Papers by Christoph Lienau
Laser & Photonics Reviews, Jun 16, 2021
Recently, asymmetric plasmonic nanojunctions have shown promise as on-chip electronic devices to ... more Recently, asymmetric plasmonic nanojunctions have shown promise as on-chip electronic devices to convert femtosecond optical pulses to current bursts, with a bandwidth of multi-terahertz scale, although yet at low temperatures and pressures. Such nanoscale devices are of great interest for novel ultrafast electronics and opto-electronic applications. Here, the device is operated in air and at room temperature, revealing the mechanisms of photoemission from plasmonic nanojunctions, and the fundamental limitations on the speed of optical-to-electronic conversion. Inter-cycle interference of coherent electronic wavepackets results in a complex energy electron distribution and birth of multiphoton effects. This energy structure, as well as reshaping of the wavepackets during their propagation from one tip to the other, determine the ultrafast dynamics of the current. It is shown that, up to some level of approximation, the electron flight time is well-determined by the mean ponderomotive velocity in the driving field.
arXiv (Cornell University), Mar 4, 2021
Recently, asymmetric plasmonic nanojunctions [Karnetzky et. al., Nature Comm. 2471, 9 (2018)] hav... more Recently, asymmetric plasmonic nanojunctions [Karnetzky et. al., Nature Comm. 2471, 9 (2018)] have shown promise as on-chip electronic devices to convert femtosecond optical pulses to current bursts, with a bandwidth of multi-terahertz scale, although yet at low temperatures and pressures. Such nanoscale devices are of great interest for novel ultrafast electronics and opto-electronic applications. Here, we operate the device in air and at room temperature, revealing the mechanisms of photoemission from plasmonic nanojunctions, and the fundamental limitations on the speed of optical-to-electronic conversion. Inter-cycle interference of coherent electronic wavepackets results in a complex energy electron distribution and birth of multiphoton effects. This energy structure, as well as reshaping of the wavepackets during their propagation from one tip to the other, determine the ultrafast dynamics of the current. We show that, up to some level of approximation, the electron flight time is well-determined by the mean ponderomotive velocity in the driving field.
Physical review, Sep 1, 2001
A coupled GaAs/AlGaAs quantum wire ͑QWR͒-dot sample grown by molecular beam epitaxy on a patterne... more A coupled GaAs/AlGaAs quantum wire ͑QWR͒-dot sample grown by molecular beam epitaxy on a patterned (311)A GaAs substrate is studied by near-field spectroscopy at a temperature of 10 K with a spectral resolution of 100 eV. The two-dimensional potential energy profiles of the sample including localized excitonic states caused by structural disorder are determined in photoluminescence measurements with a spatial resolution of 150 nm. One finds a potential barrier of 20 meV between the quantum wire and the embedding quantum well ͑QW͒ on the mesa top of the structure. This is due to local thinning of the GaAs layer. In contrast, the wire-dot interface results free of energy barriers. The spatial variation of the GaAs layer thickness provides information on the growth mechanism determined by lateral diffusion of Ga atoms which is modeled by an analytical model. By performing spatially resolved photoluminescence excitation measurements on this wire-dot structure, we present a method for investigating carrier transport in low-dimensional systems: The dot area is used as an optical marker for excitonic diffusion via QW and QWR states. The two-dimensional ͑2D͒ and 1D diffusion coefficients are extracted as a function of the temperature and discussed.
Nature Photonics, Nov 19, 2013
Efficient Emission of Ultrafast Electron Bursts by Plasmonic Nanofocusing of Light
Epj Web of Conferences, 2019
We study the interaction of swift electrons with laser and solids using a numerical approach, and... more We study the interaction of swift electrons with laser and solids using a numerical approach, and specifically show that low-energy electrons can be used to map the time-resolved response of a Fermi gas.
