太赫兹技术在爆炸物检测中的应用

研究了太赫兹成像技术在爆炸物探测中的应用,分析了太赫兹透射型时域光谱系统的实验装置,介绍了太赫兹时域光谱的测量步骤。确定了四种爆炸物样品(TNT,RDX,DNT,HMX)在太赫兹波段的吸收谱。结果表明,这四种爆炸物样品在0~2.5THz的频率范围内均存在特征吸收峰,这为太赫兹技术检测爆炸物提供了一种有效的途径。     

A novel integrated MEMS helix antenna for terahertz applications

This paper reports the design and analysis of a novel helix antenna based on Micro-electromechanical Systems (MEMS) technology, which is used in terahertz (THz) applications. The structure of the antenna includes two parts, the metallic helix and the coplanar waveguide (CPW) on the substrate for feed, the fabrication of the structure needs only one wafer, and the antenna can be easily integrated with other parts of on-chip circuits. There are many tunable parameters of the helix, so that high performance THz antenna can be achieved by optimizing these parameters. The proposed antenna can be manufactured by MEMS processing with low fabrication cost, suitable for many terahertz systems.     

Vibrational spectra of chloroform, freon-11 and selected isotopomers in the terahertz region

The fundamental bands of the CCl₃ asymmetric deformation modes of selected isotopomers of chloroform (CHCl₃) and freon-11 (CFCl₃) have been measured in a static cell at ambient temperature using a laser-based source of tunable radiation in the terahertz region of the electromagnetic spectrum. The analysis of the rotational contours of the bands enabled the derivation of the fundamental frequencies with an accuracy of better than 3 GHz.     

The terahertz spectrum detection of transgenic food

This paper presents the optical characteristic of the four transgenic foods in the terahertz (THz) by means of electro-optic sampling. The transmission spectra and complex refractive index of the four transgenic foods are obtained. This paper finds that transgenic maize (TGM), transgenic rice (TGR), transgenic soybean (TGS) and transgenic potato (TGP) all have absorption within the frequency range of 0.2 and 2.5 THz. It can be seen that the TGM and TGR have obvious absorption peaks at 1.08 and 1.82 THz respectively, the TGS has a plurality of absorption peak in this frequency band, compared to the other three samples, and the TGP is slow. The unique absorption properties in THz of four transgenic foods show that the time-resolved terahertz spectroscopy can be applied to detect and identify transgenic food.     

表面等离子体平面金属透镜及其应用

由于衍射极限的存在,传统光学透镜成像分辨率理论上只能达到入射光波长的一半。通过恢复和增强携带物体细部特征信息的高频倏逝波,基于表面等离子体的平面金属透镜有望突破这种光学衍射极限,实现超分辨成像。本文对平面薄膜式与纳米结构式两类平面金属透镜进行了综述,详细介绍了若干典型平面金属透镜的结构设计、工作机理及其聚焦性能,并对其特点与存在的问题进行了分析与讨论。由于光波在金属中传播时存在一定损耗,如何更高效地增强高频倏逝波信号并转换成传播波,使其参与成像,以更好地实现远场超分辨成像,以及如何进一步增大近场超高分辨率聚焦光斑焦深以及减小远场聚焦光斑尺寸,是表面等离子体平面金属透镜进一步研究的重点。     

复合折射透镜的进展和应用

文章介绍了X射线复合折射透镜的工作原理,详细回顾了X射线复合折射透镜的发展历程,综述了近年来X射线复合折射透镜的研究成果及其主要应用领域.     

XPS study of silicon surface after ultra-low-energy ion implantation

Ultra-low-energy ion implantation of silicon with a hydrogen-terminated (0 0 1) surface was carried out using a mass-separated ³¹P⁺ ion beam. The ion energy was 30 eV, the displacement energy of silicon, and the ion doses were 6 × 10¹³ ions/cm². Annealing after the implantation was not carried out. The effects of ion implantation on the surface electrical state of silicon were investigated using X-ray photoelectron spectroscopy (XPS). The Si 2p peak position using XPS depends on the doping conditions because the Fermi level of the hydrogen-terminated silicon surface is unpinned. The Si 2p peak position of the specimen after ion implantation at a vacuum pressure of 3 × 10⁻⁷ Pa was shifted to the higher energy region. It suggested the possibility of phosphorus doping in silicon without annealing. In the case of ion implantation at 5 × 10⁻⁵ Pa, the Si 2p peak position was not shifted, and the peak was broadened because of the damage by the fast neutrals. Ultra-low-energy ion doping can be achieved at ultra-high-vacuum conditions.     

