大孔径光电导天线产生的太赫兹脉冲时间特性研究

在电流涌流模型中考虑了电场屏蔽效应、有限载流子寿命和有限弛豫时间的影响，得到了大孔径光电导天线表面辐射场和辐射远场的解析表达式，讨论了辐射场对载流子寿命、弛豫时间、激励光脉冲通量和脉冲宽度的依赖关系。     

Active control of terahertz multimode resonance transmission through subwavelength metal annular aperture arrays

Ultrafast optical properties of U-shaped annular aperture arrays (UAAAs) fabricated on a silicon substrate were investigated for varying photodoping levels of the silicon from the back to front interfaces of the sample. Experimental data demonstrate that the transmission modulation depth of the multimode resonance can be realized about 90% under optical power 60 mW, and the off switch of these resonance peaks transmission can be also simultaneously achieved within several picoseconds. Such plasmonic structure is able to be used for ultrafast optical modulators, active terahertz plasmonics, and ultrafast optical off switch.     

Focusing of Novosibirsk Free Electron Laser (NovoFEL) radiation into paraxial segment

Abstract

We demonstrate results of studies of a silicon binary diffractive optical element (DOE) focusing a terahertz laser Gaussian beam into a paraxial segment. The characteristics of the DOE were examined on a Novosibirsk Free Electron Laser beam of 141-μm wavelength.     

Photo-Doped Active Electrically Controlled Terahertz Modulator

We demonstrate an electric-controlled terahertz (THz) modulator which can be used to realize amplitude modulation of terahertz waves with slight photo-doping. The THz pulse transmission was efficiently...     

Heterojunction DDR THz IMPATT diodes based on AlxGa1-xN/GaN material system

Simulation studies are made on the large-signal RF performance and avalanche noise properties of heterojunction double-drift region (DDR) impact avalanche transit time (IMPATT) diodes based on Al_xGa_1-xN/GaN material system designed to operate at 1.0 THz frequency. Two different heterojunction DDR structures such as n-Al_0.4Ga_0.6N/p-GaN and n-GaN/p-Al_0.4Ga_0.6N are proposed in this study. The large-signal output power, conversion efficiency and noise properties of the heterojunction DDR IMPATTs are compared with homojunction DDR IMPATT devices based on GaN and Al_0.4Ga_0.6N. The results show that the n-Al_0.4Ga_0.6N/p-GaN heterojunction DDR device not only surpasses the n-GaN/p-Al_0.4Ga_0.6N DDR device but also homojunction DDR IMPATTs based on GaN and Al_0.4Ga_0.6N as regards large-signal conversion efficiency, power output and avalanche noise performance at 1.0 THz.     

太赫兹频段三倍频器设计中的关键问题

在太赫兹频段外差设备中,倍频源是重要的组成部件。最近几年,国内许多科研单位利用分立的平面肖特基二极管开展了关于太赫兹频段倍频器的研究。除了设计方法以外,仍有许多问题需要考虑。本文结合完成的225 GHz三倍频器的实际测试结果,从三方面讨论了在研制过程中遇到的关键问题。首先,二极管模型的准确性决定了仿真结果的可靠性。依据已知的管子Spice参数和倍频器测试结果,对肖特基二极管的物理结构尺寸和直流参数不断进行修正,直到仿真和测试结果趋于一致。其次,当大功率输入时,在肖特基结处会有热量的累积。因此进行了一个稳态热分析的仿真,结果显示当250 mW功率输入时,产生的最高温度大约为140°C,这对于该二极管而言是安全的。最后,在装配过程中会有很多不理想因素的引入,例如导电胶形状的不确定以及电路安装位置的偏移。在文章中会进一步计算出这些不理想因素对倍频器性能产生的影响。     

调频连续波太赫兹雷达方案研究及系统验证

太赫兹雷达由于其极高的分辨率而日益受到研究者的重视。该文展示了一种工作在220 GHz频段的线性调频连续波体制太赫兹雷达的设计方案和实验结果。该雷达采用超外差结构,以获得更低的相位噪声和更大的动态范围。在雷达发射机基带部分采用了直接数字波形合成技术以获得稳定、快速的线性调频信号频率源,扫频时间40 μs,扫频带宽14.4 GHz。实验结果表明,解线频调结果与理论分析值相吻合,该雷达非常适合用于高分辨率安检成像和无损检测。     

Two-Dimensional Terahertz Time-Domain Spectroscopy and Its Applications

In this work, we review the developing progress of two-dimensional terahertz time-domain spectroscopy (THz-TDS) and its diverse applications, including analyzing the polarization of THz radiation from a laser-induced plasma source and studying the corresponding physical mechanism, and characterizing the optical properties of crystals, etc.