Modeling of Terahertz Radiation from InSb and InAs

In this paper the THz radiation dynamics of InSb and InAs, two typical narrow band semiconductors, was investigated using the ensemble Monte Carlo method. Our simulations indicated that the single mechanism of current surge only can result in small difference of THz emission efficiency for InSb and InAs. The great advantage of InAs over InSb in THz emission efficiency that was found in a published work is possibly due to the mechanism of optical rectification. In addition, under low excitation level, we found the emission efficiency of InSb is advantage over that of InAs, but under high excitation level, the result is reversed. On the other hand, through the Fourier transforms of temporal THz waveforms we found that the main frequency of THz pulses from InAs is always higher than that of InSb.     

Generation of Intense Narrow-Band Tunable Terahertz Radiation from Highly Bunched Electron Pulse Train

We present the analysis and start-to-end simulation of an intense narrow-band terahertz (THz) source with a broad tuning range of radiation frequency, using a single-pass free electron laser (FEL) driven by a THz-pulse-train photoinjector. The fundamental radiation frequency, corresponding to the spacing between the electron microbunches, can be easily tuned by varying the spacing time between the laser micropulses. Since the prebunched electron beam is highly bunched at the first several harmonics, with the harmonic generation technique, the radiation frequency range can be further enlarged by several times. The start-to-end simulation results show that this FEL is capable of generating a few tens megawatts power, several tens micro-joules pulse energy, and a few percent bandwidth at the frequencies of 0.5–5 THz. In addition, several practical issues are considered.     

ZnO薄膜的制备及其热辐射性能研究

采用溶胶-凝胶法在玻璃基底上制备了不同厚度的氧化锌薄膜。研究了不同的溶胶配比、浓度对热辐射性能的影响。结果表明,当溶胶配比为1：1、浓度为0．8％时,ZnO薄膜的热辐射性能最好,吸波能力最强。用X射线衍射仪（XRD）和扫描电子显微镜（SEM）对薄膜的组织结构和形貌进行了表征。结果表明,该ZnO薄膜呈（002）面择优取向的六方纤锌矿晶体结构,具有较好的结晶性能。     

Terahertz Photon-Assisted Tunneling in InAs Quantum Dots

We have investigated electron transport in a single self-assembled InAs quantum dot (QD) coupled to nanogap metal electrodes under terahertz (THz) radiation. The fabricated QD samples operated as single electron transistors in a few electron regime, exhibiting clear shell structures. Under the THz radiation, in addition to the original Coulomb oscillation peaks, new side-peaks showed up. The dependence of the new side-peak current on the THz power follows the prediction of the photon-assisted tunneling (PAT) theory. Moreover, two types of PAT processes were observed in the THz range; the ground state resonance and the photon-induced excited state resonance, depending on the relative magnitude between the orbital quantization energy of the QDs and the THz photon energy. Furthermore, a very high coupling efficiency between the THz waves and the QDs was realized in our system and we observed multi-photon absorption up to the fourth-order during the tunneling process, resulting in almost complete lifting of the Coulomb blockade. This high coupling efficiency between THz wave and electrons in QDs opens a way to the manipulation of single electron charge/spin states in the THz frequency range.     

光电导天线太赫兹辐射研究

利用超短激光脉冲触发光电导天线产生太赫兹波是目前研究比较深入,同时得到广泛采用的一种太赫兹波源.电流瞬冲模型能较好地解释光电导天线辐射太赫兹波的机理,并且与实验相吻合,因而被普遍接受.影响光电导天线的因素有材料性质、偏转电压、激光脉冲宽度和单脉冲能量等,其中激光脉冲宽度和激光脉冲能量对太赫兹辐射有很重要的影响.材料中的光生载流子寿命对辐射也有一定的影响.当改变这些参数时,辐射的太赫兹波有不同的特性变化.此外,逐步增大激光脉冲能量,会发现辐射的太赫兹波强度存在一个饱和特性.     

Intense Terahertz Pulse-Induced Nonlinear Responses in Carbon Nanotubes

By using intense terahertz(THz) monocycle pulses, nonlinear light-matter interaction in aligned semiconducting single-walled carbon nanotubes(SWNTs) embedded in a polymer film was investigated. THz electric-field-induced ultrafast Stark effect of one-dimensional excitons in SWNTs was observed at room temperature, suggesting the potential functionality of SWNTs for high speed electro-optic devices operating at telecom wavelength with a THz bandwidth. When the peak electric field amplitude exceeds 200 kV/cm, the generation of excitons by the THz pump becomes prominent. The mechanism is described by the above-gap excitation of electrons and holes in SWNTs due to the impact excitation process induced by the intense THz electric field.     

