- 标题
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- 实验方案
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Programmable anisotropic digital metasurface for independent manipulation of dual-polarized THz waves based on a voltage-controlled phase transition of VO <sub/>2</sub> microwires
摘要： Programmable metasurfaces incorporated with tunable materials controlled by external stimuli can provide an unprecedented degree of freedom in dynamical wave manipulation in real-time. Beyond the scope of isotropic reconfigurable metasurfaces that only support unique tunable responses for excitation with a certain single-polarization, here, for the first time a new generation of ultrafast reprogrammable multi-functional anisotropic metasurface is reported to enable interchangeable missions independently for two orthogonal linearly polarized THz wavefront excitations. The reconfigurability of the proposed anisotropic meta-device was guaranteed by elaborately designed meta-particle composed of two perpendicular VO2 microwires whose operational statuses can be arbitrarily and dynamically tuned among two digital states of "0" and "1" independent for dual-polarization channels by mere changing the biasing voltage via two independent computer-programmed multichannel DC network. Capitalizing on such meta-particle design furnish an inspiring platform to manipulate the far-field scattering patterns and near-field behavior in each desired polarization channel. Anisotropic meta-device bringing new degrees of freedom in achieving versatile tunable control of differently polarized electromagnetic waves which will significantly enhance storage density and data capacities and has the potential for complicated wave manipulation such as ultrafast THz communication and dynamic holography.
关键词： anisotropic metasurface,wavefront engineering,VO2 microwires,THz waves,Programmable metasurfaces
更新于2025-09-23 15:19:57
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Laser Raman scattering by graphene plasmons
摘要： A new scheme of Raman scattering of a laser by THz graphene plasmons in the presence of both space charge and electromagnetic surface plasmons is proposed. Plasmon–laser coupling arises through the two dimensional response of electrons in graphene. For optical frequency laser scattering by THz plasmons, phase matching conditions are satis?ed for near normal incidence and the Raman scattered wave also propagates normal to the graphene surface. The amplitude of the electric ?eld of the Raman scattered wave scales linearly with the plasmon density ?uctuation level and laser amplitude and inversely with the electron effective mass. Raman scattering would provide in situ diagnostics of the amplitude and frequency of the THz wave.
关键词： THz,diagnostics,Raman scattering,graphene plasmons,laser
更新于2025-09-23 15:19:57
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Full-mode analysis of the plasmon oscillations of 2D electron gas subjected to electric field
摘要： Plasmon dispersion law including wave vector dependencies of the oscillation frequency, !′(q), and the damping !′′(q) of 2D electron gas subjected to the steady-state electric field were analyzed in the frameworks of general kinetic theory of collisionless plasma. Two particular cases of ungated and gated 2D electron gas were considered. We found that the spectra of 2D plasmons have the following peculiarities: multi-branched character, strong dependence of Landau damping vs dielectric surrounding of 2D gas, the strong non-reciprocal dispersion with respect to the direction of electron drift, existence of an extended instability range of wave vectors where plasmons propagating along the electron drift have essential increment of oscillations, !′′>0. Also, the effect of the mode interaction under applied field was identified.
关键词： plasmon instability,THz plasmonics,non-reciprocity,Landau damping
更新于2025-09-23 15:19:57
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Extremely high-intensity operation of a THz free-electron laser using an electron beam with a higher bunch charge
摘要： A higher intensity THz beam is generated with a free-electron laser (FEL) based on the L-band (1.3 GHz) electron linac at Osaka University by increasing the electron bunch charge four times higher from 1 nC in the conventional mode (the 108 MHz mode) to 4 nC in the new mode (the 27 MHz mode). This is realized by expanding the electron bunch intervals four times longer with the grid pulser of the electron gun, generating a series of 5 ns pulses at a repetition frequency of 27 MHz (the 48th subharmonic of 1.3 GHz), whereas the beam loading of the linac remains unchanged. The energy of an FEL macropulse comprised of many micropulses is measured in the 27 MHz mode to be approximately 28.5 mJ at a maximum of around 65 μm or 4.6 THz compared with the maximum macropulse energy of 13 mJ in the 108 MHz mode. The maximum micropulse energy in the 27 MHz mode is approximately 260 μJ using 110 micropulses, which is estimated by a macropulse duration of 4 μs and micropulse intervals of 36.9 ns. The micropulse energy is nearly 10 times higher than the micropulse energies in the conventional mode and in other FELs in the same wavelength or frequency region.
