Harald Giessen | Universität Stuttgart (original) (raw)

Papers by Harald Giessen

We introduce the new concept of microcavity plasmonics: A cut-wire pair is strongly coupled to ph... more We introduce the new concept of microcavity plasmonics: A cut-wire pair is strongly coupled to photonic modes in a microcavity. Large anticrossings of the symmetric and antisymmetric plasmon modes and the cavity modes are observed.

Reports on Progress in Physics, Oct 1, 2018

The Faraday effect describes the phenomenon that a magnetized material can alter the polarization... more The Faraday effect describes the phenomenon that a magnetized material can alter the polarization state of transmitted light. Interestingly, unlike most light-matter interactions in nature, it breaks Lorentz reciprocity. This exceptional behavior is utilized for applications such as optical isolators, which are core elements in communication and laser systems. While there is high demand for sub-micron nonreciprocal photonic devices, the realization of such systems is extremely challenging as conventional magneto-optic materials only provide weak magnetooptic response within small volumes. Plasmonics could be a key to overcome this hurdle in the future: over the last years there have been several lines of work demonstrating that different types of metallic nanostrutures can be utilized to greatly enhance the magneto-optic response of conventional materials. In this review we give an overview over the state of the art in the field and highlight recent developments on hybrid plasmonic Faraday rotators. Our discussions are mainly focused on the visible and near-infrared wavelength regions and cover both experimental realizations as well as analytical descriptions. Special attention will be paid to recent developments on hybrid plasmonic thin film systems consisting of gold and europium chalcogenides.

Physical Review Letters, Jun 8, 2016

We present a first-order perturbation theory to calculate the frequency shift and linewidth chang... more We present a first-order perturbation theory to calculate the frequency shift and linewidth change of photonic resonances in one-and two-dimensional periodic structures under modifications of the surrounding refractive index. Our method is based on the resonant state expansion, for which we extend the analytical mode normalization to periodic structures. We apply this theory to calculate the sensitivity of bright dipolar and much darker quadrupolar plasmonic modes by determining the maximum shift and optimal sensing volume.

Plasmon polaritons have revolutionized our world of nanophotonics. They have created a platform f... more Plasmon polaritons have revolutionized our world of nanophotonics. They have created a platform for enhanced light-matter interactions, propagation of light beyond the diffraction limit, and nanofocusing of electromagnetic energy. However, for applications in data processing and telecommunication, dissipation of optical energy in metallic waveguides is much beyond what can be tolerated for nanocircuitry. Recently other groups of polaritonic waves, namely photon polaritons, exciton polaritons, and Dirac plasmons have been demonstrated as possible candidates for nanophotonics1. Interestingly, a topological insulator like Bi2Se32, as well as heterostructures like graphene/hBN 3, can support coexisting polaritonic waves of all the kinds stated above. At THz frequencies and near to the Fermi energy level, those materials support both hyperbolic phonon polaritons and Dirac plasmons, whereas at infrared and visible ranges4,5 exists another channel for exciton-polariton mode. Here, we mainly discuss the dispersion of the surface polaritons and their spatiotemporal behaviors, at all the energy ranges stated above. We however mainly focus on an aspect of topological insulators which is less discussed beforehand, i.e. topological magnetoelectric effect6. We study the criteria for existence of propagating optical modes which are transversely bound at the interface of two materials. In particular, quite general cases are considered, where the materials involved are assumed to be anisotropic, but also demonstrating magneto-electric effects7. We also discuss the situations where the coexistence of Dirac and hyperbolic polaritons result in level repulsion. We further study the effect of topological magnetoelectric effect on the appearance of hybrid optical modes with various polarization states. In addition to surface polaritons, existence of wedges support another channel for long range propagation of hyperbolic polaritons, due to the coupling of two edge polaritons. We study here the behavior of hyperbolic wedge polaritons at visible and ultraviolet energy ranges. We discuss the radiation damping and long range propagation of hyperbolic wedge and surface polaritons, both theoretically and experimentally using electron energy-loss spectroscopy and finite-difference time-domain method. References 1 Basov, D. N., Fogler, M. M. & de Abajo, F. J. G. Polaritons in van der Waals materials. Science 354, aag1992 (2016). 2 Wu, J.-S., Basov, D. N. & Fogler, M. M. Topological insulators are tunable waveguides for hyperbolic polaritons. Phys. Rev. B 92, 205430 (2015). 3 Woessner, A. et al. Highly confined low-loss plasmons in graphene-boron nitride heterostructures. Nat. Mater. 14, 421-425 (2015). 4 Esslinger, M. et al. Tetradymites as Natural Hyperbolic Materials for the Near-Infrared to Visible. Acs Photon. 1, 1285-1289 (2014). 5 Talebi, N. et al. Wedge Dyakonov Waves and Dyakonov Plasmons in Topological Insulator Bi2Se3 Probed by Electron Beams. Acs Nano 10, 6988-6994 (2016). 6 Dziom, V. et al. Observation of the universal magnetoelectric effect in a 3D topological insulator. Nat. Commun. 8 15197 (2017). 7 Talebi, N. Optical modes in slab waveguides with magnetoelectric effect. J. Opt.-Uk 18, 055607 (2016)

