis and background-free biosensing. To obtain brighter nonlinear nanoscale sources, approaches that enhance the electromagnetic field intensity and counter the lack of phase matching in nanoplasmonic systems are often employed. However, the high degree of symmetry in the crystalline structure of plasmonic materials (metals in particular) and in nanoantenna designs strongly quenches second harmonic generation. Here, we describe doubly-resonant single-crystalline gold nanostructures with no axial symmetry displaying spatial mode overlap at both the excitation and second harmonic wavelengths. The combination of these features allows the attainment of a nonlinear coefficient for second harmonic generation of ∼5 × 10{\textasciicircum}(–10) W{\textasciicircum}(–1), enabling a second harmonic photon yield higher than 3 × 10{\textasciicircum}6 photons per second. Theoretical estimations point toward the use of our nonlinear plasmonic nanoantennas as efficient platforms for label-free molecular sensing.
Emission Engineering in Germanium Nanoresonators. Celebrano, Michele; Baselli, Milena; Bollani, Monica; Frigerio, Jacopo; Bahgat Shehata, Andrea; Della Frera, Adriano; Tosi, Alberto; Farina, Andrea; Pezzoli, Fabio; Osmond, Johann; Wu, Xiaofei; Hecht, Bert; Sordan, Roman; Chrastina, Daniel; Isella, Giovanni; Duò, Lamberto; Finazzi, Marco; Biagioni, Paolo. In ACS Photonics, 2(1), pp. 53–59. 2015.
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We experimentally investigate the smallest germanium waveguide cavity resonators on silicon that can be designed to work around 1.55 μm wavelength and observe an almost 30-fold enhancement in the collected spontaneous emission per unit volume when compared to a continuous germanium film of the same thickness. The enhancement is due to an effective combination of (i) excitation enhancement at the pump wavelength, (ii) emission enhancement (Purcell effect) at the emission wavelength, and (iii) effective beaming by the nanoresonators, which act as optical antennas to enhance the radiation efficiency. Our results set a basis for the understanding and engineering of light emission based on subwavelength, CMOS-compatible nanostructures operating at telecommunication wavelengths.

@article{celebrano2015emission, abstract = {We experimentally investigate the smallest germanium waveguide cavity resonators on silicon that can be designed to work around 1.55 μm wavelength and observe an almost 30-fold enhancement in the collected spontaneous emission per unit volume when compared to a continuous germanium film of the same thickness. The enhancement is due to an effective combination of (i) excitation enhancement at the pump wavelength, (ii) emission enhancement (Purcell effect) at the emission wavelength, and (iii) effective beaming by the nanoresonators, which act as optical antennas to enhance the radiation efficiency. Our results set a basis for the understanding and engineering of light emission based on subwavelength, CMOS-compatible nanostructures operating at telecommunication wavelengths.}, author = {Celebrano, Michele and Baselli, Milena and Bollani, Monica and Frigerio, Jacopo and Bahgat Shehata, Andrea and Della Frera, Adriano and Tosi, Alberto and Farina, Andrea and Pezzoli, Fabio and Osmond, Johann and Wu, Xiaofei and Hecht, Bert and Sordan, Roman and Chrastina, Daniel and Isella, Giovanni and Duò, Lamberto and Finazzi, Marco and Biagioni, Paolo}, journal = {ACS Photonics}, keywords = {nano-optics}, month = {01}, number = 1, pages = {53-59}, title = {Emission Engineering in Germanium Nanoresonators}, volume = 2, year = 2015 }

%0 Journal Article %1 celebrano2015emission %A Celebrano, Michele %A Baselli, Milena %A Bollani, Monica %A Frigerio, Jacopo %A Bahgat Shehata, Andrea %A Della Frera, Adriano %A Tosi, Alberto %A Farina, Andrea %A Pezzoli, Fabio %A Osmond, Johann %A Wu, Xiaofei %A Hecht, Bert %A Sordan, Roman %A Chrastina, Daniel %A Isella, Giovanni %A Duò, Lamberto %A Finazzi, Marco %A Biagioni, Paolo %D 2015 %J ACS Photonics %N 1 %P 53-59 %R 10.1021/ph500432k %T Emission Engineering in Germanium Nanoresonators %V 2 %X We experimentally investigate the smallest germanium waveguide cavity resonators on silicon that can be designed to work around 1.55 μm wavelength and observe an almost 30-fold enhancement in the collected spontaneous emission per unit volume when compared to a continuous germanium film of the same thickness. The enhancement is due to an effective combination of (i) excitation enhancement at the pump wavelength, (ii) emission enhancement (Purcell effect) at the emission wavelength, and (iii) effective beaming by the nanoresonators, which act as optical antennas to enhance the radiation efficiency. Our results set a basis for the understanding and engineering of light emission based on subwavelength, CMOS-compatible nanostructures operating at telecommunication wavelengths.

Shaping and spatiotemporal characterization of sub-10-fs pulses focused by a high-NA objective. Pawlowska, Monika; Goetz, Sebastian; Dreher, Christian; Wurdack, Matthias; Krauss, Enno; Razinskas, Gary; Geisler, Peter; Hecht, Bert; Brixner, Tobias. In Opt. Express, 22(25), pp. 31496–31510. OSA, 2014.
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We describe a setup consisting of a 4f pulse shaper and a microscope with a high-NA objective lens and discuss the aspects most relevant for an undistorted spatiotemporal profile of the focused beam. We demonstrate shaper-assisted pulse compression in focus to a sub-10-fs duration using phase-resolved interferometric spectral modulation (PRISM). We introduce a nanostructure-based method for sub-diffraction spatiotemporal characterization of strongly focused pulses. The distortions caused by optical aberrations and space--time coupling from the shaper can be reduced by careful setup design and alignment to about 10 nm in space and 1 fs in time.

@article{pawlowska2014shaping, abstract = {We describe a setup consisting of a 4f pulse shaper and a microscope with a high-NA objective lens and discuss the aspects most relevant for an undistorted spatiotemporal profile of the focused beam. We demonstrate shaper-assisted pulse compression in focus to a sub-10-fs duration using phase-resolved interferometric spectral modulation (PRISM). We introduce a nanostructure-based method for sub-diffraction spatiotemporal characterization of strongly focused pulses. The distortions caused by optical aberrations and space–time coupling from the shaper can be reduced by careful setup design and alignment to about 10 nm in space and 1 fs in time.}, author = {Pawlowska, Monika and Goetz, Sebastian and Dreher, Christian and Wurdack, Matthias and Krauss, Enno and Razinskas, Gary and Geisler, Peter and Hecht, Bert and Brixner, Tobias}, journal = {Opt. Express}, keywords = {PRISM}, month = 12, number = 25, pages = {31496-31510}, publisher = {OSA}, title = {Shaping and spatiotemporal characterization of sub-10-fs pulses focused by a high-NA objective}, volume = 22, year = 2014 }

%0 Journal Article %1 pawlowska2014shaping %A Pawlowska, Monika %A Goetz, Sebastian %A Dreher, Christian %A Wurdack, Matthias %A Krauss, Enno %A Razinskas, Gary %A Geisler, Peter %A Hecht, Bert %A Brixner, Tobias %D 2014 %I OSA %J Opt. Express %N 25 %P 31496-31510 %R 10.1364/OE.22.031496 %T Shaping and spatiotemporal characterization of sub-10-fs pulses focused by a high-NA objective %V 22 %X We describe a setup consisting of a 4f pulse shaper and a microscope with a high-NA objective lens and discuss the aspects most relevant for an undistorted spatiotemporal profile of the focused beam. We demonstrate shaper-assisted pulse compression in focus to a sub-10-fs duration using phase-resolved interferometric spectral modulation (PRISM). We introduce a nanostructure-based method for sub-diffraction spatiotemporal characterization of strongly focused pulses. The distortions caused by optical aberrations and space--time coupling from the shaper can be reduced by careful setup design and alignment to about 10 nm in space and 1 fs in time.
Remote detection of single emitters via optical waveguides. Then, Patrick; Razinskas, Gary; Feichtner, Thorsten; Haas, Philippe; Wild, Andreas; Bellini, Nicola; Osellame, Roberto; Cerullo, Giulio; Hecht, Bert. In Phys. Rev. A, 89(5), p. 053801. 2014.
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The integration of lab-on-a-chip technologies with single-molecule detection techniques may enable new applications in analytical chemistry, biotechnology, and medicine. We describe a method based on the reciprocity theorem of electromagnetic theory to determine and optimize the detection efficiency of photons emitted by single quantum emitters through truncated dielectric waveguides of arbitrary shape positioned in their proximity. We demonstrate experimentally that detection of single quantum emitters via such waveguides is possible, confirming the predicted behavior of the detection efficiency. Our findings blaze the trail towards efficient lensless single-emitter detection compatible with large-scale optofluidic integration.

@article{then2014remote, abstract = {The integration of lab-on-a-chip technologies with single-molecule detection techniques may enable new applications in analytical chemistry, biotechnology, and medicine. We describe a method based on the reciprocity theorem of electromagnetic theory to determine and optimize the detection efficiency of photons emitted by single quantum emitters through truncated dielectric waveguides of arbitrary shape positioned in their proximity. We demonstrate experimentally that detection of single quantum emitters via such waveguides is possible, confirming the predicted behavior of the detection efficiency. Our findings blaze the trail towards efficient lensless single-emitter detection compatible with large-scale optofluidic integration.}, author = {Then, Patrick and Razinskas, Gary and Feichtner, Thorsten and Haas, Philippe and Wild, Andreas and Bellini, Nicola and Osellame, Roberto and Cerullo, Giulio and Hecht, Bert}, journal = {Phys. Rev. A}, keywords = {nano-optics}, month = {05}, number = 5, pages = {053801}, title = {Remote detection of single emitters via optical waveguides}, volume = 89, year = 2014 }

%0 Journal Article %1 then2014remote %A Then, Patrick %A Razinskas, Gary %A Feichtner, Thorsten %A Haas, Philippe %A Wild, Andreas %A Bellini, Nicola %A Osellame, Roberto %A Cerullo, Giulio %A Hecht, Bert %D 2014 %J Phys. Rev. A %N 5 %P 053801 %R 10.1103/PhysRevA.89.053801 %T Remote detection of single emitters via optical waveguides %V 89 %X The integration of lab-on-a-chip technologies with single-molecule detection techniques may enable new applications in analytical chemistry, biotechnology, and medicine. We describe a method based on the reciprocity theorem of electromagnetic theory to determine and optimize the detection efficiency of photons emitted by single quantum emitters through truncated dielectric waveguides of arbitrary shape positioned in their proximity. We demonstrate experimentally that detection of single quantum emitters via such waveguides is possible, confirming the predicted behavior of the detection efficiency. Our findings blaze the trail towards efficient lensless single-emitter detection compatible with large-scale optofluidic integration.
Coherent Control of Plasmon Propagation in a Nanocircuit. Rewitz, Christian; Razinskas, Gary; Geisler, Peter; Krauss, Enno; Goetz, Sebastian; Pawłowska, Monika; Hecht, Bert; Brixner, Tobias. In Phys. Rev. Applied, 1(1), p. 014007. 2014.
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The miniaturization of optical devices is a prerequisite for broadband data-processing technology to compete with cutting-edge nanoelectronic circuits. For these future nano-optical circuits, controlling the spatial and temporal evolution of surface plasmons, i.e., propagating optical near fields at metal-insulator interfaces, is a key feature. Here, we design, optimize, and fabricate a nanoscale directional coupler with one input and two output ports, a device that is an essential element of nano-optical circuits. The directional coupler is based on a two-wire transmission line supporting two plasmonic eigenmodes that can be selectively excited. By manipulating the input polarization of ultrashort pulses and pulse pairs and by characterizing the light emitted from both output ports, we demonstrate open-loop ultrafast spatial and spatiotemporal coherent control of plasmon propagation. Because of the intuitive and optimized design, which exploits a controlled near-field interference mechanism, varying the linear input polarization is enough to switch between both output ports of the nanoscale directional coupler. Since we exploit the interference of a finite spectrum of eigenmodes, our experiments represent a very intuitive classical analogue to quantum control in molecules.

@article{rewitz2014coherent, abstract = {The miniaturization of optical devices is a prerequisite for broadband data-processing technology to compete with cutting-edge nanoelectronic circuits. For these future nano-optical circuits, controlling the spatial and temporal evolution of surface plasmons, i.e., propagating optical near fields at metal-insulator interfaces, is a key feature. Here, we design, optimize, and fabricate a nanoscale directional coupler with one input and two output ports, a device that is an essential element of nano-optical circuits. The directional coupler is based on a two-wire transmission line supporting two plasmonic eigenmodes that can be selectively excited. By manipulating the input polarization of ultrashort pulses and pulse pairs and by characterizing the light emitted from both output ports, we demonstrate open-loop ultrafast spatial and spatiotemporal coherent control of plasmon propagation. Because of the intuitive and optimized design, which exploits a controlled near-field interference mechanism, varying the linear input polarization is enough to switch between both output ports of the nanoscale directional coupler. Since we exploit the interference of a finite spectrum of eigenmodes, our experiments represent a very intuitive classical analogue to quantum control in molecules.}, author = {Rewitz, Christian and Razinskas, Gary and Geisler, Peter and Krauss, Enno and Goetz, Sebastian and Pawłowska, Monika and Hecht, Bert and Brixner, Tobias}, journal = {Phys. Rev. Applied}, keywords = {plasmon}, month = {02}, number = 1, pages = {014007}, title = {Coherent Control of Plasmon Propagation in a Nanocircuit}, volume = 1, year = 2014 }

%0 Journal Article %1 rewitz2014coherent %A Rewitz, Christian %A Razinskas, Gary %A Geisler, Peter %A Krauss, Enno %A Goetz, Sebastian %A Pawłowska, Monika %A Hecht, Bert %A Brixner, Tobias %D 2014 %J Phys. Rev. Applied %N 1 %P 014007 %R 10.1103/PhysRevApplied.1.014007 %T Coherent Control of Plasmon Propagation in a Nanocircuit %V 1 %X The miniaturization of optical devices is a prerequisite for broadband data-processing technology to compete with cutting-edge nanoelectronic circuits. For these future nano-optical circuits, controlling the spatial and temporal evolution of surface plasmons, i.e., propagating optical near fields at metal-insulator interfaces, is a key feature. Here, we design, optimize, and fabricate a nanoscale directional coupler with one input and two output ports, a device that is an essential element of nano-optical circuits. The directional coupler is based on a two-wire transmission line supporting two plasmonic eigenmodes that can be selectively excited. By manipulating the input polarization of ultrashort pulses and pulse pairs and by characterizing the light emitted from both output ports, we demonstrate open-loop ultrafast spatial and spatiotemporal coherent control of plasmon propagation. Because of the intuitive and optimized design, which exploits a controlled near-field interference mechanism, varying the linear input polarization is enough to switch between both output ports of the nanoscale directional coupler. Since we exploit the interference of a finite spectrum of eigenmodes, our experiments represent a very intuitive classical analogue to quantum control in molecules.

Multimode Plasmon Excitation and In Situ Analysis in Top-Down Fabricated Nanocircuits. Geisler, Peter; Razinskas, Gary; Krauss, Enno; Wu, Xiao-Fei; Rewitz, Christian; Tuchscherer, Philip; Goetz, Sebastian; Huang, Chen-Bin; Brixner, Tobias; Hecht, Bert. In Phys. Rev. Lett., 111(18), p. 183901. 2013.

» arXiv:1304.1737
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We experimentally demonstrate synthesis and in situ analysis of multimode plasmonic excitations in two-wire transmission lines supporting a symmetric and an antisymmetric eigenmode. To this end we irradiate an incoupling antenna with a diffraction-limited excitation spot exploiting a polarization- and position-dependent excitation efficiency. Modal analysis is performed by recording the far-field emission of two mode-specific spatially separated emission spots at the far end of the transmission line. To illustrate the power of the approach we selectively determine the group velocities of symmetric and antisymmetric contributions of a multimode ultrafast plasmon pulse.

@article{geisler2013multimode, abstract = {We experimentally demonstrate synthesis and in situ analysis of multimode plasmonic excitations in two-wire transmission lines supporting a symmetric and an antisymmetric eigenmode. To this end we irradiate an incoupling antenna with a diffraction-limited excitation spot exploiting a polarization- and position-dependent excitation efficiency. Modal analysis is performed by recording the far-field emission of two mode-specific spatially separated emission spots at the far end of the transmission line. To illustrate the power of the approach we selectively determine the group velocities of symmetric and antisymmetric contributions of a multimode ultrafast plasmon pulse.}, author = {Geisler, Peter and Razinskas, Gary and Krauss, Enno and Wu, Xiao-Fei and Rewitz, Christian and Tuchscherer, Philip and Goetz, Sebastian and Huang, Chen-Bin and Brixner, Tobias and Hecht, Bert}, journal = {Phys. Rev. Lett.}, keywords = {plasmon}, month = 10, note = {<a href="https://arxiv.org/abs/1304.1737" style="font-style: normal;">» arXiv:1304.1737 </a>}, number = 18, pages = 183901, title = {Multimode Plasmon Excitation and In Situ Analysis in Top-Down Fabricated Nanocircuits}, volume = 111, year = 2013 }

%0 Journal Article %1 geisler2013multimode %A Geisler, Peter %A Razinskas, Gary %A Krauss, Enno %A Wu, Xiao-Fei %A Rewitz, Christian %A Tuchscherer, Philip %A Goetz, Sebastian %A Huang, Chen-Bin %A Brixner, Tobias %A Hecht, Bert %D 2013 %J Phys. Rev. Lett. %N 18 %P 183901 %R 10.1103/PhysRevLett.111.183901 %T Multimode Plasmon Excitation and In Situ Analysis in Top-Down Fabricated Nanocircuits %V 111 %X We experimentally demonstrate synthesis and in situ analysis of multimode plasmonic excitations in two-wire transmission lines supporting a symmetric and an antisymmetric eigenmode. To this end we irradiate an incoupling antenna with a diffraction-limited excitation spot exploiting a polarization- and position-dependent excitation efficiency. Modal analysis is performed by recording the far-field emission of two mode-specific spatially separated emission spots at the far end of the transmission line. To illustrate the power of the approach we selectively determine the group velocities of symmetric and antisymmetric contributions of a multimode ultrafast plasmon pulse.

Atomic-Scale Confinement of Resonant Optical Fields. Kern, Johannes; Großmann, Swen; Tarakina, Nadezda V.; Häckel, Tim; Emmerling, Monika; Kamp, Martin; Huang, Jer-Shing; Biagioni, Paolo; Prangsma, Jord C.; Hecht, Bert. In Nano Lett., 12(11), pp. 5504–5509. 2012.

» arXiv:1112.5008
press: » Atomic-scale confinement of resonant optical fields, coverimage on » pro-physik.de (german)
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In the presence of matter, there is no fundamental limit preventing confinement of visible light even down to atomic scales. Achieving such confinement and the corresponding resonant intensity enhancement inevitably requires simultaneous control over atomic-scale details of material structures and over the optical modes that such structures support. By means of self-assembly we have obtained side-by-side aligned gold nanorod dimers with robust atomically defined gaps reaching below 0.5 nm. The existence of atomically confined light fields in these gaps is demonstrated by observing extreme Coulomb splitting of corresponding symmetric and antisymmetric dimer eigenmodes of more than 800 meV in white-light scattering experiments. Our results open new perspectives for atomically resolved spectroscopic imaging, deeply nonlinear optics, ultrasensing, cavity optomechanics, as well as for the realization of novel quantum-optical devices.

@article{kern2012atomicscale, abstract = {In the presence of matter, there is no fundamental limit preventing confinement of visible light even down to atomic scales. Achieving such confinement and the corresponding resonant intensity enhancement inevitably requires simultaneous control over atomic-scale details of material structures and over the optical modes that such structures support. By means of self-assembly we have obtained side-by-side aligned gold nanorod dimers with robust atomically defined gaps reaching below 0.5 nm. The existence of atomically confined light fields in these gaps is demonstrated by observing extreme Coulomb splitting of corresponding symmetric and antisymmetric dimer eigenmodes of more than 800 meV in white-light scattering experiments. Our results open new perspectives for atomically resolved spectroscopic imaging, deeply nonlinear optics, ultrasensing, cavity optomechanics, as well as for the realization of novel quantum-optical devices.}, author = {Kern, Johannes and Großmann, Swen and Tarakina, Nadezda V. and Häckel, Tim and Emmerling, Monika and Kamp, Martin and Huang, Jer-Shing and Biagioni, Paolo and Prangsma, Jord C. and Hecht, Bert}, journal = {Nano Lett.}, keywords = {resonance}, month = 11, note = {<a href="https://arxiv.org/abs/1112.5008">» arXiv:1112.5008</a> press: <a href="http://www.nanowerk.com/news2/newsid=26870.php">» Atomic-scale confinement of resonant optical fields</a>, coverimage on <a href="http://www.pro-physik.de/details/opnews/2686931/Lokalisiertes_Lichtfeld_im_Luftspalt.html">» pro-physik.de</a> (german)}, number = 11, pages = {5504-5509}, title = {Atomic-Scale Confinement of Resonant Optical Fields}, volume = 12, year = 2012 }

%0 Journal Article %1 kern2012atomicscale %A Kern, Johannes %A Großmann, Swen %A Tarakina, Nadezda V. %A Häckel, Tim %A Emmerling, Monika %A Kamp, Martin %A Huang, Jer-Shing %A Biagioni, Paolo %A Prangsma, Jord C. %A Hecht, Bert %D 2012 %J Nano Lett. %N 11 %P 5504-5509 %R 10.1021/nl302315g %T Atomic-Scale Confinement of Resonant Optical Fields %V 12 %X In the presence of matter, there is no fundamental limit preventing confinement of visible light even down to atomic scales. Achieving such confinement and the corresponding resonant intensity enhancement inevitably requires simultaneous control over atomic-scale details of material structures and over the optical modes that such structures support. By means of self-assembly we have obtained side-by-side aligned gold nanorod dimers with robust atomically defined gaps reaching below 0.5 nm. The existence of atomically confined light fields in these gaps is demonstrated by observing extreme Coulomb splitting of corresponding symmetric and antisymmetric dimer eigenmodes of more than 800 meV in white-light scattering experiments. Our results open new perspectives for atomically resolved spectroscopic imaging, deeply nonlinear optics, ultrasensing, cavity optomechanics, as well as for the realization of novel quantum-optical devices.
Evolutionary Optimization of Optical Antennas. Feichtner, Thorsten; Selig, Oleg; Kiunke, Markus; Hecht, Bert. In Phys. Rev. Lett., 109(12), p. 127701. 2012.

» arXiv:1204.5422, » cover image
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The design of nanoantennas has so far been mainly inspired by radio-frequency technology. However, the material properties and experimental settings need to be reconsidered at optical frequencies, which would entail the need for alternative optimal antenna designs. Here we subject a checkerboard-type, initially random array of gold cubes to evolutionary optimization. To illustrate the power of the approach, we demonstrate that by optimizing the near-field intensity enhancement, the evolutionary algorithm finds a new antenna geometry, essentially a split-ring–two-wire antenna hybrid that surpasses by far the performance of a conventional gap antenna by shifting the n=1 split-ring resonance into the optical regime.

@article{feichtner2012evolutionary, abstract = {The design of nanoantennas has so far been mainly inspired by radio-frequency technology. However, the material properties and experimental settings need to be reconsidered at optical frequencies, which would entail the need for alternative optimal antenna designs. Here we subject a checkerboard-type, initially random array of gold cubes to evolutionary optimization. To illustrate the power of the approach, we demonstrate that by optimizing the near-field intensity enhancement, the evolutionary algorithm finds a new antenna geometry, essentially a split-ring–two-wire antenna hybrid that surpasses by far the performance of a conventional gap antenna by shifting the n=1 split-ring resonance into the optical regime.}, author = {Feichtner, Thorsten and Selig, Oleg and Kiunke, Markus and Hecht, Bert}, journal = {Phys. Rev. Lett.}, keywords = {gold}, month = {09}, note = {<a href="http://arxiv.org/abs/1204.5422"style="font-style: normal;">» arXiv:1204.5422</a>, <a href="http://journals.aps.org/prl/covers/109/12"style="font-style: normal;">» cover image</a>}, number = 12, pages = 127701, title = {Evolutionary Optimization of Optical Antennas}, volume = 109, year = 2012 }

%0 Journal Article %1 feichtner2012evolutionary %A Feichtner, Thorsten %A Selig, Oleg %A Kiunke, Markus %A Hecht, Bert %D 2012 %J Phys. Rev. Lett. %N 12 %P 127701 %R 10.1103/PhysRevLett.109.127701 %T Evolutionary Optimization of Optical Antennas %V 109 %X The design of nanoantennas has so far been mainly inspired by radio-frequency technology. However, the material properties and experimental settings need to be reconsidered at optical frequencies, which would entail the need for alternative optimal antenna designs. Here we subject a checkerboard-type, initially random array of gold cubes to evolutionary optimization. To illustrate the power of the approach, we demonstrate that by optimizing the near-field intensity enhancement, the evolutionary algorithm finds a new antenna geometry, essentially a split-ring–two-wire antenna hybrid that surpasses by far the performance of a conventional gap antenna by shifting the n=1 split-ring resonance into the optical regime.
Electrically Connected Resonant Optical Antennas. Prangsma, Jord C.; Kern, Johannes; Knapp, Alexander G.; Grossmann, Swen; Emmerling, Monika; Kamp, Martin; Hecht, Bert. In Nano Lett., 12(8), pp. 3915–3919. 2012.
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Electrically connected resonant optical antennas hold promise for the realization of highly efficient nanoscale electro-plasmonic devices that rely on a combination of electric fields and local near-field intensity enhancement. Here we demonstrate the feasibility of such a concept by attaching leads to the arms of a two-wire antenna at positions of minimal near-field intensity with negligible influence on the antenna resonance. White-light scattering experiments in accordance with simulations show that the optical tunability of connected antennas is fully retained. Analysis of the electric properties demonstrates that in the antenna gaps direct current (DC) electric fields of 108 V/m can consistently be achieved and maintained over extended periods of time without noticeable damage.

@article{prangsma2012electrically, abstract = {Electrically connected resonant optical antennas hold promise for the realization of highly efficient nanoscale electro-plasmonic devices that rely on a combination of electric fields and local near-field intensity enhancement. Here we demonstrate the feasibility of such a concept by attaching leads to the arms of a two-wire antenna at positions of minimal near-field intensity with negligible influence on the antenna resonance. White-light scattering experiments in accordance with simulations show that the optical tunability of connected antennas is fully retained. Analysis of the electric properties demonstrates that in the antenna gaps direct current (DC) electric fields of 108 V/m can consistently be achieved and maintained over extended periods of time without noticeable damage.}, author = {Prangsma, Jord C. and Kern, Johannes and Knapp, Alexander G. and Grossmann, Swen and Emmerling, Monika and Kamp, Martin and Hecht, Bert}, journal = {Nano Lett.}, keywords = {resonance}, month = {08}, number = 8, pages = {3915-3919}, title = {Electrically Connected Resonant Optical Antennas}, volume = 12, year = 2012 }

%0 Journal Article %1 prangsma2012electrically %A Prangsma, Jord C. %A Kern, Johannes %A Knapp, Alexander G. %A Grossmann, Swen %A Emmerling, Monika %A Kamp, Martin %A Hecht, Bert %D 2012 %J Nano Lett. %N 8 %P 3915-3919 %R 10.1021/nl3007374 %T Electrically Connected Resonant Optical Antennas %V 12 %X Electrically connected resonant optical antennas hold promise for the realization of highly efficient nanoscale electro-plasmonic devices that rely on a combination of electric fields and local near-field intensity enhancement. Here we demonstrate the feasibility of such a concept by attaching leads to the arms of a two-wire antenna at positions of minimal near-field intensity with negligible influence on the antenna resonance. White-light scattering experiments in accordance with simulations show that the optical tunability of connected antennas is fully retained. Analysis of the electric properties demonstrates that in the antenna gaps direct current (DC) electric fields of 108 V/m can consistently be achieved and maintained over extended periods of time without noticeable damage.
Dynamics of Four-Photon Photoluminescence in Gold Nanoantennas. Biagioni, Paolo; Brida, Daniele; Huang, Jer-Shing; Kern, Johannes; Duò, Lamberto; Hecht, Bert; Finazzi, Marco; Cerullo, Giulio. In Nano Lett., 12(6), pp. 2941–2947. 2012.

» arXiv:1109.5475 (2012)
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Two-pulse correlation is employed to investigate the temporal dynamics of both two-photon photoluminescence (2PPL) and four-photon photoluminescence (4PPL) in resonant and nonresonant nanoantennas excited at a wavelength of 800 nm. Both 2PPL and 4PPL data are consistent with the same two-step model already established for 2PPL, implying that the first excitation step in 4PPL is a three-photon sp → sp direct interband transition. Considering energy and parity conservation, we also explain why 4PPL behavior is favored over, for example, three- and five-photon photoluminescence in the power range below the damage threshold of our antennas. Since sizable 4PPL requires larger peak intensities of the local field, we are able to select either 2PPL or 4PPL in the same gold nanoantennas by choosing a suitable laser pulse duration. We thus provide a first consistent model for the understanding of multiphoton photoluminescence generation in gold nanoantennas, opening new perspectives for applications ranging from the characterization of plasmonic resonances to biomedical imaging.

@article{biagioni2012dynamics, abstract = {Two-pulse correlation is employed to investigate the temporal dynamics of both two-photon photoluminescence (2PPL) and four-photon photoluminescence (4PPL) in resonant and nonresonant nanoantennas excited at a wavelength of 800 nm. Both 2PPL and 4PPL data are consistent with the same two-step model already established for 2PPL, implying that the first excitation step in 4PPL is a three-photon sp → sp direct interband transition. Considering energy and parity conservation, we also explain why 4PPL behavior is favored over, for example, three- and five-photon photoluminescence in the power range below the damage threshold of our antennas. Since sizable 4PPL requires larger peak intensities of the local field, we are able to select either 2PPL or 4PPL in the same gold nanoantennas by choosing a suitable laser pulse duration. We thus provide a first consistent model for the understanding of multiphoton photoluminescence generation in gold nanoantennas, opening new perspectives for applications ranging from the characterization of plasmonic resonances to biomedical imaging.}, author = {Biagioni, Paolo and Brida, Daniele and Huang, Jer-Shing and Kern, Johannes and Duò, Lamberto and Hecht, Bert and Finazzi, Marco and Cerullo, Giulio}, journal = {Nano Lett.}, keywords = {resonance}, month = {06}, note = {<a href="https://arxiv.org/abs/1109.5475" style="font-style: normal;">» arXiv:1109.5475 (2012)</a>}, number = 6, pages = {2941-2947}, title = {Dynamics of Four-Photon Photoluminescence in Gold Nanoantennas}, volume = 12, year = 2012 }

%0 Journal Article %1 biagioni2012dynamics %A Biagioni, Paolo %A Brida, Daniele %A Huang, Jer-Shing %A Kern, Johannes %A Duò, Lamberto %A Hecht, Bert %A Finazzi, Marco %A Cerullo, Giulio %D 2012 %J Nano Lett. %N 6 %P 2941-2947 %R 10.1021/nl300616s %T Dynamics of Four-Photon Photoluminescence in Gold Nanoantennas %V 12 %X Two-pulse correlation is employed to investigate the temporal dynamics of both two-photon photoluminescence (2PPL) and four-photon photoluminescence (4PPL) in resonant and nonresonant nanoantennas excited at a wavelength of 800 nm. Both 2PPL and 4PPL data are consistent with the same two-step model already established for 2PPL, implying that the first excitation step in 4PPL is a three-photon sp → sp direct interband transition. Considering energy and parity conservation, we also explain why 4PPL behavior is favored over, for example, three- and five-photon photoluminescence in the power range below the damage threshold of our antennas. Since sizable 4PPL requires larger peak intensities of the local field, we are able to select either 2PPL or 4PPL in the same gold nanoantennas by choosing a suitable laser pulse duration. We thus provide a first consistent model for the understanding of multiphoton photoluminescence generation in gold nanoantennas, opening new perspectives for applications ranging from the characterization of plasmonic resonances to biomedical imaging.
Spectral-interference microscopy for characterization of functional plasmonic elements. Rewitz, Christian; Keitzl, Thomas; Tuchscherer, Philip; Goetz, Sebastian; Geisler, Peter; Razinskas, Gary; Hecht, Bert; Brixner, Tobias. In Opt. Express, 20(13), pp. 14632–14647. 2012.
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Plasmonic modes supported by noble-metal nanostructures offer strong subwavelength electric-field confinement and promise the realization of nanometer-scale integrated optical circuits with well-defined functionality. In order to measure the spectral and spatial response functions of such plasmonic elements, we combine a confocal microscope setup with spectral interferometry detection. The setup, data acquisition, and data evaluation are discussed in detail by means of exemplary experiments involving propagating plasmons transmitted through silver nanowires. By considering and experimentally calibrating any setup-inherent signal delay with an accuracy of 1 fs, we are able to extract correct timing information of propagating plasmons. The method can be applied, e.g., to determine the dispersion and group velocity of propagating plasmons in nanostructures, and can be extended towards the investigation of nonlinear phenomena.