Strong dispersion of the surface optical phonon of silicon carbide in the near vicinity of the surface Brillouin zone center

The surface optical or Fuchs-Kliewer phonons of the (0 0 1) surface of 3C-SiC and the Si-terminated (0 0 0 1) surfaces of 4H- and 6H-SiC have been investigated with high resolution electron energy loss spectroscopy (HREELS). For each of the SiC polytypes the frequency of the surface optical phonon changes with surface reconstruction, indicating subtle differences in the static polarization at differently reconstructed surfaces. Due to their anisotropy, hexagonal surfaces exhibit a second, much weaker Fuchs-Kliewer mode. For all surfaces under examination, a linear dispersion of the Fuchs-Kliewer mode frequency has been found for wave vectors close to the -point. This dispersion can be explained by dynamical dipole coupling between atomic oscillators at the surface of the highly polar silicon carbide.     

低温生长砷化镓的超快光抽运-太赫兹探测光谱

本文采用光抽运-太赫兹探测技术系统研究了低温生长砷化镓(LT-GaAs)中光生载流子的超快动力学过程.光激发LT-GaAs薄层电导率峰值随抽运光强增加而增加,最后达到饱和,其饱和功率为54μJ/cm~2.当载流子浓度增大时,电子间的库仑相互作用将部分屏蔽缺陷对电子的俘获概率,从而导致LT-GaAs的快速载流子俘获时间随抽运光强增加而变长.光激发薄层电导率的色散关系可以用Cole-Cole Drude模型很好地拟合,结果表明LT-GaAs内部载流子的散射时间随抽运光强增加和延迟时间(产生光和抽运光)变长而增加,主要来源于电子-电子散射以及电子-杂质缺陷散射共同贡献,其中电子-杂质缺陷散射的强度与光激发薄层载流子浓度密切相关,并可由散射时间分布函数α来描述.通过对光激发载流子动力学、光激发薄层电导率以及迁移率变化的研究,我们提出适当增加缺陷浓度,可以进一步降低载流子迁移率和寿命,为研制和设计优良的THz发射器提供了实验依据.     

Hydrogen related point defects in silicon based layers: Si(·)H and SiOOH

Layers prepared by pulsed TEA CO₂ pulsed laser ablation (PLA) of SiO and SiO₂ targets in helium were exposed to hydrogen and deuterium atmosphere up to several kPa. The deposited layers were investigated by FTIR, EPR and XP spectroscopy. Among various Si species silyl radical Si(·)H (Si(·)D) at 2166 (1568) cm⁻¹—H(I) center—and silyl hydroperoxide SiOOH (SiOOD) at 3587 (2648) cm⁻¹ were identified in FTIR spectra. Chemical pathways for production of these species are discussed. Experimental results are supported by quantum chemical calculations.     

太赫兹偏振测量系统及其应用

麦克斯韦方程中的介质响应特性一般由本构关系中的介电函数ε(ω)和磁导率μ(ω)来描述,对于介质中传播的电磁场,通常存在两个独立的本征传播模式,它们是齐次麦克斯韦方程组的特解,各自具有特定的色散关系和偏振态。如果介质中传播的电磁场为两个本征模分量的线性迭加,其偏振态将会随着传播的过程而改变。常见的现象有各向异性晶体中的双折射、超材料中的偏振调制效应、自然界中手性材料的旋光响应以及外磁场作用下产生的Faraday效应等。本文从测量方法、数据处理、测量精度等方面介绍太赫兹时域偏振检测系统及其发展状况,特别是利用线栅、超材料以及光学手段调制太赫兹电场偏振态的方法。对近几年太赫兹偏振检测系统在分析手性超材料、太赫兹圆二色谱以及Faraday效应等实验中的应用进行了总结和讨论。最后展望了太赫兹偏振检测系统未来进一步的发展空间及应用前景。     

Observation of THz coherent transition radiation from single-bunch beam at KURRI-LINAC as an intense pulsed light source

A single-bunch beam has been generated using a developed high-speed avalanche-type pulser in KURRI-LINAC in order to lift restrictions of the spectral resolution in the spectroscopic study and the delay time in the time-resolved measurement. Both of the rise and fall times of the developed pulser are 110 ps. The observation of CTR has confirmed the single-bunch beam. The degree of impurity of single bunch has been estimated to be 1.5% by the analysis of the interferogram.     

pH-controlled silicon nanowires fluorescence switch

Covalently immobilizing photoinduced electronic transfer (PET) fluorophore 3-[N, N-bis(9-anthrylmethyl)amino]-propyltriethoxysilane (DiAN) on the surface of silicon nanowires (SiNWs) resulted a SiNWs-based fluorescence switch. This fluorescence switch is operated by adjustment of the acidity of the environment and exhibits sensitive response to pH at the range from 8 to 10. Such response is attributed to the effect of pH on the PET process. The successful combination of logic switch and SiNWs provides a rational approach to assemble different logic molecules on SiNWs for realization of miniaturization and modularization of switches and logic devices.     