Conference on Lasers and Electro-Optics, 2021

Nanophotonic chiral sensing has recently attracted a lot of attention. The idea is to exploit the... more Nanophotonic chiral sensing has recently attracted a lot of attention. The idea is to exploit the strong light-matter interaction in nanophotonic resonators to determine the concentration of chiral molecules at ultra-low thresholds, which is highly attractive for numerous applications in life science and chemistry. However, a thorough understanding of the underlying interactions is still missing. The theoretical description relies on either simple approximations or on purely numerical approaches. We close this gap and present a general theory of chiral light-matter interactions in arbitrary resonators. Our theory describes the chiral interaction as a perturbation of the resonator modes, also known as resonant states or quasinormal modes. We observe two dominant contributions: A chirality-induced resonance shift and changes in the modes excitation and emission efficiencies. Our theory brings new and deep insights for tailoring and enhancing chiral lightmatter interactions. Furthermore, it allows to predict spectra much more efficiently in comparison to conventional approaches. This is particularly true as chiral interactions are inherently weak and therefore perturbation theory fits extremely well for this problem.

Nature Communications, Apr 5, 2011

Future photonic circuits with the capability of high-speed data processing at optical frequencies... more Future photonic circuits with the capability of high-speed data processing at optical frequencies will rely on the implementation of efficient emitters and detectors on the nanoscale. Towards this goal, bridging the size mismatch between optical radiation and subwavelength emitters or detectors by optical nanoantennas is a subject of current research in the field of plasmonics. Here we introduce an array of three-dimensional optical Yagi-uda antennas, fabricated using top-down fabrication techniques combined with layer-by-layer processing. We show that the concepts of radiofrequency antenna arrays can be applied to the optical regime proving superior directional properties compared with a single planar optical antenna, particularly for emission and reception into the third dimension. measuring the optical properties of the structure reveals that impinging light on the array is efficiently absorbed on the subwavelength scale because of the high directivity. moreover, we show in simulations that combining the array with suitable feeding circuits gives rise to the prospect of beam steering at optical wavelengths.

arXiv (Cornell University), May 16, 2022

Manipulating light on the nanoscale has become a central challenge in metadevices, resonant surfa... more Manipulating light on the nanoscale has become a central challenge in metadevices, resonant surfaces, nanoscale optical sensors, and many more, and it is largely based on resonant light confinement in dispersive and lossy metals and dielectrics. Here, we experimentally implement a novel strategy for dielectric nanophotonics: Resonant subwavelength confinement of light in air. We demonstrate that voids created in high-index dielectric host materials support localized resonant modes with exceptional optical properties. Due to the confinement in air, the modes do not suffer from the loss and dispersion of the dielectric host medium. We experimentally realize these resonant Mie voids by focused ion beam milling into bulk silicon wafers and experimentally demonstrate resonant light confinement down to the UV spectral range at 265 nm (4.68 eV). Furthermore, we utilize the bright, intense, and naturalistic colours for nanoscale colour printing. The combination of resonant dielectric Mie voids with dielectric nanoparticles will more than double the parameter space for the future design of metasurfaces and other micro-and nanoscale optical elements and push their operation into the blue and UV spectral range. In particular, this extension will enable novel antenna and structure designs which benefit from the full access to the modal field inside the void as well as the nearly free choice of the high-index material.