@article{rewitz2012spectralinterference, abstract = {Plasmonic modes supported by noble-metal nanostructures offer strong subwavelength electric-field confinement and promise the realization of nanometer-scale integrated optical circuits with well-defined functionality. In order to measure the spectral and spatial response functions of such plasmonic elements, we combine a confocal microscope setup with spectral interferometry detection. The setup, data acquisition, and data evaluation are discussed in detail by means of exemplary experiments involving propagating plasmons transmitted through silver nanowires. By considering and experimentally calibrating any setup-inherent signal delay with an accuracy of 1 fs, we are able to extract correct timing information of propagating plasmons. The method can be applied, e.g., to determine the dispersion and group velocity of propagating plasmons in nanostructures, and can be extended towards the investigation of nonlinear phenomena.}, author = {Rewitz, Christian and Keitzl, Thomas and Tuchscherer, Philip and Goetz, Sebastian and Geisler, Peter and Razinskas, Gary and Hecht, Bert and Brixner, Tobias}, journal = {Opt. Express}, keywords = {plasmon}, month = {06}, number = 13, pages = {14632-14647}, title = {Spectral-interference microscopy for characterization of functional plasmonic elements}, volume = 20, year = 2012 }

%0 Journal Article %1 rewitz2012spectralinterference %A Rewitz, Christian %A Keitzl, Thomas %A Tuchscherer, Philip %A Goetz, Sebastian %A Geisler, Peter %A Razinskas, Gary %A Hecht, Bert %A Brixner, Tobias %D 2012 %J Opt. Express %N 13 %P 14632-14647 %R 10.1364/OE.20.014632 %T Spectral-interference microscopy for characterization of functional plasmonic elements %V 20 %X Plasmonic modes supported by noble-metal nanostructures offer strong subwavelength electric-field confinement and promise the realization of nanometer-scale integrated optical circuits with well-defined functionality. In order to measure the spectral and spatial response functions of such plasmonic elements, we combine a confocal microscope setup with spectral interferometry detection. The setup, data acquisition, and data evaluation are discussed in detail by means of exemplary experiments involving propagating plasmons transmitted through silver nanowires. By considering and experimentally calibrating any setup-inherent signal delay with an accuracy of 1 fs, we are able to extract correct timing information of propagating plasmons. The method can be applied, e.g., to determine the dispersion and group velocity of propagating plasmons in nanostructures, and can be extended towards the investigation of nonlinear phenomena.
Circular Dichroism Probed by Two-Photon Fluorescence Microscopy in Enantiopure Chiral Polyfluorene Thin Films. Savoini, Matteo; Wu, Xiaofei; Celebrano, Michele; Ziegler, Johannes; Biagioni, Paolo; Meskers, Stefan C. J.; Duò, Lamberto; Hecht, Bert; Finazzi, Marco. In J. Am. Chem. Soc., 134(13), pp. 5832–5835. 2012.
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Two-photon fluorescence scanning confocal microscopy sensitive to circular dichroism with a diffraction-limited resolution well below 500 nm is demonstrated. With this method, the spatial variation of the circular dichroism of thermally annealed chiral polyfluorene thin films has been imaged. We observed circular dichroism associated with submicrometer-sized domains showing helicoidally twisted macromolecular organization. Domains with opposite chiroptical properties, corresponding to left- or right-handed molecular organization, coexist in the film. Our results are consistent with those obtained by one-photon imaging and illustrate the potential of two-photon imaging for use in studying helical macromolecular organization.

@article{savoini2012circular, abstract = {Two-photon fluorescence scanning confocal microscopy sensitive to circular dichroism with a diffraction-limited resolution well below 500 nm is demonstrated. With this method, the spatial variation of the circular dichroism of thermally annealed chiral polyfluorene thin films has been imaged. We observed circular dichroism associated with submicrometer-sized domains showing helicoidally twisted macromolecular organization. Domains with opposite chiroptical properties, corresponding to left- or right-handed molecular organization, coexist in the film. Our results are consistent with those obtained by one-photon imaging and illustrate the potential of two-photon imaging for use in studying helical macromolecular organization.}, author = {Savoini, Matteo and Wu, Xiaofei and Celebrano, Michele and Ziegler, Johannes and Biagioni, Paolo and Meskers, Stefan C. J. and Duò, Lamberto and Hecht, Bert and Finazzi, Marco}, journal = {J. Am. Chem. Soc.}, keywords = {nano-optics}, month = {04}, number = 13, pages = {5832-5835}, title = {Circular Dichroism Probed by Two-Photon Fluorescence Microscopy in Enantiopure Chiral Polyfluorene Thin Films}, volume = 134, year = 2012 }

%0 Journal Article %1 savoini2012circular %A Savoini, Matteo %A Wu, Xiaofei %A Celebrano, Michele %A Ziegler, Johannes %A Biagioni, Paolo %A Meskers, Stefan C. J. %A Duò, Lamberto %A Hecht, Bert %A Finazzi, Marco %D 2012 %J J. Am. Chem. Soc. %N 13 %P 5832-5835 %R 10.1021/ja209916y %T Circular Dichroism Probed by Two-Photon Fluorescence Microscopy in Enantiopure Chiral Polyfluorene Thin Films %V 134 %X Two-photon fluorescence scanning confocal microscopy sensitive to circular dichroism with a diffraction-limited resolution well below 500 nm is demonstrated. With this method, the spatial variation of the circular dichroism of thermally annealed chiral polyfluorene thin films has been imaged. We observed circular dichroism associated with submicrometer-sized domains showing helicoidally twisted macromolecular organization. Domains with opposite chiroptical properties, corresponding to left- or right-handed molecular organization, coexist in the film. Our results are consistent with those obtained by one-photon imaging and illustrate the potential of two-photon imaging for use in studying helical macromolecular organization.
Nanoantennas for visible and infrared radiation. Biagioni, Paolo; Huang, Jer-Shing; Hecht, Bert. In Rep. Prog. Phys., 75(2), p. 024402. 2012.

» arXiv:1103.1568 (2012), » cover image
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Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-of-states engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of metallic optical antennas based on the background of both well-developed radiowave antenna engineering and plasmonics. In particular, we discuss the role of plasmonic resonances on the performance of nanoantennas and address the influence of geometrical parameters imposed by nanofabrication. Finally, we give a brief account of the current status of the field and the major established and emerging lines of investigation in this vivid area of research.

@article{biagioni2012nanoantennas, abstract = {Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-of-states engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of metallic optical antennas based on the background of both well-developed radiowave antenna engineering and plasmonics. In particular, we discuss the role of plasmonic resonances on the performance of nanoantennas and address the influence of geometrical parameters imposed by nanofabrication. Finally, we give a brief account of the current status of the field and the major established and emerging lines of investigation in this vivid area of research.}, author = {Biagioni, Paolo and Huang, Jer-Shing and Hecht, Bert}, journal = {Rep. Prog. Phys.}, keywords = {theory}, month = {01}, note = {<a href="https://arxiv.org/abs/1103.1568" style="font-style: normal;">» arXiv:1103.1568 (2012)</a>, <a href="http://www.nanoscale-optics.de/images/ROPPcoverFeb.pdf" style="font-style: normal;">» cover image</a>}, number = 2, pages = {024402}, title = {Nanoantennas for visible and infrared radiation}, volume = 75, year = 2012 }

%0 Journal Article %1 biagioni2012nanoantennas %A Biagioni, Paolo %A Huang, Jer-Shing %A Hecht, Bert %D 2012 %J Rep. Prog. Phys. %N 2 %P 024402 %R 10.1088/0034-4885/75/2/024402 %T Nanoantennas for visible and infrared radiation %V 75 %X Nanoantennas for visible and infrared radiation can strongly enhance the interaction of light with nanoscale matter by their ability to efficiently link propagating and spatially localized optical fields. This ability unlocks an enormous potential for applications ranging from nanoscale optical microscopy and spectroscopy over solar energy conversion, integrated optical nanocircuitry, opto-electronics and density-of-states engineering to ultra-sensing as well as enhancement of optical nonlinearities. Here we review the current understanding of metallic optical antennas based on the background of both well-developed radiowave antenna engineering and plasmonics. In particular, we discuss the role of plasmonic resonances on the performance of nanoantennas and address the influence of geometrical parameters imposed by nanofabrication. Finally, we give a brief account of the current status of the field and the major established and emerging lines of investigation in this vivid area of research.
Ultrafast Plasmon Propagation in Nanowires Characterized by Far-Field Spectral Interferometry. Rewitz, Christian; Keitzl, Thomas; Tuchscherer, Philip; Huang, Jer-Shing; Geisler, Peter; Razinskas, Gary; Hecht, Bert; Brixner, Tobias. In Nano Lett., 12(1), pp. 45–49. 2012.
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Spectral interferometry is employed to fully characterize amplitude and phase of propagating plasmons that are transmitted through silver nanowires in the form of ultrashort pulses. For nanowire diameters below 100 nm, the plasmon group velocity is found to decrease drastically in accordance with the theory of adiabatic focusing. Furthermore, the dependence of the plasmon group velocity on the local nanowire environment is demonstrated. Our findings are of relevance for the design and implementation of nanoplasmonic signal processing and in view of coherent control applications.

@article{rewitz2012ultrafast, abstract = {Spectral interferometry is employed to fully characterize amplitude and phase of propagating plasmons that are transmitted through silver nanowires in the form of ultrashort pulses. For nanowire diameters below 100 nm, the plasmon group velocity is found to decrease drastically in accordance with the theory of adiabatic focusing. Furthermore, the dependence of the plasmon group velocity on the local nanowire environment is demonstrated. Our findings are of relevance for the design and implementation of nanoplasmonic signal processing and in view of coherent control applications.}, author = {Rewitz, Christian and Keitzl, Thomas and Tuchscherer, Philip and Huang, Jer-Shing and Geisler, Peter and Razinskas, Gary and Hecht, Bert and Brixner, Tobias}, journal = {Nano Lett.}, keywords = {plasmon}, month = {01}, number = 1, pages = {45-49}, title = {Ultrafast Plasmon Propagation in Nanowires Characterized by Far-Field Spectral Interferometry}, volume = 12, year = 2012 }

%0 Journal Article %1 rewitz2012ultrafast %A Rewitz, Christian %A Keitzl, Thomas %A Tuchscherer, Philip %A Huang, Jer-Shing %A Geisler, Peter %A Razinskas, Gary %A Hecht, Bert %A Brixner, Tobias %D 2012 %J Nano Lett. %N 1 %P 45-49 %R 10.1021/nl202864n %T Ultrafast Plasmon Propagation in Nanowires Characterized by Far-Field Spectral Interferometry %V 12 %X Spectral interferometry is employed to fully characterize amplitude and phase of propagating plasmons that are transmitted through silver nanowires in the form of ultrashort pulses. For nanowire diameters below 100 nm, the plasmon group velocity is found to decrease drastically in accordance with the theory of adiabatic focusing. Furthermore, the dependence of the plasmon group velocity on the local nanowire environment is demonstrated. Our findings are of relevance for the design and implementation of nanoplasmonic signal processing and in view of coherent control applications.

Spontaneous Formation of Left- and Right-Handed Cholesterically Ordered Domains in an Enantiopure Chiral Polyfluorene Film. Savoini, Matteo; Biagioni, Paolo; Meskers, Stefan C. J.; Duò, Lamberto; Hecht, Bert; Finazzi, Marco. In J. Phys. Chem. Lett., 2(12), pp. 1359–1362. 2011.
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Thermally annealed chiral polyfluorene films are studied by circular differential optical microscopy. We observe the presence of micrometer-sized domains displaying circular dichroism of opposite sign. Our findings suggest the spontaneous occurrence of left- and right-handed cholesterically ordered domains from an enantiopure precursor. The role of enantiopure stereo centers in the side chains of the polymer is to lower the energy of the left-handed cholesteric domains with respect to the right-handed ones.

@article{savoini2011spontaneous, abstract = {Thermally annealed chiral polyfluorene films are studied by circular differential optical microscopy. We observe the presence of micrometer-sized domains displaying circular dichroism of opposite sign. Our findings suggest the spontaneous occurrence of left- and right-handed cholesterically ordered domains from an enantiopure precursor. The role of enantiopure stereo centers in the side chains of the polymer is to lower the energy of the left-handed cholesteric domains with respect to the right-handed ones.}, author = {Savoini, Matteo and Biagioni, Paolo and Meskers, Stefan C. J. and Duò, Lamberto and Hecht, Bert and Finazzi, Marco}, journal = {J. Phys. Chem. Lett.}, keywords = {nano-optics}, month = {06}, number = 12, pages = {1359-1362}, title = {Spontaneous Formation of Left- and Right-Handed Cholesterically Ordered Domains in an Enantiopure Chiral Polyfluorene Film}, volume = 2, year = 2011 }

%0 Journal Article %1 savoini2011spontaneous %A Savoini, Matteo %A Biagioni, Paolo %A Meskers, Stefan C. J. %A Duò, Lamberto %A Hecht, Bert %A Finazzi, Marco %D 2011 %J J. Phys. Chem. Lett. %N 12 %P 1359-1362 %R 10.1021/jz200524m %T Spontaneous Formation of Left- and Right-Handed Cholesterically Ordered Domains in an Enantiopure Chiral Polyfluorene Film %V 2 %X Thermally annealed chiral polyfluorene films are studied by circular differential optical microscopy. We observe the presence of micrometer-sized domains displaying circular dichroism of opposite sign. Our findings suggest the spontaneous occurrence of left- and right-handed cholesterically ordered domains from an enantiopure precursor. The role of enantiopure stereo centers in the side chains of the polymer is to lower the energy of the left-handed cholesteric domains with respect to the right-handed ones.
Tailoring the interaction between matter and polarized light with plasmonic optical antennas. Biagioni, Paolo; Wu, X.; Savoini, Matteo; Ziegler, J.; Huang, Jer-Shing; Duò, Lamberto; Finazzi, Marco; Hecht, Bert. In Synthesis and Photonics of Nanoscale Materials VIII, Vol. 7922, p. 79220C. International Society for Optics and Photonics, 2011.
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We explore the possibility to control the polarization state of light confined into sub-diffraction volumes by means of plasmonic optical antennas. To this aim, we describe a resonant cross antenna, constituted of two perpendicular two-wire antennas sharing the same gap, which is able to maintain the polarization state in the plane of the antenna. We also discuss how, by proper tuning of the arm length in a slightly off-resonance cross antenna, it is possible to effectively realize a nanoscale quarter-waveplate antenna. We present experimental results for the preparation of individual cross antennas by means of focused ion beam milling starting from single-crystalline Au microflakes, and finally show preliminary characterization results based on two-photon photoluminescence confocal imaging with linearly-polarized light.

@inproceedings{biagioni2011tailoring, abstract = {We explore the possibility to control the polarization state of light confined into sub-diffraction volumes by means of plasmonic optical antennas. To this aim, we describe a resonant cross antenna, constituted of two perpendicular two-wire antennas sharing the same gap, which is able to maintain the polarization state in the plane of the antenna. We also discuss how, by proper tuning of the arm length in a slightly off-resonance cross antenna, it is possible to effectively realize a nanoscale quarter-waveplate antenna. We present experimental results for the preparation of individual cross antennas by means of focused ion beam milling starting from single-crystalline Au microflakes, and finally show preliminary characterization results based on two-photon photoluminescence confocal imaging with linearly-polarized light.}, author = {Biagioni, Paolo and Wu, X. and Savoini, Matteo and Ziegler, J. and Huang, Jer-Shing and Duò, Lamberto and Finazzi, Marco and Hecht, Bert}, booktitle = {Synthesis and Photonics of Nanoscale Materials VIII}, keywords = {resonance}, month = {02}, pages = {79220C}, publisher = {International Society for Optics and Photonics}, title = {Tailoring the interaction between matter and polarized light with plasmonic optical antennas}, volume = 7922, year = 2011 }

%0 Conference Paper %1 biagioni2011tailoring %A Biagioni, Paolo %A Wu, X. %A Savoini, Matteo %A Ziegler, J. %A Huang, Jer-Shing %A Duò, Lamberto %A Finazzi, Marco %A Hecht, Bert %B Synthesis and Photonics of Nanoscale Materials VIII %D 2011 %I International Society for Optics and Photonics %P 79220C %R 10.1117/12.876571 %T Tailoring the interaction between matter and polarized light with plasmonic optical antennas %V 7922 %X We explore the possibility to control the polarization state of light confined into sub-diffraction volumes by means of plasmonic optical antennas. To this aim, we describe a resonant cross antenna, constituted of two perpendicular two-wire antennas sharing the same gap, which is able to maintain the polarization state in the plane of the antenna. We also discuss how, by proper tuning of the arm length in a slightly off-resonance cross antenna, it is possible to effectively realize a nanoscale quarter-waveplate antenna. We present experimental results for the preparation of individual cross antennas by means of focused ion beam milling starting from single-crystalline Au microflakes, and finally show preliminary characterization results based on two-photon photoluminescence confocal imaging with linearly-polarized light.

Atomically flat single-crystalline gold nanostructures for plasmonic nanocircuitry. Huang, Jer-Shing; Callegari, Victor; Geisler, Peter; Brüning, Christoph; Kern, Johannes; Prangsma, Jord C.; Wu, Xiaofei; Feichtner, Thorsten; Ziegler, Johannes; Weinmann, Pia; Kamp, Martin; Forchel, Alfred; Biagioni, Paolo; Sennhauser, Urs; Hecht, Bert. In Nat Commun, 1(1), pp. 1–8. 2010.

» arXiv:1004.1961 (2010)
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Deep subwavelength integration of high-definition plasmonic nanostructures is of key importance in the development of future optical nanocircuitry for high-speed communication, quantum computation and lab-on-a-chip applications. To date, the experimental realization of proposed extended plasmonic networks consisting of multiple functional elements remains challenging, mainly because of the multi-crystallinity of commonly used thermally evaporated gold layers. This can produce structural imperfections in individual circuit elements that drastically reduce the yield of functional integrated nanocircuits. In this paper we demonstrate the use of large ({\textgreater}100 μm2) but thin ({\textless}80 nm) chemically grown single-crystalline gold flakes that, after immobilization, serve as an ideal basis for focused ion beam milling and other top-down nanofabrication techniques on any desired substrate. Using this methodology we obtain high-definition ultrasmooth gold nanostructures with superior optical properties and reproducible nano-sized features over micrometre-length scales. Our approach provides a possible solution to overcome the current fabrication bottleneck and realize high-definition plasmonic nanocircuitry.

@article{huang2010atomically, abstract = {Deep subwavelength integration of high-definition plasmonic nanostructures is of key importance in the development of future optical nanocircuitry for high-speed communication, quantum computation and lab-on-a-chip applications. To date, the experimental realization of proposed extended plasmonic networks consisting of multiple functional elements remains challenging, mainly because of the multi-crystallinity of commonly used thermally evaporated gold layers. This can produce structural imperfections in individual circuit elements that drastically reduce the yield of functional integrated nanocircuits. In this paper we demonstrate the use of large ({\textgreater}100 μm2) but thin ({\textless}80 nm) chemically grown single-crystalline gold flakes that, after immobilization, serve as an ideal basis for focused ion beam milling and other top-down nanofabrication techniques on any desired substrate. Using this methodology we obtain high-definition ultrasmooth gold nanostructures with superior optical properties and reproducible nano-sized features over micrometre-length scales. Our approach provides a possible solution to overcome the current fabrication bottleneck and realize high-definition plasmonic nanocircuitry.}, author = {Huang, Jer-Shing and Callegari, Victor and Geisler, Peter and Brüning, Christoph and Kern, Johannes and Prangsma, Jord C. and Wu, Xiaofei and Feichtner, Thorsten and Ziegler, Johannes and Weinmann, Pia and Kamp, Martin and Forchel, Alfred and Biagioni, Paolo and Sennhauser, Urs and Hecht, Bert}, journal = {Nat Commun}, keywords = {plasmon}, month = 12, note = {<a href="https://arxiv.org/abs/1004.1961" style="font-style: normal;">» arXiv:1004.1961 (2010)</a>}, number = 1, pages = {1-8}, title = {Atomically flat single-crystalline gold nanostructures for plasmonic nanocircuitry}, volume = 1, year = 2010 }

%0 Journal Article %1 huang2010atomically %A Huang, Jer-Shing %A Callegari, Victor %A Geisler, Peter %A Brüning, Christoph %A Kern, Johannes %A Prangsma, Jord C. %A Wu, Xiaofei %A Feichtner, Thorsten %A Ziegler, Johannes %A Weinmann, Pia %A Kamp, Martin %A Forchel, Alfred %A Biagioni, Paolo %A Sennhauser, Urs %A Hecht, Bert %D 2010 %J Nat Commun %N 1 %P 1-8 %R 10.1038/ncomms1143 %T Atomically flat single-crystalline gold nanostructures for plasmonic nanocircuitry %V 1 %X Deep subwavelength integration of high-definition plasmonic nanostructures is of key importance in the development of future optical nanocircuitry for high-speed communication, quantum computation and lab-on-a-chip applications. To date, the experimental realization of proposed extended plasmonic networks consisting of multiple functional elements remains challenging, mainly because of the multi-crystallinity of commonly used thermally evaporated gold layers. This can produce structural imperfections in individual circuit elements that drastically reduce the yield of functional integrated nanocircuits. In this paper we demonstrate the use of large ({\textgreater}100 μm2) but thin ({\textless}80 nm) chemically grown single-crystalline gold flakes that, after immobilization, serve as an ideal basis for focused ion beam milling and other top-down nanofabrication techniques on any desired substrate. Using this methodology we obtain high-definition ultrasmooth gold nanostructures with superior optical properties and reproducible nano-sized features over micrometre-length scales. Our approach provides a possible solution to overcome the current fabrication bottleneck and realize high-definition plasmonic nanocircuitry.
Fast Quantitative Single-Molecule Detection at Ultralow Concentrations. Haas, Philippe; Then, Patrick; Wild, Andreas; Grange, Wilfried; Zorman, Sylvain; Hegner, Martin; Calame, Michel; Aebi, Ueli; Flammer, Josef; Hecht, Bert. In Anal. Chem., 82(14), pp. 6299–6302. 2010.
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The applicability of single-molecule fluorescence assays in liquids is limited by diffusion to concentrations in the low picomolar range. Here, we demonstrate quantitative single-molecule detection at attomolar concentrations within 1 min by excitation and detection of fluorescence through a single-mode optical fiber in presence of turbulent flow. The combination of high detectability and short measurement times promises applications in ultrasensitive assays, sensors, and point-of-care medical diagnostics.

@article{haas2010quantitative, abstract = {The applicability of single-molecule fluorescence assays in liquids is limited by diffusion to concentrations in the low picomolar range. Here, we demonstrate quantitative single-molecule detection at attomolar concentrations within 1 min by excitation and detection of fluorescence through a single-mode optical fiber in presence of turbulent flow. The combination of high detectability and short measurement times promises applications in ultrasensitive assays, sensors, and point-of-care medical diagnostics.}, author = {Haas, Philippe and Then, Patrick and Wild, Andreas and Grange, Wilfried and Zorman, Sylvain and Hegner, Martin and Calame, Michel and Aebi, Ueli and Flammer, Josef and Hecht, Bert}, journal = {Anal. Chem.}, keywords = {single-molecules}, month = {07}, number = 14, pages = {6299-6302}, title = {Fast Quantitative Single-Molecule Detection at Ultralow Concentrations}, volume = 82, year = 2010 }

%0 Journal Article %1 haas2010quantitative %A Haas, Philippe %A Then, Patrick %A Wild, Andreas %A Grange, Wilfried %A Zorman, Sylvain %A Hegner, Martin %A Calame, Michel %A Aebi, Ueli %A Flammer, Josef %A Hecht, Bert %D 2010 %J Anal. Chem. %N 14 %P 6299-6302 %R 10.1021/ac100779c %T Fast Quantitative Single-Molecule Detection at Ultralow Concentrations %V 82 %X The applicability of single-molecule fluorescence assays in liquids is limited by diffusion to concentrations in the low picomolar range. Here, we demonstrate quantitative single-molecule detection at attomolar concentrations within 1 min by excitation and detection of fluorescence through a single-mode optical fiber in presence of turbulent flow. The combination of high detectability and short measurement times promises applications in ultrasensitive assays, sensors, and point-of-care medical diagnostics.
Mode Imaging and Selection in Strongly Coupled Nanoantennas. Huang, Jer-Shing; Kern, Johannes; Geisler, Peter; Weinmann, Pia; Kamp, Martin; Forchel, Alfred; Biagioni, Paolo; Hecht, Bert. In Nano Lett., 10(6), pp. 2105–2110. 2010.

» arXiv:1002.3887v1
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The number of eigenmodes in plasmonic nanostructures increases with complexity due to mode hybridization, raising the need for efficient mode characterization and selection. Here we experimentally demonstrate direct imaging and selective excitation of the “bonding” and “antibonding” plasmon mode in symmetric dipole nanoantennas using confocal two-photon photoluminescence mapping. Excitation of a high-quality-factor antibonding resonance manifests itself as a two-lobed pattern instead of the single spot observed for the broad “bonding” resonance in accordance with numerical simulations. The two-lobed pattern is observed due to the fact that excitation of the antibonding mode is forbidden for symmetric excitation at the feedgap, while concomitantly the mode energy splitting is large enough to suppress excitation of the “bonding” mode. The controlled excitation of modes in strongly coupled plasmonic nanostructures is mandatory for efficient sensors, in coherent control as well as for implementing well-defined functionalities in complex plasmonic devices.

@article{huang2010imaging, abstract = {The number of eigenmodes in plasmonic nanostructures increases with complexity due to mode hybridization, raising the need for efficient mode characterization and selection. Here we experimentally demonstrate direct imaging and selective excitation of the “bonding” and “antibonding” plasmon mode in symmetric dipole nanoantennas using confocal two-photon photoluminescence mapping. Excitation of a high-quality-factor antibonding resonance manifests itself as a two-lobed pattern instead of the single spot observed for the broad “bonding” resonance in accordance with numerical simulations. The two-lobed pattern is observed due to the fact that excitation of the antibonding mode is forbidden for symmetric excitation at the feedgap, while concomitantly the mode energy splitting is large enough to suppress excitation of the “bonding” mode. The controlled excitation of modes in strongly coupled plasmonic nanostructures is mandatory for efficient sensors, in coherent control as well as for implementing well-defined functionalities in complex plasmonic devices.}, author = {Huang, Jer-Shing and Kern, Johannes and Geisler, Peter and Weinmann, Pia and Kamp, Martin and Forchel, Alfred and Biagioni, Paolo and Hecht, Bert}, journal = {Nano Lett.}, keywords = {plasmon}, month = {06}, note = {<a href="https://arxiv.org/abs/1002.3887v1" style="font-style: normal;">» arXiv:1002.3887v1 </a>}, number = 6, pages = {2105-2110}, title = {Mode Imaging and Selection in Strongly Coupled Nanoantennas}, volume = 10, year = 2010 }

%0 Journal Article %1 huang2010imaging %A Huang, Jer-Shing %A Kern, Johannes %A Geisler, Peter %A Weinmann, Pia %A Kamp, Martin %A Forchel, Alfred %A Biagioni, Paolo %A Hecht, Bert %D 2010 %J Nano Lett. %N 6 %P 2105-2110 %R 10.1021/nl100614p %T Mode Imaging and Selection in Strongly Coupled Nanoantennas %V 10 %X The number of eigenmodes in plasmonic nanostructures increases with complexity due to mode hybridization, raising the need for efficient mode characterization and selection. Here we experimentally demonstrate direct imaging and selective excitation of the “bonding” and “antibonding” plasmon mode in symmetric dipole nanoantennas using confocal two-photon photoluminescence mapping. Excitation of a high-quality-factor antibonding resonance manifests itself as a two-lobed pattern instead of the single spot observed for the broad “bonding” resonance in accordance with numerical simulations. The two-lobed pattern is observed due to the fact that excitation of the antibonding mode is forbidden for symmetric excitation at the feedgap, while concomitantly the mode energy splitting is large enough to suppress excitation of the “bonding” mode. The controlled excitation of modes in strongly coupled plasmonic nanostructures is mandatory for efficient sensors, in coherent control as well as for implementing well-defined functionalities in complex plasmonic devices.
Subwavelength broadband splitters and switches for femtosecond plasmonic signals. Reiserer, Andreas A.; Huang, Jer-Shing; Hecht, Bert; Brixner, Tobias. In Opt. Express, 18(11), pp. 11810–11820. 2010.
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Numerical simulations and an analytic approach based on transmission line theory are used to design splitters for nano-plasmonic signal processing that allow to arbitrarily adjust the ratio of transmission from an input into two different output arms. By adjusting the geometrical parameters of the structure, either a high bandwidth or a sharp transmission resonance is obtained. Switching between the two arms can be achieved by modulating the effective refractive index of the waveguide. Employing the instantaneous Kerr effect, switching rates in the THz regime are potentially feasible. The suggested devices are of interest for future applications in nanoplasmonic information processing.

@article{reiserer2010subwavelength, abstract = {Numerical simulations and an analytic approach based on transmission line theory are used to design splitters for nano-plasmonic signal processing that allow to arbitrarily adjust the ratio of transmission from an input into two different output arms. By adjusting the geometrical parameters of the structure, either a high bandwidth or a sharp transmission resonance is obtained. Switching between the two arms can be achieved by modulating the effective refractive index of the waveguide. Employing the instantaneous Kerr effect, switching rates in the THz regime are potentially feasible. The suggested devices are of interest for future applications in nanoplasmonic information processing.}, author = {Reiserer, Andreas A. and Huang, Jer-Shing and Hecht, Bert and Brixner, Tobias}, journal = {Opt. Express}, keywords = {plasmon}, month = {05}, number = 11, pages = {11810-11820}, title = {Subwavelength broadband splitters and switches for femtosecond plasmonic signals}, volume = 18, year = 2010 }

%0 Journal Article %1 reiserer2010subwavelength %A Reiserer, Andreas A. %A Huang, Jer-Shing %A Hecht, Bert %A Brixner, Tobias %D 2010 %J Opt. Express %N 11 %P 11810-11820 %R 10.1364/OE.18.011810 %T Subwavelength broadband splitters and switches for femtosecond plasmonic signals %V 18 %X Numerical simulations and an analytic approach based on transmission line theory are used to design splitters for nano-plasmonic signal processing that allow to arbitrarily adjust the ratio of transmission from an input into two different output arms. By adjusting the geometrical parameters of the structure, either a high bandwidth or a sharp transmission resonance is obtained. Switching between the two arms can be achieved by modulating the effective refractive index of the waveguide. Employing the instantaneous Kerr effect, switching rates in the THz regime are potentially feasible. The suggested devices are of interest for future applications in nanoplasmonic information processing.

Near-field polarization shaping by a near-resonant plasmonic cross antenna. Biagioni, Paolo; Savoini, Matteo; Huang, Jer-Shing; Duò, Lamberto; Finazzi, Marco; Hecht, Bert. In Phys. Rev. B, 80(15), p. 153409. 2009.
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The optical phase in the feed gap of a plasmonic dipole antenna shows a transition from in-phase to counter-phase response, when its length is varied across the resonance length. We exploit this behavior in an asymmetric cross antenna structure, constituted of two perpendicular dipole antennas with different lengths, sharing the same feed gap, in order to shape the local polarization state. As an application of this concept, we propose a λ/4 nanowaveplate, able to shape and confine linearly polarized propagating waves into circularly polarized fields localized in the feed gap.

@article{biagioni2009nearfield, abstract = {The optical phase in the feed gap of a plasmonic dipole antenna shows a transition from in-phase to counter-phase response, when its length is varied across the resonance length. We exploit this behavior in an asymmetric cross antenna structure, constituted of two perpendicular dipole antennas with different lengths, sharing the same feed gap, in order to shape the local polarization state. As an application of this concept, we propose a λ/4 nanowaveplate, able to shape and confine linearly polarized propagating waves into circularly polarized fields localized in the feed gap.}, author = {Biagioni, Paolo and Savoini, Matteo and Huang, Jer-Shing and Duò, Lamberto and Finazzi, Marco and Hecht, Bert}, journal = {Phys. Rev. B}, keywords = {resonance}, month = 10, number = 15, pages = 153409, title = {Near-field polarization shaping by a near-resonant plasmonic cross antenna}, volume = 80, year = 2009 }

%0 Journal Article %1 biagioni2009nearfield %A Biagioni, Paolo %A Savoini, Matteo %A Huang, Jer-Shing %A Duò, Lamberto %A Finazzi, Marco %A Hecht, Bert %D 2009 %J Phys. Rev. B %N 15 %P 153409 %R 10.1103/PhysRevB.80.153409 %T Near-field polarization shaping by a near-resonant plasmonic cross antenna %V 80 %X The optical phase in the feed gap of a plasmonic dipole antenna shows a transition from in-phase to counter-phase response, when its length is varied across the resonance length. We exploit this behavior in an asymmetric cross antenna structure, constituted of two perpendicular dipole antennas with different lengths, sharing the same feed gap, in order to shape the local polarization state. As an application of this concept, we propose a λ/4 nanowaveplate, able to shape and confine linearly polarized propagating waves into circularly polarized fields localized in the feed gap.
Dependence of the two-photon photoluminescence yield of gold nanostructures on the laser pulse duration. Biagioni, Paolo; Celebrano, Michele; Savoini, Matteo; Grancini, Giulia; Brida, Daniele; Mátéfi-Tempfli, Stefan; Mátéfi-Tempfli, M.; Duò, Lamberto; Hecht, Bert; Cerullo, Giulio; Finazzi, Marco. In Phys. Rev. B, 80(4), p. 045411. 2009.
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Two-photon photoluminescence (TPPL) from gold nanostructures is becoming one of the most relevant tools for plasmon-assisted biological imaging and photothermal therapy as well as for the investigation of plasmonic devices. Here we study the yield of TPPL as a function of the temporal width δ of the excitation laser pulses for a fixed average power. In the δ>1 ps regime, the TPPL yield decreases as δ is increased, while for shorter pulse widths it becomes independent of δ and, consequently, of the laser-pulse peak power. This peculiar dynamics is understood and modeled by considering that two-photon absorption in Au is a two-step process governed by the lifetime of the metastable state populated by the first photon absorption.

