光电导天线太赫兹波辐射特性研究进展

太赫兹科学技术已经成为当前电磁领域研究的热点,太赫兹波的产生是其关键技术,光电导天线(PCA)是目前产生宽频太赫兹波的重要手段。根据光电导天线太赫兹波的辐射特性的文献报道,对光电导天线产生太赫兹波的耦合输出效率、辐射场型、极化特性等研究进展做了较全面的评述,并针对光电导天线辐射特性对光电导天线应用的意义进行了探讨和展望,以期对光电导天线产生太赫兹波的研究和应用提供参考。     

Photoconductive terahertz transceiver

A photoconductive dipole antenna can be used as a transceiver, which alternately transmits pulsed electromagnetic radiation and receives the return signal. Preliminary results of using a photoconductive terahertz transceiver with femtosecond optics are reported     

光导器件及其背景限探测度

本文就ＭＣＴ光导型探测器作一总结性的讨论，对光导器件的扫出问题作了更详尽的阐述，并定义了扫出因子。关于背景限探测度提出了新的见解，认为背景限探测度不是不可逾越。     

Tunnel generation and locking stimulated Raman radiation components

Stimulated Raman radiation is considered in a ring optical resonator. It is supposed that the resonator is partly filled with a condensed medium at the full length of the medium close to several tunnel lengths. A Raman-active medium and an optical waveguide are assumed to occupy a part of the condensed medium. The feasibility is shown of tunnel generation and synchronization of a great number of Stokes components of stimulated Raman radiation. Here, femtosecond light pulses are shown to be formed in a spacing adjacent to the Raman-active medium, the pulses being single over the periodT = 2pi/omega_{R}(ωRis the Raman frequency shift). Predicted and considered also are tunnel generation and locking of new light modes in an optical parametric oscillator. The effects are due to a correction for the dispersion of the full effective refractive index of the medium inside the resonator. Numerical calculations of the correction for a glass thin-film optical waveguide, quartz, and the Raman-active media CaCO3, C6H6, CS2inside the resonator are represented. Here, five or six Stokes components are shown to be generated and locked for CaCO3and C6H6, eight Stokes components for CS2. A similar numerical calculation is represented for the active medium LiNbO3in the corresponding optical parameteric oscillator. Here, new modes covering a frequency bandwidth of 5000 cm^-1are shown to be feasible. Noted and discussed is also a higher-order correction for the effective refractive index dispersion making it feasible to broaden the frequency bandwidth for tunnel generation and locking.     

Angle-dependent pulse distortion in UWB radiation and its impact on UWB impulse communications

The bit-error-rate of an ultra-wideband (UWB) impulse communication system may vary significantly with respect to communication direction due to angle-dependent pulse distortion in UWB radiation. Simulations of rectangular aperture radiation show that an impulse communication system with uniform aperture electric field excitation suffers more than that with Gaussian aperture field excitation.     

砷化镓光控半导体开关

光控半导体开关在脉冲功率等方面具有广泛的应用前景,越来越受到人们的重视。本文对光控半导体开关进行了简要介绍,包括ＧａＡｓ：Ｓｉ：Ｃｕ开关的原理和应用;ＧａＡｓ：Ｓｉ：Ｃｕ基本材料的制备;开关过程中的锁定现象及其机理;以及设计和实验中的几个问题．     

光导开关及其两种工作模式

简要地回顾了光导开关的发展历程,描述了光导开关的基本工作原理及两种工作模式,比较了两种工作模式的主要特性。     

光电导太赫兹天线及其研究进展

太赫兹科学技术是一门新学科,其关键技术是太赫兹波的产生。光电导天线是目前产生宽频带太赫兹波最重要的方法之一。光电导天线的几何结构对提高天线在太赫兹频段的效率、方向性、带宽等都非常重要。因此有必要对光电导太赫兹天线的各种几何结构和国内外研究进展做较为全面的评述,对其中存在的问题和解决思路进行分析,对未来研究发展的方向进行探讨。     

Soliton-Raman generation with pump radiation in normal dispersionregime

It has been shown experimentally that the broad spectral bandwidths associated with soliton-Raman generation need not necessarily be generated via the process of modulation instability, and that Raman scattering quite effectively acts as the seed     

Visible and ultraviolet radiation generation using a gas-loaded free-electron laser

Gas loading of a free-electron laser modifies the phase-matching condition while the small-signal gain expression remains the same when written in appropriate form. This permits a wider parameter space than the vacuum FEL, which is particularly advantageous at shorter wavelength operation. Scattering of the electrons by the gas limits the interaction length, but available gains are still high enough to allow oscillation build-up. For example, a 0.5-μm wavelength helical wiggler FEL utilizing a 41 MeV electron beam is restricted to a length of 14 cm, has a small signal gain of 21 percent, and builds up to saturation in less than 1μs. Tunability of this device over several microns is easily obtained by changing the gas pressure.     

High-efficiency generation of narrow bandwidth tunable VUV radiation

Frequency tunable VUV radiation has been generated using excimer lasers and very narrow bandwidth dye lasers by two-photon resonant difference frequency mixing in xenon. Conversion efficiencies of >0.1 percent have been achieved.     

