A5044199100- Terahertz technology and applications
- Plasmonic and Surface Plasmon Research
- Photonic and Optical Devices
- 2D Materials and Applications
- Graphene research and applications
- Superconducting and THz Device Technology
- Semiconductor Quantum Structures and Devices
- Topological Materials and Phenomena
- Thermal Radiation and Cooling Technologies
- Advanced Fiber Laser Technologies
- Quantum and electron transport phenomena
- Advanced Semiconductor Detectors and Materials
- Perovskite Materials and Applications
- Metamaterials and Metasurfaces Applications
- Spectroscopy and Laser Applications
- Photonic Crystals and Applications
- Mechanical and Optical Resonators
- Photocathodes and Microchannel Plates
- Electron and X-Ray Spectroscopy Techniques
- Carbon Nanotubes in Composites
- Orbital Angular Momentum in Optics
- Radio Frequency Integrated Circuit Design
- Thermal properties of materials
- Particle Accelerators and Free-Electron Lasers
- Gyrotron and Vacuum Electronics Research
University of Duisburg-Essen
2018-2025
University of Maryland, College Park
2014-2020
Helmholtz-Zentrum Dresden-Rossendorf
2012-2019
Tianjin University
2018
Technische Universität Dresden
2012-2015
American Institute for Voice and Ear Research
2015
Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute
2013
Xi'an University of Technology
2013
Friedrich-Alexander-Universität Erlangen-Nürnberg
2012
University of California, Santa Barbara
2012
This paper reports on field-effect-transistor-based terahertz detectors for the operation at discrete frequencies spanning from 0.2 to 4.3 THz. They are implemented using a 150-nm CMOS process technology, employ self-mixing in n-channels of transistors and operate well above transistors' cutoff frequency. The theoretical description device by Dyakonov Shur is extended order describe impedance, responsivity, noise-equivalent power novel detection concept, which couples signal drain. approach...
We present an ultrafast graphene-based detector, working in the THz range at room temperature. A logarithmic-periodic antenna is coupled to a graphene flake that produced by exfoliation on SiO2. The detector was characterized with free-electron laser FELBE for wavelengths from 8 um 220 um. rise time 50 ps wavelength 30 Autocorrelation measurements exploiting nonlinear photocurrent response high intensities reveal intrinsic below 10 ps. This has potential characterizing temporal overlaps, e....
One of the major difficulties in development optoelectronic THz modulators is finding an active material that allows for large modulation depth. Graphene a promising candidate because terahertz regime it behaves as Drude metal with conductivity can be electrostatically tuned through application gate voltage. However, maximum absorption incurred when signal passes monolayer graphene still only on order 10–20%, even highest practically achievable carrier concentrations. We demonstrate here...
Sub-wavelength graphene structures support localized plasmonic resonances in the terahertz and mid-infrared spectral regimes. The strong field confinement at resonant frequency is predicted to significantly enhance light-graphene interaction, which could enable nonlinear optics low intensity atomically thin, sub-wavelength devices. To date, response of plasmons their energy loss dynamics have not been experimentally studied. We measure theoretically model relaxation nanoribbons. employ a THz...
We turn graphene from an inert electronic material to the most nonlinear for terahertz range using a small voltage.
We present a pump-probe experiment on graphene, which reveals pronounced dependence of the pump-induced transmission angle between pump and probe polarization. It reflects strong anisotropy occupation photogenerated carriers in momentum space. Within 150 fs after excitation, an isotropic carrier distribution is established. The experiments are well described by microscopic modeling, identifies carrier-phonon scattering to be main relaxation mechanism giving rise distribution.
Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and superconducting gap frequency $2\ensuremath{\Delta}/h$. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned just below above $2\ensuremath{\Delta}/h$ BCS superconductor NbN, we demonstrate that can be transiently increased also in type-II dirty-limit superconductor. The effect is particularly...
We present the results of pump–probe experiments on multilayer graphene samples performed in a wide spectral range, namely from near infrared (photon energy 1.5 eV) to terahertz 8 meV) range. In infrared, exciting carriers and probing at higher photon energies provides direct evidence for hot carrier distribution. Furthermore, spectroscopic signatures highly doped layers interface SiC are observed near-infrared mid-infrared various relaxation mechanisms, particular scattering via optical...
We present polarization-resolved transient transmission measurements on multi-layer black phosphorus. Background free two-color pump-probe spectroscopy are carried out mechanically exfoliated phosphorus flakes that have been transferred to a large-bandgap, silicon carbide substrate. The blue-shifted pump pulse (780 nm) induces an increased of the probe (1560 over time scale commensurate with measurement resolution (hundreds fs). After initial pump-induced transparency, sign flips and slower...
Abstract The terahertz (THz) region of the electromagnetic spectrum spans gap between optics and electronics has historically suffered from a paucity optoelectronic devices, in large part because inadequate optical materials that function this spectral range. 2D materials, including graphene growing family related van der Waals have been shown to exhibit unusual electrical properties can enable diverse new applications THz regime. In review, some make them promising for are explained, recent...