@article{biagioni2009dependence, abstract = {Two-photon photoluminescence (TPPL) from gold nanostructures is becoming one of the most relevant tools for plasmon-assisted biological imaging and photothermal therapy as well as for the investigation of plasmonic devices. Here we study the yield of TPPL as a function of the temporal width δ of the excitation laser pulses for a fixed average power. In the δ>1 ps regime, the TPPL yield decreases as δ is increased, while for shorter pulse widths it becomes independent of δ and, consequently, of the laser-pulse peak power. This peculiar dynamics is understood and modeled by considering that two-photon absorption in Au is a two-step process governed by the lifetime of the metastable state populated by the first photon absorption.}, author = {Biagioni, Paolo and Celebrano, Michele and Savoini, Matteo and Grancini, Giulia and Brida, Daniele and Mátéfi-Tempfli, Stefan and Mátéfi-Tempfli, M. and Duò, Lamberto and Hecht, Bert and Cerullo, Giulio and Finazzi, Marco}, journal = {Phys. Rev. B}, keywords = {gold}, month = {07}, number = 4, pages = {045411}, title = {Dependence of the two-photon photoluminescence yield of gold nanostructures on the laser pulse duration}, volume = 80, year = 2009 }

%0 Journal Article %1 biagioni2009dependence %A Biagioni, Paolo %A Celebrano, Michele %A Savoini, Matteo %A Grancini, Giulia %A Brida, Daniele %A Mátéfi-Tempfli, Stefan %A Mátéfi-Tempfli, M. %A Duò, Lamberto %A Hecht, Bert %A Cerullo, Giulio %A Finazzi, Marco %D 2009 %J Phys. Rev. B %N 4 %P 045411 %R 10.1103/PhysRevB.80.045411 %T Dependence of the two-photon photoluminescence yield of gold nanostructures on the laser pulse duration %V 80 %X Two-photon photoluminescence (TPPL) from gold nanostructures is becoming one of the most relevant tools for plasmon-assisted biological imaging and photothermal therapy as well as for the investigation of plasmonic devices. Here we study the yield of TPPL as a function of the temporal width δ of the excitation laser pulses for a fixed average power. In the δ>1 ps regime, the TPPL yield decreases as δ is increased, while for shorter pulse widths it becomes independent of δ and, consequently, of the laser-pulse peak power. This peculiar dynamics is understood and modeled by considering that two-photon absorption in Au is a two-step process governed by the lifetime of the metastable state populated by the first photon absorption.
Cross Resonant Optical Antenna. Biagioni, Paolo; Huang, Jer-Shing; Duò, Lamberto; Finazzi, Marco; Hecht, Bert. In Phys. Rev. Lett., 102(25), p. 256801. 2009.
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We propose a novel cross resonant optical antenna consisting of two perpendicular nanosized gold dipole antennas with a common feed gap. We demonstrate that the cross antenna is able to convert propagating fields of any polarization state into correspondingly polarized, localized, and enhanced fields and vice versa. The cross antenna structure therefore opens the road towards the control of light-matter interactions based on polarized light as well as the analysis of polarized fields on the nanometer scale.

@article{biagioni2009cross, abstract = {We propose a novel cross resonant optical antenna consisting of two perpendicular nanosized gold dipole antennas with a common feed gap. We demonstrate that the cross antenna is able to convert propagating fields of any polarization state into correspondingly polarized, localized, and enhanced fields and vice versa. The cross antenna structure therefore opens the road towards the control of light-matter interactions based on polarized light as well as the analysis of polarized fields on the nanometer scale.}, author = {Biagioni, Paolo and Huang, Jer-Shing and Duò, Lamberto and Finazzi, Marco and Hecht, Bert}, journal = {Phys. Rev. Lett.}, keywords = {resonance}, month = {06}, number = 25, pages = 256801, title = {Cross Resonant Optical Antenna}, volume = 102, year = 2009 }

%0 Journal Article %1 biagioni2009cross %A Biagioni, Paolo %A Huang, Jer-Shing %A Duò, Lamberto %A Finazzi, Marco %A Hecht, Bert %D 2009 %J Phys. Rev. Lett. %N 25 %P 256801 %R 10.1103/PhysRevLett.102.256801 %T Cross Resonant Optical Antenna %V 102 %X We propose a novel cross resonant optical antenna consisting of two perpendicular nanosized gold dipole antennas with a common feed gap. We demonstrate that the cross antenna is able to convert propagating fields of any polarization state into correspondingly polarized, localized, and enhanced fields and vice versa. The cross antenna structure therefore opens the road towards the control of light-matter interactions based on polarized light as well as the analysis of polarized fields on the nanometer scale.
Impedance Matching and Emission Properties of Nanoantennas in an Optical Nanocircuit. Huang, Jer-Shing; Feichtner, Thorsten; Biagioni, Paolo; Hecht, Bert. In Nano Lett., 9(5), pp. 1897–1902. 2009.
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An experimentally realizable prototype optical nanocircuit consisting of a receiving and an emitting nanoantenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between optical nanocircuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the emitting nanoantenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nanoantenna impedance to the transmission line by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the emitting antenna also depends on its geometry but is independent of the degree of impedance matching. The case study presented here provides the basis for experimental realizations of general optical nanocircuits based on readily available gold nanostructures and a large variety of derived novel devices.

@article{huang2009impedance, abstract = {An experimentally realizable prototype optical nanocircuit consisting of a receiving and an emitting nanoantenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between optical nanocircuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the emitting nanoantenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nanoantenna impedance to the transmission line by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the emitting antenna also depends on its geometry but is independent of the degree of impedance matching. The case study presented here provides the basis for experimental realizations of general optical nanocircuits based on readily available gold nanostructures and a large variety of derived novel devices.}, author = {Huang, Jer-Shing and Feichtner, Thorsten and Biagioni, Paolo and Hecht, Bert}, journal = {Nano Lett.}, keywords = {nano-optics}, month = {05}, number = 5, pages = {1897-1902}, title = {Impedance Matching and Emission Properties of Nanoantennas in an Optical Nanocircuit}, volume = 9, year = 2009 }

%0 Journal Article %1 huang2009impedance %A Huang, Jer-Shing %A Feichtner, Thorsten %A Biagioni, Paolo %A Hecht, Bert %D 2009 %J Nano Lett. %N 5 %P 1897-1902 %R 10.1021/nl803902t %T Impedance Matching and Emission Properties of Nanoantennas in an Optical Nanocircuit %V 9 %X An experimentally realizable prototype optical nanocircuit consisting of a receiving and an emitting nanoantenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between optical nanocircuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the emitting nanoantenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nanoantenna impedance to the transmission line by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the emitting antenna also depends on its geometry but is independent of the degree of impedance matching. The case study presented here provides the basis for experimental realizations of general optical nanocircuits based on readily available gold nanostructures and a large variety of derived novel devices.
Deterministic spatiotemporal control of optical fields in nanoantennas and plasmonic circuits. Huang, Jer-Shing; Voronine, Dmitri V.; Tuchscherer, Philip; Brixner, Tobias; Hecht, Bert. In Phys. Rev. B, 79(19), p. 195441. 2009.
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We show that laser pulse shaping techniques can be applied to tailor the ultrafast temporal response of localized and propagating optical near fields in resonant optical antennas (ROAs) and plasmonic transmission lines, respectively. Using finite-difference time-domain simulations followed by Fourier transformation, we obtain the impulse response of a nanostructure in the frequency domain, which allows obtaining its temporal response to any arbitrary pulse shape. To illustrate the potential of the method we demonstrate deterministic optimal temporal pulse compression in ROAs with reduced symmetry, in a plasmonic two-wire transmission line, and in a prototype plasmonic circuit combining propagation effects and local resonances. The method described here will be of importance for the coherent control of field propagation in nanophotonic structures and light-induced processes in nanoscopic volumes.

@article{huang2009deterministic, abstract = {We show that laser pulse shaping techniques can be applied to tailor the ultrafast temporal response of localized and propagating optical near fields in resonant optical antennas (ROAs) and plasmonic transmission lines, respectively. Using finite-difference time-domain simulations followed by Fourier transformation, we obtain the impulse response of a nanostructure in the frequency domain, which allows obtaining its temporal response to any arbitrary pulse shape. To illustrate the potential of the method we demonstrate deterministic optimal temporal pulse compression in ROAs with reduced symmetry, in a plasmonic two-wire transmission line, and in a prototype plasmonic circuit combining propagation effects and local resonances. The method described here will be of importance for the coherent control of field propagation in nanophotonic structures and light-induced processes in nanoscopic volumes.}, author = {Huang, Jer-Shing and Voronine, Dmitri V. and Tuchscherer, Philip and Brixner, Tobias and Hecht, Bert}, journal = {Phys. Rev. B}, keywords = {plasmon}, month = {05}, number = 19, pages = 195441, title = {Deterministic spatiotemporal control of optical fields in nanoantennas and plasmonic circuits}, volume = 79, year = 2009 }

%0 Journal Article %1 huang2009deterministic %A Huang, Jer-Shing %A Voronine, Dmitri V. %A Tuchscherer, Philip %A Brixner, Tobias %A Hecht, Bert %D 2009 %J Phys. Rev. B %N 19 %P 195441 %R 10.1103/PhysRevB.79.195441 %T Deterministic spatiotemporal control of optical fields in nanoantennas and plasmonic circuits %V 79 %X We show that laser pulse shaping techniques can be applied to tailor the ultrafast temporal response of localized and propagating optical near fields in resonant optical antennas (ROAs) and plasmonic transmission lines, respectively. Using finite-difference time-domain simulations followed by Fourier transformation, we obtain the impulse response of a nanostructure in the frequency domain, which allows obtaining its temporal response to any arbitrary pulse shape. To illustrate the potential of the method we demonstrate deterministic optimal temporal pulse compression in ROAs with reduced symmetry, in a plasmonic two-wire transmission line, and in a prototype plasmonic circuit combining propagation effects and local resonances. The method described here will be of importance for the coherent control of field propagation in nanophotonic structures and light-induced processes in nanoscopic volumes.

Detection of Transient Events in the Presence of Background Noise. Grange, Wilfried; Haas, Philippe; Wild, Andreas; Lieb, Michael Andreas; Calame, Michel; Hegner, Martin; Hecht, Bert. In J. Phys. Chem. B., 112(23), pp. 7140–7144. 2008.
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We describe a method to detect and count transient burstlike signals in the presence of a significant stationary noise. To discriminate a transient signal from the background noise, an optimum threshold is determined using an iterative algorithm that yields the probability distribution of the background noise. Knowledge of the probability distribution of the noise then allows the determination of the number of transient events with a quantifiable error (wrong-positives). We apply the method, which does not rely on the choice of free parameters, to the detection and counting of transient single-molecule fluorescence events in the presence of a strong background noise. The method will be of importance in various ultra sensing applications.

@article{grange2008detection, abstract = {We describe a method to detect and count transient burstlike signals in the presence of a significant stationary noise. To discriminate a transient signal from the background noise, an optimum threshold is determined using an iterative algorithm that yields the probability distribution of the background noise. Knowledge of the probability distribution of the noise then allows the determination of the number of transient events with a quantifiable error (wrong-positives). We apply the method, which does not rely on the choice of free parameters, to the detection and counting of transient single-molecule fluorescence events in the presence of a strong background noise. The method will be of importance in various ultra sensing applications.}, author = {Grange, Wilfried and Haas, Philippe and Wild, Andreas and Lieb, Michael Andreas and Calame, Michel and Hegner, Martin and Hecht, Bert}, journal = {J. Phys. Chem. B.}, keywords = {theory}, month = {06}, number = 23, pages = {7140-7144}, title = {Detection of Transient Events in the Presence of Background Noise}, volume = 112, year = 2008 }

%0 Journal Article %1 grange2008detection %A Grange, Wilfried %A Haas, Philippe %A Wild, Andreas %A Lieb, Michael Andreas %A Calame, Michel %A Hegner, Martin %A Hecht, Bert %D 2008 %J J. Phys. Chem. B. %N 23 %P 7140-7144 %R 10.1021/jp7114862 %T Detection of Transient Events in the Presence of Background Noise %V 112 %X We describe a method to detect and count transient burstlike signals in the presence of a significant stationary noise. To discriminate a transient signal from the background noise, an optimum threshold is determined using an iterative algorithm that yields the probability distribution of the background noise. Knowledge of the probability distribution of the noise then allows the determination of the number of transient events with a quantifiable error (wrong-positives). We apply the method, which does not rely on the choice of free parameters, to the detection and counting of transient single-molecule fluorescence events in the presence of a strong background noise. The method will be of importance in various ultra sensing applications.
A simple method for producing flattened atomic force microscopy tips. Biagioni, Paolo; Farahani, Javad N.; Mühlschlegel, Peter; Eisler, Hans-Jürgen; Pohl, Dieter W.; Hecht, Bert. In Rev. Sci. Instrum., 79(1), p. 016103. 2008.
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We describe a simple and reliable procedure for obtaining a flat plateau on top of standard silicon nitride atomic force microscopy tips by scanning them over the focus of a high-numerical-aperture objective illuminated by near-infrared ultrashort laser pulses. Flattened tips produced this way exhibit a plateau that is parallel to the substrate when the cantilever is mounted. They represent a valid and cost-effective alternative to commercially available plateau tips.

@article{biagioni2008simple, abstract = {We describe a simple and reliable procedure for obtaining a flat plateau on top of standard silicon nitride atomic force microscopy tips by scanning them over the focus of a high-numerical-aperture objective illuminated by near-infrared ultrashort laser pulses. Flattened tips produced this way exhibit a plateau that is parallel to the substrate when the cantilever is mounted. They represent a valid and cost-effective alternative to commercially available plateau tips.}, author = {Biagioni, Paolo and Farahani, Javad N. and Mühlschlegel, Peter and Eisler, Hans-Jürgen and Pohl, Dieter W. and Hecht, Bert}, journal = {Rev. Sci. Instrum.}, keywords = {nano-optics}, month = {01}, number = 1, pages = {016103}, title = {A simple method for producing flattened atomic force microscopy tips}, volume = 79, year = 2008 }

%0 Journal Article %1 biagioni2008simple %A Biagioni, Paolo %A Farahani, Javad N. %A Mühlschlegel, Peter %A Eisler, Hans-Jürgen %A Pohl, Dieter W. %A Hecht, Bert %D 2008 %J Rev. Sci. Instrum. %N 1 %P 016103 %R 10.1063/1.2834875 %T A simple method for producing flattened atomic force microscopy tips %V 79 %X We describe a simple and reliable procedure for obtaining a flat plateau on top of standard silicon nitride atomic force microscopy tips by scanning them over the focus of a high-numerical-aperture objective illuminated by near-infrared ultrashort laser pulses. Flattened tips produced this way exhibit a plateau that is parallel to the substrate when the cantilever is mounted. They represent a valid and cost-effective alternative to commercially available plateau tips.

Bow-tie optical antenna probes for single-emitter scanning near-field optical microscopy. Farahani, Javad N.; Eisler, Hans-Jürgen; Pohl, Dieter W.; Pavius, Michaël; Flückiger, Philippe; Gasser, Philippe; Hecht, Bert. In Nanotechnology, 18(12), p. 125506. 2007.
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A method for the fabrication of bow-tie optical antennas at the apex of pyramidal Si3N4 atomic force microscopy tips is described. We demonstrate that these novel optical probes are capable of sub-wavelength imaging of single quantum dots at room temperature. The enhanced and confined optical near-field at the antenna feed gap leads to locally enhanced photoluminescence (PL) of single quantum dots. Photoluminescence quenching due to the proximity of metal is found to be insignificant. The method holds promise for single quantum emitter imaging and spectroscopy at spatial resolution limited by the engineered antenna gap width exclusively.

@article{farahani2007bowtie, abstract = {A method for the fabrication of bow-tie optical antennas at the apex of pyramidal Si3N4 atomic force microscopy tips is described. We demonstrate that these novel optical probes are capable of sub-wavelength imaging of single quantum dots at room temperature. The enhanced and confined optical near-field at the antenna feed gap leads to locally enhanced photoluminescence (PL) of single quantum dots. Photoluminescence quenching due to the proximity of metal is found to be insignificant. The method holds promise for single quantum emitter imaging and spectroscopy at spatial resolution limited by the engineered antenna gap width exclusively.}, author = {Farahani, Javad N. and Eisler, Hans-Jürgen and Pohl, Dieter W. and Pavius, Michaël and Flückiger, Philippe and Gasser, Philippe and Hecht, Bert}, journal = {Nanotechnology}, keywords = {SNOM}, month = {02}, number = 12, pages = 125506, title = {Bow-tie optical antenna probes for single-emitter scanning near-field optical microscopy}, volume = 18, year = 2007 }

%0 Journal Article %1 farahani2007bowtie %A Farahani, Javad N. %A Eisler, Hans-Jürgen %A Pohl, Dieter W. %A Pavius, Michaël %A Flückiger, Philippe %A Gasser, Philippe %A Hecht, Bert %D 2007 %J Nanotechnology %N 12 %P 125506 %R 10.1088/0957-4484/18/12/125506 %T Bow-tie optical antenna probes for single-emitter scanning near-field optical microscopy %V 18 %X A method for the fabrication of bow-tie optical antennas at the apex of pyramidal Si3N4 atomic force microscopy tips is described. We demonstrate that these novel optical probes are capable of sub-wavelength imaging of single quantum dots at room temperature. The enhanced and confined optical near-field at the antenna feed gap leads to locally enhanced photoluminescence (PL) of single quantum dots. Photoluminescence quenching due to the proximity of metal is found to be insignificant. The method holds promise for single quantum emitter imaging and spectroscopy at spatial resolution limited by the engineered antenna gap width exclusively.

Prospects of Resonant Optical Antennas for Nano-Analysis. Hecht, Bert; Mühlschlegel, Peter; Farahani, Javad N.; Eisler, Hans-Jürgen; Pohl, Dieter W.; Martin, Olivier J. F.; Biagioni, Paolo. In CHIMIA, 60(11), pp. 765–769. 2006.
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Suitably shaped metal nano structures act as resonant optical antennas that efficiently collect light and confine it to a subwavelength volume. Vice versa, light emission from nano volumes can be enhanced by coupling to antenna structures. We give a short introduction to antenna theory and discuss recent experiments that show the feasibility of achieving strong field enhancement using resonant dipole antennas for near infrared wavelengths. By scanning an optical antenna fabricated at the apex of an AFM tip over individual quantum dots, we observe enhanced emission of the latter while it is in close proximity of the antenna feed gap. Resonant optical antennas hold promise to be applied for spectroscopic characterization of nano structures with high spatial resolutions and single-molecule sensitivity.

@article{hecht2006prospects, abstract = {Suitably shaped metal nano structures act as resonant optical antennas that efficiently collect light and confine it to a subwavelength volume. Vice versa, light emission from nano volumes can be enhanced by coupling to antenna structures. We give a short introduction to antenna theory and discuss recent experiments that show the feasibility of achieving strong field enhancement using resonant dipole antennas for near infrared wavelengths. By scanning an optical antenna fabricated at the apex of an AFM tip over individual quantum dots, we observe enhanced emission of the latter while it is in close proximity of the antenna feed gap. Resonant optical antennas hold promise to be applied for spectroscopic characterization of nano structures with high spatial resolutions and single-molecule sensitivity.}, author = {Hecht, Bert and Mühlschlegel, Peter and Farahani, Javad N. and Eisler, Hans-Jürgen and Pohl, Dieter W. and Martin, Olivier J. F. and Biagioni, Paolo}, journal = {CHIMIA}, keywords = {theory}, month = 11, number = 11, pages = {765-769}, title = {Prospects of Resonant Optical Antennas for Nano-Analysis}, volume = 60, year = 2006 }

%0 Journal Article %1 hecht2006prospects %A Hecht, Bert %A Mühlschlegel, Peter %A Farahani, Javad N. %A Eisler, Hans-Jürgen %A Pohl, Dieter W. %A Martin, Olivier J. F. %A Biagioni, Paolo %D 2006 %J CHIMIA %N 11 %P 765-769 %R 10.2533/chimia.2006.765 %T Prospects of Resonant Optical Antennas for Nano-Analysis %V 60 %X Suitably shaped metal nano structures act as resonant optical antennas that efficiently collect light and confine it to a subwavelength volume. Vice versa, light emission from nano volumes can be enhanced by coupling to antenna structures. We give a short introduction to antenna theory and discuss recent experiments that show the feasibility of achieving strong field enhancement using resonant dipole antennas for near infrared wavelengths. By scanning an optical antenna fabricated at the apex of an AFM tip over individual quantum dots, we observe enhanced emission of the latter while it is in close proximity of the antenna feed gap. Resonant optical antennas hold promise to be applied for spectroscopic characterization of nano structures with high spatial resolutions and single-molecule sensitivity.
Single Hepatitis-B Virus Core Capsid Binding to Individual Nuclear Pore Complexes in HeLa Cells. Lill, Yoriko; Lill, Markus A.; Fahrenkrog, Birthe; Schwarz-Herion, Kyrill; Paulillo, Sara; Aebi, Ueli; Hecht, Bert. In Biophys. J., 91(8), pp. 3123–3130. 2006.
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We investigate the interaction of hepatitis B virus capsids lacking a nuclear localization signal with nuclear pore complexes (NPCs) in permeabilized HeLa cells. Confocal and wide-field optical images of the nuclear envelope show well-spaced individual NPCs. Specific interactions of capsids with single NPCs are characterized by extended residence times of capsids in the focal volume which are characterized by fluorescence correlation spectroscopy. In addition, single-capsid-tracking experiments using fast wide-field fluorescence microscopy at 50 frames/s allow us to directly observe specific binding via a dual-color colocalization of capsids and NPCs. We find that binding occurs with high probability on the nuclear-pore ring moiety, at 44 ± 9 nm radial distance from the central axis.

@article{lill2006single, abstract = {We investigate the interaction of hepatitis B virus capsids lacking a nuclear localization signal with nuclear pore complexes (NPCs) in permeabilized HeLa cells. Confocal and wide-field optical images of the nuclear envelope show well-spaced individual NPCs. Specific interactions of capsids with single NPCs are characterized by extended residence times of capsids in the focal volume which are characterized by fluorescence correlation spectroscopy. In addition, single-capsid-tracking experiments using fast wide-field fluorescence microscopy at 50 frames/s allow us to directly observe specific binding via a dual-color colocalization of capsids and NPCs. We find that binding occurs with high probability on the nuclear-pore ring moiety, at 44 ± 9 nm radial distance from the central axis.}, author = {Lill, Yoriko and Lill, Markus A. and Fahrenkrog, Birthe and Schwarz-Herion, Kyrill and Paulillo, Sara and Aebi, Ueli and Hecht, Bert}, journal = {Biophys. J.}, keywords = {single-molecules}, month = 10, number = 8, pages = {3123-3130}, title = {Single Hepatitis-B Virus Core Capsid Binding to Individual Nuclear Pore Complexes in HeLa Cells}, volume = 91, year = 2006 }

%0 Journal Article %1 lill2006single %A Lill, Yoriko %A Lill, Markus A. %A Fahrenkrog, Birthe %A Schwarz-Herion, Kyrill %A Paulillo, Sara %A Aebi, Ueli %A Hecht, Bert %D 2006 %J Biophys. J. %N 8 %P 3123-3130 %R 10.1529/biophysj.106.087650 %T Single Hepatitis-B Virus Core Capsid Binding to Individual Nuclear Pore Complexes in HeLa Cells %V 91 %X We investigate the interaction of hepatitis B virus capsids lacking a nuclear localization signal with nuclear pore complexes (NPCs) in permeabilized HeLa cells. Confocal and wide-field optical images of the nuclear envelope show well-spaced individual NPCs. Specific interactions of capsids with single NPCs are characterized by extended residence times of capsids in the focal volume which are characterized by fluorescence correlation spectroscopy. In addition, single-capsid-tracking experiments using fast wide-field fluorescence microscopy at 50 frames/s allow us to directly observe specific binding via a dual-color colocalization of capsids and NPCs. We find that binding occurs with high probability on the nuclear-pore ring moiety, at 44 ± 9 nm radial distance from the central axis.
Absorption and fluorescence of single molecules. Butter, Jacqueline Y. P.; Hecht, Bert; Crenshaw, B. R.; Weder, Christoph. In J. Chem. Phys., 125(15), p. 154710. 2006.
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Simultaneous detection of single molecules by absorption and fluorescence is demonstrated using confocal microscopy at cryogenic temperature. Dynamical processes such as blinking and spectral jumping of single emitters are observed in both detection channels. The relative magnitude of fluorescence and absorption varies between molecules. In particular, we observe molecules that do not emit detectable Stokes-shifted fluorescence but show a strong absorption signal. The fact that coherent resonant scattering underlies the absorption process is demonstrated by a correlation between small linewidth and large absorption amplitude.

@article{butter2006absorption, abstract = {Simultaneous detection of single molecules by absorption and fluorescence is demonstrated using confocal microscopy at cryogenic temperature. Dynamical processes such as blinking and spectral jumping of single emitters are observed in both detection channels. The relative magnitude of fluorescence and absorption varies between molecules. In particular, we observe molecules that do not emit detectable Stokes-shifted fluorescence but show a strong absorption signal. The fact that coherent resonant scattering underlies the absorption process is demonstrated by a correlation between small linewidth and large absorption amplitude.}, author = {Butter, Jacqueline Y. P. and Hecht, Bert and Crenshaw, B. R. and Weder, Christoph}, journal = {J. Chem. Phys.}, keywords = {single-molecules}, month = 10, number = 15, pages = 154710, title = {Absorption and fluorescence of single molecules}, volume = 125, year = 2006 }

%0 Journal Article %1 butter2006absorption %A Butter, Jacqueline Y. P. %A Hecht, Bert %A Crenshaw, B. R. %A Weder, Christoph %D 2006 %J J. Chem. Phys. %N 15 %P 154710 %R 10.1063/1.2360268 %T Absorption and fluorescence of single molecules %V 125 %X Simultaneous detection of single molecules by absorption and fluorescence is demonstrated using confocal microscopy at cryogenic temperature. Dynamical processes such as blinking and spectral jumping of single emitters are observed in both detection channels. The relative magnitude of fluorescence and absorption varies between molecules. In particular, we observe molecules that do not emit detectable Stokes-shifted fluorescence but show a strong absorption signal. The fact that coherent resonant scattering underlies the absorption process is demonstrated by a correlation between small linewidth and large absorption amplitude.
Fast determination of saturation intensity and maximum emission rate by single-emitter imaging. Butter, Jacqueline Y. P.; Hecht, Bert. In Opt. Express, 14(20), pp. 9350–9357. 2006.
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We investigate the dependence of the spot size in single-emitter confocal imaging on the degree of saturation. We show that single-emitter spots are broadened and flattened significantly already at excitation intensities well below saturation. The resulting single-emitter spot shapes thus deviate significantly from the excitation point spread function. We show and support by Monte Carlo simulations that fitting of a single spot is sufficient to extract the saturation intensity and the maximum emission rate of a single emitter with high accuracy. Our results will be of interest in all areas of single-emitter studies.

@article{butter2006determination, abstract = {We investigate the dependence of the spot size in single-emitter confocal imaging on the degree of saturation. We show that single-emitter spots are broadened and flattened significantly already at excitation intensities well below saturation. The resulting single-emitter spot shapes thus deviate significantly from the excitation point spread function. We show and support by Monte Carlo simulations that fitting of a single spot is sufficient to extract the saturation intensity and the maximum emission rate of a single emitter with high accuracy. Our results will be of interest in all areas of single-emitter studies.}, author = {Butter, Jacqueline Y. P. and Hecht, Bert}, journal = {Opt. Express}, keywords = {single-molecules}, month = 10, number = 20, pages = {9350-9357}, title = {Fast determination of saturation intensity and maximum emission rate by single-emitter imaging}, volume = 14, year = 2006 }

%0 Journal Article %1 butter2006determination %A Butter, Jacqueline Y. P. %A Hecht, Bert %D 2006 %J Opt. Express %N 20 %P 9350-9357 %R 10.1364/OE.14.009350 %T Fast determination of saturation intensity and maximum emission rate by single-emitter imaging %V 14 %X We investigate the dependence of the spot size in single-emitter confocal imaging on the degree of saturation. We show that single-emitter spots are broadened and flattened significantly already at excitation intensities well below saturation. The resulting single-emitter spot shapes thus deviate significantly from the excitation point spread function. We show and support by Monte Carlo simulations that fitting of a single spot is sufficient to extract the saturation intensity and the maximum emission rate of a single emitter with high accuracy. Our results will be of interest in all areas of single-emitter studies.
Resorcin[4]arene Cavitand-Based Molecular Switches. Azov, V. A.; Beeby, A.; Cacciarini, M.; Cheetham, A. G.; Diederich, F.; Frei, M.; Gimzewski, J. K.; Gramlich, V.; Hecht, Bert; Jaun, B.; Latychevskaia, T.; Lieb, A.; Lill, Y.; Marotti, F.; Schlegel, A.; Schlittler, R. R.; Skinner, P. J.; Seiler, P.; Yamakoshi, Y. In Adv. Funct. Mater., 16(2), pp. 147–156. 2006.
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Resorcin[4]arene cavitands with four quinoxaline bridges are a family of macrocycles that adopt, at elevated temperature, a contracted, vase-type conformation, capable of guest inclusion, whereas at low temperature they switch to an expanded, kite-type conformation with a large flat surface. The present investigations lay the foundation for the use of such dynamic cavitands as miniaturized mechanical grippers for supramolecular construction at the single-molecule level. New vase–kite switching modes, stimulated by pH changes or stoichiometric metal-ion complexation, have been discovered and monitored by 1H NMR and optical absorption spectroscopy. The solid-state geometries of the two states have been revealed by X-ray crystallography, and the kinetics and thermodynamics of the switching processes in solution as well as their solvent dependency has been investigated in great detail. Monolayers of the cavitand in the vase form have been studied by scanning tunneling microscopy at molecular resolution; conformational switching is also observed in Langmuir monolayers at the air/water interface. Synthetic protocols have been developed for preparation of partially and asymmetrically bridged resorcin[4]arene cavitands, which are also shown to undergo conformational switching. These synthetic advances pave the way to new, dynamic molecular receptors for steroids, tetrathiofulvalene-bridged grippers with the potential to undergo electrochemically induced conformational switching, and systems with greatly extended, rigid cavity walls functionalized at the termini by dipyrrometheneboron difluoride dyes. The latter cavitands are shown by fluorescence resonance energy transfer to undergo geometrically precisely defined motions between a contracted (≈ 7 Å linear extension) and a strongly expanded (≈ 7 nm linear extension) state.

@article{azov2006resorcin4arene, abstract = {Resorcin[4]arene cavitands with four quinoxaline bridges are a family of macrocycles that adopt, at elevated temperature, a contracted, vase-type conformation, capable of guest inclusion, whereas at low temperature they switch to an expanded, kite-type conformation with a large flat surface. The present investigations lay the foundation for the use of such dynamic cavitands as miniaturized mechanical grippers for supramolecular construction at the single-molecule level. New vase–kite switching modes, stimulated by pH changes or stoichiometric metal-ion complexation, have been discovered and monitored by 1H NMR and optical absorption spectroscopy. The solid-state geometries of the two states have been revealed by X-ray crystallography, and the kinetics and thermodynamics of the switching processes in solution as well as their solvent dependency has been investigated in great detail. Monolayers of the cavitand in the vase form have been studied by scanning tunneling microscopy at molecular resolution; conformational switching is also observed in Langmuir monolayers at the air/water interface. Synthetic protocols have been developed for preparation of partially and asymmetrically bridged resorcin[4]arene cavitands, which are also shown to undergo conformational switching. These synthetic advances pave the way to new, dynamic molecular receptors for steroids, tetrathiofulvalene-bridged grippers with the potential to undergo electrochemically induced conformational switching, and systems with greatly extended, rigid cavity walls functionalized at the termini by dipyrrometheneboron difluoride dyes. The latter cavitands are shown by fluorescence resonance energy transfer to undergo geometrically precisely defined motions between a contracted (≈ 7 Å linear extension) and a strongly expanded (≈ 7 nm linear extension) state.}, author = {Azov, V. A. and Beeby, A. and Cacciarini, M. and Cheetham, A. G. and Diederich, F. and Frei, M. and Gimzewski, J. K. and Gramlich, V. and Hecht, Bert and Jaun, B. and Latychevskaia, T. and Lieb, A. and Lill, Y. and Marotti, F. and Schlegel, A. and Schlittler, R. R. and Skinner, P. J. and Seiler, P. and Yamakoshi, Y.}, journal = {Adv. Funct. Mater.}, keywords = {single-molecules}, month = {09}, number = 2, pages = {147-156}, title = {Resorcin[4]arene Cavitand-Based Molecular Switches}, volume = 16, year = 2006 }

%0 Journal Article %1 azov2006resorcin4arene %A Azov, V. A. %A Beeby, A. %A Cacciarini, M. %A Cheetham, A. G. %A Diederich, F. %A Frei, M. %A Gimzewski, J. K. %A Gramlich, V. %A Hecht, Bert %A Jaun, B. %A Latychevskaia, T. %A Lieb, A. %A Lill, Y. %A Marotti, F. %A Schlegel, A. %A Schlittler, R. R. %A Skinner, P. J. %A Seiler, P. %A Yamakoshi, Y. %D 2006 %J Adv. Funct. Mater. %N 2 %P 147-156 %R 10.1002/adfm.200500181 %T Resorcin[4]arene Cavitand-Based Molecular Switches %V 16 %X Resorcin[4]arene cavitands with four quinoxaline bridges are a family of macrocycles that adopt, at elevated temperature, a contracted, vase-type conformation, capable of guest inclusion, whereas at low temperature they switch to an expanded, kite-type conformation with a large flat surface. The present investigations lay the foundation for the use of such dynamic cavitands as miniaturized mechanical grippers for supramolecular construction at the single-molecule level. New vase–kite switching modes, stimulated by pH changes or stoichiometric metal-ion complexation, have been discovered and monitored by 1H NMR and optical absorption spectroscopy. The solid-state geometries of the two states have been revealed by X-ray crystallography, and the kinetics and thermodynamics of the switching processes in solution as well as their solvent dependency has been investigated in great detail. Monolayers of the cavitand in the vase form have been studied by scanning tunneling microscopy at molecular resolution; conformational switching is also observed in Langmuir monolayers at the air/water interface. Synthetic protocols have been developed for preparation of partially and asymmetrically bridged resorcin[4]arene cavitands, which are also shown to undergo conformational switching. These synthetic advances pave the way to new, dynamic molecular receptors for steroids, tetrathiofulvalene-bridged grippers with the potential to undergo electrochemically induced conformational switching, and systems with greatly extended, rigid cavity walls functionalized at the termini by dipyrrometheneboron difluoride dyes. The latter cavitands are shown by fluorescence resonance energy transfer to undergo geometrically precisely defined motions between a contracted (≈ 7 Å linear extension) and a strongly expanded (≈ 7 nm linear extension) state.
Stark-shift microscopy of single emitters. Karotke, S.; Lieb, A.; Hecht, Bert. In Appl. Phys. Lett., 89(2), p. 023106. 2006.
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We study the interaction of a biased, metallized tip in close proximity to single fluorescent molecules at cryogenic temperature. By scanning over the sample, the tip’s inhomogeneous electric field induces Stark shifts of the zero-phonon lines of nearby molecules. When illuminated with an off-resonant laser, molecules are tuned into resonance for specific tip positions located on circular patterns around the molecules’ spatial positions. The origins of circles belonging to different molecules can be determined with high precision. We demonstrate a spatial resolution of neighboring individual molecules of ∼50nm using a tip scanned in a distance of ∼3μm above the sample.