铁磁异质结构中的超快自旋流调制实现相干太赫兹辐射

利用飞秒激光脉冲在生长于二氧化硅衬底上的W/CoFeB/Pt和Ta/CoFeB/Pt两类铁磁/非磁性金属异质结构中实现高效、宽带的相干THz脉冲辐射.实验中, THz脉冲的相位随外加磁场的反转而反转,表明THz辐射与样品的磁有序密切相关.为了考察三层膜结构THz辐射的物理机制,分别研究了构成三层膜结构的双层异质结构(包括CoFeB/W, CoFeB/Pt和CoFeB/Ta)的THz辐射.实验结果都与逆自旋霍尔效应相符合, W/CoFeB/Pt和Ta/CoFeB/Pt三层膜结构所辐射的THz强度优于同等激发功率下的ZnTe (厚度0.5 mm)晶体.此外,还研究了两款异质结构和ZnTe的THz辐射强度与激发光脉冲能量密度的关系,发现Ta/CoFeB/Pt的饱和能量密度略大于W/CoFeB/Pt的饱和能量密度,表明自旋电子在Ta/CoFeB/Pt中的界面积累效应相对较小.     

Charge transport in anodic TiO2 nanotubes studied by terahertz spectroscopy

We report on the photoelectrochemical and terahertz measurements, of the charge transport properties of 1 μm thick self‐organized TiO₂ nanotube layers, prepared by the anodization of titanium. We provide evidence regarding the complexity of electron transport, and dynamics in the nanotubes. Shortly after photoexcitation, charge mobilites in amorphous and crystalline nanotubes are similar, but still lower compared to the bulk anatase. The mobility subsequently decreases due to trapping‐detrapping processes. The recombination rate in anatase nanotubes is much slower than in the amorphous ones, enabling the material to reach an internal photon to electron conversion efficiency exceeding 60%.     

The progress towards terahertz quantum cascade lasers on silicon substrates

A review is presented of work over the last 10 years which has been aimed at trying to produce a Si‐based THz quantum cascade laser. Potential THz applications and present THz sources will be briefly discussed before the materials issues with the Si/SiGe system is discussed. Waveguide designs and waveguide losses will be presented. Experimental measurements of the non‐radiative lifetimes for intersubband transitions in Si_1‐xGe_x quantum wells will be presented along with theory explaining the important scattering mechanisms which determine the lifetimes. Examples of p‐type Si/SiGe quantum cascade designs with the experimental electroluminescence will be reviewed and examples of n‐type Si‐based designs will be presented. In the conclusion designs and structures will be discussed with the greatest potential to achieve an electrically pumped Si‐based THz laser.     

Vibrational spectroscopy characterization of magnetron sputtered silicon oxide and silicon oxynitride films

Vibrational (infrared and Raman) spectroscopy has been used to characterize SiO_xN_y and SiO_x films prepared by magnetron sputtering on steel and silicon substrates. Interference bands in the infrared reflectivity measurements provided the film thickness and the dielectric function of the films. Vibrational modes bands were obtained both from infrared and Raman spectra providing useful information on the bonding structure and the microstructure (formation of nano-voids in some coatings) for these amorphous (or nanocrystalline) coatings. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis have also been carried out to determine the composition and texture of the films, and to correlate these data with the vibrational spectroscopy studies. The angular dependence of the reflectivity spectra provides the dispersion of vibrational and interference polaritons modes, what allows to separate these two types of bands especially in the frequency regions where overlaps/resonances occurred. Finally the attenuated total reflection Fourier transform infrared measurements have been also carried out demonstrating the feasibility and high sensitivity of the technique. Comparison of the spectra of the SiO_xN_y films prepared in various conditions demonstrates how films can be prepared from pure silicon oxide to silicon oxynitride with reduced oxygen content.     

THz wave sensing for petroleum industrial applications

We present the results of terahertz (THz) sensing of gasoline products. The frequency-dependent absorption coefficients, refractive indices, and complex dielectric constants of gasoline and xylene isomers were extracted in the spectral range from 0.5–3.0 THz. The THz spectra of gasoline (#87, #89, #93) and related BTEX (benzene, toluene, ethylbenzene, and xylene) compounds were studied by using Fourier transform infrared spectroscopy (FTIR) in the 1.5–20 THz (50–660 cm⁻¹). The xylene isomers, which are used as antiknock agent in gasoline were determined quantitatively in gasoline in the THz range. Our investigations show the potential of THz technology for the petroleum industrial applications.     

硅基全光宽带太赫兹幅度调制器的研究

提出了一种基于掺金硅的全光学宽带太赫兹波幅度调制器, 研究了金(Au)点阵掺杂后硅(Si)体内的少数载流子寿命及其太赫兹波调制特性. 实验结果表明, 掺杂的Au原子为Si中的光生电子- 空穴对提供了有效复合中心, 使其少数载流子寿命由原来十几微秒降低至110 ns左右. 利用波长915 nm 调制激光作为抽运光源, 在340 GHz载波的动态调制测试中获得4.3 MHz的调制速率和21%的调制深度, 使Si基调制器的调制速率提高了两个数量级. 该全光太赫兹调制器可工作在整个太赫兹频段内, 具有极化不敏感特性, 因而在太赫兹波高速和宽带调控方面具有重要的应用价值, 也是构建光控型Si 基太赫兹功能器件的重要基础.