Conference on Lasers and Electro-Optics, 2020

Excitons in monolayer transition-metal-dichalcogenides dominate their optical response, however, ... more Excitons in monolayer transition-metal-dichalcogenides dominate their optical response, however, the achieved light-exciton interaction strength have been far below unity, and a complete picture of its underlying physics and fundamental limits has not been provided. Using a van der Waals heterostructure cavity, we demonstrate near-unity excitonic absorption, together with efficient emission at ultra-low excitation powers. We find that the interplay between the radiative, non-radiative and dephasing decay rates plays a crucial role in this interaction, and unveil a universal absorption law for excitons in 2D systems.

Conference on Lasers and Electro-Optics, 2021

We introduce a new technique, namely time-resolved vector microscopy, that enables us to compose ... more We introduce a new technique, namely time-resolved vector microscopy, that enables us to compose entire movies on a sub-femtosecond time scale and a 10 nm scale of the electric field vectors of surface plasmon skyrmions.

Chirality is found at all length scales in nature, and chiral metasurfaces have recently attracte... more Chirality is found at all length scales in nature, and chiral metasurfaces have recently attracted attention due to their exceptional optical properties and their potential applications. Most of these metasurfaces are fabricated by top-down methods or bottom-up approaches that cannot be tuned in terms of structure and composition. By combining grazing incidence spraying of plasmonic nanowires and nanorods and Layer-by-Layer assembly, we show that nonchiral 1D nano-objects can be assembled into scalable chiral Bouligand nanostructures whose mesoscale anisotropy is controlled with simple macroscopic tools. Such multilayer helical assemblies of linearly oriented nanowires and nanorods display very high circular dichroism up to 13 000 mdeg and giant dissymmetry factors up to g ≈ 0.30 over the entire visible and near-infrared range. The chiroptical properties of the chiral multilayer stack are successfully modeled using a transfer matrix formalism based on the experimentally determined properties of each individual layer. The proposed approach can be extended to much more elaborate architectures and gives access to template-free and enantiomerically pure nanocomposites whose structure can be finely tuned through simple design principles.

ACS Photonics, 2019

Highly efficient counter-propagating fiber-based optical traps are presented which utilize conver... more Highly efficient counter-propagating fiber-based optical traps are presented which utilize converging beams from fibers with 3D printed diffractive Fresnel lenses on their facet. The use of a converging beam instead of diverging beam in dual-fiber traps creates a strong trapping efficiency in both the axial and the transverse directions. Converging beams with a numerical aperture of up to 0.7 are produced by diffractive Fresnel lenses. These lenses also provide a large focal distance of up to 200 μm in a moderately high refractive index medium. Fabrication of such diffractive lenses with microsized features at the tip of a fiber is possible by femtosecond two photon lithography. In comparison to chemically etched fiber tips, the normalized trap stiffness of dual-fiber tweezers is increased by a substantial factor of 35−50 when using a converging beam produced by diffractive Fresnel lenses. The large focal length provided by these diffractive structures allows working at a large fiber-to-fiber distance, which leads to larger space and the freedom to combine other spectroscopy and analytical methods in combination with trapping.

Optics Letters, 2019

We present a novel light source specifically tailored for stimulated Raman scatteringspectroscopi... more We present a novel light source specifically tailored for stimulated Raman scatteringspectroscopic optical coherence tomography (SRS-SOCT), which is, to the best of our knowledge, a novel molecular imaging method that combines the molecular sensitivity of SRS with the spatial and spectral multiplexing capabilities of SOCT. The novel laser consists of an 8 W, 450 fs Yb:KGW oscillator, with a repetition rate of 40 MHz, which delivers the Stokes beam for SRS-SOCT and also pumps and amplifies an optical parametric oscillator (OPO). The output of the amplified OPO is then frequency doubled and coherently broadened using a custom-made tapered fiber that generates bandwidth pulses >40 nm, compressible to <50 fs, with the average power over 150 mW, near the shot-noise limit above 250 kHz. The broadened and compressed pulse simultaneously serves as the pump beam and SOCT light source for SRS-SOCT. This light source is assessed for SRS-SOCT, and its implications for other imaging methods are discussed.