@article{karotke2006starkshift, abstract = {We study the interaction of a biased, metallized tip in close proximity to single fluorescent molecules at cryogenic temperature. By scanning over the sample, the tip’s inhomogeneous electric field induces Stark shifts of the zero-phonon lines of nearby molecules. When illuminated with an off-resonant laser, molecules are tuned into resonance for specific tip positions located on circular patterns around the molecules’ spatial positions. The origins of circles belonging to different molecules can be determined with high precision. We demonstrate a spatial resolution of neighboring individual molecules of ∼50nm using a tip scanned in a distance of ∼3μm above the sample.}, author = {Karotke, S. and Lieb, A. and Hecht, Bert}, journal = {Appl. Phys. Lett.}, keywords = {resonance}, month = {07}, number = 2, pages = {023106}, title = {Stark-shift microscopy of single emitters}, volume = 89, year = 2006 }

%0 Journal Article %1 karotke2006starkshift %A Karotke, S. %A Lieb, A. %A Hecht, Bert %D 2006 %J Appl. Phys. Lett. %N 2 %P 023106 %R 10.1063/1.2219137 %T Stark-shift microscopy of single emitters %V 89 %X We study the interaction of a biased, metallized tip in close proximity to single fluorescent molecules at cryogenic temperature. By scanning over the sample, the tip’s inhomogeneous electric field induces Stark shifts of the zero-phonon lines of nearby molecules. When illuminated with an off-resonant laser, molecules are tuned into resonance for specific tip positions located on circular patterns around the molecules’ spatial positions. The origins of circles belonging to different molecules can be determined with high precision. We demonstrate a spatial resolution of neighboring individual molecules of ∼50nm using a tip scanned in a distance of ∼3μm above the sample.
Aperture scanning near-field optical microscopy and spectroscopy of single terrylene molecules at 1.8 K. Butter, Jacqueline Y. P.; Hecht, Bert. In Nanotechnology, 17(6), pp. 1547–1550. 2006.
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Single-molecule imaging and spectroscopy using an aperture scanning near-field optical microscope operating at 1.8 K in a helium bath cryostat is demonstrated. From near-field images at constant excitation frequency, the orientation of single molecules can be deduced. Spectral information is obtained using both near-field and confocal excitation schemes by scanning the excitation frequency at a fixed sample position. Differences between near-field and confocal spectra are discussed in terms of the position with respect to the aperture and the molecular orientation.

@article{butter2006aperture, abstract = {Single-molecule imaging and spectroscopy using an aperture scanning near-field optical microscope operating at 1.8 K in a helium bath cryostat is demonstrated. From near-field images at constant excitation frequency, the orientation of single molecules can be deduced. Spectral information is obtained using both near-field and confocal excitation schemes by scanning the excitation frequency at a fixed sample position. Differences between near-field and confocal spectra are discussed in terms of the position with respect to the aperture and the molecular orientation.}, author = {Butter, Jacqueline Y. P. and Hecht, Bert}, journal = {Nanotechnology}, keywords = {single-molecules}, month = {02}, number = 6, pages = {1547-1550}, title = {Aperture scanning near-field optical microscopy and spectroscopy of single terrylene molecules at 1.8 K}, volume = 17, year = 2006 }

%0 Journal Article %1 butter2006aperture %A Butter, Jacqueline Y. P. %A Hecht, Bert %D 2006 %J Nanotechnology %N 6 %P 1547-1550 %R 10.1088/0957-4484/17/6/002 %T Aperture scanning near-field optical microscopy and spectroscopy of single terrylene molecules at 1.8 K %V 17 %X Single-molecule imaging and spectroscopy using an aperture scanning near-field optical microscope operating at 1.8 K in a helium bath cryostat is demonstrated. From near-field images at constant excitation frequency, the orientation of single molecules can be deduced. Spectral information is obtained using both near-field and confocal excitation schemes by scanning the excitation frequency at a fixed sample position. Differences between near-field and confocal spectra are discussed in terms of the position with respect to the aperture and the molecular orientation.
Glue-free tuning fork shear-force microscope. Mühlschlegel, Peter; Toquant, Julien; Pohl, Dieter W.; Hecht, Bert. In Rev. Sci. Instrum., 77(1), p. 016105. 2006.
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A scanning near-field optical microscope without any glued parts is described. Key elements are the optical fiber probe/tuning fork junction and the piezotube scanner assembly. In both cases, fixation is achieved by means of controlled pressure and elastic deformation. The avoidance of glued connections was found to improve the Q factor of the shear-force sensor as well as to facilitate the replacement of the fiber probe and other parts of the scanner head. We present approach curves and shear-force images that demonstrate the performance and stability of the system.

@article{mhlschlegel2006gluefree, abstract = {A scanning near-field optical microscope without any glued parts is described. Key elements are the optical fiber probe/tuning fork junction and the piezotube scanner assembly. In both cases, fixation is achieved by means of controlled pressure and elastic deformation. The avoidance of glued connections was found to improve the Q factor of the shear-force sensor as well as to facilitate the replacement of the fiber probe and other parts of the scanner head. We present approach curves and shear-force images that demonstrate the performance and stability of the system.}, author = {Mühlschlegel, Peter and Toquant, Julien and Pohl, Dieter W. and Hecht, Bert}, journal = {Rev. Sci. Instrum.}, keywords = {SNOM}, month = {01}, number = 1, pages = {016105}, title = {Glue-free tuning fork shear-force microscope}, volume = 77, year = 2006 }

%0 Journal Article %1 mhlschlegel2006gluefree %A Mühlschlegel, Peter %A Toquant, Julien %A Pohl, Dieter W. %A Hecht, Bert %D 2006 %J Rev. Sci. Instrum. %N 1 %P 016105 %R 10.1063/1.2165548 %T Glue-free tuning fork shear-force microscope %V 77 %X A scanning near-field optical microscope without any glued parts is described. Key elements are the optical fiber probe/tuning fork junction and the piezotube scanner assembly. In both cases, fixation is achieved by means of controlled pressure and elastic deformation. The avoidance of glued connections was found to improve the Q factor of the shear-force sensor as well as to facilitate the replacement of the fiber probe and other parts of the scanner head. We present approach curves and shear-force images that demonstrate the performance and stability of the system.
Single-Molecule Spectroscopy of Uniaxially Oriented Terrylene in Polyethylene. Butter, Jacqueline Y. P.; Crenshaw, Brent R.; Weder, Christoph; Hecht, Bert. In ChemPhysChem, 7(1), pp. 261–265. 2006.
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Single terrylene molecules doped into linear low-density polyethylene can be oriented by tensile deformation of the matrix. In measurements on ensembles at ambient and on single terrylene molecules at cryogenic temperature, strong orientation along the stretching direction was observed by polarization-resolved confocal microscopy. At cryogenic temperatures narrow and spectrally stable zero-phonon lines were found. The low saturation intensity of 0.07 W cm−2 is consistent with an uniaxial orientation of terrylene in the sample plane.

@article{butter2006singlemolecule, abstract = {Single terrylene molecules doped into linear low-density polyethylene can be oriented by tensile deformation of the matrix. In measurements on ensembles at ambient and on single terrylene molecules at cryogenic temperature, strong orientation along the stretching direction was observed by polarization-resolved confocal microscopy. At cryogenic temperatures narrow and spectrally stable zero-phonon lines were found. The low saturation intensity of 0.07 W cm−2 is consistent with an uniaxial orientation of terrylene in the sample plane.}, author = {Butter, Jacqueline Y. P. and Crenshaw, Brent R. and Weder, Christoph and Hecht, Bert}, journal = {ChemPhysChem}, keywords = {single-molecules}, month = {01}, number = 1, pages = {261-265}, title = {Single-Molecule Spectroscopy of Uniaxially Oriented Terrylene in Polyethylene}, volume = 7, year = 2006 }

%0 Journal Article %1 butter2006singlemolecule %A Butter, Jacqueline Y. P. %A Crenshaw, Brent R. %A Weder, Christoph %A Hecht, Bert %D 2006 %J ChemPhysChem %N 1 %P 261-265 %R 10.1002/cphc.200500409 %T Single-Molecule Spectroscopy of Uniaxially Oriented Terrylene in Polyethylene %V 7 %X Single terrylene molecules doped into linear low-density polyethylene can be oriented by tensile deformation of the matrix. In measurements on ensembles at ambient and on single terrylene molecules at cryogenic temperature, strong orientation along the stretching direction was observed by polarization-resolved confocal microscopy. At cryogenic temperatures narrow and spectrally stable zero-phonon lines were found. The low saturation intensity of 0.07 W cm−2 is consistent with an uniaxial orientation of terrylene in the sample plane.

Excitation and superfocusing of surface plasmon polaritons on a silver-coated optical fiber tip. Janunts, Norik A.; Baghdasaryan, K. S.; Nerkararyan, Khachatur V.; Hecht, Bert. In Optics Commun., 253(1), pp. 118–124. 2005.
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We theoretically study the transfer of energy from a fiber mode to surface plasmon polaritons at the silver/air interface in the taper region of a silver-coated fiber tip. We describe conditions, under which a transfer efficiency from the fiber mode to the surface plasmon polariton of up to 46\% can be achieved. Propagation of the surface plasmon polaritons towards the tip of the tapered structure leads to a strong subwavelength localization of the excitation enabled by a substantial increase of the surface plasmon polariton wave vector approaching the tip. The resulting strong field enhancement and confinement has a tremendous potential for applications in ultrahigh resolution tip-enhanced near-field optical microscopy.

@article{janunts2005excitation, abstract = {We theoretically study the transfer of energy from a fiber mode to surface plasmon polaritons at the silver/air interface in the taper region of a silver-coated fiber tip. We describe conditions, under which a transfer efficiency from the fiber mode to the surface plasmon polariton of up to 46\% can be achieved. Propagation of the surface plasmon polaritons towards the tip of the tapered structure leads to a strong subwavelength localization of the excitation enabled by a substantial increase of the surface plasmon polariton wave vector approaching the tip. The resulting strong field enhancement and confinement has a tremendous potential for applications in ultrahigh resolution tip-enhanced near-field optical microscopy.}, author = {Janunts, Norik A. and Baghdasaryan, K. S. and Nerkararyan, Khachatur V. and Hecht, Bert}, journal = {Optics Commun.}, keywords = {theory}, month = {09}, number = 1, pages = {118-124}, title = {Excitation and superfocusing of surface plasmon polaritons on a silver-coated optical fiber tip}, volume = 253, year = 2005 }

%0 Journal Article %1 janunts2005excitation %A Janunts, Norik A. %A Baghdasaryan, K. S. %A Nerkararyan, Khachatur V. %A Hecht, Bert %D 2005 %J Optics Commun. %N 1 %P 118-124 %R 10.1016/j.optcom.2005.04.076 %T Excitation and superfocusing of surface plasmon polaritons on a silver-coated optical fiber tip %V 253 %X We theoretically study the transfer of energy from a fiber mode to surface plasmon polaritons at the silver/air interface in the taper region of a silver-coated fiber tip. We describe conditions, under which a transfer efficiency from the fiber mode to the surface plasmon polariton of up to 46\% can be achieved. Propagation of the surface plasmon polaritons towards the tip of the tapered structure leads to a strong subwavelength localization of the excitation enabled by a substantial increase of the surface plasmon polariton wave vector approaching the tip. The resulting strong field enhancement and confinement has a tremendous potential for applications in ultrahigh resolution tip-enhanced near-field optical microscopy.
Optische Antennen. Hecht, Bert; Eisler, Hans-Jürgen; Pohl, Dieter W.; Martin, Olivier J. F. In Physik in unserer Zeit, 36(5), pp. 209–210. 2005.
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Die heutige Telekommunikation basiert großteils auf der effizienten Erzeugung und dem Empfang von elektromagnetischen Wellen. Die relevanten Wellenlängen liegen dabei im Bereich von Kilometern beim Langwellenrundfunk bis hinunter zu wenigen Zentimetern für die mobile Kommunikation. Physikern aus Basel und Lausanne gelang es kürzlich, Antennen für Licht herzustellen.

@article{hecht2005optische, abstract = {Die heutige Telekommunikation basiert großteils auf der effizienten Erzeugung und dem Empfang von elektromagnetischen Wellen. Die relevanten Wellenlängen liegen dabei im Bereich von Kilometern beim Langwellenrundfunk bis hinunter zu wenigen Zentimetern für die mobile Kommunikation. Physikern aus Basel und Lausanne gelang es kürzlich, Antennen für Licht herzustellen.}, author = {Hecht, Bert and Eisler, Hans-Jürgen and Pohl, Dieter W. and Martin, Olivier J. F.}, journal = {Physik in unserer Zeit}, keywords = {nano-optics}, month = {08}, number = 5, pages = {209-210}, title = {Optische Antennen}, volume = 36, year = 2005 }

%0 Journal Article %1 hecht2005optische %A Hecht, Bert %A Eisler, Hans-Jürgen %A Pohl, Dieter W. %A Martin, Olivier J. F. %D 2005 %J Physik in unserer Zeit %N 5 %P 209-210 %R 10.1002/piuz.200590077 %T Optische Antennen %V 36 %X Die heutige Telekommunikation basiert großteils auf der effizienten Erzeugung und dem Empfang von elektromagnetischen Wellen. Die relevanten Wellenlängen liegen dabei im Bereich von Kilometern beim Langwellenrundfunk bis hinunter zu wenigen Zentimetern für die mobile Kommunikation. Physikern aus Basel und Lausanne gelang es kürzlich, Antennen für Licht herzustellen.
Kinetics of the Initial Steps of G Protein-Coupled Receptor-Mediated Cellular Signaling Revealed by Single-Molecule Imaging. Lill, Yoriko; Martinez, Karen L.; Lill, Markus A.; Meyer, Bruno H.; Vogel, Horst; Hecht, Bert. In ChemPhysChem, 6(8), pp. 1633–1640. 2005.
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We report on an in vivo single-molecule study of the signaling kinetics of G protein-coupled receptors (GPCR) performed using the neurokinin 1 receptor (NK1R) as a representative member. The NK1R signaling cascade is triggered by the specific binding of a fluorescently labeled agonist, substance P (SP). The diffusion of single receptor–ligand complexes in plasma membrane of living HEK 293 cells is imaged using fast single-molecule wide-field fluorescence microscopy at 100 ms time resolution. Diffusion trajectories are obtained which show intra- and intertrace heterogeneity in the diffusion mode. To investigate universal patterns in the diffusion trajectories we take the ligand-binding event as the common starting point. This synchronization allows us to observe changes in the character of the ligand–receptor-complex diffusion. Specifically, we find that the diffusion of ligand–receptor complexes is slowed down significantly and becomes more constrained as a function of time during the first 1000 ms. The decelerated and more constrained diffusion is attributed to an increasing interaction of the GPCR with cellular structures after the ligand–receptor complex is formed.

@article{lill2005kinetics, abstract = {We report on an in vivo single-molecule study of the signaling kinetics of G protein-coupled receptors (GPCR) performed using the neurokinin 1 receptor (NK1R) as a representative member. The NK1R signaling cascade is triggered by the specific binding of a fluorescently labeled agonist, substance P (SP). The diffusion of single receptor–ligand complexes in plasma membrane of living HEK 293 cells is imaged using fast single-molecule wide-field fluorescence microscopy at 100 ms time resolution. Diffusion trajectories are obtained which show intra- and intertrace heterogeneity in the diffusion mode. To investigate universal patterns in the diffusion trajectories we take the ligand-binding event as the common starting point. This synchronization allows us to observe changes in the character of the ligand–receptor-complex diffusion. Specifically, we find that the diffusion of ligand–receptor complexes is slowed down significantly and becomes more constrained as a function of time during the first 1000 ms. The decelerated and more constrained diffusion is attributed to an increasing interaction of the GPCR with cellular structures after the ligand–receptor complex is formed.}, author = {Lill, Yoriko and Martinez, Karen L. and Lill, Markus A. and Meyer, Bruno H. and Vogel, Horst and Hecht, Bert}, journal = {ChemPhysChem}, keywords = {single-molecules}, month = {08}, number = 8, pages = {1633-1640}, title = {Kinetics of the Initial Steps of G Protein-Coupled Receptor-Mediated Cellular Signaling Revealed by Single-Molecule Imaging}, volume = 6, year = 2005 }

%0 Journal Article %1 lill2005kinetics %A Lill, Yoriko %A Martinez, Karen L. %A Lill, Markus A. %A Meyer, Bruno H. %A Vogel, Horst %A Hecht, Bert %D 2005 %J ChemPhysChem %N 8 %P 1633-1640 %R 10.1002/cphc.200500111 %T Kinetics of the Initial Steps of G Protein-Coupled Receptor-Mediated Cellular Signaling Revealed by Single-Molecule Imaging %V 6 %X We report on an in vivo single-molecule study of the signaling kinetics of G protein-coupled receptors (GPCR) performed using the neurokinin 1 receptor (NK1R) as a representative member. The NK1R signaling cascade is triggered by the specific binding of a fluorescently labeled agonist, substance P (SP). The diffusion of single receptor–ligand complexes in plasma membrane of living HEK 293 cells is imaged using fast single-molecule wide-field fluorescence microscopy at 100 ms time resolution. Diffusion trajectories are obtained which show intra- and intertrace heterogeneity in the diffusion mode. To investigate universal patterns in the diffusion trajectories we take the ligand-binding event as the common starting point. This synchronization allows us to observe changes in the character of the ligand–receptor-complex diffusion. Specifically, we find that the diffusion of ligand–receptor complexes is slowed down significantly and becomes more constrained as a function of time during the first 1000 ms. The decelerated and more constrained diffusion is attributed to an increasing interaction of the GPCR with cellular structures after the ligand–receptor complex is formed.
Single Quantum Dot Coupled to a Scanning Optical Antenna: A Tunable Superemitter. Farahani, Javad N.; Pohl, Dieter W.; Eisler, Hans-Jürgen; Hecht, Bert. In Phys. Rev. Lett., 95(1), p. 017402. 2005.
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The interaction of a single quantum dot with a bowtie antenna is demonstrated for visible light. The antenna is generated at the apex of a Si3N4 atomic force microscopy tip by focused ion beam milling. When scanned over the quantum dot, its photoluminescence is enhanced while its excited-state lifetime is decreased. Our observations demonstrate that the relaxation channels of a single quantum emitter can be controlled by coupling to an efficiently radiating metallic nanoantenna.

@article{farahani2005single, abstract = {The interaction of a single quantum dot with a bowtie antenna is demonstrated for visible light. The antenna is generated at the apex of a Si3N4 atomic force microscopy tip by focused ion beam milling. When scanned over the quantum dot, its photoluminescence is enhanced while its excited-state lifetime is decreased. Our observations demonstrate that the relaxation channels of a single quantum emitter can be controlled by coupling to an efficiently radiating metallic nanoantenna.}, author = {Farahani, Javad N. and Pohl, Dieter W. and Eisler, Hans-Jürgen and Hecht, Bert}, journal = {Phys. Rev. Lett.}, keywords = {FIB}, month = {06}, number = 1, pages = {017402}, title = {Single Quantum Dot Coupled to a Scanning Optical Antenna: A Tunable Superemitter}, volume = 95, year = 2005 }

%0 Journal Article %1 farahani2005single %A Farahani, Javad N. %A Pohl, Dieter W. %A Eisler, Hans-Jürgen %A Hecht, Bert %D 2005 %J Phys. Rev. Lett. %N 1 %P 017402 %R 10.1103/PhysRevLett.95.017402 %T Single Quantum Dot Coupled to a Scanning Optical Antenna: A Tunable Superemitter %V 95 %X The interaction of a single quantum dot with a bowtie antenna is demonstrated for visible light. The antenna is generated at the apex of a Si3N4 atomic force microscopy tip by focused ion beam milling. When scanned over the quantum dot, its photoluminescence is enhanced while its excited-state lifetime is decreased. Our observations demonstrate that the relaxation channels of a single quantum emitter can be controlled by coupling to an efficiently radiating metallic nanoantenna.
Resonant Optical Antennas. Muehlschlegel, Peter; Eisler, Hans-Jürgen; Martin, Olivier J. F.; Hecht, Bert; Pohl, Dieter W. In Science, 308(5728), pp. 1607–1609. 2005.
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We have fabricated nanometer-scale gold dipole antennas designed to be resonant at optical frequencies. On resonance, strong field enhancement in the antenna feed gap leads to white-light supercontinuum generation. The antenna length at resonance is considerably shorter than one-half the wavelength of the incident light. This is in contradiction to classical antenna theory but in qualitative accordance with computer simulations that take into account the finite metallic conductivity at optical frequencies. Because optical antennas link propagating radiation and confined/enhanced optical fields, they should find applications in optical characterization, manipulation of nanostructures, and optical information processing. Split strips of gold, each with a width of about half the wavelength of light, can act as optical antennas, capturing incident light in the gold arms and focusing the energy into the small gap. Split strips of gold, each with a width of about half the wavelength of light, can act as optical antennas, capturing incident light in the gold arms and focusing the energy into the small gap.

@article{muehlschlegel2005resonant, abstract = {We have fabricated nanometer-scale gold dipole antennas designed to be resonant at optical frequencies. On resonance, strong field enhancement in the antenna feed gap leads to white-light supercontinuum generation. The antenna length at resonance is considerably shorter than one-half the wavelength of the incident light. This is in contradiction to classical antenna theory but in qualitative accordance with computer simulations that take into account the finite metallic conductivity at optical frequencies. Because optical antennas link propagating radiation and confined/enhanced optical fields, they should find applications in optical characterization, manipulation of nanostructures, and optical information processing. Split strips of gold, each with a width of about half the wavelength of light, can act as optical antennas, capturing incident light in the gold arms and focusing the energy into the small gap. Split strips of gold, each with a width of about half the wavelength of light, can act as optical antennas, capturing incident light in the gold arms and focusing the energy into the small gap.}, author = {Muehlschlegel, Peter and Eisler, Hans-Jürgen and Martin, Olivier J. F. and Hecht, Bert and Pohl, Dieter W.}, journal = {Science}, keywords = {gold}, month = {06}, number = 5728, pages = {1607-1609}, title = {Resonant Optical Antennas}, volume = 308, year = 2005 }

%0 Journal Article %1 muehlschlegel2005resonant %A Muehlschlegel, Peter %A Eisler, Hans-Jürgen %A Martin, Olivier J. F. %A Hecht, Bert %A Pohl, Dieter W. %D 2005 %J Science %N 5728 %P 1607-1609 %R 10.1126/science.1111886 %T Resonant Optical Antennas %V 308 %X We have fabricated nanometer-scale gold dipole antennas designed to be resonant at optical frequencies. On resonance, strong field enhancement in the antenna feed gap leads to white-light supercontinuum generation. The antenna length at resonance is considerably shorter than one-half the wavelength of the incident light. This is in contradiction to classical antenna theory but in qualitative accordance with computer simulations that take into account the finite metallic conductivity at optical frequencies. Because optical antennas link propagating radiation and confined/enhanced optical fields, they should find applications in optical characterization, manipulation of nanostructures, and optical information processing. Split strips of gold, each with a width of about half the wavelength of light, can act as optical antennas, capturing incident light in the gold arms and focusing the energy into the small gap. Split strips of gold, each with a width of about half the wavelength of light, can act as optical antennas, capturing incident light in the gold arms and focusing the energy into the small gap.

Nano-optics with single quantum systems. Richards, David; Zayats, Anatoly; Hecht, Bert. In Phil. Trans. R. Soc. Lond. A, 362(1817), pp. 881–899. 2004.
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This paper reviews the recent progress in using single quantum systems, here mainly single fluorescent molecules, as local probes for nano–optical field distributions. We start by discussing the role of the absorption cross–section for the spatial resolution attainable in such experiments and its behaviour for different environmental conditions. It is shown that the spatial distribution of field components in a high–numerical aperture laser focus can be mapped with high precision using single fluorescent molecules embedded in a thin polymer film on glass. With this proof–of–principle experiment as a starting point, the possibility of mapping strongly confined and enhanced nano–optical fields close to material structures, e.g. sharp metal tips, is discussed. The mapping of the spatial distribution of the enhanced field at an etched gold tip using a single molecule is presented as an example. Energy transfer effects and quenching are identified as possible artefacts in this context. Finally, it is demonstrated that the local quenching at a sharp metal structure nevertheless can be exploited as a novel contrast mechanism for ultrahigh–resolution optical microscopy with single–molecule sensitivity.

@article{richards2004nanooptics, abstract = {This paper reviews the recent progress in using single quantum systems, here mainly single fluorescent molecules, as local probes for nano–optical field distributions. We start by discussing the role of the absorption cross–section for the spatial resolution attainable in such experiments and its behaviour for different environmental conditions. It is shown that the spatial distribution of field components in a high–numerical aperture laser focus can be mapped with high precision using single fluorescent molecules embedded in a thin polymer film on glass. With this proof–of–principle experiment as a starting point, the possibility of mapping strongly confined and enhanced nano–optical fields close to material structures, e.g. sharp metal tips, is discussed. The mapping of the spatial distribution of the enhanced field at an etched gold tip using a single molecule is presented as an example. Energy transfer effects and quenching are identified as possible artefacts in this context. Finally, it is demonstrated that the local quenching at a sharp metal structure nevertheless can be exploited as a novel contrast mechanism for ultrahigh–resolution optical microscopy with single–molecule sensitivity.}, author = {Richards, David and Zayats, Anatoly and Hecht, Bert}, journal = {Phil. Trans. R. Soc. Lond. A}, keywords = {theory}, month = {04}, number = 1817, pages = {881-899}, title = {Nano-optics with single quantum systems}, volume = 362, year = 2004 }

%0 Journal Article %1 richards2004nanooptics %A Richards, David %A Zayats, Anatoly %A Hecht, Bert %D 2004 %J Phil. Trans. R. Soc. Lond. A %N 1817 %P 881-899 %R 10.1098/rsta.2003.1352 %T Nano-optics with single quantum systems %V 362 %X This paper reviews the recent progress in using single quantum systems, here mainly single fluorescent molecules, as local probes for nano–optical field distributions. We start by discussing the role of the absorption cross–section for the spatial resolution attainable in such experiments and its behaviour for different environmental conditions. It is shown that the spatial distribution of field components in a high–numerical aperture laser focus can be mapped with high precision using single fluorescent molecules embedded in a thin polymer film on glass. With this proof–of–principle experiment as a starting point, the possibility of mapping strongly confined and enhanced nano–optical fields close to material structures, e.g. sharp metal tips, is discussed. The mapping of the spatial distribution of the enhanced field at an etched gold tip using a single molecule is presented as an example. Energy transfer effects and quenching are identified as possible artefacts in this context. Finally, it is demonstrated that the local quenching at a sharp metal structure nevertheless can be exploited as a novel contrast mechanism for ultrahigh–resolution optical microscopy with single–molecule sensitivity.
Single dye molecules in an oxygen-depleted environment as photostable organic triggered single-photon sources. Lill, Yoriko; Hecht, Bert. In Appl. Phys. Lett., 84(10), pp. 1665–1667. 2004.
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We demonstrate, that under nitrogen atmosphere, 20\% of single DiIC18(3) (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) molecules in poly(methylmethacrylate) show an extremely low photobleaching quantum yield of (4.66±0.07)×10−8 together with a reasonably short triplet lifetime. We exploit these properties to demonstrate that the system can be used to produce a triggered single-photon source based exclusively on organic materials.

@article{lill2004single, abstract = {We demonstrate, that under nitrogen atmosphere, 20\% of single DiIC18(3) (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) molecules in poly(methylmethacrylate) show an extremely low photobleaching quantum yield of (4.66±0.07)×10−8 together with a reasonably short triplet lifetime. We exploit these properties to demonstrate that the system can be used to produce a triggered single-photon source based exclusively on organic materials.}, author = {Lill, Yoriko and Hecht, Bert}, journal = {Appl. Phys. Lett.}, keywords = {single-molecules}, month = {03}, number = 10, pages = {1665-1667}, title = {Single dye molecules in an oxygen-depleted environment as photostable organic triggered single-photon sources}, volume = 84, year = 2004 }

%0 Journal Article %1 lill2004single %A Lill, Yoriko %A Hecht, Bert %D 2004 %J Appl. Phys. Lett. %N 10 %P 1665-1667 %R 10.1063/1.1667591 %T Single dye molecules in an oxygen-depleted environment as photostable organic triggered single-photon sources %V 84 %X We demonstrate, that under nitrogen atmosphere, 20\% of single DiIC18(3) (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate) molecules in poly(methylmethacrylate) show an extremely low photobleaching quantum yield of (4.66±0.07)×10−8 together with a reasonably short triplet lifetime. We exploit these properties to demonstrate that the system can be used to produce a triggered single-photon source based exclusively on organic materials.

Synthesis and Conformational Switching of Partially and Differentially Bridged Resorcin[4]arenes Bearing Fluorescent Dye Labels. Azov, Vladimir A.; Diederich, François; Lill, Yoriko; Hecht, Bert. In Helv. Chim. Acta, 86(6), pp. 2149–2155. 2003.
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We report the synthesis of modified Cram-type cavitands bearing one or two fluorescent labels for single-molecule spectroscopic studies of vase-kite conformational switching. Syntheses were performed by stepwise bridging of the four couples of neighboring H-bonded OH groups of resorcin[4]arene bowls. The new substitution patterns enable the construction of a large variety of future functional architectures. H-NMR Investigations showed that the new partially and differentially bridged cavitands feature temperature- and pH-triggered vase-kite conformational isomerism similar to symmetrical cavitands with four identical quinoxaline bridges. It was discovered that vase-kite switching of cavitands is strongly solvent-dependent.

@article{azov2003synthesis, abstract = {We report the synthesis of modified Cram-type cavitands bearing one or two fluorescent labels for single-molecule spectroscopic studies of vase-kite conformational switching. Syntheses were performed by stepwise bridging of the four couples of neighboring H-bonded OH groups of resorcin[4]arene bowls. The new substitution patterns enable the construction of a large variety of future functional architectures. H-NMR Investigations showed that the new partially and differentially bridged cavitands feature temperature- and pH-triggered vase-kite conformational isomerism similar to symmetrical cavitands with four identical quinoxaline bridges. It was discovered that vase-kite switching of cavitands is strongly solvent-dependent.}, author = {Azov, Vladimir A. and Diederich, François and Lill, Yoriko and Hecht, Bert}, journal = {Helv. Chim. Acta}, keywords = {single-molecules}, month = {07}, number = 6, pages = {2149-2155}, title = {Synthesis and Conformational Switching of Partially and Differentially Bridged Resorcin[4]arenes Bearing Fluorescent Dye Labels}, volume = 86, year = 2003 }

%0 Journal Article %1 azov2003synthesis %A Azov, Vladimir A. %A Diederich, François %A Lill, Yoriko %A Hecht, Bert %D 2003 %J Helv. Chim. Acta %N 6 %P 2149-2155 %R 10.1002/hlca.200390172 %T Synthesis and Conformational Switching of Partially and Differentially Bridged Resorcin[4]arenes Bearing Fluorescent Dye Labels %V 86 %X We report the synthesis of modified Cram-type cavitands bearing one or two fluorescent labels for single-molecule spectroscopic studies of vase-kite conformational switching. Syntheses were performed by stepwise bridging of the four couples of neighboring H-bonded OH groups of resorcin[4]arene bowls. The new substitution patterns enable the construction of a large variety of future functional architectures. H-NMR Investigations showed that the new partially and differentially bridged cavitands feature temperature- and pH-triggered vase-kite conformational isomerism similar to symmetrical cavitands with four identical quinoxaline bridges. It was discovered that vase-kite switching of cavitands is strongly solvent-dependent.
Three-dimensional optical polarization tomography of single molecules. Prummer, Michael; Sick, Beate; Hecht, Bert; Wild, Urs P. In J. Chem. Phys., 118(21), pp. 9824–9829. 2003.
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We apply the concept of tomography to polarization-sensitive optical microscopy of single fluorophores to determine the three-dimensional orientation of molecular absorption dipoles with isotropic sensitivity. Wide-field microscopy provides the opportunity to monitor simultaneously three-dimensional rotation and two-dimensional translation of many molecules in parallel. For orientation determination the molecules are illuminated from different directions of incidence with linearly polarized light. In each exposure the excitation along a particular projection of the absorption dipole on the electric field leads to a distinct fluorescence intensity. Five exposures are sufficient to determine the full orientation of the fluorophores. To demonstrate the potential of the method we determine the orientation and position of individual immobilized lipid membrane markers. The shot-noise-limited isotropic angular resolution is 2°. For time-resolved studies the bandwidth can be expanded up to 200 Hz.