Terahertz band-gap in InAs/GaSb type-II superlattices

We demonstrate theoretically that it is possible to realize terahertz (THz) fundamental band-gap in InAs/GaSb type-II superlattices (SLs). The presence of such band-gap can result in a strong cut-off of optical absorption at THz bandwidth. This study is pertinent to the application of InAs/GaSb type-II SLs as THz photodetectors.     

Optically- and Electrically-Stimulated Terahertz Radiation Emission from Indium Nitride

Indium nitride is a novel narrow band gap semiconductor. The material is a potential strong source of terahertz frequency electromagnetic radiation with applications in time-domain terahertz spectroscopy and imaging systems. This article reviews recent experimental research on terahertz emission from the binary compound semiconductor indium nitride excited by near-infrared laser beams or microseconds electrical pulses. Advantages of indium nitride as terahertz radiation source material are discussed. It is demonstrated that different mechanisms contribute to the emission of terahertz radiation from indium nitride. The emission of up to 2.4 μW of THz radiation power is observed when InN is excited with near-infrared femtosecond laser pulses at an average power of 1 W.     

溶胶-凝胶法制备WO3薄膜

以金属W粉为无机原料,采用多步溶胶一凝胶技术结合浸渍镀膜方法制备出WO3薄膜,借助化学刻蚀、可见光分光光度计、椭偏仪等仪器测量了薄膜的特性。实验表明：采用本方法,可使薄膜的折射率增大(从1．76增加至1．89),同时保持了薄膜良好的电致变色性能,增强了薄膜的稳定性。     

光学薄膜,光电子薄膜及光学有机薄膜

本文评介了新技术，新材料和新工艺在薄膜技术的应用及其最新发展。     

太赫兹辐射源的研究进展

太赫兹技术在物理、化学等基础研究学科,以及安全检查、空间通信等应用学科都具有重要的研究价值和应用前景,而太赫兹辐射源正是太赫兹技术发展的关键部分.概述了基于激光光学技术、真空电子技术和超快激光技术产生太赫兹辐射的常用方法和主要特点,以及目前的研究状况,并对这各种太赫兹波辐射源的发展方向进行了展望.     

非晶SiHxOy薄膜的强可见荧光

采用 PECVD方法制备了非晶 Si Hx Oy 薄膜 ,室温下观察到了性能稳定的强荧光发射现象 ,其中3 65nm、4 70 nm、73 0 nm三个带由分立能级的荧光峰组成 ,说明这些荧光带起源于氧有关的能级。通过能级间相对荧光强度的变化解释了发射带中心位置的移动现象     

Terahertz Radiation Effects and Biological Applications

We present a brief overview of the literature on biological applications and experimental data on the effects of THz radiation. The region of the electromagnetic spectrum from 0.1 to 10 THz is a frontier area for research in physics, chemistry, biology, materials science and medicine. This area has recently begun to be filled by a variety of sources of high quality radiation with a wide range of new technologies related to it. New sources have led to new science in many areas, as scientists begin to become aware of the opportunities for research progress in their fields using THz radiation. Therefore the opportunities for THz science in chemistry and biology are wide ranging. Some of them will extend the range of already established work, many others have not yet been realized but show great promise, and the rest fall somewhere in between.     

太赫兹辐射产生技术进展

分别就光学技术和电子学技术产生太赫兹波的方法,介绍其产生原理、研发现状和最新进展,重点介绍了光电导、光整流、参量振荡器和太赫兹量子级联激光器.     

强等离子体相干辐射放大

提出一种获得相干辐射的新方法。基于这种方法,有希望使自由电子激光器结构变得比较简单,容易实施振荡频率连续调谐。文中给出获得激光增益的条件。     

Terahertz Properties of Cellulose Nanocrystals and Films

Terahertz (THz) radiation properties of cellulose nanocrystal (CNC) films, a CNC powder, and a dissolving pulp film are examined using THz time-domain spectroscopy. The relative permittivity (real component) of the CNC samples are found to vary between 1.78 and 3.81, over the frequency range of 0.2–1.5 THz, despite the fact that they are made from the same linear chain of glucose monomers. The results show that the permittivity is strongly dependent on the source from which the CNC glucose monomers are extracted, as well as on the drying process used. The THz loss tangent (0.043?<?tan(δ)?<?0.145), absorption coefficient (3.5 cm^?1?<?α?<?63.7 cm^?1), and growth-varying permittivity, combined with other appealing thermal and mechanical characteristic of CNC, make such material attractive for use in both passive and potential THz bandwidth electronic components.