ACS Photonics, 2017

We develop a theoretical model of the excitation and interference of surface plasmon polariton (S... more We develop a theoretical model of the excitation and interference of surface plasmon polariton (SPP) waves with femtosecond laser pulses and use the model to understand the features in images from subfemtosecond time-resolved two-photon photoelectron microscopy (2PPE-PEEM). The numerically efficient model is based on the optics of SPP modes on multi-layer thin films and takes account of the excitation and interference by the incident light, its polarization, the boundary shape on the film where the plasmons are generated, the pulsed form of the excitation and the time integration associated with the PEEM method. The model explains the dominant features observed in the images including the complex patterns formed in experiments involving orbital 1 Page 1 of 31 ACS Paragon Plus Environment ACS Photonics angular momentum. The model forms the basis of an efficient numerical method for simulating time-resolved 2PPE-PEEM images of SPP wave propagation. The numerics is extremely fast, efficient and accurate, so that each image can takes as little as a few seconds to calculate on a laptop computer, enabling entire PEEM movies to be calculated within minutes.

Light: Science & Applications, 2017

Compact nanophotonic elements exhibiting adaptable properties are essential components for the mi... more Compact nanophotonic elements exhibiting adaptable properties are essential components for the miniaturization of powerful optical technologies such as adaptive optics and spatial light modulators. While the larger counterparts typically rely on mechanical actuation, this can be undesirable in some cases on a microscopic scale due to inherent space restrictions. Here, we present a novel design concept for highly integrated active optical components that employs a combination of resonant plasmonic metasurfaces and the phase-change material Ge 3 Sb 2 Te 6. In particular, we demonstrate beam switching and bifocal lensing, thus, paving the way for a plethora of active optical elements employing plasmonic metasurfaces, which follow the same design principles.

Science Advances, 2017

A highly miniaturized vision system is realized by directly 3D-printing different multilens objec... more A highly miniaturized vision system is realized by directly 3D-printing different multilens objectives onto a CMOS image sensor.

ACS Photonics, 2016

The key property of metal nanostructures is their unique ability to channel far-field radiation t... more The key property of metal nanostructures is their unique ability to channel far-field radiation to sub-wavelength dimensions. The resulting strongly confined and enhanced electromagnetic fields boost nonlinear optical effects at the nanoscale. In this review article we highlight and summarize the recent most important investigations and advances in the field of "Nonlinear Plasmonic Spectroscopy" and we present results of second and third-harmonic spectroscopy experiments of plasmonic nanoantenna arrays that consist of different unit cell elements, ranging from dipole nanoantennas to complex hybrid plasmonic structures. The experiments on dipole nanoantennas show that nonlinear optical processes can be enhanced either by plasmonic resonances at the fundamental laser wavelength or at the spectral position of the harmonic signal. Furthermore, we investigate the quadrupolar third-harmonic response of dolmen-type plasmonic Fano structures and find that the third-harmonic polarization-field of the quadrupolar mode does not radiate to the far-field due to destructive interference. Finally, we incorporate indium tin oxide nanocrystals into the hot-spot of plasmonic gap-antennas and find a doubling of the third-harmonic response of the hybrid antennas when compared to bare gold gap-antennas. The experimental results of the nanoantenna arrays can be modeled and understood using a classical model of anharmonic oscillators and are supported by finite element simulations. Parts of this review article are based on previous publications. 1-4

2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006

» View Full Text: Acrobat PDF (26 KB) * * Note that full-text PDFs from conferences typically con... more » View Full Text: Acrobat PDF (26 KB) * * Note that full-text PDFs from conferences typically contain 1-3 pages of content, some or all of which might be an abstract, summary, or miscellaneous items. ... Coupling of localized plasmons and propagating waveguide modes leads to ...

Photonic Metamaterials: From Random to Periodic, 2006

Abstract The influence of the specific split-ring resonator geometry on the electromagnetic reson... more Abstract The influence of the specific split-ring resonator geometry on the electromagnetic resonances and especially their spectral width is analyzed experimentally and theoretically. Furthermore, we separate radiative and nonradiative contributions to the linewidth of the resonances.

Physical Review B, 2008

We study the scattering parameters of typical transmission line resonant circuits and their corre... more We study the scattering parameters of typical transmission line resonant circuits and their corresponding nonlocal effective material parameters at optical frequencies using transmission line theory. We find that each circuit has specific features in terms of nonlocal permittivity and permeability and can be utilized to quantitatively synthesize transmission line circuit models for metamaterial slabs. As application examples, we construct circuit models for cut wires, cut-wire pairs, metallic meshes, and mesh pairs. Moreover, we calculate local material parameters in a simple way using fitted impedance parameters together with a transmission line homogenization procedure. Using transmission line ͑TL͒ models, we show how the material parameters can be optimized in actual metamaterials. The physical dependence of circuit parameters on structure geometries validates our TL model further.