@article{prummer2003threedimensional, abstract = {We apply the concept of tomography to polarization-sensitive optical microscopy of single fluorophores to determine the three-dimensional orientation of molecular absorption dipoles with isotropic sensitivity. Wide-field microscopy provides the opportunity to monitor simultaneously three-dimensional rotation and two-dimensional translation of many molecules in parallel. For orientation determination the molecules are illuminated from different directions of incidence with linearly polarized light. In each exposure the excitation along a particular projection of the absorption dipole on the electric field leads to a distinct fluorescence intensity. Five exposures are sufficient to determine the full orientation of the fluorophores. To demonstrate the potential of the method we determine the orientation and position of individual immobilized lipid membrane markers. The shot-noise-limited isotropic angular resolution is 2°. For time-resolved studies the bandwidth can be expanded up to 200 Hz.}, author = {Prummer, Michael and Sick, Beate and Hecht, Bert and Wild, Urs P.}, journal = {J. Chem. Phys.}, keywords = {single-molecules}, month = {05}, number = 21, pages = {9824-9829}, title = {Three-dimensional optical polarization tomography of single molecules}, volume = 118, year = 2003 }

%0 Journal Article %1 prummer2003threedimensional %A Prummer, Michael %A Sick, Beate %A Hecht, Bert %A Wild, Urs P. %D 2003 %J J. Chem. Phys. %N 21 %P 9824-9829 %R 10.1063/1.1569848 %T Three-dimensional optical polarization tomography of single molecules %V 118 %X We apply the concept of tomography to polarization-sensitive optical microscopy of single fluorophores to determine the three-dimensional orientation of molecular absorption dipoles with isotropic sensitivity. Wide-field microscopy provides the opportunity to monitor simultaneously three-dimensional rotation and two-dimensional translation of many molecules in parallel. For orientation determination the molecules are illuminated from different directions of incidence with linearly polarized light. In each exposure the excitation along a particular projection of the absorption dipole on the electric field leads to a distinct fluorescence intensity. Five exposures are sufficient to determine the full orientation of the fluorophores. To demonstrate the potential of the method we determine the orientation and position of individual immobilized lipid membrane markers. The shot-noise-limited isotropic angular resolution is 2°. For time-resolved studies the bandwidth can be expanded up to 200 Hz.
Single-molecule near-field optical energy transfer microscopy with dielectric tips. Trabesinger, Werner; Kramer, Andrei; Kreiter, Maximilian; Hecht, Bert; Wild, Urs P. In J. Microscopy, 209(3), pp. 249–253. 2003.
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The fluorescence lifetime and the fluorescence rate of single molecules are recorded as a function of the position of a Si3N4 atomic force microscopy tip with respect to the molecule. We observe a decrease of the excited state lifetime and the fluorescence rate when the tip apex is in close proximity to the molecule. These effects are attributed to the fact that the dielectric tip converts non-propagating near-fields to propagating fields within the dielectric tip effectively quenching the fluorescence. The spatial extension of the quenching area is of subwavelength dimensions. The results are discussed in terms of molecular fluorescence in a system of stratified media. The experiment provides surprising new insights into the interactions between a fluorescent molecule and a dielectric tip. The methodology holds promise for applications in ultra high-resolution near-field optical imaging at the level of single fluorophores.

@article{trabesinger2003singlemolecule, abstract = {The fluorescence lifetime and the fluorescence rate of single molecules are recorded as a function of the position of a Si3N4 atomic force microscopy tip with respect to the molecule. We observe a decrease of the excited state lifetime and the fluorescence rate when the tip apex is in close proximity to the molecule. These effects are attributed to the fact that the dielectric tip converts non-propagating near-fields to propagating fields within the dielectric tip effectively quenching the fluorescence. The spatial extension of the quenching area is of subwavelength dimensions. The results are discussed in terms of molecular fluorescence in a system of stratified media. The experiment provides surprising new insights into the interactions between a fluorescent molecule and a dielectric tip. The methodology holds promise for applications in ultra high-resolution near-field optical imaging at the level of single fluorophores.}, author = {Trabesinger, Werner and Kramer, Andrei and Kreiter, Maximilian and Hecht, Bert and Wild, Urs P.}, journal = {J. Microscopy}, keywords = {single-molecules}, month = {03}, number = 3, pages = {249-253}, title = {Single-molecule near-field optical energy transfer microscopy with dielectric tips}, volume = 209, year = 2003 }

%0 Journal Article %1 trabesinger2003singlemolecule %A Trabesinger, Werner %A Kramer, Andrei %A Kreiter, Maximilian %A Hecht, Bert %A Wild, Urs P. %D 2003 %J J. Microscopy %N 3 %P 249-253 %R 10.1046/j.1365-2818.2003.01124.x %T Single-molecule near-field optical energy transfer microscopy with dielectric tips %V 209 %X The fluorescence lifetime and the fluorescence rate of single molecules are recorded as a function of the position of a Si3N4 atomic force microscopy tip with respect to the molecule. We observe a decrease of the excited state lifetime and the fluorescence rate when the tip apex is in close proximity to the molecule. These effects are attributed to the fact that the dielectric tip converts non-propagating near-fields to propagating fields within the dielectric tip effectively quenching the fluorescence. The spatial extension of the quenching area is of subwavelength dimensions. The results are discussed in terms of molecular fluorescence in a system of stratified media. The experiment provides surprising new insights into the interactions between a fluorescent molecule and a dielectric tip. The methodology holds promise for applications in ultra high-resolution near-field optical imaging at the level of single fluorophores.
Fabricating Arrays of Single Protein Molecules on Glass Using Microcontact Printing. Renault, J.-P.; Bernard, A.; Bietsch, A.; Michel, B.; Bosshard, H. R.; Delamarche, E.; Kreiter, Maximilian; Hecht, Bert; Wild, Urs P. In J. Phys. Chem. B., 107(3), pp. 703–711. 2003.
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Microcontact printing biomolecules from elastomeric micropatterned stamps onto surfaces is a versatile method to prepare surfaces for diagnostic applications. We show how to create patterns of proteins having a lengthscale lower than 100 nm using high-resolution microcontact printing. The elastomeric stamps used have meshes composed of 100- and 40-nm-wide lines, arrays of 100 × 400 nm2 features, and arrays of 100-nm-wide posts. The spherical geometry of the posts on the stamps contributes to reduce the printed areas below the effective size of the molded features. Proteins adsorb onto the hydrophobic surface of the stamp during the inking step, and by varying the concentration of the protein solutions, it is possible to adsorb a single or a few protein molecules, such as antibodies (fluorescently labeled) or green fluorescence proteins, on each of the elements forming the high-resolution pattern of the stamp. The transfer of the proteins from the stamp to a hydrophilic glass surface occurs during the printing step. Characterization of the printed patterns using atomic force microscopy and fluorescence confocal microscopy reveals sites unoccupied or occupied by one or more protein molecules that are located within 50 nm of the expected printed locations. The placement of a small number of protein molecules on a surface at precise locations is the key to localizing and identifying single proteins and might constitute a method of choice to study single protein molecules on surfaces.

@article{renault2003fabricating, abstract = {Microcontact printing biomolecules from elastomeric micropatterned stamps onto surfaces is a versatile method to prepare surfaces for diagnostic applications. We show how to create patterns of proteins having a lengthscale lower than 100 nm using high-resolution microcontact printing. The elastomeric stamps used have meshes composed of 100- and 40-nm-wide lines, arrays of 100 × 400 nm2 features, and arrays of 100-nm-wide posts. The spherical geometry of the posts on the stamps contributes to reduce the printed areas below the effective size of the molded features. Proteins adsorb onto the hydrophobic surface of the stamp during the inking step, and by varying the concentration of the protein solutions, it is possible to adsorb a single or a few protein molecules, such as antibodies (fluorescently labeled) or green fluorescence proteins, on each of the elements forming the high-resolution pattern of the stamp. The transfer of the proteins from the stamp to a hydrophilic glass surface occurs during the printing step. Characterization of the printed patterns using atomic force microscopy and fluorescence confocal microscopy reveals sites unoccupied or occupied by one or more protein molecules that are located within 50 nm of the expected printed locations. The placement of a small number of protein molecules on a surface at precise locations is the key to localizing and identifying single proteins and might constitute a method of choice to study single protein molecules on surfaces.}, author = {Renault, J.-P. and Bernard, A. and Bietsch, A. and Michel, B. and Bosshard, H. R. and Delamarche, E. and Kreiter, Maximilian and Hecht, Bert and Wild, Urs P.}, journal = {J. Phys. Chem. B.}, keywords = {single-molecules}, month = {01}, number = 3, pages = {703-711}, title = {Fabricating Arrays of Single Protein Molecules on Glass Using Microcontact Printing}, volume = 107, year = 2003 }

%0 Journal Article %1 renault2003fabricating %A Renault, J.-P. %A Bernard, A. %A Bietsch, A. %A Michel, B. %A Bosshard, H. R. %A Delamarche, E. %A Kreiter, Maximilian %A Hecht, Bert %A Wild, Urs P. %D 2003 %J J. Phys. Chem. B. %N 3 %P 703-711 %R 10.1021/jp0263424 %T Fabricating Arrays of Single Protein Molecules on Glass Using Microcontact Printing %V 107 %X Microcontact printing biomolecules from elastomeric micropatterned stamps onto surfaces is a versatile method to prepare surfaces for diagnostic applications. We show how to create patterns of proteins having a lengthscale lower than 100 nm using high-resolution microcontact printing. The elastomeric stamps used have meshes composed of 100- and 40-nm-wide lines, arrays of 100 × 400 nm2 features, and arrays of 100-nm-wide posts. The spherical geometry of the posts on the stamps contributes to reduce the printed areas below the effective size of the molded features. Proteins adsorb onto the hydrophobic surface of the stamp during the inking step, and by varying the concentration of the protein solutions, it is possible to adsorb a single or a few protein molecules, such as antibodies (fluorescently labeled) or green fluorescence proteins, on each of the elements forming the high-resolution pattern of the stamp. The transfer of the proteins from the stamp to a hydrophilic glass surface occurs during the printing step. Characterization of the printed patterns using atomic force microscopy and fluorescence confocal microscopy reveals sites unoccupied or occupied by one or more protein molecules that are located within 50 nm of the expected printed locations. The placement of a small number of protein molecules on a surface at precise locations is the key to localizing and identifying single proteins and might constitute a method of choice to study single protein molecules on surfaces.

Orientation dependence of fluorescence lifetimes near an interface. Kreiter, Maximilian; Prummer, Michael; Hecht, Bert; Wild, Urs P. In J. Chem. Phys., 117(20), pp. 9430–9433. 2002.
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The fluorescence lifetime of single DiI-dye molecules in a 20 nm polymer film on glass is measured as a function of the orientation of the absorption dipole moment. A strong dependence of the lifetime on the orientation of the dye molecules relative to the polymer/air interface is found. Molecules with a dipole moment perpendicular to the interface exhibit a lifetime which is by a factor of 2.1±0.1 longer than the lifetime of molecules with parallel dipole moments. The general trend of the results is in good agreement with theoretical predictions. However there are significant deviations which are attributed to varying molecular environments.

@article{kreiter2002orientation, abstract = {The fluorescence lifetime of single DiI-dye molecules in a 20 nm polymer film on glass is measured as a function of the orientation of the absorption dipole moment. A strong dependence of the lifetime on the orientation of the dye molecules relative to the polymer/air interface is found. Molecules with a dipole moment perpendicular to the interface exhibit a lifetime which is by a factor of 2.1±0.1 longer than the lifetime of molecules with parallel dipole moments. The general trend of the results is in good agreement with theoretical predictions. However there are significant deviations which are attributed to varying molecular environments.}, author = {Kreiter, Maximilian and Prummer, Michael and Hecht, Bert and Wild, Urs P.}, journal = {J. Chem. Phys.}, keywords = {single-molecules}, month = 11, number = 20, pages = {9430-9433}, title = {Orientation dependence of fluorescence lifetimes near an interface}, volume = 117, year = 2002 }

%0 Journal Article %1 kreiter2002orientation %A Kreiter, Maximilian %A Prummer, Michael %A Hecht, Bert %A Wild, Urs P. %D 2002 %J J. Chem. Phys. %N 20 %P 9430-9433 %R 10.1063/1.1515732 %T Orientation dependence of fluorescence lifetimes near an interface %V 117 %X The fluorescence lifetime of single DiI-dye molecules in a 20 nm polymer film on glass is measured as a function of the orientation of the absorption dipole moment. A strong dependence of the lifetime on the orientation of the dye molecules relative to the polymer/air interface is found. Molecules with a dipole moment perpendicular to the interface exhibit a lifetime which is by a factor of 2.1±0.1 longer than the lifetime of molecules with parallel dipole moments. The general trend of the results is in good agreement with theoretical predictions. However there are significant deviations which are attributed to varying molecular environments.
Single-molecule near-field optical energy transfer microscopy. Trabesinger, W.; Kramer, Andrei; Kreiter, Maximilian; Hecht, Bert; Wild, Urs P. In Appl. Phys. Lett., 81(11), pp. 2118–2120. 2002.
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The nano-optical interaction between a sharp tip and a single dipolar emitter is investigated. Changes of the excited state lifetime and the fluorescence rate of single molecules are recorded simultaneously as a function of the tip position relative to the molecule. A subdiffraction-limited area of decreased fluorescence and shortened lifetime is observed for gold-coated Si3N4 tips. The results are discussed in terms of molecular fluorescence in a system of stratified media. The outlined methodology holds promise for applications in ultrahigh-resolution near-field optical imaging at the level of single fluorophores.

@article{trabesinger2002singlemolecule, abstract = {The nano-optical interaction between a sharp tip and a single dipolar emitter is investigated. Changes of the excited state lifetime and the fluorescence rate of single molecules are recorded simultaneously as a function of the tip position relative to the molecule. A subdiffraction-limited area of decreased fluorescence and shortened lifetime is observed for gold-coated Si3N4 tips. The results are discussed in terms of molecular fluorescence in a system of stratified media. The outlined methodology holds promise for applications in ultrahigh-resolution near-field optical imaging at the level of single fluorophores.}, author = {Trabesinger, W. and Kramer, Andrei and Kreiter, Maximilian and Hecht, Bert and Wild, Urs P.}, journal = {Appl. Phys. Lett.}, keywords = {single-molecules}, month = {09}, number = 11, pages = {2118-2120}, title = {Single-molecule near-field optical energy transfer microscopy}, volume = 81, year = 2002 }

%0 Journal Article %1 trabesinger2002singlemolecule %A Trabesinger, W. %A Kramer, Andrei %A Kreiter, Maximilian %A Hecht, Bert %A Wild, Urs P. %D 2002 %J Appl. Phys. Lett. %N 11 %P 2118-2120 %R 10.1063/1.1506952 %T Single-molecule near-field optical energy transfer microscopy %V 81 %X The nano-optical interaction between a sharp tip and a single dipolar emitter is investigated. Changes of the excited state lifetime and the fluorescence rate of single molecules are recorded simultaneously as a function of the tip position relative to the molecule. A subdiffraction-limited area of decreased fluorescence and shortened lifetime is observed for gold-coated Si3N4 tips. The results are discussed in terms of molecular fluorescence in a system of stratified media. The outlined methodology holds promise for applications in ultrahigh-resolution near-field optical imaging at the level of single fluorophores.
A cryogenic scanning near-field optical microscope with shear-force gapwidth control. Kramer, Andrei; Segura, Jean-Manuel; Hunkeler, A.; Renn, Alois; Hecht, Bert. In Rev. Sci. Instrum., 73(8), pp. 2937–2941. 2002.
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We present a scanning near-field optical microscope designed for nanoscale optical imaging and spectroscopy as well as simultaneous tuning fork shear-force topographic imaging at cryogenic temperatures. The whole setup is immersed in superfluid helium (T=1.8 K). In this medium we observe resonance frequency fluctuations of the tuning fork sensor with an amplitude of Δν≈5\%–10\% of the full width at half-maximum of the resonance. Possible reasons for the occurrence of the frequency fluctuations are discussed. A stable gapwidth feedback can still be achieved if the set value of the frequency shift is chosen slightly larger than the fluctuation amplitude. As an example we demonstrate shear-force topographic imaging of a silicon grating in superfluid helium.

@article{kramer2002cryogenic, abstract = {We present a scanning near-field optical microscope designed for nanoscale optical imaging and spectroscopy as well as simultaneous tuning fork shear-force topographic imaging at cryogenic temperatures. The whole setup is immersed in superfluid helium (T=1.8 K). In this medium we observe resonance frequency fluctuations of the tuning fork sensor with an amplitude of Δν≈5\%–10\% of the full width at half-maximum of the resonance. Possible reasons for the occurrence of the frequency fluctuations are discussed. A stable gapwidth feedback can still be achieved if the set value of the frequency shift is chosen slightly larger than the fluctuation amplitude. As an example we demonstrate shear-force topographic imaging of a silicon grating in superfluid helium.}, author = {Kramer, Andrei and Segura, Jean-Manuel and Hunkeler, A. and Renn, Alois and Hecht, Bert}, journal = {Rev. Sci. Instrum.}, keywords = {SNOM}, month = {07}, number = 8, pages = {2937-2941}, title = {A cryogenic scanning near-field optical microscope with shear-force gapwidth control}, volume = 73, year = 2002 }

%0 Journal Article %1 kramer2002cryogenic %A Kramer, Andrei %A Segura, Jean-Manuel %A Hunkeler, A. %A Renn, Alois %A Hecht, Bert %D 2002 %J Rev. Sci. Instrum. %N 8 %P 2937-2941 %R 10.1063/1.1491028 %T A cryogenic scanning near-field optical microscope with shear-force gapwidth control %V 73 %X We present a scanning near-field optical microscope designed for nanoscale optical imaging and spectroscopy as well as simultaneous tuning fork shear-force topographic imaging at cryogenic temperatures. The whole setup is immersed in superfluid helium (T=1.8 K). In this medium we observe resonance frequency fluctuations of the tuning fork sensor with an amplitude of Δν≈5\%–10\% of the full width at half-maximum of the resonance. Possible reasons for the occurrence of the frequency fluctuations are discussed. A stable gapwidth feedback can still be achieved if the set value of the frequency shift is chosen slightly larger than the fluctuation amplitude. As an example we demonstrate shear-force topographic imaging of a silicon grating in superfluid helium.
Continuous real-time measurement of fluorescence lifetimes. Trabesinger, Werner; Hübner, Christian G.; Hecht, Bert; Wild, Urs P. In Rev. Sci. Instrum., 73(8), pp. 3122–3124. 2002.
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We report on the continuous measurement of fluorescence lifetimes at low light levels. Fluorescence photons following pulsed excitation generate a pulse sequence with exponentially distributed amplitudes and interphoton times at the output of a time-to-amplitude converter. This sequence is turned into a continuous step function and is time averaged with an adjustable bandwidth. For a single-exponential decay, our approach yields identical results as would be obtained from fitting fluorescence decays, while being a real-time technique. The proposed technique performs especially well at low count rates. We demonstrate the applicability of the method at the example of confocal fluorescence lifetime imaging of single molecules.

@article{trabesinger2002continuous, abstract = {We report on the continuous measurement of fluorescence lifetimes at low light levels. Fluorescence photons following pulsed excitation generate a pulse sequence with exponentially distributed amplitudes and interphoton times at the output of a time-to-amplitude converter. This sequence is turned into a continuous step function and is time averaged with an adjustable bandwidth. For a single-exponential decay, our approach yields identical results as would be obtained from fitting fluorescence decays, while being a real-time technique. The proposed technique performs especially well at low count rates. We demonstrate the applicability of the method at the example of confocal fluorescence lifetime imaging of single molecules.}, author = {Trabesinger, Werner and Hübner, Christian G. and Hecht, Bert and Wild, Urs P.}, journal = {Rev. Sci. Instrum.}, keywords = {single-molecules}, month = {07}, number = 8, pages = {3122-3124}, title = {Continuous real-time measurement of fluorescence lifetimes}, volume = 73, year = 2002 }

%0 Journal Article %1 trabesinger2002continuous %A Trabesinger, Werner %A Hübner, Christian G. %A Hecht, Bert %A Wild, Urs P. %D 2002 %J Rev. Sci. Instrum. %N 8 %P 3122-3124 %R 10.1063/1.1488676 %T Continuous real-time measurement of fluorescence lifetimes %V 73 %X We report on the continuous measurement of fluorescence lifetimes at low light levels. Fluorescence photons following pulsed excitation generate a pulse sequence with exponentially distributed amplitudes and interphoton times at the output of a time-to-amplitude converter. This sequence is turned into a continuous step function and is time averaged with an adjustable bandwidth. For a single-exponential decay, our approach yields identical results as would be obtained from fitting fluorescence decays, while being a real-time technique. The proposed technique performs especially well at low count rates. We demonstrate the applicability of the method at the example of confocal fluorescence lifetime imaging of single molecules.
Optical near-field enhancement at a metal tip probed by a single fluorophore. Kramer, Andrei; Trabesinger, Werner; Hecht, Bert; Wild, Urs P. In Appl. Phys. Lett., 80(9), pp. 1652–1654. 2002.
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The optical near-field in the vicinity of a metal tip is mapped using a single-molecule optical probe. We observe an enhancement of the fluorescence signal by a factor of 5.7±0.3, clearly larger than the fourfold enhancement that can arise from constructive interference if the tip acts as a simple mirror. Considering the tip apex as a nanoparticle of nonregular shape, we suggest that, in the case of gold tips, the enhancement is due to resonant plasmon excitation. Consistently, no enhancement has been observed using Pt/Ir tips.

@article{kramer2002optical, abstract = {The optical near-field in the vicinity of a metal tip is mapped using a single-molecule optical probe. We observe an enhancement of the fluorescence signal by a factor of 5.7±0.3, clearly larger than the fourfold enhancement that can arise from constructive interference if the tip acts as a simple mirror. Considering the tip apex as a nanoparticle of nonregular shape, we suggest that, in the case of gold tips, the enhancement is due to resonant plasmon excitation. Consistently, no enhancement has been observed using Pt/Ir tips.}, author = {Kramer, Andrei and Trabesinger, Werner and Hecht, Bert and Wild, Urs P.}, journal = {Appl. Phys. Lett.}, keywords = {single-molecules}, month = {02}, number = 9, pages = {1652-1654}, title = {Optical near-field enhancement at a metal tip probed by a single fluorophore}, volume = 80, year = 2002 }

%0 Journal Article %1 kramer2002optical %A Kramer, Andrei %A Trabesinger, Werner %A Hecht, Bert %A Wild, Urs P. %D 2002 %J Appl. Phys. Lett. %N 9 %P 1652-1654 %R 10.1063/1.1453479 %T Optical near-field enhancement at a metal tip probed by a single fluorophore %V 80 %X The optical near-field in the vicinity of a metal tip is mapped using a single-molecule optical probe. We observe an enhancement of the fluorescence signal by a factor of 5.7±0.3, clearly larger than the fourfold enhancement that can arise from constructive interference if the tip acts as a simple mirror. Considering the tip apex as a nanoparticle of nonregular shape, we suggest that, in the case of gold tips, the enhancement is due to resonant plasmon excitation. Consistently, no enhancement has been observed using Pt/Ir tips.

Probing confined fields with single molecules and vice versa. Sick, Beate; Hecht, Bert; Wild, Urs P.; Novotny, Lukas. In J. Microscopy, 202(2), pp. 365–373. 2001.
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Single dye molecules are used as local probes to map the spatial distribution of the squared electric field components in the focus of a high numerical aperture lens. Simulated field distributions are quantitatively verified by experimentally obtained fluorescence excitation maps. We show that annular illumination can be used to engineer the field distribution in the focus at a dielectric/air interface such that electric field components in all directions acquire comparable magnitudes. The 3D orientation of molecular absorption dipoles can be determined by comparing measured to simulated image patterns. The presence of longitudinal electric field components in a focus is of particular interest in tip-enhanced scanning near-field optical microscopy.

@article{sick2001probing, abstract = {Single dye molecules are used as local probes to map the spatial distribution of the squared electric field components in the focus of a high numerical aperture lens. Simulated field distributions are quantitatively verified by experimentally obtained fluorescence excitation maps. We show that annular illumination can be used to engineer the field distribution in the focus at a dielectric/air interface such that electric field components in all directions acquire comparable magnitudes. The 3D orientation of molecular absorption dipoles can be determined by comparing measured to simulated image patterns. The presence of longitudinal electric field components in a focus is of particular interest in tip-enhanced scanning near-field optical microscopy.}, author = {Sick, Beate and Hecht, Bert and Wild, Urs P. and Novotny, Lukas}, journal = {J. Microscopy}, keywords = {single-molecules}, month = 12, number = 2, pages = {365-373}, title = {Probing confined fields with single molecules and vice versa}, volume = 202, year = 2001 }

%0 Journal Article %1 sick2001probing %A Sick, Beate %A Hecht, Bert %A Wild, Urs P. %A Novotny, Lukas %D 2001 %J J. Microscopy %N 2 %P 365-373 %R 10.1046/j.1365-2818.2001.00795.x %T Probing confined fields with single molecules and vice versa %V 202 %X Single dye molecules are used as local probes to map the spatial distribution of the squared electric field components in the focus of a high numerical aperture lens. Simulated field distributions are quantitatively verified by experimentally obtained fluorescence excitation maps. We show that annular illumination can be used to engineer the field distribution in the focus at a dielectric/air interface such that electric field components in all directions acquire comparable magnitudes. The 3D orientation of molecular absorption dipoles can be determined by comparing measured to simulated image patterns. The presence of longitudinal electric field components in a focus is of particular interest in tip-enhanced scanning near-field optical microscopy.
Photon statistics in single-molecule fluorescence at room temperature. Fleury, Ludovic; Segura, Jean-Manuel; Zumofen, Gert; Hecht, Bert; Wild, Urs P. In J. of Luminescence, 94-95, pp. 805–809. 2001.
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The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of inter-photon time distribution, second-order correlation function, and Mandel's Q-function. Nonclassical photon statistics is observed and a reverse intersystem crossing is detected that accelerates linearly with the applied laser power. Rate equations for the time evolution of the molecular level populations are shown to be appropriate for the analysis of the observations.

@article{fleury2001photon, abstract = {The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of inter-photon time distribution, second-order correlation function, and Mandel's Q-function. Nonclassical photon statistics is observed and a reverse intersystem crossing is detected that accelerates linearly with the applied laser power. Rate equations for the time evolution of the molecular level populations are shown to be appropriate for the analysis of the observations.}, author = {Fleury, Ludovic and Segura, Jean-Manuel and Zumofen, Gert and Hecht, Bert and Wild, Urs P.}, journal = {J. of Luminescence}, keywords = {single-molecules}, month = 12, pages = {805-809}, series = {International Conference on Dynamical Processes in Excited States of Solids}, title = {Photon statistics in single-molecule fluorescence at room temperature}, volume = {94-95}, year = 2001 }

%0 Journal Article %1 fleury2001photon %A Fleury, Ludovic %A Segura, Jean-Manuel %A Zumofen, Gert %A Hecht, Bert %A Wild, Urs P. %B International Conference on Dynamical Processes in Excited States of Solids %D 2001 %J J. of Luminescence %P 805-809 %R 10.1016/S0022-2313(01)00367-2 %T Photon statistics in single-molecule fluorescence at room temperature %V 94-95 %X The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of inter-photon time distribution, second-order correlation function, and Mandel's Q-function. Nonclassical photon statistics is observed and a reverse intersystem crossing is detected that accelerates linearly with the applied laser power. Rate equations for the time evolution of the molecular level populations are shown to be appropriate for the analysis of the observations.
Molecular rearrangements observed by single-molecule microscopy. Trabesinger, Werner; Renn, Alois; Hecht, Bert; Wild, Urs P.; Montali, Andrea T.; Smith, Paul F.; Weder, Christoph. In Synthetic Metals, 124(1), pp. 113–115. 2001.
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We have applied quantitative single-molecule photoluminescence microscopy for directly observing molecular rearrangements in a polymeric material subjected to tensile deformation. The system examined is a blend of fluorescent conjugated polymer molecules embedded in polyethylene, known to exhibit strong phase separation. Statistical analysis of the sizes of phase-separated domains reveals that during tensile deformation large domains of fluorescent molecules are transformed into smaller clusters and ultimately isolated single molecules. In addition to elucidating the nature of the stretch-induced morphology change, our work underscores the fundamental value of single-molecule techniques for material analysis.

@article{trabesinger2001molecular, abstract = {We have applied quantitative single-molecule photoluminescence microscopy for directly observing molecular rearrangements in a polymeric material subjected to tensile deformation. The system examined is a blend of fluorescent conjugated polymer molecules embedded in polyethylene, known to exhibit strong phase separation. Statistical analysis of the sizes of phase-separated domains reveals that during tensile deformation large domains of fluorescent molecules are transformed into smaller clusters and ultimately isolated single molecules. In addition to elucidating the nature of the stretch-induced morphology change, our work underscores the fundamental value of single-molecule techniques for material analysis.}, author = {Trabesinger, Werner and Renn, Alois and Hecht, Bert and Wild, Urs P. and Montali, Andrea T. and Smith, Paul F. and Weder, Christoph}, journal = {Synthetic Metals}, keywords = {single-molecules}, month = 10, number = 1, pages = {113-115}, series = {Molecular photonics: from macroscopic to nanoscopic applications}, title = {Molecular rearrangements observed by single-molecule microscopy}, volume = 124, year = 2001 }

%0 Journal Article %1 trabesinger2001molecular %A Trabesinger, Werner %A Renn, Alois %A Hecht, Bert %A Wild, Urs P. %A Montali, Andrea T. %A Smith, Paul F. %A Weder, Christoph %B Molecular photonics: from macroscopic to nanoscopic applications %D 2001 %J Synthetic Metals %N 1 %P 113-115 %R 10.1016/S0379-6779(01)00442-8 %T Molecular rearrangements observed by single-molecule microscopy %V 124 %X We have applied quantitative single-molecule photoluminescence microscopy for directly observing molecular rearrangements in a polymeric material subjected to tensile deformation. The system examined is a blend of fluorescent conjugated polymer molecules embedded in polyethylene, known to exhibit strong phase separation. Statistical analysis of the sizes of phase-separated domains reveals that during tensile deformation large domains of fluorescent molecules are transformed into smaller clusters and ultimately isolated single molecules. In addition to elucidating the nature of the stretch-induced morphology change, our work underscores the fundamental value of single-molecule techniques for material analysis.
Tip-induced spectral dynamics of single molecules. Segura, Jean-Manuel; Zumofen, Gert; Renn, Alois; Hecht, Bert; Wild, Urs P. In Chem. Phys. Lett., 340(1), pp. 77–82. 2001.
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Manipulation of spectral dynamics of single molecules (SM) by a metallized scanning probe tip is demonstrated. The Stark effect of the zero-phonon lines of single pentacene molecules in a p-terphenyl host at 1.8 K is investigated by applying a voltage to the tip in contact with the sample. The measured Stark shifts exhibit a plateau and the line widths depend on the electric field. These anomalies are explained by a model based on two-level systems with field-dependent double-well potentials. The experimental data show that the two-level systems are induced by the tip.

@article{segura2001tipinduced, abstract = {Manipulation of spectral dynamics of single molecules (SM) by a metallized scanning probe tip is demonstrated. The Stark effect of the zero-phonon lines of single pentacene molecules in a p-terphenyl host at 1.8 K is investigated by applying a voltage to the tip in contact with the sample. The measured Stark shifts exhibit a plateau and the line widths depend on the electric field. These anomalies are explained by a model based on two-level systems with field-dependent double-well potentials. The experimental data show that the two-level systems are induced by the tip.}, author = {Segura, Jean-Manuel and Zumofen, Gert and Renn, Alois and Hecht, Bert and Wild, Urs P.}, journal = {Chem. Phys. Lett.}, keywords = {single-molecules}, month = {05}, number = 1, pages = {77-82}, title = {Tip-induced spectral dynamics of single molecules}, volume = 340, year = 2001 }

%0 Journal Article %1 segura2001tipinduced %A Segura, Jean-Manuel %A Zumofen, Gert %A Renn, Alois %A Hecht, Bert %A Wild, Urs P. %D 2001 %J Chem. Phys. Lett. %N 1 %P 77-82 %R 10.1016/S0009-2614(01)00384-0 %T Tip-induced spectral dynamics of single molecules %V 340 %X Manipulation of spectral dynamics of single molecules (SM) by a metallized scanning probe tip is demonstrated. The Stark effect of the zero-phonon lines of single pentacene molecules in a p-terphenyl host at 1.8 K is investigated by applying a voltage to the tip in contact with the sample. The measured Stark shifts exhibit a plateau and the line widths depend on the electric field. These anomalies are explained by a model based on two-level systems with field-dependent double-well potentials. The experimental data show that the two-level systems are induced by the tip.
Statistical Analysis of Single-Molecule Colocalization Assays. Trabesinger, Werner; Hecht, Bert; Wild, Urs P.; Schütz, Gerhard J.; Schindler, H.; Schmidt, Th. In Anal. Chem., 73(6), pp. 1100–1105. 2001.
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In chemical assays, specific molecular recognition events result in close physical proximity of two molecular species, e.g., ligands and receptors. Microscopy techniques that are able to image individual molecules allow for achieving a positional accuracy far beyond the resolution limit. Therefore, independent position determination, e.g., by dual-color microscopy, becomes possible, permitting determination of intermolecular distances beyond the resolution limit. Nonzero measured distances occur due to experimental inaccuracies in case of a recognition event or due to accidental close proximity between ligand−receptor pairs. Using general statistical considerations, finite measured distances between single ligand−receptor pairs are directly translated into probabilities for true molecular recognition or mere accidental proximity. This enables a quantitative statistical analysis of single recognition events. It is demonstrated that in a general assay, even in the presence of strong unspecific background, the probability for a certain diagnosis and a measure for its reliability can be extracted from the observation of a few binding events. The power of the method is demonstrated at the example of a single-molecule DNA hybridization assay. Our findings are of major importance for future assay miniaturization and assaying with minute amounts of analyte.