光电导THz源及其研究进展

THz科学技术是近20年来发展起来的一门新学科,其关键技术是THz波的产生和探测。本文介绍了光电导THz源的辐射原理和本领域的研究进展等,并简要分析了今后的发展方向。     

HgCdTe光导探测器的优化设计

利用牛顿迭代法,在一维理论的基础上,计算机模拟优化设计了工作在8～14μm波段HgCdTe光导探测器的各项参数。结果表明,器件厚度取6μm,长度取100～150μm,环氧树脂胶粘层<3μm,净掺杂浓度取1.4×10~(15)cm~(-3),表面复合速度取500cm/s,电场强度取10V/cm为佳。该法亦可使用于其他光导探测器的优化设计中。     

Scalable Microstructured Photoconductive Terahertz Emitters

The development of scalable emitters for pulsed broadband terahertz (THz) radiation is reviewed. Their large active area in the 1 – 100 mm² range allows for using the full power of state-of-the-art femtosecond lasers for excitation of charge carriers. Large fields for acceleration of the photogenerated carriers are achieved at moderate voltages by interdigitated electrodes. This results in efficient emission of single-cycle THz waves. THz field amplitudes in the range of 300 V/cm and 17 kV/cm are reached for excitation with 10 nJ pulses from Ti:sapphire oscillators and for excitation with 5 μJ pulses from amplified lasers, respectively. The corresponding efficiencies for conversion of near-infrared to THz radiation are 2.5 × 10^-4 (oscillator excitation) and 2 × 10^-3 (amplifier excitation). In this article the principle of operation of scalable emitters is explained and different technical realizations are described. We demonstrate that the scalable concept provides freedom for designing optimized antenna patterns for different polarization modes. In particular emitters for linearly, radially and azimuthally polarized radiation are discussed. The success story of photoconductive THz emitters is closely linked to the development of mode-locked Ti:sapphire lasers. GaAs is an ideal photoconductive material for THz emitters excited with Ti:sapphire lasers, which are widely used in research laboratories. For many applications, especially in industrial environments, however, fiber-based lasers are strongly preferred due to their lower cost, compactness and extremely stable operation. Designing photoconductive emitters on InGaAs materials, which have a low enough energy gap for excitation with fiber lasers, is challenging due to the electrical properties of the materials. We discuss why the challenges are even larger for microstructured THz emitters as compared to conventional photoconductive antennas and present first results of emitters suitable for excitation with ytterbium-based fiber lasers. Furthermore an alternative concept, namely the lateral photo-Dember emitter, is presented. Due to the strong THz output scalable emitters are well suited for THz systems with fast data acquisition. Here the application of scalable emitters in THz spectrometers without mechanical delay stages, providing THz spectra with 1 GHz spectral resolution and a signal-to-noise ratio of 37 dB within 1 s, is presented. Finally a few highlight experiments with radiation from scalable THz emitters are reviewed. This includes a brief discussion of near-field microscopy experiments as well as an overview over gain studies of quantum-cascade lasers.     

ZnO光电导紫外探测器的制备和特性研究

以Si(111)衬底,用脉冲激光沉积(PLD)法制得C轴高度择优取向的ZnO薄膜,并利用剥离技术制备了ZnO光导型紫外探测器.Al叉指状电极是由平面磁控溅射技术沉积得到的.对Al/ZnO/Al的伏安特性和紫外光响应的研究表明,金属铝和ZnO能形成很好的欧姆接触,紫外探测器的电阻值在100KΩ左右.在紫外区域,其5V偏压下的光响应度为0.5A/W.     

Noise Analysis of Photoconductive Terahertz Detectors

The noise performance of photoconductive terahertz detectors is analyzed and the tradeoff between low-noise and high-responsivity operation of photoconductive detectors is investigated as a function of device parameters and operational settings. The analysis is conducted on two general photoconductive detector architectures, symmetrically pumped and asymmetrically pumped photoconductive detector architectures. The results indicate that the highest signal-to-noise ratios are offered by the symmetrically pumped and asymmetrically pumped detector architectures for the photoconductive detectors based on short-carrier lifetime and long-carrier lifetime semiconductors, respectively.     

光电导开关面临的问题及发展趋势

光电导开关具有传统高功率脉冲器件不具备的优良性能,在产生高功率脉冲领域有很大发展潜力。使用光导开关能直接从直流电源产生电磁脉冲。根据各种应用对光导开关性能指标的不同要求,将其归纳为大功率脉冲应用与超短电磁脉冲应用两类。阐述了光电导开关在理论、实用化方面遇到的问题以及目前学术界、业界对其解决的方法。对各种解决方法做出评价并展望光导开关未来发展趋势。     

Photoconductive Terahertz antenna with radial symmetry

It has been demonstrated recently that it is possible to guide broadband Terahertz pulses utilising a novel coaxial waveguide. This technique is hindered by the difficulty in exciting the radially polarised fundamental mode of the waveguide. To optimise mode matching, a novel radially symmetric photoconductive Terahertz antenna is proposed. Using finite element method simulations and analytical calculations, it is shown that this antenna can generate the desired radial polarisation.     

高压超快GaAs光电导开关的研制

本文首次报导了采用全固态绝缘，微带线低电感输出的Ｓｉ－ＧａＡｓ高压超快光电导开关的研制结果，该器件的耐压强庶３５ｋＶ／ｃｍ，典型的电流脉冲上升时间为２００ｐｓ，电流达１００Ａ。并在实验中观测到典型的高倍增现象。     

弱P型碲镉汞材料和陷阱模式光导探测器

窄禁带碲镉汞(HgCdTe)为电子和空穴混合导电的多载流子体系材料,特别是对于弱p型材料,由于电子和空穴的迁移率相差大约两个数量级,更容易受到少数载流子电子的干扰,因此单一磁场的霍尔测试无法区分迁移率较低性能较差的n型材料和p型材料.通过变温变磁场的霍尔测试对两种碲镉汞材料的磁输运特性进行了测试区分.另外对由弱p型材料...