We introduce the new concept of microcavity plasmonics: A cut-wire pair is strongly coupled to ph... more We introduce the new concept of microcavity plasmonics: A cut-wire pair is strongly coupled to photonic modes in a microcavity. Large anticrossings of the symmetric and antisymmetric plasmon modes and the cavity modes are observed.

Reports on Progress in Physics, Oct 1, 2018

The Faraday effect describes the phenomenon that a magnetized material can alter the polarization... more The Faraday effect describes the phenomenon that a magnetized material can alter the polarization state of transmitted light. Interestingly, unlike most light-matter interactions in nature, it breaks Lorentz reciprocity. This exceptional behavior is utilized for applications such as optical isolators, which are core elements in communication and laser systems. While there is high demand for sub-micron nonreciprocal photonic devices, the realization of such systems is extremely challenging as conventional magneto-optic materials only provide weak magnetooptic response within small volumes. Plasmonics could be a key to overcome this hurdle in the future: over the last years there have been several lines of work demonstrating that different types of metallic nanostrutures can be utilized to greatly enhance the magneto-optic response of conventional materials. In this review we give an overview over the state of the art in the field and highlight recent developments on hybrid plasmonic Faraday rotators. Our discussions are mainly focused on the visible and near-infrared wavelength regions and cover both experimental realizations as well as analytical descriptions. Special attention will be paid to recent developments on hybrid plasmonic thin film systems consisting of gold and europium chalcogenides.

Physical Review Letters, Jun 8, 2016

We present a first-order perturbation theory to calculate the frequency shift and linewidth chang... more We present a first-order perturbation theory to calculate the frequency shift and linewidth change of photonic resonances in one-and two-dimensional periodic structures under modifications of the surrounding refractive index. Our method is based on the resonant state expansion, for which we extend the analytical mode normalization to periodic structures. We apply this theory to calculate the sensitivity of bright dipolar and much darker quadrupolar plasmonic modes by determining the maximum shift and optimal sensing volume.

Plasmon polaritons have revolutionized our world of nanophotonics. They have created a platform f... more Plasmon polaritons have revolutionized our world of nanophotonics. They have created a platform for enhanced light-matter interactions, propagation of light beyond the diffraction limit, and nanofocusing of electromagnetic energy. However, for applications in data processing and telecommunication, dissipation of optical energy in metallic waveguides is much beyond what can be tolerated for nanocircuitry. Recently other groups of polaritonic waves, namely photon polaritons, exciton polaritons, and Dirac plasmons have been demonstrated as possible candidates for nanophotonics1. Interestingly, a topological insulator like Bi2Se32, as well as heterostructures like graphene/hBN 3, can support coexisting polaritonic waves of all the kinds stated above. At THz frequencies and near to the Fermi energy level, those materials support both hyperbolic phonon polaritons and Dirac plasmons, whereas at infrared and visible ranges4,5 exists another channel for exciton-polariton mode. Here, we mainly discuss the dispersion of the surface polaritons and their spatiotemporal behaviors, at all the energy ranges stated above. We however mainly focus on an aspect of topological insulators which is less discussed beforehand, i.e. topological magnetoelectric effect6. We study the criteria for existence of propagating optical modes which are transversely bound at the interface of two materials. In particular, quite general cases are considered, where the materials involved are assumed to be anisotropic, but also demonstrating magneto-electric effects7. We also discuss the situations where the coexistence of Dirac and hyperbolic polaritons result in level repulsion. We further study the effect of topological magnetoelectric effect on the appearance of hybrid optical modes with various polarization states. In addition to surface polaritons, existence of wedges support another channel for long range propagation of hyperbolic polaritons, due to the coupling of two edge polaritons. We study here the behavior of hyperbolic wedge polaritons at visible and ultraviolet energy ranges. We discuss the radiation damping and long range propagation of hyperbolic wedge and surface polaritons, both theoretically and experimentally using electron energy-loss spectroscopy and finite-difference time-domain method. References 1 Basov, D. N., Fogler, M. M. & de Abajo, F. J. G. Polaritons in van der Waals materials. Science 354, aag1992 (2016). 2 Wu, J.-S., Basov, D. N. & Fogler, M. M. Topological insulators are tunable waveguides for hyperbolic polaritons. Phys. Rev. B 92, 205430 (2015). 3 Woessner, A. et al. Highly confined low-loss plasmons in graphene-boron nitride heterostructures. Nat. Mater. 14, 421-425 (2015). 4 Esslinger, M. et al. Tetradymites as Natural Hyperbolic Materials for the Near-Infrared to Visible. Acs Photon. 1, 1285-1289 (2014). 5 Talebi, N. et al. Wedge Dyakonov Waves and Dyakonov Plasmons in Topological Insulator Bi2Se3 Probed by Electron Beams. Acs Nano 10, 6988-6994 (2016). 6 Dziom, V. et al. Observation of the universal magnetoelectric effect in a 3D topological insulator. Nat. Commun. 8 15197 (2017). 7 Talebi, N. Optical modes in slab waveguides with magnetoelectric effect. J. Opt.-Uk 18, 055607 (2016)