@article{trabesinger2001statistical, abstract = {In chemical assays, specific molecular recognition events result in close physical proximity of two molecular species, e.g., ligands and receptors. Microscopy techniques that are able to image individual molecules allow for achieving a positional accuracy far beyond the resolution limit. Therefore, independent position determination, e.g., by dual-color microscopy, becomes possible, permitting determination of intermolecular distances beyond the resolution limit. Nonzero measured distances occur due to experimental inaccuracies in case of a recognition event or due to accidental close proximity between ligand−receptor pairs. Using general statistical considerations, finite measured distances between single ligand−receptor pairs are directly translated into probabilities for true molecular recognition or mere accidental proximity. This enables a quantitative statistical analysis of single recognition events. It is demonstrated that in a general assay, even in the presence of strong unspecific background, the probability for a certain diagnosis and a measure for its reliability can be extracted from the observation of a few binding events. The power of the method is demonstrated at the example of a single-molecule DNA hybridization assay. Our findings are of major importance for future assay miniaturization and assaying with minute amounts of analyte.}, author = {Trabesinger, Werner and Hecht, Bert and Wild, Urs P. and Schütz, Gerhard J. and Schindler, H. and Schmidt, Th.}, journal = {Anal. Chem.}, keywords = {theory}, month = {03}, number = 6, pages = {1100-1105}, title = {Statistical Analysis of Single-Molecule Colocalization Assays}, volume = 73, year = 2001 }

%0 Journal Article %1 trabesinger2001statistical %A Trabesinger, Werner %A Hecht, Bert %A Wild, Urs P. %A Schütz, Gerhard J. %A Schindler, H. %A Schmidt, Th. %D 2001 %J Anal. Chem. %N 6 %P 1100-1105 %R 10.1021/ac000810t %T Statistical Analysis of Single-Molecule Colocalization Assays %V 73 %X In chemical assays, specific molecular recognition events result in close physical proximity of two molecular species, e.g., ligands and receptors. Microscopy techniques that are able to image individual molecules allow for achieving a positional accuracy far beyond the resolution limit. Therefore, independent position determination, e.g., by dual-color microscopy, becomes possible, permitting determination of intermolecular distances beyond the resolution limit. Nonzero measured distances occur due to experimental inaccuracies in case of a recognition event or due to accidental close proximity between ligand−receptor pairs. Using general statistical considerations, finite measured distances between single ligand−receptor pairs are directly translated into probabilities for true molecular recognition or mere accidental proximity. This enables a quantitative statistical analysis of single recognition events. It is demonstrated that in a general assay, even in the presence of strong unspecific background, the probability for a certain diagnosis and a measure for its reliability can be extracted from the observation of a few binding events. The power of the method is demonstrated at the example of a single-molecule DNA hybridization assay. Our findings are of major importance for future assay miniaturization and assaying with minute amounts of analyte.

Phase behavior and anisotropic optical properties of photoluminescent polarizers. Montali, Andrea; Palmans, Anja R. A.; Eglin, Michael; Weder, Christoph; Smith, Paul; Trabesinger, Werner; Renn, Alois; Hecht, Bert; Wild, Urs P. In Macromol Sym., 154(1), pp. 105–116. 2000.
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The phase behavior and anisotropic optical properties of tensile deformed blends of a photoluminescent polymer guest in an ultra-high molecular weight polyethylene matrix were studied on the level of single molecules by means of scanning confocal optical microscopy. It is shown that upon tensile deformation of the blends, the system transforms from a phase-separated system into a quasi-molecular solid solution. The influence of this phase transition on the anisotropic optical properties of oriented blend films was also investigated with polarized steady-state photoluminescence spectroscopy. We show that well-dissolved guest molecules tend to reach higher degrees of orientation at lower draw ratios of the blend films compared to guests that phase-separate from the matrix polymer. Dichroic ratios in emission in the range of 50 were observed in optimized blend films based on photoluminescent oligomers and linear low density polyethylene.

@article{montali2000phase, abstract = {The phase behavior and anisotropic optical properties of tensile deformed blends of a photoluminescent polymer guest in an ultra-high molecular weight polyethylene matrix were studied on the level of single molecules by means of scanning confocal optical microscopy. It is shown that upon tensile deformation of the blends, the system transforms from a phase-separated system into a quasi-molecular solid solution. The influence of this phase transition on the anisotropic optical properties of oriented blend films was also investigated with polarized steady-state photoluminescence spectroscopy. We show that well-dissolved guest molecules tend to reach higher degrees of orientation at lower draw ratios of the blend films compared to guests that phase-separate from the matrix polymer. Dichroic ratios in emission in the range of 50 were observed in optimized blend films based on photoluminescent oligomers and linear low density polyethylene.}, author = {Montali, Andrea and Palmans, Anja R. A. and Eglin, Michael and Weder, Christoph and Smith, Paul and Trabesinger, Werner and Renn, Alois and Hecht, Bert and Wild, Urs P.}, journal = {Macromol Sym.}, keywords = {single-molecules}, month = 12, number = 1, pages = {105-116}, title = {Phase behavior and anisotropic optical properties of photoluminescent polarizers}, volume = 154, year = 2000 }

%0 Journal Article %1 montali2000phase %A Montali, Andrea %A Palmans, Anja R. A. %A Eglin, Michael %A Weder, Christoph %A Smith, Paul %A Trabesinger, Werner %A Renn, Alois %A Hecht, Bert %A Wild, Urs P. %D 2000 %J Macromol Sym. %N 1 %P 105-116 %R 10.1002/1521-3900(200004)154:1<105::AID-MASY105>3.0.CO;2-J %T Phase behavior and anisotropic optical properties of photoluminescent polarizers %V 154 %X The phase behavior and anisotropic optical properties of tensile deformed blends of a photoluminescent polymer guest in an ultra-high molecular weight polyethylene matrix were studied on the level of single molecules by means of scanning confocal optical microscopy. It is shown that upon tensile deformation of the blends, the system transforms from a phase-separated system into a quasi-molecular solid solution. The influence of this phase transition on the anisotropic optical properties of oriented blend films was also investigated with polarized steady-state photoluminescence spectroscopy. We show that well-dissolved guest molecules tend to reach higher degrees of orientation at lower draw ratios of the blend films compared to guests that phase-separate from the matrix polymer. Dichroic ratios in emission in the range of 50 were observed in optimized blend films based on photoluminescent oligomers and linear low density polyethylene.
Orientational Imaging of Single Molecules by Annular Illumination. Sick, Beate; Hecht, Bert; Novotny, Lukas. In Phys. Rev. Lett., 85(21), pp. 4482–4485. 2000.
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The absorption dipole orientation of single fluorescent molecules is determined by mapping the spatial distribution of the squared electric field components in a high-numerical-aperture laser focus. Annular illumination geometry and the vicinity of a plane dielectric/air interface strongly enhance the longitudinal field component and the transverse fields perpendicular to the polarization direction. As a result, all three excitation field components in the focus are of comparable magnitude. The scheme holds promise to monitor rotational diffusion of single molecules in complex environments.

@article{sick2000orientational, abstract = {The absorption dipole orientation of single fluorescent molecules is determined by mapping the spatial distribution of the squared electric field components in a high-numerical-aperture laser focus. Annular illumination geometry and the vicinity of a plane dielectric/air interface strongly enhance the longitudinal field component and the transverse fields perpendicular to the polarization direction. As a result, all three excitation field components in the focus are of comparable magnitude. The scheme holds promise to monitor rotational diffusion of single molecules in complex environments.}, author = {Sick, Beate and Hecht, Bert and Novotny, Lukas}, journal = {Phys. Rev. Lett.}, keywords = {single-molecules}, month = 11, number = 21, pages = {4482-4485}, title = {Orientational Imaging of Single Molecules by Annular Illumination}, volume = 85, year = 2000 }

%0 Journal Article %1 sick2000orientational %A Sick, Beate %A Hecht, Bert %A Novotny, Lukas %D 2000 %J Phys. Rev. Lett. %N 21 %P 4482-4485 %R 10.1103/PhysRevLett.85.4482 %T Orientational Imaging of Single Molecules by Annular Illumination %V 85 %X The absorption dipole orientation of single fluorescent molecules is determined by mapping the spatial distribution of the squared electric field components in a high-numerical-aperture laser focus. Annular illumination geometry and the vicinity of a plane dielectric/air interface strongly enhance the longitudinal field component and the transverse fields perpendicular to the polarization direction. As a result, all three excitation field components in the focus are of comparable magnitude. The scheme holds promise to monitor rotational diffusion of single molecules in complex environments.
Optical microscopy of single ions and morphological inhomogeneities in Sm-doped CaF2 thin films. Rodrigues-Herzog, Rosana; Trotta, F.; Bill, Hans; Segura, Jean-Manuel; Hecht, Bert; Güntherodt, Hans-Joachim. In Phys. Rev. B, 62(16), pp. 11163–11169. 2000.
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We have investigated the luminescence of CaF2 thin films doped with very low concentrations of Sm2+ ions using scanning confocal optical microscopy at low temperatures. The film morphology was studied independently by atomic force microscopy. The Sm2+ ions are homogeneously distributed in the films and show photobleaching. Unexpectedly, on the film surface strongly luminescent small topographic features are observed that are found to contain Sm3+ by spectral analysis. The formation of Sm3+ is probably due to the presence of oxygen during film growth. In the lowest doped films on-off blinking behavior of isolated luminescent spots provides strong evidence for the first observation of single ions in a crystal.

@article{rodriguesherzog2000optical, abstract = {We have investigated the luminescence of CaF2 thin films doped with very low concentrations of Sm2+ ions using scanning confocal optical microscopy at low temperatures. The film morphology was studied independently by atomic force microscopy. The Sm2+ ions are homogeneously distributed in the films and show photobleaching. Unexpectedly, on the film surface strongly luminescent small topographic features are observed that are found to contain Sm3+ by spectral analysis. The formation of Sm3+ is probably due to the presence of oxygen during film growth. In the lowest doped films on-off blinking behavior of isolated luminescent spots provides strong evidence for the first observation of single ions in a crystal.}, author = {Rodrigues-Herzog, Rosana and Trotta, F. and Bill, Hans and Segura, Jean-Manuel and Hecht, Bert and Güntherodt, Hans-Joachim}, journal = {Phys. Rev. B}, keywords = {nano-optics}, month = 10, number = 16, pages = {11163-11169}, title = {Optical microscopy of single ions and morphological inhomogeneities in Sm-doped CaF2 thin films}, volume = 62, year = 2000 }

%0 Journal Article %1 rodriguesherzog2000optical %A Rodrigues-Herzog, Rosana %A Trotta, F. %A Bill, Hans %A Segura, Jean-Manuel %A Hecht, Bert %A Güntherodt, Hans-Joachim %D 2000 %J Phys. Rev. B %N 16 %P 11163-11169 %R 10.1103/PhysRevB.62.11163 %T Optical microscopy of single ions and morphological inhomogeneities in Sm-doped CaF2 thin films %V 62 %X We have investigated the luminescence of CaF2 thin films doped with very low concentrations of Sm2+ ions using scanning confocal optical microscopy at low temperatures. The film morphology was studied independently by atomic force microscopy. The Sm2+ ions are homogeneously distributed in the films and show photobleaching. Unexpectedly, on the film surface strongly luminescent small topographic features are observed that are found to contain Sm3+ by spectral analysis. The formation of Sm3+ is probably due to the presence of oxygen during film growth. In the lowest doped films on-off blinking behavior of isolated luminescent spots provides strong evidence for the first observation of single ions in a crystal.
Single-Molecule Imaging Revealing the Deformation-Induced Formation of a Molecular Polymer Blend. Trabesinger, Werner; Renn, Alois; Hecht, Bert; Wild, Urs P.; Montali, Andrea; Smith, Paul; Weder, Christoph. In J. Phys. Chem., 104(22), pp. 5221–5224. 2000.
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Photoluminescence microscopy of conjugated polymer molecules in a polyethylene host has been applied to monitor the transition of a phase-separated polymer blend into a molecular dispersion induced by solid-state tensile deformation. Statistical analysis of conjugated polymer cluster sizes as a function of the degree of matrix deformation shows that phase-separated domains of conjugated polymer transform into smaller clusters and single molecules as the degree of matrix deformation increases. Concomitantly, the conjugated guest molecules tend to adopt the preferential orientation of the surrounding matrix. We demonstrate that single-molecule detection can be readily extended and applied to probing molecular dispersion, orientation, and morphology in polymer−polymer blends.

@article{trabesinger2000singlemolecule, abstract = {Photoluminescence microscopy of conjugated polymer molecules in a polyethylene host has been applied to monitor the transition of a phase-separated polymer blend into a molecular dispersion induced by solid-state tensile deformation. Statistical analysis of conjugated polymer cluster sizes as a function of the degree of matrix deformation shows that phase-separated domains of conjugated polymer transform into smaller clusters and single molecules as the degree of matrix deformation increases. Concomitantly, the conjugated guest molecules tend to adopt the preferential orientation of the surrounding matrix. We demonstrate that single-molecule detection can be readily extended and applied to probing molecular dispersion, orientation, and morphology in polymer−polymer blends.}, author = {Trabesinger, Werner and Renn, Alois and Hecht, Bert and Wild, Urs P. and Montali, Andrea and Smith, Paul and Weder, Christoph}, journal = {J. Phys. Chem.}, keywords = {single-molecules}, month = {06}, number = 22, pages = {5221-5224}, title = {Single-Molecule Imaging Revealing the Deformation-Induced Formation of a Molecular Polymer Blend}, volume = 104, year = 2000 }

%0 Journal Article %1 trabesinger2000singlemolecule %A Trabesinger, Werner %A Renn, Alois %A Hecht, Bert %A Wild, Urs P. %A Montali, Andrea %A Smith, Paul %A Weder, Christoph %D 2000 %J J. Phys. Chem. %N 22 %P 5221-5224 %R 10.1021/jp000213a %T Single-Molecule Imaging Revealing the Deformation-Induced Formation of a Molecular Polymer Blend %V 104 %X Photoluminescence microscopy of conjugated polymer molecules in a polyethylene host has been applied to monitor the transition of a phase-separated polymer blend into a molecular dispersion induced by solid-state tensile deformation. Statistical analysis of conjugated polymer cluster sizes as a function of the degree of matrix deformation shows that phase-separated domains of conjugated polymer transform into smaller clusters and single molecules as the degree of matrix deformation increases. Concomitantly, the conjugated guest molecules tend to adopt the preferential orientation of the surrounding matrix. We demonstrate that single-molecule detection can be readily extended and applied to probing molecular dispersion, orientation, and morphology in polymer−polymer blends.
A sample-scanning confocal optical microscope for cryogenic operation. Segura, Jean-Manuel; Renn, Alois; Hecht, Bert. In Rev. Sci. Instrum., 71(4), pp. 1706–1711. 2000.
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A sample-scanning confocal optical microscope for single-molecule imaging and spectroscopy working at superfluid helium temperature, liquid nitrogen, and room temperature is described. An optical resolution of 800 nm full width at half maximum as well as a detection efficiency of ≈3.5\% are achieved. The sample scanner features an exceptionally large scan range of 23 μm at 1.8 K. A position sensor allows for continuous observation of the scanner motion and for a correction of piezoelectric hysteresis and creep at 77 K and at room temperature. Coarse positioning of the sample in x-y is achieved by an inertia drive with high reproducibility and nanometer precision. We demonstrate combined high–resolution confocal imaging and spectroscopy of single molecules at 1.8 K.

@article{segura2000samplescanning, abstract = {A sample-scanning confocal optical microscope for single-molecule imaging and spectroscopy working at superfluid helium temperature, liquid nitrogen, and room temperature is described. An optical resolution of 800 nm full width at half maximum as well as a detection efficiency of ≈3.5\% are achieved. The sample scanner features an exceptionally large scan range of 23 μm at 1.8 K. A position sensor allows for continuous observation of the scanner motion and for a correction of piezoelectric hysteresis and creep at 77 K and at room temperature. Coarse positioning of the sample in x-y is achieved by an inertia drive with high reproducibility and nanometer precision. We demonstrate combined high–resolution confocal imaging and spectroscopy of single molecules at 1.8 K.}, author = {Segura, Jean-Manuel and Renn, Alois and Hecht, Bert}, journal = {Rev. Sci. Instrum.}, keywords = {single-molecules}, month = {04}, number = 4, pages = {1706-1711}, title = {A sample-scanning confocal optical microscope for cryogenic operation}, volume = 71, year = 2000 }

%0 Journal Article %1 segura2000samplescanning %A Segura, Jean-Manuel %A Renn, Alois %A Hecht, Bert %D 2000 %J Rev. Sci. Instrum. %N 4 %P 1706-1711 %R 10.1063/1.1150524 %T A sample-scanning confocal optical microscope for cryogenic operation %V 71 %X A sample-scanning confocal optical microscope for single-molecule imaging and spectroscopy working at superfluid helium temperature, liquid nitrogen, and room temperature is described. An optical resolution of 800 nm full width at half maximum as well as a detection efficiency of ≈3.5\% are achieved. The sample scanner features an exceptionally large scan range of 23 μm at 1.8 K. A position sensor allows for continuous observation of the scanner motion and for a correction of piezoelectric hysteresis and creep at 77 K and at room temperature. Coarse positioning of the sample in x-y is achieved by an inertia drive with high reproducibility and nanometer precision. We demonstrate combined high–resolution confocal imaging and spectroscopy of single molecules at 1.8 K.
Scanning near-field optical microscopy with aperture probes: Fundamentals and applications. Hecht, Bert; Sick, Beate; Wild, Urs P.; Deckert, Volker; Zenobi, Renato; Martin, Olivier J. F.; Pohl, Wolfgang Dieter. In J. Chem. Phys., 112(18), pp. 7761–7774. 2000.
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In this review we describe fundamentals of scanning near-field optical microscopy with aperture probes. After the discussion of instrumentation and probe fabrication, aspects of light propagation in metal-coated, tapered optical fibers are considered. This includes transmission properties and field distributions in the vicinity of subwavelength apertures. Furthermore, the near-field optical image formation mechanism is analyzed with special emphasis on potential sources of artifacts. To underline the prospects of the technique, selected applications including amplitude and phase contrast imaging, fluorescence imaging, and Raman spectroscopy, as well as near-field optical desorption, are presented. These examples demonstrate that scanning near-field optical microscopy is no longer an exotic method but has matured into a valuable tool.

@article{hecht2000scanning, abstract = {In this review we describe fundamentals of scanning near-field optical microscopy with aperture probes. After the discussion of instrumentation and probe fabrication, aspects of light propagation in metal-coated, tapered optical fibers are considered. This includes transmission properties and field distributions in the vicinity of subwavelength apertures. Furthermore, the near-field optical image formation mechanism is analyzed with special emphasis on potential sources of artifacts. To underline the prospects of the technique, selected applications including amplitude and phase contrast imaging, fluorescence imaging, and Raman spectroscopy, as well as near-field optical desorption, are presented. These examples demonstrate that scanning near-field optical microscopy is no longer an exotic method but has matured into a valuable tool.}, author = {Hecht, Bert and Sick, Beate and Wild, Urs P. and Deckert, Volker and Zenobi, Renato and Martin, Olivier J. F. and Pohl, Wolfgang Dieter}, journal = {J. Chem. Phys.}, keywords = {theory}, month = {04}, number = 18, pages = {7761-7774}, title = {Scanning near-field optical microscopy with aperture probes: Fundamentals and applications}, volume = 112, year = 2000 }

%0 Journal Article %1 hecht2000scanning %A Hecht, Bert %A Sick, Beate %A Wild, Urs P. %A Deckert, Volker %A Zenobi, Renato %A Martin, Olivier J. F. %A Pohl, Wolfgang Dieter %D 2000 %J J. Chem. Phys. %N 18 %P 7761-7774 %R 10.1063/1.481382 %T Scanning near-field optical microscopy with aperture probes: Fundamentals and applications %V 112 %X In this review we describe fundamentals of scanning near-field optical microscopy with aperture probes. After the discussion of instrumentation and probe fabrication, aspects of light propagation in metal-coated, tapered optical fibers are considered. This includes transmission properties and field distributions in the vicinity of subwavelength apertures. Furthermore, the near-field optical image formation mechanism is analyzed with special emphasis on potential sources of artifacts. To underline the prospects of the technique, selected applications including amplitude and phase contrast imaging, fluorescence imaging, and Raman spectroscopy, as well as near-field optical desorption, are presented. These examples demonstrate that scanning near-field optical microscopy is no longer an exotic method but has matured into a valuable tool.
Nonclassical Photon Statistics in Single-Molecule Fluorescence at Room Temperature. Fleury, Ludovic; Segura, Jean-Manuel; Zumofen, Gert; Hecht, Bert; Wild, Urs P. In Phys. Rev. Lett., 84(6), pp. 1148–1151. 2000.
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The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of interphoton time distributions, second order correlation functions, and the variance of the photon number probability distribution. Antibunching at short times and bunching behavior for longer times is observed, associated with sub- and super-Poissonian statistics, respectively. A rate-equation analysis of the molecular level populations indicates an accelerated reverse intersystem crossing.

@article{fleury2000nonclassical, abstract = {The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of interphoton time distributions, second order correlation functions, and the variance of the photon number probability distribution. Antibunching at short times and bunching behavior for longer times is observed, associated with sub- and super-Poissonian statistics, respectively. A rate-equation analysis of the molecular level populations indicates an accelerated reverse intersystem crossing.}, author = {Fleury, Ludovic and Segura, Jean-Manuel and Zumofen, Gert and Hecht, Bert and Wild, Urs P.}, journal = {Phys. Rev. Lett.}, keywords = {single-molecules}, month = {02}, number = 6, pages = {1148-1151}, title = {Nonclassical Photon Statistics in Single-Molecule Fluorescence at Room Temperature}, volume = 84, year = 2000 }

%0 Journal Article %1 fleury2000nonclassical %A Fleury, Ludovic %A Segura, Jean-Manuel %A Zumofen, Gert %A Hecht, Bert %A Wild, Urs P. %D 2000 %J Phys. Rev. Lett. %N 6 %P 1148-1151 %R 10.1103/PhysRevLett.84.1148 %T Nonclassical Photon Statistics in Single-Molecule Fluorescence at Room Temperature %V 84 %X The fluorescence of single terrylene molecules in a crystalline host is investigated at room temperature by scanning confocal optical microscopy. Photon arrival times are analyzed in terms of interphoton time distributions, second order correlation functions, and the variance of the photon number probability distribution. Antibunching at short times and bunching behavior for longer times is observed, associated with sub- and super-Poissonian statistics, respectively. A rate-equation analysis of the molecular level populations indicates an accelerated reverse intersystem crossing.
Single-Molecule Identification by Spectrally and Time-Resolved Fluorescence Detection. Prummer, Michael; Hübner, Christian G.; Sick, Beate; Hecht, Bert; Renn, Alois; Wild, Urs P. In Anal. Chem., 72(3), pp. 443–447. 2000.
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A method to identify single molecules rapidly and with high efficiency based on simple probability considerations is proposed. In principle, any property of a detected photon in a single-molecule fluorescence experiment, e.g., emission wavelength, arrival time after pulsed excitation, and polarization, can be analyzed within the framework of the outlined methodology. Monte Carlo simulations show that less than 500 photons are needed to assign an observed single molecule to one out of four species with a confidence level higher than 99.9\%. We show that single dye molecules of four different dyes embedded in a polymer film can be identified with time-correlated single-photon counting spectrally resolved in two channels.

@article{prummer2000singlemolecule, abstract = {A method to identify single molecules rapidly and with high efficiency based on simple probability considerations is proposed. In principle, any property of a detected photon in a single-molecule fluorescence experiment, e.g., emission wavelength, arrival time after pulsed excitation, and polarization, can be analyzed within the framework of the outlined methodology. Monte Carlo simulations show that less than 500 photons are needed to assign an observed single molecule to one out of four species with a confidence level higher than 99.9\%. We show that single dye molecules of four different dyes embedded in a polymer film can be identified with time-correlated single-photon counting spectrally resolved in two channels.}, author = {Prummer, Michael and Hübner, Christian G. and Sick, Beate and Hecht, Bert and Renn, Alois and Wild, Urs P.}, journal = {Anal. Chem.}, keywords = {theory}, month = {02}, number = 3, pages = {443-447}, title = {Single-Molecule Identification by Spectrally and Time-Resolved Fluorescence Detection}, volume = 72, year = 2000 }

%0 Journal Article %1 prummer2000singlemolecule %A Prummer, Michael %A Hübner, Christian G. %A Sick, Beate %A Hecht, Bert %A Renn, Alois %A Wild, Urs P. %D 2000 %J Anal. Chem. %N 3 %P 443-447 %R 10.1021/ac991116k %T Single-Molecule Identification by Spectrally and Time-Resolved Fluorescence Detection %V 72 %X A method to identify single molecules rapidly and with high efficiency based on simple probability considerations is proposed. In principle, any property of a detected photon in a single-molecule fluorescence experiment, e.g., emission wavelength, arrival time after pulsed excitation, and polarization, can be analyzed within the framework of the outlined methodology. Monte Carlo simulations show that less than 500 photons are needed to assign an observed single molecule to one out of four species with a confidence level higher than 99.9\%. We show that single dye molecules of four different dyes embedded in a polymer film can be identified with time-correlated single-photon counting spectrally resolved in two channels.

High-quality near-field optical probes by tube etching. Stöckle, Raoul; Fokas, Christian; Deckert, Volker; Zenobi, Renato; Sick, Beate; Hecht, Bert; Wild, Urs P. In Appl. Phys. Lett., 75(2), pp. 160–162. 1999.
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A method called tube etching for the fabrication of near-field optical probes is presented. Tip formation occurs inside a cylindrical cavity formed by the polymer coating of an optical fiber which is not stripped away prior to etching in hydrofluoric acid. The influence of temperature, etchant concentration, and fiber type on the tip quality is studied. A tip formation mechanism for the given geometry is proposed. The procedure overcomes drawbacks of the conventional etching techniques while still producing large cone angles: (i) tips with reproducible shapes are formed in a high yield, (ii) the surface roughness on the taper is drastically reduced, and (iii) the tip quality is insensitive to vibrations and temperature fluctuations during the etching process. After aluminum coating, optical probes with well-defined apertures are obtained. Due to the smooth glass surface the aluminum coating is virtually free of pinholes.

@article{stckle1999highquality, abstract = {A method called tube etching for the fabrication of near-field optical probes is presented. Tip formation occurs inside a cylindrical cavity formed by the polymer coating of an optical fiber which is not stripped away prior to etching in hydrofluoric acid. The influence of temperature, etchant concentration, and fiber type on the tip quality is studied. A tip formation mechanism for the given geometry is proposed. The procedure overcomes drawbacks of the conventional etching techniques while still producing large cone angles: (i) tips with reproducible shapes are formed in a high yield, (ii) the surface roughness on the taper is drastically reduced, and (iii) the tip quality is insensitive to vibrations and temperature fluctuations during the etching process. After aluminum coating, optical probes with well-defined apertures are obtained. Due to the smooth glass surface the aluminum coating is virtually free of pinholes.}, author = {Stöckle, Raoul and Fokas, Christian and Deckert, Volker and Zenobi, Renato and Sick, Beate and Hecht, Bert and Wild, Urs P.}, journal = {Appl. Phys. Lett.}, keywords = {near-field}, month = {07}, number = 2, pages = {160-162}, title = {High-quality near-field optical probes by tube etching}, volume = 75, year = 1999 }

%0 Journal Article %1 stckle1999highquality %A Stöckle, Raoul %A Fokas, Christian %A Deckert, Volker %A Zenobi, Renato %A Sick, Beate %A Hecht, Bert %A Wild, Urs P. %D 1999 %J Appl. Phys. Lett. %N 2 %P 160-162 %R 10.1063/1.124305 %T High-quality near-field optical probes by tube etching %V 75 %X A method called tube etching for the fabrication of near-field optical probes is presented. Tip formation occurs inside a cylindrical cavity formed by the polymer coating of an optical fiber which is not stripped away prior to etching in hydrofluoric acid. The influence of temperature, etchant concentration, and fiber type on the tip quality is studied. A tip formation mechanism for the given geometry is proposed. The procedure overcomes drawbacks of the conventional etching techniques while still producing large cone angles: (i) tips with reproducible shapes are formed in a high yield, (ii) the surface roughness on the taper is drastically reduced, and (iii) the tip quality is insensitive to vibrations and temperature fluctuations during the etching process. After aluminum coating, optical probes with well-defined apertures are obtained. Due to the smooth glass surface the aluminum coating is virtually free of pinholes.

High photo-stability of single molecules in an organic crystal at room temperature observed by scanning confocal optical microscopy. Ludovic, Fleury; Sick, Beate; Zumofen, Gert; Hecht, Bert; Wild, Urs P. In Mol. Phys., 95(6), pp. 1333–1338. 1998.
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Single molecules have been observed in a molecular crystal at room temperature using scanning confocal fluorescence microscopy. Individual terrylene molecules in a p-terphenyl crystal show high photo-stability with a corresponding ensemble-averaged photo-destruction quantum efficiency lower than 1.2 × 10−8. On average, with a detection efficiency of 6.5\%, a stable fluorescence signal of 10−5 photons s−1 could be detected from single molecules during 1 min of continuous photo-excitation. Both irreversible and reversible abrupt fluorescence intensity jumps to the background have been observed. The experimental data indicate that diffusing quenchers at low concentration in the crystal contribute to fluorescence bleaching of single molecules. All molecular fluorescence signals follow a typical power saturation law with a mean saturation count rate of 4.3 × 105 photons s−1. The large photo-stability allows for long illumination times and high emission rates of single molecules trapped in a crystal at room temperature. A potential application as single organic quantum light sources under ambient conditions is conceivable.

@article{ludovic1998photostability, abstract = {Single molecules have been observed in a molecular crystal at room temperature using scanning confocal fluorescence microscopy. Individual terrylene molecules in a p-terphenyl crystal show high photo-stability with a corresponding ensemble-averaged photo-destruction quantum efficiency lower than 1.2 × 10−8. On average, with a detection efficiency of 6.5\%, a stable fluorescence signal of 10−5 photons s−1 could be detected from single molecules during 1 min of continuous photo-excitation. Both irreversible and reversible abrupt fluorescence intensity jumps to the background have been observed. The experimental data indicate that diffusing quenchers at low concentration in the crystal contribute to fluorescence bleaching of single molecules. All molecular fluorescence signals follow a typical power saturation law with a mean saturation count rate of 4.3 × 105 photons s−1. The large photo-stability allows for long illumination times and high emission rates of single molecules trapped in a crystal at room temperature. A potential application as single organic quantum light sources under ambient conditions is conceivable.}, author = {Ludovic, Fleury and Sick, Beate and Zumofen, Gert and Hecht, Bert and Wild, Urs P.}, journal = {Mol. Phys.}, keywords = {single-molecules}, month = 12, number = 6, pages = {1333-1338}, title = {High photo-stability of single molecules in an organic crystal at room temperature observed by scanning confocal optical microscopy}, volume = 95, year = 1998 }

%0 Journal Article %1 ludovic1998photostability %A Ludovic, Fleury %A Sick, Beate %A Zumofen, Gert %A Hecht, Bert %A Wild, Urs P. %D 1998 %J Mol. Phys. %N 6 %P 1333-1338 %R 10.1080/00268979809483263 %T High photo-stability of single molecules in an organic crystal at room temperature observed by scanning confocal optical microscopy %V 95 %X Single molecules have been observed in a molecular crystal at room temperature using scanning confocal fluorescence microscopy. Individual terrylene molecules in a p-terphenyl crystal show high photo-stability with a corresponding ensemble-averaged photo-destruction quantum efficiency lower than 1.2 × 10−8. On average, with a detection efficiency of 6.5\%, a stable fluorescence signal of 10−5 photons s−1 could be detected from single molecules during 1 min of continuous photo-excitation. Both irreversible and reversible abrupt fluorescence intensity jumps to the background have been observed. The experimental data indicate that diffusing quenchers at low concentration in the crystal contribute to fluorescence bleaching of single molecules. All molecular fluorescence signals follow a typical power saturation law with a mean saturation count rate of 4.3 × 105 photons s−1. The large photo-stability allows for long illumination times and high emission rates of single molecules trapped in a crystal at room temperature. A potential application as single organic quantum light sources under ambient conditions is conceivable.
Influence of detection conditions on near-field optical imaging. Hecht, Bert; Bielefeldt, Hartmut; Pohl, Wolfgang Dieter; Novotny, Lukas; Heinzelmann, Harry. In J. Appl. Phys., 84(11), pp. 5873–5882. 1998.
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The process of image formation in transmission mode scanning near-field optical microscopy is analyzed both theoretically and experimentally. Changes in the dielectric and topographic properties of the sample influence not only the total transmitted intensity, but also its angular distribution in the far field. This opens up an additional source of optical information about the sample. Some of this additional information is retrieved by separate but simultaneous detection of the radiation emitted at angles smaller (allowed light) and larger (forbidden light) than the critical angle of total internal reflection, respectively. Different experimental setups and their respective advantages are discussed. High resolution, constant height mode optical images of test structures are compared with theoretical predictions. Forbidden-light optical images frequently provide enhanced resolution and/or contrast as compared to allowed light images. For small phase objects, in contrast to amplitude objects, a contrast reversal between forbidden and allowed light images is observed.