Ultrafast coherent dynamics of Rydberg electrons bound in the image potential near a single metallic nano-object (Presentation Recording)
Proceedings of SPIE, Sep 2, 2015
Image potential states are well established surface states of metallic films [1]. For a single me... more Image potential states are well established surface states of metallic films [1]. For a single metallic nanostructure these surface states can be localized in the near-field arising from illumination by a strong laser field. Thus single metallic nanostructures offer the unique possibility to study quantum systems with both high spatial and ultrafast temporal resolution. Here, we investigate the dynamics of Rydberg states localized to a sharp metallic nanotaper. For this purpose we realized a laser system delivering few-cycle pulses tunable over a wide wavelength range [2]. Pulses from a regenerative titanium:sapphire amplifier generate a white light continuum, from which both a proportion in the visible and in the infrared are amplified in two non-collinear optical parametric amplification (NOPA) stages. Difference frequency generation (DFG) of both stages provides pulses in the near-infrared. With a precisely delayed sequence of few-cycle pulses centered around 600 nm (NOPA#1 output) and 1600 nm (DFG output) we illuminate the apex of a sharply etched gold tip. Varying the delay we observe an exponential decay of photoemitted electrons with a distinctly asymmetric decay length on both sides, indicating the population of different states. Superimposed on the decay is a clearly discernible quantum beat pattern with a period of <50 fs, which arises from the motion of Rydberg photoelectrons bound within their own image potential. These results therefore constitute a step towards controlling single electron wavepackets released from a gold tip opening up fascinating perspectives for applications in ultrafast electron microscopy [3]. [1] Hofer, U. et al. Science 277, 1480 (1997) [2] Vogelsang, J., Robin J. et al. Opt. Express 22, 25295 (2014) [3] Petek, H. et al. ACS Nano 8, 5 (2014)
Suppression of Radiative Damping and Enhancement of Second Harmonic Generation in Bull’s Eye Nanoresonators
ACS Nano, Dec 9, 2015
We report a drastic increase of the damping time of plasmonic eigenmodes in resonant bull&amp... more We report a drastic increase of the damping time of plasmonic eigenmodes in resonant bull&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s eye (BE) nanoresonators to more than 35 fs. This is achieved by tailoring the groove depth of the resonator and by coupling the confined plasmonic field in the aperture to an extended resonator mode such that spatial coherence is preserved over distances of more than 10 μm. Experimentally, this is demonstrated by probing the plasmon dynamics at the field level using broadband spectral interferometry. The nanoresonator allows us to efficiently concentrate the incident field inside the central aperture of the BE and to tailor its local optical nonlinearity by varying the aperture geometry. By replacing the central circular hole with an annular ring structure, we obtain 50-times higher second harmonic generation efficiency, allowing us to demonstrate the efficient concentration of long-lived plasmonic modes inside nanoapertures by interferometric frequency-resolved autocorrelation. Such a light concentration in a nanoresonator with high quality factor has high potential for sensing and coherent control of light-matter interactions on the nanoscale.
Photon-Induced Near-Field Interaction in Ultrafast Low Energy Electron Microscopy
The International Conference on Ultrafast Phenomena (UP) 2022, 2022
We report the first observation of optical near-field coupling to an ultrafast wavepacket of free... more We report the first observation of optical near-field coupling to an ultrafast wavepacket of free, low-energy electrons. Transient optical near-fields, highly spatially confined around a nanometer-sized Yagi-Uda-antenna are probed in a point-projection-microscope with 30-fs resolution.
Photon-Induced Near-Field Interaction in Ultrafast Point-Projection Electron Microscopy
We report the first study of ultrafast, slow (&lt;100 eV) free electron wavepackets with opti... more We report the first study of ultrafast, slow (&lt;100 eV) free electron wavepackets with optical near fields. This interaction is probed in a point-projection-microscope with 50fs temporal resolution using strongly localized fields around a nano-antenna.
Quantum Coherent Control of Slow Electron Wave Packets with Light
Interaction of a moving electron wave packet in free space with light and nanostructures have tak... more Interaction of a moving electron wave packet in free space with light and nanostructures have taken much attention recently, by the emergence of photon-induced near-field electron microscopy [1–2]. Electron beams can inelastically interact by laser-induced nearfield distribution of the nanostructures, opening ways in shaping the electron wave packets and characterization of plasmon polaritons. The interaction of high energy electron waves with laser-induced excitations in the sample is generally discussed within eikonal approximations, neglecting other effects which arise from the pondermotive forces and experienced elastic recoils [3–4]. In contrast, coherent control of above threshold ionization and high harmonic generation can be understood by interferences between different quantum paths, related to ponderomotive and absorptive parts in the minimal coupling Hamiltonian [5].
Epj Web of Conferences, 2019
We implement a plasmon-driven ultrafast electron source in a point-projection electron microscope... more We implement a plasmon-driven ultrafast electron source in a point-projection electron microscope. A proof-of-principle experiment investigating the charge propagation in a single nanoresonator demonstrates an unprecedented spatiotemporal resolution of 20 nm and 25 fs.