关键词： Free-electron laser (FEL),Terahertz (THz),Electron beam,High charge
更新于2025-09-23 15:19:57
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Intersubband Transition Engineering in the Conduction Band of Asymmetric Coupled Ge/SiGe Quantum Wells
摘要： n-type Ge/SiGe asymmetric coupled quantum wells represent the building block of a variety of nanoscale quantum devices, including recently proposed designs for a silicon-based THz quantum cascade laser. In this paper, we combine structural and spectroscopic experiments on 20-module superstructures, each featuring two Ge wells coupled through a Ge-rich SiGe tunnel barrier, as a function of the geometry parameters of the design and the P dopant concentration. Through a comparison of THz spectroscopic data with numerical calculations of intersubband optical absorption resonances, we demonstrated that it is possible to tune, by design, the energy and the spatial overlap of quantum confined subbands in the conduction band of the heterostructures. The high structural/interface quality of the samples and the control achieved on subband hybridization are promising starting points towards a working electrically pumped light-emitting device.
关键词： quantum wells,THz spectroscopy,group IV epitaxy,intersubband transitions,silicon–germanium heterostructures
更新于2025-09-23 15:19:57
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The TeraFERMI Electro-Optic Sampling Set-Up for Fluence-Dependent Spectroscopic Measurements
摘要： TeraFERMI is the THz beamline at the FERMI free-electron-laser facility in Trieste (Italy). It uses superradiant Coherent Transition Radiation emission to produce THz pulses of 10 to 100 μJ intensity over a spectral range which can extend up to 12 THz. TeraFERMI can be used to perform non-linear, ?uence-dependent THz spectroscopy and THz-pump/IR-probe measurements. We describe in this paper the optical set-up based on electro-optic-sampling, which is presently in use in our facility and discuss the properties of a representative THz electric ?eld pro?le measured from our source. The measured electric ?eld pro?le can be understood as the superimposed emission from two electron bunches of different length, as predicted by electron beam dynamics simulations.
关键词： THz spectroscopy,free-electron-lasers,nonlinear optics
更新于2025-09-23 15:19:57
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100 GHz Multiple Colliding Pulse Generation From Cleaved Facet-Free Multi-Section Semiconductor Laser Diode
摘要： Terahertz (THz) cameras comprising an uncooled micro-bolometer array have been developed for simple THz imaging, and the improvement of their sensitivity is one of the important issues. We fabricated a new micro-bolometer array with a resonant cavity structure for a real-time THz camera, alongside a new method for evaluating the sensitivity across a wide range of the THz frequency region. The frequency dependence of the sensitivity of the THz camera is measured in the 0.5–2.0-THz frequency range taking the polarization dependence into account. It was found that the resonant cavity structure effectively increased the sensitivity of the THz camera, and, actually, the improvement by one order of magnitude was achieved in the frequency range below 1 THz. The THz camera with much enhanced sensitivity will expand the frontiers of real-time THz imaging such as molecular imaging and nondestructive inspection.