Conference on Lasers and Electro-Optics, 2021

Nanophotonic chiral sensing has recently attracted a lot of attention. The idea is to exploit the... more Nanophotonic chiral sensing has recently attracted a lot of attention. The idea is to exploit the strong light-matter interaction in nanophotonic resonators to determine the concentration of chiral molecules at ultra-low thresholds, which is highly attractive for numerous applications in life science and chemistry. However, a thorough understanding of the underlying interactions is still missing. The theoretical description relies on either simple approximations or on purely numerical approaches. We close this gap and present a general theory of chiral light-matter interactions in arbitrary resonators. Our theory describes the chiral interaction as a perturbation of the resonator modes, also known as resonant states or quasinormal modes. We observe two dominant contributions: A chirality-induced resonance shift and changes in the modes excitation and emission efficiencies. Our theory brings new and deep insights for tailoring and enhancing chiral lightmatter interactions. Furthermore, it allows to predict spectra much more efficiently in comparison to conventional approaches. This is particularly true as chiral interactions are inherently weak and therefore perturbation theory fits extremely well for this problem.

Nature Communications, Apr 5, 2011

Future photonic circuits with the capability of high-speed data processing at optical frequencies... more Future photonic circuits with the capability of high-speed data processing at optical frequencies will rely on the implementation of efficient emitters and detectors on the nanoscale. Towards this goal, bridging the size mismatch between optical radiation and subwavelength emitters or detectors by optical nanoantennas is a subject of current research in the field of plasmonics. Here we introduce an array of three-dimensional optical Yagi-uda antennas, fabricated using top-down fabrication techniques combined with layer-by-layer processing. We show that the concepts of radiofrequency antenna arrays can be applied to the optical regime proving superior directional properties compared with a single planar optical antenna, particularly for emission and reception into the third dimension. measuring the optical properties of the structure reveals that impinging light on the array is efficiently absorbed on the subwavelength scale because of the high directivity. moreover, we show in simulations that combining the array with suitable feeding circuits gives rise to the prospect of beam steering at optical wavelengths.

arXiv (Cornell University), May 16, 2022

Manipulating light on the nanoscale has become a central challenge in metadevices, resonant surfa... more Manipulating light on the nanoscale has become a central challenge in metadevices, resonant surfaces, nanoscale optical sensors, and many more, and it is largely based on resonant light confinement in dispersive and lossy metals and dielectrics. Here, we experimentally implement a novel strategy for dielectric nanophotonics: Resonant subwavelength confinement of light in air. We demonstrate that voids created in high-index dielectric host materials support localized resonant modes with exceptional optical properties. Due to the confinement in air, the modes do not suffer from the loss and dispersion of the dielectric host medium. We experimentally realize these resonant Mie voids by focused ion beam milling into bulk silicon wafers and experimentally demonstrate resonant light confinement down to the UV spectral range at 265 nm (4.68 eV). Furthermore, we utilize the bright, intense, and naturalistic colours for nanoscale colour printing. The combination of resonant dielectric Mie voids with dielectric nanoparticles will more than double the parameter space for the future design of metasurfaces and other micro-and nanoscale optical elements and push their operation into the blue and UV spectral range. In particular, this extension will enable novel antenna and structure designs which benefit from the full access to the modal field inside the void as well as the nearly free choice of the high-index material.