Zenodo (CERN European Organization for Nuclear Research), Sep 17, 2019
Three-dimensional plasmonic gold tapers are widely used structures in nano-optics for achieving i... more Three-dimensional plasmonic gold tapers are widely used structures in nano-optics for achieving imaging at the nanometer scale, enhanced spectroscopy, confined light sources, and ultrafast photoelectron emission. To understand their radiation properties further, especially in the proximity of the apex at the nanoscale, we employ cathodoluminescence spectroscopy with high spatial and energy resolution. The plasmon-induced radiation in the visible spectral range from three-dimensional gold tapers with opening angles of 13°and 47°is investigated under local electron excitation. We observe a much weaker radiation from the apex of the 13°taper than from that of the 47°taper. By means of finitedifference time-domain simulations we show that for small opening angles plasmon modes that are created at the apex are efficiently guided along the taper shaft. In contrast for tapers with larger opening angles, generated plasmon polaritons experience larger radiation damping. Interestingly, we find for both tapers that the most intense radiation comes from locations a few hundreds of nanometers behind the apexes, instead of exactly at the apexes. Our findings provide useful details for the design of plasmonic gold tapers as confined light sources or light absorbers.
arXiv (Cornell University), Jul 15, 2021
The interaction of swift, free-space electrons with confined optical near fields has recently spa... more The interaction of swift, free-space electrons with confined optical near fields has recently sparked much interest. It enables a new type of photon-induced near-field electron microscopy, mapping local optical near fields around nanoparticles with exquisite spatial and spectral resolution and lies at the heart of quantum state manipulation and attosecond pulse shaping of free electrons. The corresponding interaction of optical near fields with slow electrons has achieved much less attention, even though the lower electron velocity may enhance electron-near-field coupling for small nanoparticles. A first-principle theoretical study of such interactions has been reported very recently [N. Talebi, Phys. Rev. Lett. 125, 080401 (2020)]. Building up on this work, we investigate, both analytically and numerically, the inelastic scattering of slow electrons by near fields of small nanostructures. For weak fields, this results in distinct angular diffraction patterns that represent, to first order, the Fourier transform of the transverse variation of the scalar near-field potential along the direction perpendicular to the electron propagation. For stronger fields, scattering by the near-field component along the electron trajectory results in a break-up of the energy spectrum into multiple photon orders. Their angular diffraction patterns are given by integer powers of the Fourier transform of the transverse potential variation and are shifting in phase with photon order. Our analytical model offers an efficient approach for studying the effects of electron kinetic energy, near field shape and strength on the diffraction and thus may facilitate the experimental observation of these phenomena 2 by, e.g., ultrafast low-energy point-projection microscopy or related techniques. This could provide simultaneous access to different vectorial components of the optical near fields of small nanoparticles.
Electron Photoemission and Acceleration from Sharp Gold Nanotapers in the Strong-Field, Few-Cycle Regime
Quantum matter, Aug 1, 2014
ABSTRACT We investigate experimentally and numerically the effect of the strongly confined near f... more ABSTRACT We investigate experimentally and numerically the effect of the strongly confined near field around sharply etched, nanometer-sized gold tapers on the photoemission and acceleration of electrons. When such tapers are illuminated by ultrafast laser pulses, the enhancement of the local electric field strength at the taper apex is sufficiently large to enable tunneling of the electrons out of the metal. For sharp tapers with a nanometer-sized apex, the decay length of the near field can become shorter than the quiver amplitude, leading to acceleration of the electrons out of the near field within less than one half cycle of the driving laser field. We present measure-ments of kinetic energy spectra that highlight the transition from multi-photon to strong-field photoemission, as well as the transition from quiver motion of the electrons in the oscillating laser field to sub-cycle acceleration. The measurements are complemented by numerical simulations as a powerful supporting tool allowing analysis of the kinetic energy spectra. The numerical simulations are based on a modified Simpleman model which, for the first time, includes fully three-dimensional calculations of the electron trajectories as well as charged-particle interactions of multiple electrons generated during one pulse. A wide variety of experimental observations are well reproduced by the simulations, changing only the taper radius and laser pulse characteristics as the exper-imentally accessible parameters. Furthermore, when including electron–electron repulsion effects, the model is capable of explaining previously unaccounted experimental observations of electrons with exceptionally high kinetic energy. We believe that this improved Simpleman model may help in the future to analyze strong-field photoemission from a wide class of dielectric and metallic nanostructures.