@article{hecht1998influence, abstract = {The process of image formation in transmission mode scanning near-field optical microscopy is analyzed both theoretically and experimentally. Changes in the dielectric and topographic properties of the sample influence not only the total transmitted intensity, but also its angular distribution in the far field. This opens up an additional source of optical information about the sample. Some of this additional information is retrieved by separate but simultaneous detection of the radiation emitted at angles smaller (allowed light) and larger (forbidden light) than the critical angle of total internal reflection, respectively. Different experimental setups and their respective advantages are discussed. High resolution, constant height mode optical images of test structures are compared with theoretical predictions. Forbidden-light optical images frequently provide enhanced resolution and/or contrast as compared to allowed light images. For small phase objects, in contrast to amplitude objects, a contrast reversal between forbidden and allowed light images is observed.}, author = {Hecht, Bert and Bielefeldt, Hartmut and Pohl, Wolfgang Dieter and Novotny, Lukas and Heinzelmann, Harry}, journal = {J. Appl. Phys.}, keywords = {theory}, month = 11, number = 11, pages = {5873-5882}, title = {Influence of detection conditions on near-field optical imaging}, volume = 84, year = 1998 }

%0 Journal Article %1 hecht1998influence %A Hecht, Bert %A Bielefeldt, Hartmut %A Pohl, Wolfgang Dieter %A Novotny, Lukas %A Heinzelmann, Harry %D 1998 %J J. Appl. Phys. %N 11 %P 5873-5882 %R 10.1063/1.368902 %T Influence of detection conditions on near-field optical imaging %V 84 %X The process of image formation in transmission mode scanning near-field optical microscopy is analyzed both theoretically and experimentally. Changes in the dielectric and topographic properties of the sample influence not only the total transmitted intensity, but also its angular distribution in the far field. This opens up an additional source of optical information about the sample. Some of this additional information is retrieved by separate but simultaneous detection of the radiation emitted at angles smaller (allowed light) and larger (forbidden light) than the critical angle of total internal reflection, respectively. Different experimental setups and their respective advantages are discussed. High resolution, constant height mode optical images of test structures are compared with theoretical predictions. Forbidden-light optical images frequently provide enhanced resolution and/or contrast as compared to allowed light images. For small phase objects, in contrast to amplitude objects, a contrast reversal between forbidden and allowed light images is observed.
Einzelne Moleküle im Brennpunkt. Hecht, Bert; Wild, Urs P.; Sick, Beate. In Bulletin ETH Zürich, 269, pp. 44–47. 1998.
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Mit Hilfe von optischen Mikroskopen können kleinste Lichtmengen bis hin zu einzelnen Lichtquanten (Photonen) ortsaufgelöst detektiert werden. Die spektrale Analyse dieses Lichts erlaubt Aussagen über die chemische Zusammensetzung der untersuchten Probe. Dabei bleibt die Probe im Normalfall unverändert. Die Einsatzmöglichkeiten der optischen Mikroskopie sind äusserst vielfältig: Besonders interessant und wichtig ist die Untersuchung biologischer Präparate in physiologischer Umgebung. Aber auch extreme Bedingungen, wie Vakuum und tiefe Temperature, stellen keine wesentlichen Hindernisse für optische Mikroskope dar, was das Spektrum potentieller Anwendungen zusätzlich erweitert.

@article{hecht1998einzelne, abstract = {Mit Hilfe von optischen Mikroskopen können kleinste Lichtmengen bis hin zu einzelnen Lichtquanten (Photonen) ortsaufgelöst detektiert werden. Die spektrale Analyse dieses Lichts erlaubt Aussagen über die chemische Zusammensetzung der untersuchten Probe. Dabei bleibt die Probe im Normalfall unverändert. Die Einsatzmöglichkeiten der optischen Mikroskopie sind äusserst vielfältig: Besonders interessant und wichtig ist die Untersuchung biologischer Präparate in physiologischer Umgebung. Aber auch extreme Bedingungen, wie Vakuum und tiefe Temperature, stellen keine wesentlichen Hindernisse für optische Mikroskope dar, was das Spektrum potentieller Anwendungen zusätzlich erweitert.}, author = {Hecht, Bert and Wild, Urs P. and Sick, Beate}, journal = {Bulletin ETH Zürich}, keywords = {theory}, month = {04}, pages = {44-47}, title = {Einzelne Moleküle im Brennpunkt}, volume = 269, year = 1998 }

%0 Journal Article %1 hecht1998einzelne %A Hecht, Bert %A Wild, Urs P. %A Sick, Beate %D 1998 %J Bulletin ETH Zürich %P 44-47 %T Einzelne Moleküle im Brennpunkt %U http://www.nanoscale-optics.de/documents/hecht17.pdf %V 269 %X Mit Hilfe von optischen Mikroskopen können kleinste Lichtmengen bis hin zu einzelnen Lichtquanten (Photonen) ortsaufgelöst detektiert werden. Die spektrale Analyse dieses Lichts erlaubt Aussagen über die chemische Zusammensetzung der untersuchten Probe. Dabei bleibt die Probe im Normalfall unverändert. Die Einsatzmöglichkeiten der optischen Mikroskopie sind äusserst vielfältig: Besonders interessant und wichtig ist die Untersuchung biologischer Präparate in physiologischer Umgebung. Aber auch extreme Bedingungen, wie Vakuum und tiefe Temperature, stellen keine wesentlichen Hindernisse für optische Mikroskope dar, was das Spektrum potentieller Anwendungen zusätzlich erweitert.
Implications of high resolution to near-field optical microscopy. Novotny, Lukas; Hecht, Bert; Pohl, Wolfgang Dieter. In Ultramicroscopy, 71(1), pp. 341–344. 1998.
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This paper presents problems inherent to high-resolution near-field optical microscopy. It is shown on an easily understandable level, that high lateral confinement of optical fields (a prerequisite for high-resolution microscopy) leads to a fast decay of the fields. Consequently, the optical probe has to be brought very close to the sample surface, increasing the sensitivity to artifacts. Highly confined optical fields are strongly sensitive to variations in the probe–sample separation. The resulting optical images are, therefore, dominated by topographical variations and do not represent the optical properties of the sample surface.

@article{novotny1998implications, abstract = {This paper presents problems inherent to high-resolution near-field optical microscopy. It is shown on an easily understandable level, that high lateral confinement of optical fields (a prerequisite for high-resolution microscopy) leads to a fast decay of the fields. Consequently, the optical probe has to be brought very close to the sample surface, increasing the sensitivity to artifacts. Highly confined optical fields are strongly sensitive to variations in the probe–sample separation. The resulting optical images are, therefore, dominated by topographical variations and do not represent the optical properties of the sample surface.}, author = {Novotny, Lukas and Hecht, Bert and Pohl, Wolfgang Dieter}, journal = {Ultramicroscopy}, keywords = {theory}, month = {03}, number = 1, pages = {341-344}, title = {Implications of high resolution to near-field optical microscopy}, volume = 71, year = 1998 }

%0 Journal Article %1 novotny1998implications %A Novotny, Lukas %A Hecht, Bert %A Pohl, Wolfgang Dieter %D 1998 %J Ultramicroscopy %N 1 %P 341-344 %R 10.1016/S0304-3991(97)00066-1 %T Implications of high resolution to near-field optical microscopy %V 71 %X This paper presents problems inherent to high-resolution near-field optical microscopy. It is shown on an easily understandable level, that high lateral confinement of optical fields (a prerequisite for high-resolution microscopy) leads to a fast decay of the fields. Consequently, the optical probe has to be brought very close to the sample surface, increasing the sensitivity to artifacts. Highly confined optical fields are strongly sensitive to variations in the probe–sample separation. The resulting optical images are, therefore, dominated by topographical variations and do not represent the optical properties of the sample surface.
Quo Vadis, Near-Field Optics?. Pohl, Wolfgang Dieter; Hecht, Bert; Heinzelmann, Harry. In Nanoscale Science and Technology, Vol. 348, N. García, M. Nieto-Vesperinas, H. Rohrer (eds.), pp. 175–183. Springer Netherlands, Dordrecht, 1998.
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Scanning near-field optical microscopy (SNOM) has pushed today’s optical resolution limit to about 20 nm, with a potential for improvement by another order of magnitude still remaining. SNOM provides chemical specificity based on spectral (amplitude, phase), polarization, and/or fluorescence contrast; it also allows dynamic studies with femtosecond time resolution and photochemistry on the nanometer scale. In spite of these prospects and considerable ongoing research efforts, progress in near-field optical microscopy has been rather slow in the past few years.

@incollection{pohl1998vadis, abstract = {Scanning near-field optical microscopy (SNOM) has pushed today’s optical resolution limit to about 20 nm, with a potential for improvement by another order of magnitude still remaining. SNOM provides chemical specificity based on spectral (amplitude, phase), polarization, and/or fluorescence contrast; it also allows dynamic studies with femtosecond time resolution and photochemistry on the nanometer scale. In spite of these prospects and considerable ongoing research efforts, progress in near-field optical microscopy has been rather slow in the past few years.}, address = {Dordrecht}, author = {Pohl, Wolfgang Dieter and Hecht, Bert and Heinzelmann, Harry}, booktitle = {Nanoscale Science and Technology}, editor = {García, N. and Nieto-Vesperinas, M. and Rohrer, H.}, keywords = {theory}, pages = {175-183}, publisher = {Springer Netherlands}, series = {NATO ASI Series}, title = {Quo Vadis, Near-Field Optics?}, volume = 348, year = 1998 }

%0 Book Section %1 pohl1998vadis %A Pohl, Wolfgang Dieter %A Hecht, Bert %A Heinzelmann, Harry %B Nanoscale Science and Technology %C Dordrecht %D 1998 %E García, N. %E Nieto-Vesperinas, M. %E Rohrer, H. %I Springer Netherlands %P 175-183 %R 10.1007/978-94-011-5024-8_14 %T Quo Vadis, Near-Field Optics? %V 348 %X Scanning near-field optical microscopy (SNOM) has pushed today’s optical resolution limit to about 20 nm, with a potential for improvement by another order of magnitude still remaining. SNOM provides chemical specificity based on spectral (amplitude, phase), polarization, and/or fluorescence contrast; it also allows dynamic studies with femtosecond time resolution and photochemistry on the nanometer scale. In spite of these prospects and considerable ongoing research efforts, progress in near-field optical microscopy has been rather slow in the past few years. %@ 978-94-011-5024-8

Optical Microscopy in the Nano-World. Pohl, Wolfgang Dieter; Bach, Hermann; Bopp, Martin A.; Deckert, Volker; Descouts, Pierre; Eckert, Rolf; Güntherodt, Hans-Joachim; Hafner, Christian; Hecht, Bert; Heinzelmann, Harry; Huser, Thomas; Jobin, Mark; Keller, Ursula; Lacoste, Thilo; Lambelet, Patrick; Marquis-Weible, Fabienne; Martin, Olivier J. F.; Meixner, Alfred J.; Nechay, Bettina; Novotny, Lukas; Pfeiffer, Michael; Philipona, Claude; Plakhotnik, Taras; Renn, Alois; Sayah, Abdeljalil; Segura, Joao-Manuel; Sick, Beate; Siegner, Uwe; Tarrach, Guido; Vahldieck, Rüdiger; Wild, Urs P.; Zeisel, Dieter; Zenobi, Renato. In CHIMIA, 51(10), pp. 760–767. 1997.
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Scanning near-field optical microscopy (SNOM) is an optical microscopy whose resolution is not bound to the diffraction limit. It provides chemical information based upon spectral, polarization and/or fluorescence contrast images. Details as small as 20 nm can be recognized. Photophysical and photochemical effects can be studied with SNOM on a similar scale. This article reviews a good deal of the experimental and theoretical work on SNOM in Switzerland.

@article{pohl1997optical, abstract = {Scanning near-field optical microscopy (SNOM) is an optical microscopy whose resolution is not bound to the diffraction limit. It provides chemical information based upon spectral, polarization and/or fluorescence contrast images. Details as small as 20 nm can be recognized. Photophysical and photochemical effects can be studied with SNOM on a similar scale. This article reviews a good deal of the experimental and theoretical work on SNOM in Switzerland.}, author = {Pohl, Wolfgang Dieter and Bach, Hermann and Bopp, Martin A. and Deckert, Volker and Descouts, Pierre and Eckert, Rolf and Güntherodt, Hans-Joachim and Hafner, Christian and Hecht, Bert and Heinzelmann, Harry and Huser, Thomas and Jobin, Mark and Keller, Ursula and Lacoste, Thilo and Lambelet, Patrick and Marquis-Weible, Fabienne and Martin, Olivier J. F. and Meixner, Alfred J. and Nechay, Bettina and Novotny, Lukas and Pfeiffer, Michael and Philipona, Claude and Plakhotnik, Taras and Renn, Alois and Sayah, Abdeljalil and Segura, Joao-Manuel and Sick, Beate and Siegner, Uwe and Tarrach, Guido and Vahldieck, Rüdiger and Wild, Urs P. and Zeisel, Dieter and Zenobi, Renato}, journal = {CHIMIA}, keywords = {theory}, month = 10, number = 10, pages = {760-767}, title = {Optical Microscopy in the Nano-World}, volume = 51, year = 1997 }

%0 Journal Article %1 pohl1997optical %A Pohl, Wolfgang Dieter %A Bach, Hermann %A Bopp, Martin A. %A Deckert, Volker %A Descouts, Pierre %A Eckert, Rolf %A Güntherodt, Hans-Joachim %A Hafner, Christian %A Hecht, Bert %A Heinzelmann, Harry %A Huser, Thomas %A Jobin, Mark %A Keller, Ursula %A Lacoste, Thilo %A Lambelet, Patrick %A Marquis-Weible, Fabienne %A Martin, Olivier J. F. %A Meixner, Alfred J. %A Nechay, Bettina %A Novotny, Lukas %A Pfeiffer, Michael %A Philipona, Claude %A Plakhotnik, Taras %A Renn, Alois %A Sayah, Abdeljalil %A Segura, Joao-Manuel %A Sick, Beate %A Siegner, Uwe %A Tarrach, Guido %A Vahldieck, Rüdiger %A Wild, Urs P. %A Zeisel, Dieter %A Zenobi, Renato %D 1997 %J CHIMIA %N 10 %P 760-767 %T Optical Microscopy in the Nano-World %U https://www.ingentaconnect.com/content/scs/chimia/1997/00000051/00000010/art00022 %V 51 %X Scanning near-field optical microscopy (SNOM) is an optical microscopy whose resolution is not bound to the diffraction limit. It provides chemical information based upon spectral, polarization and/or fluorescence contrast images. Details as small as 20 nm can be recognized. Photophysical and photochemical effects can be studied with SNOM on a similar scale. This article reviews a good deal of the experimental and theoretical work on SNOM in Switzerland.
Facts and artifacts in near-field optical microscopy. Hecht, Bert; Bielefeldt, Hartmut; Inouye, Yasushi; Pohl, Wolfgang Dieter; Novotny, Lukas. In J. Appl. Phys., 81(6), pp. 2492–2498. 1997.
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Near-field optical (NFO) microscopes with an auxiliary gap width regulation (shear force, tunneling) may produce images that represent the path of the probe rather than optical properties of the sample. Experimental and theoretical evidence leads us to the conclusion that many NFO results reported in the past might have been affected or even dominated by the resulting artifact. The specifications derived from such results for the different types of NFO microscopes used therefore warrant reexamination. We show that the resolving power of aperture NFO microscopes, 30–50 nm, is of genuine NFO origin but can be heavily obscured by the artifact.

@article{hecht1997facts, abstract = {Near-field optical (NFO) microscopes with an auxiliary gap width regulation (shear force, tunneling) may produce images that represent the path of the probe rather than optical properties of the sample. Experimental and theoretical evidence leads us to the conclusion that many NFO results reported in the past might have been affected or even dominated by the resulting artifact. The specifications derived from such results for the different types of NFO microscopes used therefore warrant reexamination. We show that the resolving power of aperture NFO microscopes, 30–50 nm, is of genuine NFO origin but can be heavily obscured by the artifact.}, author = {Hecht, Bert and Bielefeldt, Hartmut and Inouye, Yasushi and Pohl, Wolfgang Dieter and Novotny, Lukas}, journal = {J. Appl. Phys.}, keywords = {near-field}, month = {03}, number = 6, pages = {2492-2498}, title = {Facts and artifacts in near-field optical microscopy}, volume = 81, year = 1997 }

%0 Journal Article %1 hecht1997facts %A Hecht, Bert %A Bielefeldt, Hartmut %A Inouye, Yasushi %A Pohl, Wolfgang Dieter %A Novotny, Lukas %D 1997 %J J. Appl. Phys. %N 6 %P 2492-2498 %R 10.1063/1.363956 %T Facts and artifacts in near-field optical microscopy %V 81 %X Near-field optical (NFO) microscopes with an auxiliary gap width regulation (shear force, tunneling) may produce images that represent the path of the probe rather than optical properties of the sample. Experimental and theoretical evidence leads us to the conclusion that many NFO results reported in the past might have been affected or even dominated by the resulting artifact. The specifications derived from such results for the different types of NFO microscopes used therefore warrant reexamination. We show that the resolving power of aperture NFO microscopes, 30–50 nm, is of genuine NFO origin but can be heavily obscured by the artifact.
Interference of locally excited surface plasmons. Novotny, Lukas; Hecht, Bert; Pohl, Wolfgang Dieter. In Journal of Applied Physics, 81(4), pp. 1798–1806. 1997.
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Surface plasmon interactions on a finite silver layer are theoretically investigated using a coupled dipole formalism. The studied system consists of several protruding particles located on the surface of the layer that are scanned with an optical probe. An optical scan-image of the silver surface is obtained by assigning the recorded far-field radiation to the momentary position of the optical probe. Both, probe and protrusions are considered as single dipolar particles. Interferences of the locally excited surface plasmons can be recorded by detecting the radiation emitted into the lower half-space at angles beyond the critical angle of total internal reflection (forbidden light). The resulting scan images show excellent agreement with recent experimental measurements. The theory of the coupled dipole formalism using Green’s functions of a layered reference system is outlined and electromagnetic properties of surface plasmons are discussed.

@article{novotny1997interference, abstract = {Surface plasmon interactions on a finite silver layer are theoretically investigated using a coupled dipole formalism. The studied system consists of several protruding particles located on the surface of the layer that are scanned with an optical probe. An optical scan-image of the silver surface is obtained by assigning the recorded far-field radiation to the momentary position of the optical probe. Both, probe and protrusions are considered as single dipolar particles. Interferences of the locally excited surface plasmons can be recorded by detecting the radiation emitted into the lower half-space at angles beyond the critical angle of total internal reflection (forbidden light). The resulting scan images show excellent agreement with recent experimental measurements. The theory of the coupled dipole formalism using Green’s functions of a layered reference system is outlined and electromagnetic properties of surface plasmons are discussed.}, author = {Novotny, Lukas and Hecht, Bert and Pohl, Wolfgang Dieter}, journal = {Journal of Applied Physics}, keywords = {plasmon}, month = {02}, number = 4, pages = {1798-1806}, title = {Interference of locally excited surface plasmons}, volume = 81, year = 1997 }

%0 Journal Article %1 novotny1997interference %A Novotny, Lukas %A Hecht, Bert %A Pohl, Wolfgang Dieter %D 1997 %J Journal of Applied Physics %N 4 %P 1798-1806 %R 10.1063/1.364036 %T Interference of locally excited surface plasmons %V 81 %X Surface plasmon interactions on a finite silver layer are theoretically investigated using a coupled dipole formalism. The studied system consists of several protruding particles located on the surface of the layer that are scanned with an optical probe. An optical scan-image of the silver surface is obtained by assigning the recorded far-field radiation to the momentary position of the optical probe. Both, probe and protrusions are considered as single dipolar particles. Interferences of the locally excited surface plasmons can be recorded by detecting the radiation emitted into the lower half-space at angles beyond the critical angle of total internal reflection (forbidden light). The resulting scan images show excellent agreement with recent experimental measurements. The theory of the coupled dipole formalism using Green’s functions of a layered reference system is outlined and electromagnetic properties of surface plasmons are discussed.

Local Excitation, Scattering, and Interference of Surface Plasmons. Hecht, Bert; Bielefeldt, Hartmut; Novotny, Lukas; Inouye, Yasushi; Pohl, Wolfgang Dieter. In Phys. Rev. Lett., 77(9), pp. 1889–1892. 1996.
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The optical probe of a scanning near-field optical microscope is shown to act as a point source of surface plasmon (SP) polaritons on gold and silver films. Plasmon excitation manifests itself by emission of light in the direction of the SP resonance angle, originating from an area with the shape of a dipole radiation pattern whose extension is given by the SP decay length. Interaction with selected, individual surface inhomogeneities gives rise to characteristic modifications of the emitted radiation, which provide detailed information about SP scattering, reflection, and interference phenomena.

@article{hecht1996local, abstract = {The optical probe of a scanning near-field optical microscope is shown to act as a point source of surface plasmon (SP) polaritons on gold and silver films. Plasmon excitation manifests itself by emission of light in the direction of the SP resonance angle, originating from an area with the shape of a dipole radiation pattern whose extension is given by the SP decay length. Interaction with selected, individual surface inhomogeneities gives rise to characteristic modifications of the emitted radiation, which provide detailed information about SP scattering, reflection, and interference phenomena.}, author = {Hecht, Bert and Bielefeldt, Hartmut and Novotny, Lukas and Inouye, Yasushi and Pohl, Wolfgang Dieter}, journal = {Phys. Rev. Lett.}, keywords = {plasmon}, month = {08}, number = 9, pages = {1889-1892}, title = {Local Excitation, Scattering, and Interference of Surface Plasmons}, volume = 77, year = 1996 }

%0 Journal Article %1 hecht1996local %A Hecht, Bert %A Bielefeldt, Hartmut %A Novotny, Lukas %A Inouye, Yasushi %A Pohl, Wolfgang Dieter %D 1996 %J Phys. Rev. Lett. %N 9 %P 1889-1892 %R 10.1103/PhysRevLett.77.1889 %T Local Excitation, Scattering, and Interference of Surface Plasmons %V 77 %X The optical probe of a scanning near-field optical microscope is shown to act as a point source of surface plasmon (SP) polaritons on gold and silver films. Plasmon excitation manifests itself by emission of light in the direction of the SP resonance angle, originating from an area with the shape of a dipole radiation pattern whose extension is given by the SP decay length. Interaction with selected, individual surface inhomogeneities gives rise to characteristic modifications of the emitted radiation, which provide detailed information about SP scattering, reflection, and interference phenomena.
Instrumental developments and recent experiments in near-field optical microscopy. Heinzelmann, Harry; Lacoste, Thilo D.; Huser, Thomas R.; Güntherodt, Hans-Joachim; Hecht, Bert; Pohl, Wolfgang DIeter. In Thin Solid Films, 273(1), pp. 149–153. 1996.
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Recent advances in the understanding of light propagation in small dimensions as well as in instrumentation make scanning near-field optical microscopy (SNOM) a very promising tool for studying optical phenomena on a nanometer scale. In this talk, we will demonstrate experiments carried out with the recently developed tunneling near-field optical microscope. We found superior image contrast, as compared with images taken with conventional aperture SNOM, along with the high resolution commonly achieved with fiber probes. This work was motivated by the theoretical investigations presented in Dr. Pohl's talk. We will further describe two recently built instruments. The first is a scanning tunneling optical microscope combined with a scanning force microscope. The second instrument is an aperture-type SNOM mounted on the sample stage of a conventional inverted optical microscope. Of particular interest to us is imaging with polarization contrast. One of the goals is to study liquid-crystal films which have been micro-patterned with the help of a force microscope tip. These samples are promising as waveguides and potential electro-optical devices. Additionally, they represent very convenient test samples for polarization SNOM.

@article{heinzelmann1996instrumental, abstract = {Recent advances in the understanding of light propagation in small dimensions as well as in instrumentation make scanning near-field optical microscopy (SNOM) a very promising tool for studying optical phenomena on a nanometer scale. In this talk, we will demonstrate experiments carried out with the recently developed tunneling near-field optical microscope. We found superior image contrast, as compared with images taken with conventional aperture SNOM, along with the high resolution commonly achieved with fiber probes. This work was motivated by the theoretical investigations presented in Dr. Pohl's talk. We will further describe two recently built instruments. The first is a scanning tunneling optical microscope combined with a scanning force microscope. The second instrument is an aperture-type SNOM mounted on the sample stage of a conventional inverted optical microscope. Of particular interest to us is imaging with polarization contrast. One of the goals is to study liquid-crystal films which have been micro-patterned with the help of a force microscope tip. These samples are promising as waveguides and potential electro-optical devices. Additionally, they represent very convenient test samples for polarization SNOM.}, author = {Heinzelmann, Harry and Lacoste, Thilo D. and Huser, Thomas R. and Güntherodt, Hans-Joachim and Hecht, Bert and Pohl, Wolfgang DIeter}, journal = {Thin Solid Films}, keywords = {SNOM}, month = {02}, number = 1, pages = {149-153}, series = {International Symposium on Ultra Materials for Picotransfer}, title = {Instrumental developments and recent experiments in near-field optical microscopy}, volume = 273, year = 1996 }

%0 Journal Article %1 heinzelmann1996instrumental %A Heinzelmann, Harry %A Lacoste, Thilo D. %A Huser, Thomas R. %A Güntherodt, Hans-Joachim %A Hecht, Bert %A Pohl, Wolfgang DIeter %B International Symposium on Ultra Materials for Picotransfer %D 1996 %J Thin Solid Films %N 1 %P 149-153 %R 10.1016/0040-6090(95)06808-2 %T Instrumental developments and recent experiments in near-field optical microscopy %V 273 %X Recent advances in the understanding of light propagation in small dimensions as well as in instrumentation make scanning near-field optical microscopy (SNOM) a very promising tool for studying optical phenomena on a nanometer scale. In this talk, we will demonstrate experiments carried out with the recently developed tunneling near-field optical microscope. We found superior image contrast, as compared with images taken with conventional aperture SNOM, along with the high resolution commonly achieved with fiber probes. This work was motivated by the theoretical investigations presented in Dr. Pohl's talk. We will further describe two recently built instruments. The first is a scanning tunneling optical microscope combined with a scanning force microscope. The second instrument is an aperture-type SNOM mounted on the sample stage of a conventional inverted optical microscope. Of particular interest to us is imaging with polarization contrast. One of the goals is to study liquid-crystal films which have been micro-patterned with the help of a force microscope tip. These samples are promising as waveguides and potential electro-optical devices. Additionally, they represent very convenient test samples for polarization SNOM.
Radiation coupling and image formation in scanning near-field optical microscopy. Pohl, Wolfgang Dieter; Novotny, Lukas; Hecht, Bert; Heinzelmann, Harry. In Thin Solid Films, 273(1), pp. 161–167. 1996.
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The propagation of light through an aperture scanning near-field optical microscope is studied. Rules for optimizing the confinement and throughput of aperture near-field probes are derived. The radiation from the aperture through simple sample structures, a flat substrate and a substrate with stripe-like elevations and depression, into classically allowed and forbidden directions is determined quantitatively. It is shown that small amplitude and phase objects can be distinguished by comparing “allowed” and “forbidden” light images.

@article{pohl1996radiation, abstract = {The propagation of light through an aperture scanning near-field optical microscope is studied. Rules for optimizing the confinement and throughput of aperture near-field probes are derived. The radiation from the aperture through simple sample structures, a flat substrate and a substrate with stripe-like elevations and depression, into classically allowed and forbidden directions is determined quantitatively. It is shown that small amplitude and phase objects can be distinguished by comparing “allowed” and “forbidden” light images.}, author = {Pohl, Wolfgang Dieter and Novotny, Lukas and Hecht, Bert and Heinzelmann, Harry}, journal = {Thin Solid Films}, keywords = {theory}, month = {02}, number = 1, pages = {161-167}, series = {International Symposium on Ultra Materials for Picotransfer}, title = {Radiation coupling and image formation in scanning near-field optical microscopy}, volume = 273, year = 1996 }

%0 Journal Article %1 pohl1996radiation %A Pohl, Wolfgang Dieter %A Novotny, Lukas %A Hecht, Bert %A Heinzelmann, Harry %B International Symposium on Ultra Materials for Picotransfer %D 1996 %J Thin Solid Films %N 1 %P 161-167 %R 10.1016/0040-6090(95)06810-4 %T Radiation coupling and image formation in scanning near-field optical microscopy %V 273 %X The propagation of light through an aperture scanning near-field optical microscope is studied. Rules for optimizing the confinement and throughput of aperture near-field probes are derived. The radiation from the aperture through simple sample structures, a flat substrate and a substrate with stripe-like elevations and depression, into classically allowed and forbidden directions is determined quantitatively. It is shown that small amplitude and phase objects can be distinguished by comparing “allowed” and “forbidden” light images.
Local Excitation of Surface Plasmons by “TNOM.”. Hecht, Bert; Pohl, Wolfgang Dieter; Novotny, Lukas. In Optics at the Nanometer Scale: Imaging and Storing with Photonic Near Fields, M. Nieto-Vesperinas, N. García (eds.), pp. 151–161. Springer Netherlands, Dordrecht, 1996.
- [ Abstract ]
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A point light source, such as the aperture scanning near-field optical microscope (SNOM) probe in emission mode, can excite surface plasmon polaritons (SP) in metallic films by means of its near field. We demonstrated this using a tunnel near-field optical microscope (TNOM) with thin silver films as samples. Light is transmitted through the film predominantly into the directions defined by the dispersion relation of the SP, forming a sharply confined conical sheet of radiation in the far field. The angle of emission is larger than the critical angle θC for total reflection, hence not accessible to standard SNOM. The weak emission into allowed directions mainly stems from SP scattering at film imperfections. With TNOM, it is possible to record “forbidden” (θ≥θc) and “allowed” (θ≤θc) light separately but simultaneously. The resulting scan images represent the intensities of SP excitation and SP scattering at imperfections of the silver film as a function of probe position. Their most conspicuous features are concentric circles and confocal hyperbolae, respectively, suggestive of interactions between plasmons originating from the tip and from nearby scattering centers. Our findings indicate the plasmons scattering/reflection can be studied quantitatively and on a local scale.

@incollection{hecht1996local, abstract = {A point light source, such as the aperture scanning near-field optical microscope (SNOM) probe in emission mode, can excite surface plasmon polaritons (SP) in metallic films by means of its near field. We demonstrated this using a tunnel near-field optical microscope (TNOM) with thin silver films as samples. Light is transmitted through the film predominantly into the directions defined by the dispersion relation of the SP, forming a sharply confined conical sheet of radiation in the far field. The angle of emission is larger than the critical angle θC for total reflection, hence not accessible to standard SNOM. The weak emission into allowed directions mainly stems from SP scattering at film imperfections. With TNOM, it is possible to record “forbidden” (θ≥θc) and “allowed” (θ≤θc) light separately but simultaneously. The resulting scan images represent the intensities of SP excitation and SP scattering at imperfections of the silver film as a function of probe position. Their most conspicuous features are concentric circles and confocal hyperbolae, respectively, suggestive of interactions between plasmons originating from the tip and from nearby scattering centers. Our findings indicate the plasmons scattering/reflection can be studied quantitatively and on a local scale.}, address = {Dordrecht}, author = {Hecht, Bert and Pohl, Wolfgang Dieter and Novotny, Lukas}, booktitle = {Optics at the Nanometer Scale: Imaging and Storing with Photonic Near Fields}, editor = {Nieto-Vesperinas, M. and García, N.}, keywords = {plasmon}, pages = {151-161}, publisher = {Springer Netherlands}, series = {NATO ASI Series}, title = {Local Excitation of Surface Plasmons by “TNOM”}, year = 1996 }

%0 Book Section %1 hecht1996local %A Hecht, Bert %A Pohl, Wolfgang Dieter %A Novotny, Lukas %B Optics at the Nanometer Scale: Imaging and Storing with Photonic Near Fields %C Dordrecht %D 1996 %E Nieto-Vesperinas, M. %E García, N. %I Springer Netherlands %P 151-161 %R 10.1007/978-94-009-0247-3_10 %T Local Excitation of Surface Plasmons by “TNOM” %X A point light source, such as the aperture scanning near-field optical microscope (SNOM) probe in emission mode, can excite surface plasmon polaritons (SP) in metallic films by means of its near field. We demonstrated this using a tunnel near-field optical microscope (TNOM) with thin silver films as samples. Light is transmitted through the film predominantly into the directions defined by the dispersion relation of the SP, forming a sharply confined conical sheet of radiation in the far field. The angle of emission is larger than the critical angle θC for total reflection, hence not accessible to standard SNOM. The weak emission into allowed directions mainly stems from SP scattering at film imperfections. With TNOM, it is possible to record “forbidden” (θ≥θc) and “allowed” (θ≤θc) light separately but simultaneously. The resulting scan images represent the intensities of SP excitation and SP scattering at imperfections of the silver film as a function of probe position. Their most conspicuous features are concentric circles and confocal hyperbolae, respectively, suggestive of interactions between plasmons originating from the tip and from nearby scattering centers. Our findings indicate the plasmons scattering/reflection can be studied quantitatively and on a local scale. %@ 978-94-009-0247-3

Piezoresistive cantilevers as optical sensors for scanning near-field microscopy. Bauer, Péter H.; Hecht, Bert; Rossel, Christophe P. In Ultramicroscopy, 61(1), pp. 127–130. 1995.
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To combine the high lateral resolution of AFM with near-field optical measurements, we propose the use of microfabricated piezoresistive cantilevers as miniaturized photosensitive elements. The silicon-based sensors consist of a p-doped piezoresistive path, which also includes the tip. The resistance of this path can be changed either by pressure on the lever or by light. For combined optical and topographical measurements, an evanescent field is created. Because the AFM tip is the only part of the cantilever that is exposed to the evanescent field, the tip can be used as a near-field optical probe. It is possible to extract the exponential decay of the evanescent field from combined force/optical measurements. To decouple optical and topographical information, the intensity of the evanescent field is modulated and the optical signal is measured with the lock-in technique.