Conference on Lasers and Electro-Optics, 2020

Excitons in monolayer transition-metal-dichalcogenides dominate their optical response, however, ... more Excitons in monolayer transition-metal-dichalcogenides dominate their optical response, however, the achieved light-exciton interaction strength have been far below unity, and a complete picture of its underlying physics and fundamental limits has not been provided. Using a van der Waals heterostructure cavity, we demonstrate near-unity excitonic absorption, together with efficient emission at ultra-low excitation powers. We find that the interplay between the radiative, non-radiative and dephasing decay rates plays a crucial role in this interaction, and unveil a universal absorption law for excitons in 2D systems.

Conference on Lasers and Electro-Optics, 2021

We introduce a new technique, namely time-resolved vector microscopy, that enables us to compose ... more We introduce a new technique, namely time-resolved vector microscopy, that enables us to compose entire movies on a sub-femtosecond time scale and a 10 nm scale of the electric field vectors of surface plasmon skyrmions.

Chirality is found at all length scales in nature, and chiral metasurfaces have recently attracte... more Chirality is found at all length scales in nature, and chiral metasurfaces have recently attracted attention due to their exceptional optical properties and their potential applications. Most of these metasurfaces are fabricated by top-down methods or bottom-up approaches that cannot be tuned in terms of structure and composition. By combining grazing incidence spraying of plasmonic nanowires and nanorods and Layer-by-Layer assembly, we show that nonchiral 1D nano-objects can be assembled into scalable chiral Bouligand nanostructures whose mesoscale anisotropy is controlled with simple macroscopic tools. Such multilayer helical assemblies of linearly oriented nanowires and nanorods display very high circular dichroism up to 13 000 mdeg and giant dissymmetry factors up to g ≈ 0.30 over the entire visible and near-infrared range. The chiroptical properties of the chiral multilayer stack are successfully modeled using a transfer matrix formalism based on the experimentally determined properties of each individual layer. The proposed approach can be extended to much more elaborate architectures and gives access to template-free and enantiomerically pure nanocomposites whose structure can be finely tuned through simple design principles.

ACS Photonics, 2019

Highly efficient counter-propagating fiber-based optical traps are presented which utilize conver... more Highly efficient counter-propagating fiber-based optical traps are presented which utilize converging beams from fibers with 3D printed diffractive Fresnel lenses on their facet. The use of a converging beam instead of diverging beam in dual-fiber traps creates a strong trapping efficiency in both the axial and the transverse directions. Converging beams with a numerical aperture of up to 0.7 are produced by diffractive Fresnel lenses. These lenses also provide a large focal distance of up to 200 μm in a moderately high refractive index medium. Fabrication of such diffractive lenses with microsized features at the tip of a fiber is possible by femtosecond two photon lithography. In comparison to chemically etched fiber tips, the normalized trap stiffness of dual-fiber tweezers is increased by a substantial factor of 35−50 when using a converging beam produced by diffractive Fresnel lenses. The large focal length provided by these diffractive structures allows working at a large fiber-to-fiber distance, which leads to larger space and the freedom to combine other spectroscopy and analytical methods in combination with trapping.

Optics Letters, 2019

We present a novel light source specifically tailored for stimulated Raman scatteringspectroscopi... more We present a novel light source specifically tailored for stimulated Raman scatteringspectroscopic optical coherence tomography (SRS-SOCT), which is, to the best of our knowledge, a novel molecular imaging method that combines the molecular sensitivity of SRS with the spatial and spectral multiplexing capabilities of SOCT. The novel laser consists of an 8 W, 450 fs Yb:KGW oscillator, with a repetition rate of 40 MHz, which delivers the Stokes beam for SRS-SOCT and also pumps and amplifies an optical parametric oscillator (OPO). The output of the amplified OPO is then frequency doubled and coherently broadened using a custom-made tapered fiber that generates bandwidth pulses >40 nm, compressible to <50 fs, with the average power over 150 mW, near the shot-noise limit above 250 kHz. The broadened and compressed pulse simultaneously serves as the pump beam and SOCT light source for SRS-SOCT. This light source is assessed for SRS-SOCT, and its implications for other imaging methods are discussed.