We report on high power terahertz (THz) emission from ErAs-enhanced In0.52Al0.48As-In0.53Ga0.47As superlattices for operation at 1550 nm. ErAs clusters act as efficient recombination centers. The optical is distributed among a large, microstructured area in order to reduce the local intensity. A THz field strength of 0.7 V/cm (1 peak-to-peak) 100 mW average has been obtained, with up about 4 air, limited by detection crystal used system.
We investigate the saturation of optical absorption in graphene induced by ultrafast pulses. Within a microscopic theory, we study momentum-, angle-, and time-resolved interplay anisotropic excitation, carrier-carrier, carrier-phonon scattering, its influence on transmission. In agreement with performed experiments, observe linear regime for intensity-dependence transmission at low pump fluences nonlinear high excitation regime. Applying 10 fs-pulses, obtain fluence approximately 0.65...
We directly observe longitudinal electromagnetic fields in focused freely propagating terahertz (THz) beams of radial and linear polarization. Employing electro-optic detection, which is phase sensitive, allows one to selectively detect transverse field components. A shift π/2 between the components revealed. This universal nature, as it does not depend on mode, frequency focusing conditions. show that relation a direct consequence divergence-free nature waves vacuum. In experiments, we for...
We present a microscopic explanation of the controversially discussed transient negative differential transmission observed in degenerate optical pump-probe measurements graphene. Our approach is based on density matrix formalism allowing time- and momentum-resolved study carrier-light, carrier-carrier, carrier-phonon interaction footing. show that phonon-assisted intraband transitions give rise to absorption optically excited hot carrier system counteracting pure bleaching interband...
The Coulomb scattering dynamics in graphene energetic proximity to the Dirac point is investigated by polarization resolved pump-probe spectroscopy and microscopic theory. Collinear rapidly thermalizes carrier distribution k directions pointing radially away from point. Our study reveals, however, that, almost intrinsic graphene, full thermalization all relying on noncollinear much slower. For low photon energies, carrier-optical-phonon processes are strongly suppressed mediated remarkably...
Black phosphorus has attracted interest as a material for use in optoelectronic devices due to many favorable properties such high carrier mobility, field-effect, and direct bandgap that can range from 0.3 eV its bulk crystalline form 2 single atomic layer. The low energy black allows transition photoabsorption enables detection of light out mid-infrared frequencies. In this work we characterize the room temperature optical response photoconductive detector at wavelengths ranging 1.56 $\mu$m...
Radially polarized beams represent an important member of the family vector beams, in particular due to possibility using them create strong and tightly focused longitudinal fields, a fundamental property that has been exploited by applications ranging from microscopy particle acceleration. Since properties such beam are intimately related Gouy phase shift, proper knowledge its behavior is crucial. Terahertz microscopic imaging used extract shift transverse field components focused, radially...
We report on a lightwave-driven scanning tunneling microscope based home-built and compact, commercial, cost-effective terahertz-generation unit with repetition rate of 100 MHz. The measurements are performed in an ultrahigh vacuum at temperatures between 8.5 300 K. cross-correlation the pump probe pulses indicates temporal resolution order picosecond. In terms spatial resolution, CO molecules, step edges, atomically resolved terraces readily observed terahertz images, sometimes better...
A two-dimensional electron gas (2DEG) forms at the interface of complex oxides like $SrTiO_{3}$ (STO) and $LaTiO_{3}$ (LTO), despite each material having a low native conductivity, as band Mott insulator, respectively. The 2DEG hosts charge carriers with moderate carrier density mobility that raised interest system for applications field-effect transistors or detectors. Of particular is integration these oxide systems in silicon technology. To this end we study dynamics STO/LTO/STO...
A whole class of two-color experiments involves intense, short Terahertz radiation pulses. fast detector that is sensitive and able to resolve both near-infrared pulses at the same time highly desirable. Here we present first this kind. The element a GaAs-based field effect transistor operated room temperature. THz detection successfully demonstrated frequencies up 4.9 THz. constant shorter than 30 ps, optical 150 ps. This ideally suited for precise, simultaneous resolution pulse...
Two-dimensional black phosphorus is a new material that has gained widespread interest as an active for optoelectronic applications. It features high carrier mobility allows efficient free-carrier absorption of terahertz radiation, even though the photon energy far below bandgap energy. Here we present and ultrafast detector, based on exfoliated multilayer flakes phosphorus. The device responsivity about 1 mV/W 2.5 THz beam with diameter 200 μm, primarily limited by small area in comparison...
Abstract Graphene is an ideal material to study fundamental Coulomb‐ and phonon‐induced carrier scattering processes. Its remarkable gapless linear band structure opens up new relaxation channels. In particular, Auger bridging the valence conduction changes number of charge carriers gives rise a significant multiplication ‐ ultrafast many‐particle phenomenon that promising for design highly efficient photodetectors. Furthermore, vanishing density states at Dirac point combined with intraband...