arXiv (Cornell University), May 20, 2022
The primary step in the elusive ability of migratory birds to sense weak Earth-strength magnetic ... more The primary step in the elusive ability of migratory birds to sense weak Earth-strength magnetic fields is supposedly the light-induced formation of a long-lived, magnetically sensitive radical pair inside a cryptochrome flavoprotein located in the retina of these birds. Blue light absorption by a flavin chromophore triggers a series of sequential electron transfer steps across a tetradic tryptophan chain towards the flavin acceptor. The recent ability to express cryptochrome 4 from the night-migratory European robin (Erithacus rubecula), ErCry4, and to replace the tryptophan residues individually by a redox-inactive phenylalanine offers the prospect of exploring the role of each of the tryptophan residues in the electron transfer chain. Here, we compare ultrafast transient absorption spectroscopy of wild type ErCry4 and four of its mutants having phenylalanine residues in different positions of the chain. In the mutants we observe that each of the first three tryptophan residues in the chain adds a distinct relaxation component (time constants 0.5, 30 and 150 ps) to the transient absorption data. The dynamics in the mutant with a terminal phenylalanine residue are very similar to those in wild type ErCry4, excepted for a reduced concentration of long-lived radical pairs. The experimental results are evaluated and discussed in connection with Marcus-Hopfield theory, providing a complete microscopic insight into the sequential electron transfers across the tryptophan chain. Our results offer a path to studying spin transport and dynamical spin correlations in flavoprotein radical pairs.
Photon-Induced Near-Field Interaction in Ultrafast Low Energy Electron Microscopy
The International Conference on Ultrafast Phenomena (UP) 2022
We report the first observation of optical near-field coupling to an ultrafast wavepacket of free... more We report the first observation of optical near-field coupling to an ultrafast wavepacket of free, low-energy electrons. Transient optical near-fields, highly spatially confined around a nanometer-sized Yagi-Uda-antenna are probed in a point-projection-microscope with 30-fs resolution.
Femtosecond Streaking and Control of Electrons from a Plasmonic Nanofocusing Taper by Photoemitted Charges in a Nanoantenna
2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2019
Manipulation of electrons by light forms the basis for future optoelectronic devices targeting sw... more Manipulation of electrons by light forms the basis for future optoelectronic devices targeting switching speeds close to optical frequencies. Specifically, nanolocalized optical and plasmonic fields play a key role as they reduce the interaction region down to few nanometers and thus the time electrons require to traverse the fields. In this context, the precise knowledge of the localized fields is an important prerequisite, and their metrology as well as the control of electrons in near fields are active research areas [1,2].
Nanophotonics, 2021
Localized surface plasmon resonances of individual sub-wavelength cavities milled in metallic fil... more Localized surface plasmon resonances of individual sub-wavelength cavities milled in metallic films can couple to each other to form a collective behavior. This coupling leads to a delocalization of the plasmon field at the film surface and drastically alters both the linear and nonlinear optical properties of the sample. In periodic arrays of nanocavities, the coupling results in the formation of propagating surface plasmon polaritons (SPP), eigenmodes extending across the array. When artificially introducing dislocations, defects and imperfections, multiple scattering of these SPP modes can lead to hot-spot formation, intense and spatially confined fluctuations of the local plasmonic field within the array. Here, we study the underlying coupling effects by probing plasmonic modes in well-defined individual triangular dimer cavities and in arrays of triangular cavities with and without artificial defects. Nonlinear confocal spectro-microscopy is employed to map the second harmonic ...
Nature Communications, 2020
The integration of metallic plasmonic nanoantennas with quantum emitters can dramatically enhance... more The integration of metallic plasmonic nanoantennas with quantum emitters can dramatically enhance coherent harmonic generation, often resulting from the coupling of fundamental plasmonic fields to higher-energy, electronic or excitonic transitions of quantum emitters. The ultrafast optical dynamics of such hybrid plasmon–emitter systems have rarely been explored. Here, we study those dynamics by interferometrically probing nonlinear optical emission from individual porous gold nanosponges infiltrated with zinc oxide (ZnO) emitters. Few-femtosecond time-resolved photoelectron emission microscopy reveals multiple long-lived localized plasmonic hot spot modes, at the surface of the randomly disordered nanosponges, that are resonant in a broad spectral range. The locally enhanced plasmonic near-field couples to the ZnO excitons, enhancing sum-frequency generation from individual hot spots and boosting resonant excitonic emission. The quantum pathways of the coupling are uncovered from a...
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Papers by Christoph Lienau