关键词： focal plane array,micro-bolometer,terahertz (THz),real-time imaging,Compact terahertz camera
更新于2025-09-23 15:19:57
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Single-cycle THz signal accompanying laser wake in photoionized plasmas
摘要： Photoionization of an ambient gas by a weakly relativistic, femtosecond laser pulse leaves behind the pulse a ?at-top plasma column. The uniform-density core of the column is surrounded by a micron-thin shell, within which the density of plasma species falls down to zero. As the laser pulse ponderomotive force drives the wave of charge separation (the laser wake), electron ?uid velocity oscillates along this boundary layer. Coupling velocity oscillations to the transverse density gradient forms an azimuthally polarized rotational current con?ned within the boundary layer. At each radial offset, this current oscillates with a local (THz-scale) Langmuir frequency, transforming the cylindrical electrostatic plasma wave into a radially evanescent Fourier component of an electromagnetic signal. Summing up these Fourier components yields the time-domain THz signal which is (a) non-local (i.e. not phase-locked to the Langmuir oscillation at any given location), (b) contains the entire frequency band from zero to the Langmuir frequency of the density plateau, and (c) is detectable at a distance orders of magnitude larger than the plasma column radius. A few millimeters away from the column, rapid evanescence of the higher-frequency components transforms the signal into a radially polarized, single-cycle picosecond pulse with a kV m?1-scale electric ?eld. Detecting this pulse with existing (e.g. electro-optical) techniques may bring information on the ef?ciency of laser coupling to the plasma, the amplitude of wake ?elds, and the structure of the column boundary.
关键词： electromagnetic mode conversion,optical ?eld ionization,THz pulse,laser wake?eld
更新于2025-09-23 15:19:57
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Fermi velocity renormalization in graphene probed by terahertz time-domain spectroscopy
摘要： We demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization νF* of charge carriers in graphene. This allows the quantitative extraction of all electrical parameters (DC conductivity σDC, carrier density n, and carrier mobility μ) of large-scale graphene films placed on arbitrary substrates via THz-TDS. Particularly relevant are substrates with low relative permittivity (< 5) such as polymeric films, where notable renormalization effects are observed even at relatively large carrier densities (> 1012 cm-2, Fermi level > 0.1 eV). From an application point of view, the ability to rapidly and non-destructively quantify and map the electrical (σDC, n, μ) and electronic (νF*) properties of large-scale graphene on generic substrates is key to utilize this material in applications such as metrology, flexible electronics as well as to monitor graphene transfers using polymers as handling layers.
关键词： Graphene,THz-TDS,Fermi Velocity Renormalization,Mobility Mapping,Flexible Substrates
更新于2025-09-23 15:19:57
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[IEEE ESSCIRC 2019 - IEEE 45th European Solid State Circuits Conference (ESSCIRC) - Cracow, Poland (2019.9.23-2019.9.26)] ESSCIRC 2019 - IEEE 45th European Solid State Circuits Conference (ESSCIRC) - A Hybrid THz Imaging System With a 100-Pixel CMOS Imager and a 3.25a??3.50 THz Quantum Cascade Laser Frequency Comb
摘要： The terahertz frequency range beyond 3 THz has exciting potential to have a transformative impact in a wide range of applications, including chemical and biomedical sensing, spectroscopy, imaging, and short-distance wireless communication. While there have been significant advancements in silicon-based THz imagers in the frequency ranges below 1 THz, technological development beyond 3 THz has been impeded by the lack of solid-state sources in this frequency range. In addition, the design space beyond 3 THz opens up fundamentally new challenges across electronics and the electromagnetic interface. In this spectral range, the wavelength is small enough (λox ≈ 50 μm at 3 THz) that a vertical via from the top antenna layer to the detector is a distributed element (transmission line or radiator). In this letter, we follow a careful circuits-electromagnetics co-design approach toward a hybrid imaging system with a 100-pixel CMOS imager that interfaces with a THz quantum cascade laser frequency comb that spans 3.25–3.5 THz with mode spacing of 17 GHz. The array chip, while designed for an optimal operation across 2.7–2.9 THz, demonstrates an average noise equivalent power (NEP) (across pixels) of 1260 pW/√Hz between 3.25–3.5 THz and a projected NEP of 284 pW/√Hz across the design range of 2.7–2.9 THz. To the best of our knowledge, we demonstrate for the first time full THz imaging in a hybrid quantum cascade laser (QCL)–CMOS fashion. This approach allows future works to leverage both QCL and CMOS technologies to demonstrate new technological advances for systems in the 1–10 THz range.
关键词： quantum cascade laser,THz imaging,terahertz,detector,imaging,CMOS,silicon,hybrid imaging
更新于2025-09-23 15:19:57