@article{bauer1995piezoresistive, abstract = {To combine the high lateral resolution of AFM with near-field optical measurements, we propose the use of microfabricated piezoresistive cantilevers as miniaturized photosensitive elements. The silicon-based sensors consist of a p-doped piezoresistive path, which also includes the tip. The resistance of this path can be changed either by pressure on the lever or by light. For combined optical and topographical measurements, an evanescent field is created. Because the AFM tip is the only part of the cantilever that is exposed to the evanescent field, the tip can be used as a near-field optical probe. It is possible to extract the exponential decay of the evanescent field from combined force/optical measurements. To decouple optical and topographical information, the intensity of the evanescent field is modulated and the optical signal is measured with the lock-in technique.}, author = {Bauer, Péter H. and Hecht, Bert and Rossel, Christophe P.}, journal = {Ultramicroscopy}, keywords = {SNOM}, month = 12, number = 1, pages = {127-130}, series = {Selected {Papers} from the 3rd {International} {Conference} on {Near}-{Field} {Optics} and {Related} {Techniques}}, title = {Piezoresistive cantilevers as optical sensors for scanning near-field microscopy}, volume = 61, year = 1995 }

%0 Journal Article %1 bauer1995piezoresistive %A Bauer, Péter H. %A Hecht, Bert %A Rossel, Christophe P. %B Selected {Papers} from the 3rd {International} {Conference} on {Near}-{Field} {Optics} and {Related} {Techniques} %D 1995 %J Ultramicroscopy %N 1 %P 127-130 %R 10.1016/0304-3991(95)00118-2 %T Piezoresistive cantilevers as optical sensors for scanning near-field microscopy %V 61 %X To combine the high lateral resolution of AFM with near-field optical measurements, we propose the use of microfabricated piezoresistive cantilevers as miniaturized photosensitive elements. The silicon-based sensors consist of a p-doped piezoresistive path, which also includes the tip. The resistance of this path can be changed either by pressure on the lever or by light. For combined optical and topographical measurements, an evanescent field is created. Because the AFM tip is the only part of the cantilever that is exposed to the evanescent field, the tip can be used as a near-field optical probe. It is possible to extract the exponential decay of the evanescent field from combined force/optical measurements. To decouple optical and topographical information, the intensity of the evanescent field is modulated and the optical signal is measured with the lock-in technique.
Light confinement in scanning near-field optical microscopy. Novotny, Lukas; Pohl, Wolfgang Dieter; Hecht, Bert. In Ultramicroscopy, 61(1), pp. 1–9. 1995.
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Light propagation and light confinement in scanning near-field optical microscopy (SNOM) are studied by means of the multiple multipole method (MMP). Helmholtz' vector wave equation is solved in three dimensions for four different near-field optical probes: a bare glass tip, a metal-clad aperture probe, an “entirely coated” tip and a novel plasmon probe. The latter two are capable of producing a near-field light spot of less than 20 nm (FWHM) extension. The spots have a single intensity peak at the centre, in contrast to the field distribution behind an aperture, which is doubly peaked. The effect of various parameters on light throughput and confinement is investigated for these probes.

@article{novotny1995light, abstract = {Light propagation and light confinement in scanning near-field optical microscopy (SNOM) are studied by means of the multiple multipole method (MMP). Helmholtz' vector wave equation is solved in three dimensions for four different near-field optical probes: a bare glass tip, a metal-clad aperture probe, an “entirely coated” tip and a novel plasmon probe. The latter two are capable of producing a near-field light spot of less than 20 nm (FWHM) extension. The spots have a single intensity peak at the centre, in contrast to the field distribution behind an aperture, which is doubly peaked. The effect of various parameters on light throughput and confinement is investigated for these probes.}, author = {Novotny, Lukas and Pohl, Wolfgang Dieter and Hecht, Bert}, journal = {Ultramicroscopy}, keywords = {theory}, month = 12, number = 1, pages = {1-9}, series = {Selected Papers from the 3rd International Conference on Near-Field Optics and Related Techniques}, title = {Light confinement in scanning near-field optical microscopy}, volume = 61, year = 1995 }

%0 Journal Article %1 novotny1995light %A Novotny, Lukas %A Pohl, Wolfgang Dieter %A Hecht, Bert %B Selected Papers from the 3rd International Conference on Near-Field Optics and Related Techniques %D 1995 %J Ultramicroscopy %N 1 %P 1-9 %R 10.1016/0304-3991(95)00095-X %T Light confinement in scanning near-field optical microscopy %V 61 %X Light propagation and light confinement in scanning near-field optical microscopy (SNOM) are studied by means of the multiple multipole method (MMP). Helmholtz' vector wave equation is solved in three dimensions for four different near-field optical probes: a bare glass tip, a metal-clad aperture probe, an “entirely coated” tip and a novel plasmon probe. The latter two are capable of producing a near-field light spot of less than 20 nm (FWHM) extension. The spots have a single intensity peak at the centre, in contrast to the field distribution behind an aperture, which is doubly peaked. The effect of various parameters on light throughput and confinement is investigated for these probes.
“Tunnel” near-field optical microscopy: TNOM-2. Hecht, Bert; Pohl, Wolfgang Dieter; Heinzelmann, Harry; Novotny, Lukas. In Ultramicroscopy, 61(1), pp. 99–104. 1995.
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Light emitted from the aperture of a near-field optical probe in the close vicinity of a dielectric object propagates in classically “forbidden” as well as “allowed” directions; the two zones are separated by the critical angle for total internal reflection. The new “tunnel” near-field optical microscopy (TNOM) technique makes use of forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. The influence of topography on image formation is analyzed and discussed.

@article{hecht1995tunnel, abstract = {Light emitted from the aperture of a near-field optical probe in the close vicinity of a dielectric object propagates in classically “forbidden” as well as “allowed” directions; the two zones are separated by the critical angle for total internal reflection. The new “tunnel” near-field optical microscopy (TNOM) technique makes use of forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. The influence of topography on image formation is analyzed and discussed.}, author = {Hecht, Bert and Pohl, Wolfgang Dieter and Heinzelmann, Harry and Novotny, Lukas}, journal = {Ultramicroscopy}, keywords = {near-field}, month = 12, number = 1, pages = {99-104}, series = {Selected Papers from the 3rd International Conference on Near-Field Optics and Related Techniques}, title = {“Tunnel” near-field optical microscopy: TNOM-2}, volume = 61, year = 1995 }

%0 Journal Article %1 hecht1995tunnel %A Hecht, Bert %A Pohl, Wolfgang Dieter %A Heinzelmann, Harry %A Novotny, Lukas %B Selected Papers from the 3rd International Conference on Near-Field Optics and Related Techniques %D 1995 %J Ultramicroscopy %N 1 %P 99-104 %R 10.1016/0304-3991(95)00106-9 %T “Tunnel” near-field optical microscopy: TNOM-2 %V 61 %X Light emitted from the aperture of a near-field optical probe in the close vicinity of a dielectric object propagates in classically “forbidden” as well as “allowed” directions; the two zones are separated by the critical angle for total internal reflection. The new “tunnel” near-field optical microscopy (TNOM) technique makes use of forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. The influence of topography on image formation is analyzed and discussed.
Tunnel near-field optical microscopy (TNOM-2). Hecht, Bert; Pohl, Wolfgang Dieter; Heinzelmann, Harry; Novotny, Lukas. In Near-Field Optics, Vol. 2535, pp. 61–68. International Society for Optics and Photonics, 1995.
- [ Abstract ]
- [ BibTeX ]
- [ EndNote ]
- [ DOI ]
Light emitted from the aperture of a near-field optical probe in the close vicinity of a dielectric object propagates in classically `forbidden' as well as `allowed' directions; the two zones are separated by the critical angle for total internal reflection. The new `tunnel' near-field optical microscopy (TNOM) technique makes use of forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. The influence of topography on image formation is analyzed and discussed.

@inproceedings{hecht1995tunnel, abstract = {Light emitted from the aperture of a near-field optical probe in the close vicinity of a dielectric object propagates in classically `forbidden' as well as `allowed' directions; the two zones are separated by the critical angle for total internal reflection. The new `tunnel' near-field optical microscopy (TNOM) technique makes use of forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. The influence of topography on image formation is analyzed and discussed.}, author = {Hecht, Bert and Pohl, Wolfgang Dieter and Heinzelmann, Harry and Novotny, Lukas}, booktitle = {Near-Field Optics}, keywords = {near-field}, month = {09}, pages = {61-68}, publisher = {International Society for Optics and Photonics}, title = {Tunnel near-field optical microscopy (TNOM-2)}, volume = 2535, year = 1995 }

%0 Conference Paper %1 hecht1995tunnel %A Hecht, Bert %A Pohl, Wolfgang Dieter %A Heinzelmann, Harry %A Novotny, Lukas %B Near-Field Optics %D 1995 %I International Society for Optics and Photonics %P 61-68 %R 10.1117/12.218689 %T Tunnel near-field optical microscopy (TNOM-2) %V 2535 %X Light emitted from the aperture of a near-field optical probe in the close vicinity of a dielectric object propagates in classically `forbidden' as well as `allowed' directions; the two zones are separated by the critical angle for total internal reflection. The new `tunnel' near-field optical microscopy (TNOM) technique makes use of forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. The influence of topography on image formation is analyzed and discussed.
Scanning near-field optical microscopy in Basel, Ruschlikon, and Zurich. Heinzelmann, Harry; Huser, Thomas R.; Lactose, Thilo D.; Guentherodt, Hans-Joachim; Pohl, Wolfgang Dieter; Hecht, Bert; Novotny, Lukas; Martin, Olivier JF; Hafner, Christian; Baggenstos, Heinrich; Wild, Urs P.; Renn, Alois. In Optical Engineering, 34(8), pp. 2441–2545. 1995.
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- [ DOI ]
The concepts of near-field optical microscopy and experimental and theoretical work carried out in Switzerland over the last 10 years are reviewed. After a description of the pioneering experiments of the mid-1980s, we focus on the recent efforts of the three Swiss laboratories currently working in the field in close collaboration. This newly refreshed initiative in near-field optics is supported by the Swiss Priority Program Optique.

@article{heinzelmann1995scanning, abstract = {The concepts of near-field optical microscopy and experimental and theoretical work carried out in Switzerland over the last 10 years are reviewed. After a description of the pioneering experiments of the mid-1980s, we focus on the recent efforts of the three Swiss laboratories currently working in the field in close collaboration. This newly refreshed initiative in near-field optics is supported by the Swiss Priority Program Optique.}, author = {Heinzelmann, Harry and Huser, Thomas R. and Lactose, Thilo D. and Guentherodt, Hans-Joachim and Pohl, Wolfgang Dieter and Hecht, Bert and Novotny, Lukas and Martin, Olivier JF and Hafner, Christian and Baggenstos, Heinrich and Wild, Urs P. and Renn, Alois}, journal = {Optical Engineering}, keywords = {SNOM}, month = {08}, number = 8, pages = {2441-2545}, title = {Scanning near-field optical microscopy in Basel, Ruschlikon, and Zurich}, volume = 34, year = 1995 }

%0 Journal Article %1 heinzelmann1995scanning %A Heinzelmann, Harry %A Huser, Thomas R. %A Lactose, Thilo D. %A Guentherodt, Hans-Joachim %A Pohl, Wolfgang Dieter %A Hecht, Bert %A Novotny, Lukas %A Martin, Olivier JF %A Hafner, Christian %A Baggenstos, Heinrich %A Wild, Urs P. %A Renn, Alois %D 1995 %J Optical Engineering %N 8 %P 2441-2545 %R 10.1117/12.205670 %T Scanning near-field optical microscopy in Basel, Ruschlikon, and Zurich %V 34 %X The concepts of near-field optical microscopy and experimental and theoretical work carried out in Switzerland over the last 10 years are reviewed. After a description of the pioneering experiments of the mid-1980s, we focus on the recent efforts of the three Swiss laboratories currently working in the field in close collaboration. This newly refreshed initiative in near-field optics is supported by the Swiss Priority Program Optique.
Scanning near-field optical probe with ultrasmall spot size. Novotny, Lukas; Pohl, Wolfgang Dieter; Hecht, Bert. In Optics Letters, 20(9), pp. 970–972. 1995.
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A novel light-emitting probe for scanning near-field optical microscopy is investigated theoretically. The three-dimensional vectorial Helmholtz equation is solved for the new probe geometry by using the multiple multipole method. The novel probe consists of a dielectric tip that is entirely metal coated. It provides a single near-field spot that can be smaller than 20 nm (FWHM). The dependence on tip radius, taper angle, and metal thickness in front of the tip is investigated for the power transmission through the probe as well as for the spot size.

@article{novotny1995scanning, abstract = {A novel light-emitting probe for scanning near-field optical microscopy is investigated theoretically. The three-dimensional vectorial Helmholtz equation is solved for the new probe geometry by using the multiple multipole method. The novel probe consists of a dielectric tip that is entirely metal coated. It provides a single near-field spot that can be smaller than 20 nm (FWHM). The dependence on tip radius, taper angle, and metal thickness in front of the tip is investigated for the power transmission through the probe as well as for the spot size.}, author = {Novotny, Lukas and Pohl, Wolfgang Dieter and Hecht, Bert}, journal = {Optics Letters}, keywords = {theory}, month = {05}, number = 9, pages = {970-972}, title = {Scanning near-field optical probe with ultrasmall spot size}, volume = 20, year = 1995 }

%0 Journal Article %1 novotny1995scanning %A Novotny, Lukas %A Pohl, Wolfgang Dieter %A Hecht, Bert %D 1995 %J Optics Letters %N 9 %P 970-972 %R 10.1364/OL.20.000970 %T Scanning near-field optical probe with ultrasmall spot size %V 20 %X A novel light-emitting probe for scanning near-field optical microscopy is investigated theoretically. The three-dimensional vectorial Helmholtz equation is solved for the new probe geometry by using the multiple multipole method. The novel probe consists of a dielectric tip that is entirely metal coated. It provides a single near-field spot that can be smaller than 20 nm (FWHM). The dependence on tip radius, taper angle, and metal thickness in front of the tip is investigated for the power transmission through the probe as well as for the spot size.
Combined aperture SNOM/PSTM: best of both worlds?. Hecht, Bert; Heinzelmann, Harry; Pohl, Wolfgang Dieter. In Ultramicroscopy, 57(2), pp. 228–234. 1995.
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Aperture scanning near-field optical microscopy (SNOM/NSOM) and scanning tunneling optical microscopy (STOM, also known as PSTM) are integrated into an instrument which combines the advantages of both schemes. As a result, more near-field optical information can be obtained and new modes of operation become possible. Scan images of a glass surface with a fine grating relief demonstrate some of the capabilities of the new ‘TNOM’ technique.

@article{hecht1995combined, abstract = {Aperture scanning near-field optical microscopy (SNOM/NSOM) and scanning tunneling optical microscopy (STOM, also known as PSTM) are integrated into an instrument which combines the advantages of both schemes. As a result, more near-field optical information can be obtained and new modes of operation become possible. Scan images of a glass surface with a fine grating relief demonstrate some of the capabilities of the new ‘TNOM’ technique.}, author = {Hecht, Bert and Heinzelmann, Harry and Pohl, Wolfgang Dieter}, journal = {Ultramicroscopy}, keywords = {SNOM}, month = {02}, number = 2, pages = {228-234}, title = {Combined aperture SNOM/PSTM: best of both worlds?}, volume = 57, year = 1995 }

%0 Journal Article %1 hecht1995combined %A Hecht, Bert %A Heinzelmann, Harry %A Pohl, Wolfgang Dieter %D 1995 %J Ultramicroscopy %N 2 %P 228-234 %R 10.1016/0304-3991(94)00144-C %T Combined aperture SNOM/PSTM: best of both worlds? %V 57 %X Aperture scanning near-field optical microscopy (SNOM/NSOM) and scanning tunneling optical microscopy (STOM, also known as PSTM) are integrated into an instrument which combines the advantages of both schemes. As a result, more near-field optical information can be obtained and new modes of operation become possible. Scan images of a glass surface with a fine grating relief demonstrate some of the capabilities of the new ‘TNOM’ technique.
Forbidden light scanning near-field optical microscopy. Heinzelmann, Harry; Hecht, Bert; Novotny, Lukas; Pohl, Wolfgang Dieter. In J. Microscopy, 177(2), pp. 115–118. 1995.
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Near-field optics (NFO) opens the door to light microscopy techniques with resolutions well beyond the diffraction limit. The richness of optical investigations is now applicable on a near-molecular level. Among the novel scanning near-field optical microscopy (SNOM) schemes, the most prominent representatives are aperture SNOM and scanning tunnelling optical microscopy (STOM or PSTM). New experimental and theoretical work has to be performed to study the phenomena specific to NFO. One such example is the angular dependence of light emission in aperture SNOM. The detection of radiation at angles greater than the critical angle of total internal reflection αc = arcsin(n−1), where n is the sample refractive index, can represent a microscopy scheme that combines the respective advantages of both aperture SNOM and STOM. Recent experiments have demonstrated the expected exponential dependence of light intensity on gap width (for fixed emission angle α > αc). The decay length as a function of α is in agreement with the Fresnel description of the evanescent field when total reflection occurs at an interface. These investigations were additionally motivated by calculations based on the multiple multipole method.

@article{heinzelmann1995forbidden, abstract = {Near-field optics (NFO) opens the door to light microscopy techniques with resolutions well beyond the diffraction limit. The richness of optical investigations is now applicable on a near-molecular level. Among the novel scanning near-field optical microscopy (SNOM) schemes, the most prominent representatives are aperture SNOM and scanning tunnelling optical microscopy (STOM or PSTM). New experimental and theoretical work has to be performed to study the phenomena specific to NFO. One such example is the angular dependence of light emission in aperture SNOM. The detection of radiation at angles greater than the critical angle of total internal reflection αc = arcsin(n−1), where n is the sample refractive index, can represent a microscopy scheme that combines the respective advantages of both aperture SNOM and STOM. Recent experiments have demonstrated the expected exponential dependence of light intensity on gap width (for fixed emission angle α > αc). The decay length as a function of α is in agreement with the Fresnel description of the evanescent field when total reflection occurs at an interface. These investigations were additionally motivated by calculations based on the multiple multipole method.}, author = {Heinzelmann, Harry and Hecht, Bert and Novotny, Lukas and Pohl, Wolfgang Dieter}, journal = {J. Microscopy}, keywords = {SNOM}, month = {02}, number = 2, pages = {115–118}, title = {Forbidden light scanning near-field optical microscopy}, volume = 177, year = 1995 }

%0 Journal Article %1 heinzelmann1995forbidden %A Heinzelmann, Harry %A Hecht, Bert %A Novotny, Lukas %A Pohl, Wolfgang Dieter %D 1995 %J J. Microscopy %N 2 %P 115--118 %R 10.1111/j.1365-2818.1995.tb03541.x %T Forbidden light scanning near-field optical microscopy %V 177 %X Near-field optics (NFO) opens the door to light microscopy techniques with resolutions well beyond the diffraction limit. The richness of optical investigations is now applicable on a near-molecular level. Among the novel scanning near-field optical microscopy (SNOM) schemes, the most prominent representatives are aperture SNOM and scanning tunnelling optical microscopy (STOM or PSTM). New experimental and theoretical work has to be performed to study the phenomena specific to NFO. One such example is the angular dependence of light emission in aperture SNOM. The detection of radiation at angles greater than the critical angle of total internal reflection αc = arcsin(n−1), where n is the sample refractive index, can represent a microscopy scheme that combines the respective advantages of both aperture SNOM and STOM. Recent experiments have demonstrated the expected exponential dependence of light intensity on gap width (for fixed emission angle α > αc). The decay length as a function of α is in agreement with the Fresnel description of the evanescent field when total reflection occurs at an interface. These investigations were additionally motivated by calculations based on the multiple multipole method.
“Tunnel” near-field optical microscopy: TNOM-2. Hecht, Bert; Pohl, Wolfgang Dieter; Heinzelmann, Harry; Novotny, Lukas. In Photons and Local Probes, O. Marti, R. Möller (eds.), pp. 93–107. Springer Netherlands, Dordrecht, 1995.
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Light emitted from the aperture of a near-field optical probe in close vicinity to a dielectric object propagates in classically “forbidden” as well as “allowed” directions; the two zones are separated by the critical angle for total internal reflection. The new “tunnel” near-field optical microscopy (TNOM) technique makes use of the forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. A new interferometric shear (friction) force detector allows very small-amplitude tip vibrations, which helped improve the resolution. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. Several examples of images with a resolution of ≤50 nm are presented. The influence of topography on image formation is analyzed and discussed.

@incollection{hecht1995tunnel, abstract = {Light emitted from the aperture of a near-field optical probe in close vicinity to a dielectric object propagates in classically “forbidden” as well as “allowed” directions; the two zones are separated by the critical angle for total internal reflection. The new “tunnel” near-field optical microscopy (TNOM) technique makes use of the forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. A new interferometric shear (friction) force detector allows very small-amplitude tip vibrations, which helped improve the resolution. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. Several examples of images with a resolution of ≤50 nm are presented. The influence of topography on image formation is analyzed and discussed.}, address = {Dordrecht}, author = {Hecht, Bert and Pohl, Wolfgang Dieter and Heinzelmann, Harry and Novotny, Lukas}, booktitle = {Photons and Local Probes}, editor = {Marti, Othmar and Möller, Rolf}, keywords = {near-field}, pages = {93-107}, publisher = {Springer Netherlands}, series = {NATO ASI Series}, title = {“Tunnel” near-field optical microscopy: TNOM-2}, year = 1995 }

%0 Book Section %1 hecht1995tunnel %A Hecht, Bert %A Pohl, Wolfgang Dieter %A Heinzelmann, Harry %A Novotny, Lukas %B Photons and Local Probes %C Dordrecht %D 1995 %E Marti, Othmar %E Möller, Rolf %I Springer Netherlands %P 93-107 %R 10.1007/978-94-011-0423-4_7 %T “Tunnel” near-field optical microscopy: TNOM-2 %X Light emitted from the aperture of a near-field optical probe in close vicinity to a dielectric object propagates in classically “forbidden” as well as “allowed” directions; the two zones are separated by the critical angle for total internal reflection. The new “tunnel” near-field optical microscopy (TNOM) technique makes use of the forbidden and allowed radiation, in contrast to standard scanning near-field optical microscopy (SNOM or NSOM), which records only the allowed light. A new interferometric shear (friction) force detector allows very small-amplitude tip vibrations, which helped improve the resolution. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. Several examples of images with a resolution of ≤50 nm are presented. The influence of topography on image formation is analyzed and discussed. %@ 978-94-011-0423-4

Near-Field Optical Spectroscopy of Individual Molecules in Solids. Moerner, William Esco; Plakhotnik, Taras; Irngartinger, Thomas; Wild, Urs P.; Pohl, Wolfgang Dieter; Hecht, Bert. In Phys. Rev. Lett., 73(20), pp. 2764–2767. 1994.
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Near-field single-molecule spectroscopy was performed on a crystal of pentacene-doped p-terphenyl using an Al-coated optical fiber tip with 60 nm diam aperture as a near-field light source. Individual molecules located ≅400 nm from the tip had linewidths of 10-20 MHz at 1.8 K. The background fluorescence provided a useful distance-sensing signal, as it increased exponentially during approach with a characteristic length of ≅100 nm. Single molecules closest to the tip were identified by Stark shifts.

@article{moerner1994nearfield, abstract = {Near-field single-molecule spectroscopy was performed on a crystal of pentacene-doped p-terphenyl using an Al-coated optical fiber tip with 60 nm diam aperture as a near-field light source. Individual molecules located ≅400 nm from the tip had linewidths of 10-20 MHz at 1.8 K. The background fluorescence provided a useful distance-sensing signal, as it increased exponentially during approach with a characteristic length of ≅100 nm. Single molecules closest to the tip were identified by Stark shifts.}, author = {Moerner, William Esco and Plakhotnik, Taras and Irngartinger, Thomas and Wild, Urs P. and Pohl, Wolfgang Dieter and Hecht, Bert}, journal = {Phys. Rev. Lett.}, keywords = {single-molecules}, month = 11, number = 20, pages = {2764-2767}, title = {Near-Field Optical Spectroscopy of Individual Molecules in Solids}, volume = 73, year = 1994 }

%0 Journal Article %1 moerner1994nearfield %A Moerner, William Esco %A Plakhotnik, Taras %A Irngartinger, Thomas %A Wild, Urs P. %A Pohl, Wolfgang Dieter %A Hecht, Bert %D 1994 %J Phys. Rev. Lett. %N 20 %P 2764-2767 %R 10.1103/PhysRevLett.73.2764 %T Near-Field Optical Spectroscopy of Individual Molecules in Solids %V 73 %X Near-field single-molecule spectroscopy was performed on a crystal of pentacene-doped p-terphenyl using an Al-coated optical fiber tip with 60 nm diam aperture as a near-field light source. Individual molecules located ≅400 nm from the tip had linewidths of 10-20 MHz at 1.8 K. The background fluorescence provided a useful distance-sensing signal, as it increased exponentially during approach with a characteristic length of ≅100 nm. Single molecules closest to the tip were identified by Stark shifts.

Near-field optical microscope. Hecht, Bert; Heinzelmann, Harald; Novotny, Lukas; Pohl, Wolfgang Dieter. 1993, October 4.
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- [ URL ]
The invention relates to a near-field optical microscope, in particular to a scanning near-field optical microscope (SNOM), comprising means for determining the intensity of light emerging from the near-field at a direction differing from the direction perpendicular to the surface of the sample to be examined, preferably emerging at an angle θ. larger than the critical angle. Superposing light with different azimuth angles by using suitable positioned mirrors and beamsplitters enables imaging with higher contrast. The invention allows an accurate control of the distance between the probing tip of the SNOM and the sample by using the measured intensity in a feedback loop.

@patent{hecht1993nearfield, abstract = {The invention relates to a near-field optical microscope, in particular to a scanning near-field optical microscope (SNOM), comprising means for determining the intensity of light emerging from the near-field at a direction differing from the direction perpendicular to the surface of the sample to be examined, preferably emerging at an angle θ. larger than the critical angle. Superposing light with different azimuth angles by using suitable positioned mirrors and beamsplitters enables imaging with higher contrast. The invention allows an accurate control of the distance between the probing tip of the SNOM and the sample by using the measured intensity in a feedback loop.}, annote = {ClassificationsG01Q60/22: Probes, their manufacture, or their related instrumentation, e.g. holdersY10S977/862: Near-field probe}, author = {Hecht, Bert and Heinzelmann, Harald and Novotny, Lukas and Pohl, Wolfgang Dieter}, keywords = {SNOM}, month = 10, number = {CA2170860C}, title = {Near-field optical microscope}, year = 1993 }

%0 Generic %1 hecht1993nearfield %A Hecht, Bert %A Heinzelmann, Harald %A Novotny, Lukas %A Pohl, Wolfgang Dieter %D 1993 %N CA2170860C %T Near-field optical microscope %U https://patents.google.com/patent/CA2170860C/en %X The invention relates to a near-field optical microscope, in particular to a scanning near-field optical microscope (SNOM), comprising means for determining the intensity of light emerging from the near-field at a direction differing from the direction perpendicular to the surface of the sample to be examined, preferably emerging at an angle θ. larger than the critical angle. Superposing light with different azimuth angles by using suitable positioned mirrors and beamsplitters enables imaging with higher contrast. The invention allows an accurate control of the distance between the probing tip of the SNOM and the sample by using the measured intensity in a feedback loop. %Z ClassificationsG01Q60/22: Probes, their manufacture, or their related instrumentation, e.g. holdersY10S977/862: Near-field probe
Near-field optical measurement of the surface plasmon field. Marti, Othmar; Bielefeldt, Hartmut; Hecht, Bert; Herminghaus, Stephan; Leiderer, Paul; Mlynek, Jürgen. In Optics Commun., 96(4-6), pp. 225–228. Elsevier {BV}, 1993.
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The intensity of the evanescent electromagnetic wave of optically excited surface plasmons was measured directly using a scanning tunneling optical microscope (STOM) setup. When resonant coupling of the driving field to the surface plasmons was achieved, the measured intensity was increased by a factor of 30 larger than the corresponding evanescent wave intensity on a bare glass surface, in agreement with the theoretical prediction. Experimental results are presented for three laser wavelengths (514 nm, 633 nm, 670 nm). Possible applications of the technique to study surface plasmon fields are discussed.

@article{marti1993nearfield, abstract = {The intensity of the evanescent electromagnetic wave of optically excited surface plasmons was measured directly using a scanning tunneling optical microscope (STOM) setup. When resonant coupling of the driving field to the surface plasmons was achieved, the measured intensity was increased by a factor of 30 larger than the corresponding evanescent wave intensity on a bare glass surface, in agreement with the theoretical prediction. Experimental results are presented for three laser wavelengths (514 nm, 633 nm, 670 nm). Possible applications of the technique to study surface plasmon fields are discussed.}, author = {Marti, Othmar and Bielefeldt, Hartmut and Hecht, Bert and Herminghaus, Stephan and Leiderer, Paul and Mlynek, Jürgen}, journal = {Optics Commun.}, keywords = {plasmon}, month = {02}, number = {4-6}, pages = {225-228}, publisher = {Elsevier {BV}}, title = {Near-field optical measurement of the surface plasmon field}, volume = 96, year = 1993 }

%0 Journal Article %1 marti1993nearfield %A Marti, Othmar %A Bielefeldt, Hartmut %A Hecht, Bert %A Herminghaus, Stephan %A Leiderer, Paul %A Mlynek, Jürgen %D 1993 %I Elsevier {BV} %J Optics Commun. %N 4-6 %P 225-228 %R 10.1016/0030-4018(93)90265-7 %T Near-field optical measurement of the surface plasmon field %V 96 %X The intensity of the evanescent electromagnetic wave of optically excited surface plasmons was measured directly using a scanning tunneling optical microscope (STOM) setup. When resonant coupling of the driving field to the surface plasmons was achieved, the measured intensity was increased by a factor of 30 larger than the corresponding evanescent wave intensity on a bare glass surface, in agreement with the theoretical prediction. Experimental results are presented for three laser wavelengths (514 nm, 633 nm, 670 nm). Possible applications of the technique to study surface plasmon fields are discussed.
Direct Measurement of the Field Enhancement Caused by Surface Plasmons with the Scanning Tunneling Optical Microscope. Bielefeldt, Hartmut; Hecht, Bert; Herminghaus, Stephan; Mlynek, Jürgen; Marti, Othmar. In Near Field Optics, W. D. Pohl, D. Courjon (eds.), pp. 281–286. Springer Netherlands, Dordrecht, 1993.
- [ Abstract ]
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A scanning tunneling optical microscope (STOM) is used to directly determine the electromagnetic field amplitude of optically excited surface plasma waves on a silver film. The field amplitudes are measured as a fonction of the angle of incidence of the exciting light beam. The excitation of surface plasmons on the silver film causes a characteristic field enhancement compared to evanescent waves on uncoated surfaces. The measured values for the resonance angle, resonance width and the field enhancement ratio at various wavelengths are compared with theory and with simultaneous measurements of attenuated total internal reflection (ATR). The sensitivity of near-field optical methods to the film thickness is comparable to that of the ATR method. However, while ATR measurements are limited by diffraction, the lateral resolution of STOM can be of the order of 50 nm.

@incollection{bielefeldt1993direct, abstract = {A scanning tunneling optical microscope (STOM) is used to directly determine the electromagnetic field amplitude of optically excited surface plasma waves on a silver film. The field amplitudes are measured as a fonction of the angle of incidence of the exciting light beam. The excitation of surface plasmons on the silver film causes a characteristic field enhancement compared to evanescent waves on uncoated surfaces. The measured values for the resonance angle, resonance width and the field enhancement ratio at various wavelengths are compared with theory and with simultaneous measurements of attenuated total internal reflection (ATR). The sensitivity of near-field optical methods to the film thickness is comparable to that of the ATR method. However, while ATR measurements are limited by diffraction, the lateral resolution of STOM can be of the order of 50 nm.}, address = {Dordrecht}, author = {Bielefeldt, Hartmut and Hecht, Bert and Herminghaus, Stephan and Mlynek, Jürgen and Marti, Othmar}, booktitle = {Near Field Optics}, editor = {Pohl, Wolfgang Dieter and Courjon, Daniel}, keywords = {plasmon}, pages = {281-286}, publisher = {Springer Netherlands}, series = {NATO ASI Series}, title = {Direct Measurement of the Field Enhancement Caused by Surface Plasmons with the Scanning Tunneling Optical Microscope}, year = 1993 }

%0 Book Section %1 bielefeldt1993direct %A Bielefeldt, Hartmut %A Hecht, Bert %A Herminghaus, Stephan %A Mlynek, Jürgen %A Marti, Othmar %B Near Field Optics %C Dordrecht %D 1993 %E Pohl, Wolfgang Dieter %E Courjon, Daniel %I Springer Netherlands %P 281-286 %R 10.1007/978-94-011-1978-8_31 %T Direct Measurement of the Field Enhancement Caused by Surface Plasmons with the Scanning Tunneling Optical Microscope %X A scanning tunneling optical microscope (STOM) is used to directly determine the electromagnetic field amplitude of optically excited surface plasma waves on a silver film. The field amplitudes are measured as a fonction of the angle of incidence of the exciting light beam. The excitation of surface plasmons on the silver film causes a characteristic field enhancement compared to evanescent waves on uncoated surfaces. The measured values for the resonance angle, resonance width and the field enhancement ratio at various wavelengths are compared with theory and with simultaneous measurements of attenuated total internal reflection (ATR). The sensitivity of near-field optical methods to the film thickness is comparable to that of the ATR method. However, while ATR measurements are limited by diffraction, the lateral resolution of STOM can be of the order of 50 nm. %@ 978-94-011-1978-8

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