- 标题
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- 实验方案
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Terahertz generation in quantum-cascade lasers through down-conversion optical nonlinearity: Design and modeling
摘要： In this paper, we propose an electrically driven optically excited laser structure for terahertz (THz) generation in quantum cascade lasers (QCLs) through frequency down-conversion optical nonlinearity. In our distinct design, both the pump and THz radiations are generated simultaneously by optical and electronic intersubband transitions (ISTs) between the quantized states within the conduction band of the same active region of a QCL. The modeling of laser bandstructure is achieved using a self-consistent solution of Schrodinger-Poisson equations, and the detailed analysis of electronic transport of the proposed structure is performed using the density matrix approach and energy-density balance equation that self-consistently consider the optical, electrical and thermal interactions in the structure. Additionally, the waveguide loss for the THz optical mode is considered using the bulk Drude model. Using a stationary solution of the density matrix equations, an expression for the THz intensity gain is derived as a function of pump field intensity, carrier distributions and quantum coherence contributions. Using the presented model, we analyze the steady-state and transient characteristics of the device for two different heatsink temperatures, 220 and 300 K. Simulation results show that the proposed structure has a potential to generate room-temperature THz radiation in QCLs.
关键词： Quantum-cascade laser (QCL),terahertz (THz) generation,down-conversion optical nonlinearity,density-matrix formalism
更新于2025-09-23 15:21:01
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Nonlinear Charge Transport in InGaAs Nanowires at Terahertz Frequencies
摘要： We probe the electron transport properties in the shell of GaAs/In0.2Ga0.8As core/shell nanowires at high electric fields using optical pump/THz probe spectroscopy with broadband THz pulses and peak electric fields up to 0.6 MV/cm. The plasmon resonance of the photoexcited charge carriers exhibits a systematic redshift and a suppression of its spectral weight for THz driving fields exceeding 0.4 MV/cm. This behavior is attributed to the intervalley electron scattering that results in the doubling of the average electron effective mass. Correspondingly, the electron mobility at the highest fields drops to about half of the original value. We demonstrate that the increase of the effective mass is nonuniform along the nanowires and takes place mainly in their middle part, leading to a spatially inhomogeneous carrier response. Our results quantify the nonlinear transport regime in GaAs-based nanowires and show their high potential for development of nanodevices operating at THz frequencies.
关键词： Localized Plasmon,Intervalley Scattering,Nanowire,Terahertz (THz)
更新于2025-09-23 15:21:01
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Optimization of PBG-Waveguides for Terahertz-Driven Electron Acceleration
摘要： The properties of 2-D photonic bandgap dielectric structures, also called photonic crystals, are numerically investigated to assist the design of waveguides for terahertz (THz)-driven linear electron acceleration. Given the broadband nature of the driving pulses in THz acceleration regimes, one design aim is to maximize the photonic bandgap width to allow propagation of the relevant frequencies within the photonic crystal linear defect waveguide. The proposed design is optimized to provide the best compromise between effective acceleration bandwidth and strong beam–wave interaction at the synchronism central frequency. Considerations on achieved acceleration bandwidth, accelerating voltage, and surface magnetic field are given to compare the proposed geometry to one of the main counterparts in the literature—the dielectric-lined waveguide.
关键词： Photonic crystals,terahertz (THz) electron acceleration,photonic-bandgap waveguides (PBG-Ws)
更新于2025-09-23 15:21:01
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Spectral efficiency optimization for intelligent reflecting surface aided multi-input multi-output terahertz system
摘要： Intelligent reflecting surface (IRS) is considered as a promising application in terahertz (THz) communications since it is able to enhance the THz communication with no additional power consumptions. In this letter, we consider a downlink multi-input multi-output system, where a base station (BS) communicates to a user with the aid of the IRS. Our goal is to optimize the spectral efficiency by designing discrete phase-shifts at the IRS and the precoder at the BS, which is an intractable nonconvex optimization problem. To solve it, we approximate the problem into another form where we maximize the sum of path gains by designing the phase-shifts of the IRS, and we propose a cross-entropy based algorithm to search the optimal IRS phase-shifts matrix. After that, we use the classical singular value decomposition and water-filling solution to design the optimal precoder.