ACS Photonics, 2017

We develop a theoretical model of the excitation and interference of surface plasmon polariton (S... more We develop a theoretical model of the excitation and interference of surface plasmon polariton (SPP) waves with femtosecond laser pulses and use the model to understand the features in images from subfemtosecond time-resolved two-photon photoelectron microscopy (2PPE-PEEM). The numerically efficient model is based on the optics of SPP modes on multi-layer thin films and takes account of the excitation and interference by the incident light, its polarization, the boundary shape on the film where the plasmons are generated, the pulsed form of the excitation and the time integration associated with the PEEM method. The model explains the dominant features observed in the images including the complex patterns formed in experiments involving orbital 1 Page 1 of 31 ACS Paragon Plus Environment ACS Photonics angular momentum. The model forms the basis of an efficient numerical method for simulating time-resolved 2PPE-PEEM images of SPP wave propagation. The numerics is extremely fast, efficient and accurate, so that each image can takes as little as a few seconds to calculate on a laptop computer, enabling entire PEEM movies to be calculated within minutes.

Light: Science & Applications, 2017

Compact nanophotonic elements exhibiting adaptable properties are essential components for the mi... more Compact nanophotonic elements exhibiting adaptable properties are essential components for the miniaturization of powerful optical technologies such as adaptive optics and spatial light modulators. While the larger counterparts typically rely on mechanical actuation, this can be undesirable in some cases on a microscopic scale due to inherent space restrictions. Here, we present a novel design concept for highly integrated active optical components that employs a combination of resonant plasmonic metasurfaces and the phase-change material Ge 3 Sb 2 Te 6. In particular, we demonstrate beam switching and bifocal lensing, thus, paving the way for a plethora of active optical elements employing plasmonic metasurfaces, which follow the same design principles.

Science Advances, 2017

A highly miniaturized vision system is realized by directly 3D-printing different multilens objec... more A highly miniaturized vision system is realized by directly 3D-printing different multilens objectives onto a CMOS image sensor.

ACS Photonics, 2016

The key property of metal nanostructures is their unique ability to channel far-field radiation t... more The key property of metal nanostructures is their unique ability to channel far-field radiation to sub-wavelength dimensions. The resulting strongly confined and enhanced electromagnetic fields boost nonlinear optical effects at the nanoscale. In this review article we highlight and summarize the recent most important investigations and advances in the field of "Nonlinear Plasmonic Spectroscopy" and we present results of second and third-harmonic spectroscopy experiments of plasmonic nanoantenna arrays that consist of different unit cell elements, ranging from dipole nanoantennas to complex hybrid plasmonic structures. The experiments on dipole nanoantennas show that nonlinear optical processes can be enhanced either by plasmonic resonances at the fundamental laser wavelength or at the spectral position of the harmonic signal. Furthermore, we investigate the quadrupolar third-harmonic response of dolmen-type plasmonic Fano structures and find that the third-harmonic polarization-field of the quadrupolar mode does not radiate to the far-field due to destructive interference. Finally, we incorporate indium tin oxide nanocrystals into the hot-spot of plasmonic gap-antennas and find a doubling of the third-harmonic response of the hybrid antennas when compared to bare gold gap-antennas. The experimental results of the nanoantenna arrays can be modeled and understood using a classical model of anharmonic oscillators and are supported by finite element simulations. Parts of this review article are based on previous publications. 1-4

2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006

» View Full Text: Acrobat PDF (26 KB) * * Note that full-text PDFs from conferences typically con... more » View Full Text: Acrobat PDF (26 KB) * * Note that full-text PDFs from conferences typically contain 1-3 pages of content, some or all of which might be an abstract, summary, or miscellaneous items. ... Coupling of localized plasmons and propagating waveguide modes leads to ...

Photonic Metamaterials: From Random to Periodic, 2006

Abstract The influence of the specific split-ring resonator geometry on the electromagnetic reson... more Abstract The influence of the specific split-ring resonator geometry on the electromagnetic resonances and especially their spectral width is analyzed experimentally and theoretically. Furthermore, we separate radiative and nonradiative contributions to the linewidth of the resonances.

Physical Review B, 2008

We study the scattering parameters of typical transmission line resonant circuits and their corre... more We study the scattering parameters of typical transmission line resonant circuits and their corresponding nonlocal effective material parameters at optical frequencies using transmission line theory. We find that each circuit has specific features in terms of nonlocal permittivity and permeability and can be utilized to quantitatively synthesize transmission line circuit models for metamaterial slabs. As application examples, we construct circuit models for cut wires, cut-wire pairs, metallic meshes, and mesh pairs. Moreover, we calculate local material parameters in a simple way using fitted impedance parameters together with a transmission line homogenization procedure. Using transmission line ͑TL͒ models, we show how the material parameters can be optimized in actual metamaterials. The physical dependence of circuit parameters on structure geometries validates our TL model further.