关键词： terahertz (THz) communication,intelligent reflecting surface (IRS),spectral efficiency
更新于2025-09-23 15:21:01
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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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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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[IEEE 2019 IEEE 2nd International Conference on Information Communication and Signal Processing (ICICSP) - Weihai, China (2019.9.28-2019.9.30)] 2019 IEEE 2nd International Conference on Information Communication and Signal Processing (ICICSP) - Vision-based Automatic Detection of Suspended Solids in Bottled Mineral Water
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2025-09-19 17:13:59
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High-Performance GaAs/AlAs Terahertz Quantum-Cascade Lasers For Spectroscopic Applications
摘要： We have developed terahertz (THz) quantum-cascade lasers (QCLs) based on GaAs/AlAs heterostructures for application-defined emission frequencies between 3.4 and 5.0 THz. Due to their narrow line width and rather large intrinsic tuning range, these THz QCLs can be used as local oscillators in airborne or satellite-based astronomical instruments or as radiation sources for high-resolution absorption spectroscopy, which is expected to allow for a quantitative determination of the density of atoms and ions in plasma processes. The GaAs/AlAs THz QCLs can be operated in mechanical cryocoolers and even in miniature cryocoolers due to the comparatively high wall-plug efficiency of around 0.2% and typical current densities below 500 A/cm2. These lasers emit output powers of more than 1 mW at operating temperatures up to about 70 K, which is sufficient for most of the abovementioned applications.
关键词： terahertz (THz) spectroscopy,Quantum-cascade laser (QCLs)
更新于2025-09-19 17:13:59
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Electronic–Electromagnetic Multiphysics Modeling for Terahertz Plasmonics: A Review
摘要： In this article, we review numerical and analytical methods of electronic–electromagnetic multiphysics modeling for terahertz plasmonic applications. Approaches within semiclassical regime of electronic transport are considered, as these are appropriate for examining plasma-wave phenomenology in 2-D electron gas systems, commonly found in high-electron-mobility transistors (HEMTs) and graphene sheets. In modeling of such electronic–plasmonic devices, coupling of incident electromagnetic wave to the device or emission from the device needs to be modeled. Therefore, electronic–electromagnetic coupled multiphysics multiscale models are required. In such modeling problems, the domain consists of large regions where electrodynamic equations are to be solved. Therefore, overall time efficiency relies on the speed of solution of electrodynamic equations. Nevertheless, the electrodynamic solution’s speed is limited by the smallest grid sizes, which are a function of electronic transport equations. To address these issues, unconditionally stable finite-difference time-domain (FDTD) and iterative alternating directional implicit (ADI)-FDTD methods, coupled with hydrodynamic equations, are reviewed. Advantages and compromises between FDTD, ADI-FDTD, and iterative ADI-FDTD-based global modeling are discussed and conclusions are summarized.
关键词： electronic,numerical modeling,electron transport,terahertz (THz),FDTD,multiphysics,plasmonic,Alternating directional implicit finite-difference time-domain (ADI-FDTD),multiscale modeling,hydrodynamic (HD),plasma wave,electromagnetic
更新于2025-09-16 10:30:52
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[IEEE 2019 16th International Conference on Quality in Research (QIR): International Symposium on Electrical and Computer Engineering - Padang, Indonesia (2019.7.22-2019.7.24)] 2019 16th International Conference on Quality in Research (QIR): International Symposium on Electrical and Computer Engineering - Room-Temperature Terahertz Antenna-Coupled Microbolometers with Titanium Thermistor and Heater
摘要： High-detectivity room-temperature terahertz (THz) detectors are expected to be utilized in spectroscopy and imaging for such applications as nondestructive inspection for safety, construction, noninvasive examination for medicine and pharmacy. We have studied THz antenna-coupled bolometers with titanium (Ti) thermistor and heater fabricated on a high-resistivity silicon (Si) substrate with MEMS structures in order to develop uncooled high-performance sensors. In this paper, we report the study on design, electromagnetic (EM) and thermal simulation, fabrication, experiment of THz-wave measurement, and evaluation of performance for single-detector devices, by which large THz array detectors are easily developed. We have achieved good performance as low noise-equivalent power (NEP) of the orders of 10-11 W/Hz1/2 and response frequency of 5.5 kHz by studying a Ti thermistor with thin meander line for the THz antenna-coupled bolometer.
关键词： nondestructive,terahertz (THz),meander line,sensing,thermistor,noise equivalent power (NEP),temperature coefficient of resistance (TCR),responsivity,bolometer,room temperature,uncooled,detector,array
更新于2025-09-16 10:30:52