聚四氟乙烯材料的太赫兹特性

太赫兹(THz)辐射能够穿透很多对可见光不透明的非金属、非极性材料,而用X辐射对这些材料成像的对比度又相对低,因此,太赫兹成像在安全检测和生产质量控制等领域日益受到重视。对成像材料的太赫兹特性的实际测量是太赫兹成像技术的重要组成部分。利用CO_2激光抽运太赫兹激光对聚四氟乙烯材料的太赫兹吸收特性和透过光斑轮廓进行了实验研究,获得聚四氟乙烯在70.51μm,96.5μm,118.83μm,122.4μm,158.51μm,184.31μm和214.58μm波长的吸收系数。     

太赫兹超材料吸收器的完美吸收条件与吸收特性

提出了一种复合结构三频带太赫兹超材料吸收器,其对特定频率的入射太赫兹波呈现出完全吸收的特性。设计的超材料吸收器在入射角度达到50°时仍能保持良好的吸收特性。利用干涉理论分析了完美吸收发生的条件以及介质层介电常数对吸收频率的影响。进一步利用传输线理论结合干涉理论,分析了耶路撒冷十字短边长度对吸收特性的影响,结果表明:随着短边长度增加,吸收峰发生红移。实验结果与仿真、干涉理论、传输线理论中得到的结果吻合得较好,为今后超材料吸收器的设计提供了指导。     

太赫兹波段碲化镉介电常数的理论与实验研究

该文采用密度泛函理论研究了闪锌矿型碲化镉的声子色散谱、特征向量及晶格振动频率,获得了碲化镉介电常数随频率变化的理论值。通过太赫兹时域光谱系统测量碲化镉单晶的介电常数,该实验结果与局域密度近似修正、广义梯度近似修正和广义梯度近似修正的计算结果吻合较好。最后,3种近似交换关联势的计算结果之间存在一定差异性,该差异性结果表明太赫兹波段碲化镉的介电常数由电子声子耦合所主导,但是横波和纵波声子频率敏感于电子密度分布。      

Experimental and Theoretical Study of Strong Low-Terahertz Absorption of Thymine

The absorption coefficient of a nucleobase-thymine-in powder form was measured with terahertz spectroscopy in both frequency- and time-domain experiments. For frequencies below 3 THz, a strong signature was observed at 1.27 THz. Furthermore, molecular-dynamic simulations were conducted to reveal that the 1.27 THz absorption signature is related to a transverse optical phonon mode. The simulations also indicated that bound water molecules are vital to the vibrational mode.     

Terahertz Multivariate Spectral Analysis and Molecular Dynamics Simulations of Three Pyrethroid Pesticides

The terahertz (THz) multivariate spectral characteristics and the molecular dynamics of three pyrethroid pesticides, including deltamethrin, fenvalerate, and beta-cypermethrin, were studied in this paper. THz spectra of the pesticides were measured in frequency range of 0.06–3.5 THz by using THz time-domain spectroscopy (THz-TDS). To improve the THz spectral quality, the wavelet threshold de-noising (WTD) method was used to remove spectral noise and the spectral baseline correction (SBC) method was used to remove baseline drift. Specific absorption peaks were observed in the processed THz spectra of the three pesticides. Deltamethrin showed three peaks at 0.90, 1.49, and 2.32 THz. Fenvalerate had five peaks at 1.13, 1.43, 1.61, 1.98, and 2.58 THz. Beta cypermethrin had four peaks at 1.27, 1.84, 2.12, and 2.92 THz. The density functional theory (DFT) was used to characterize the molecular dynamics and formation mechanism of the absorption peaks. Results showed that there was a good matching effect between the THz experimental spectra and the DFT quantum calculation spectra. Based on the characterized fingerprint absorption peaks, the linear addition model was used to simulate the THz spectra of mixed pesticides. The simulated spectra of multicomponent pesticides were demonstrated to be in good agreement with those obtained by THz-TDS. By analyzing the absorption peaks of THz spectra, the composition and concentration of multicomponent pesticides could be determined. The proposed strategy presented an analytical methodology for studying the THz spectral characteristics of pesticides. In addition, this work provided experimental and theoretical basis for the detection potential of pesticides in agricultural products based on THz technology.     

Theoretical and Experimental Studies of Terahertz Wave Propagation in Unmagnetized Plasma

The spacecraft will experience the well-known “blackout” problem when it re-entry into the Earth’s atmosphere, which results in communication failures between the spacecraft and the ground control center. It is important to study the properties of terahertz (THz) wave propagation in plasma for communications using THz wave is an alternative method for solving the blackout problem. The properties of THz wave propagation in plasma have been studied with the ZT-FDTD (Z-Transform Finite Difference Time Domain) method and experimental method in this paper. The dependence of plasma density, plasma collision frequency, thickness of plasma and THz wave frequency on the THz wave propagation are presented. The properties of 0.22THz electromagnetic wave propagation in plasma have been studied experimentally with shock tube, and the experimental results are in good agreement with the FDTD ones. Both the FDTD and experimental results indicate that communications using THz wave is an alternative and effective way to solve the blackout problem.     

大半径同轴谐振腔太赫兹回旋管研究

 为了发展大功率太赫兹辐射源,本文对大半径同轴谐振腔回旋管进行了理论和数值模拟研究,理论计算结果表明在同轴谐振腔中其角向对称的TE_0n模式的截止频率与n近似成正比关系,与内外导体之间的距离近似成反比关系.根据上述特点作者设计了一只大半径同轴腔0.3THz、TE₀₄模回旋管,数值计算和粒子模拟结果表明:大半径同轴谐振腔太赫兹回旋管与空心波导谐振腔回旋管相比具有很多优点:腔体尺寸相对较大,工作电流可以大幅度提高;其对称的TE_0n模式与非对称的TE_mn模式的间隔较大,有利于克服模式竞争.     

大孔径积分球辐射源光谱辐射特性测试方法研究

本文系统地介绍了积分球辐射源的光谱辐射特性的测试方法,通过实验测量了一内径为1200mm,出光面直径为200mm的积分球辐射源在350－2500nm波段内的绝对光谱辐亮度,分析了测量不确定度,并对系统的稳定性,出光面的平面和角度辐射均匀法、各亮阶之间的线笥等辐射特性做了定量评估。     

量子阱太赫兹探测材料设计与生长的研究*

子带跃迁的量子阱结构太赫兹探测器具有响应速度快等特点,有广泛的应用前景,越来越受到研究 人员的关注。以量子力学基本原理,量子阱结构材料光吸收的特性,以及光导型探测器暗电流分析为基础,进行了 量子阱厚度、势垒层Al 含量和量子阱掺杂浓度等参数的AlGaAs/ GaAs 量子阱太赫兹探测材料结构设计,按照优化 后的外延参数进行了材料生长,获得了符合设计要求的探测材料。     

基于机器学习的太赫兹光谱分析与识别

国内对转基因作物的监管非常严格,但是对转基因作物的检测缺乏快速准确的计量方法。太赫兹时域光谱结合机器学习分类算法可以实现对转基因作物快速有效地检测识别。通过太赫兹时域光谱技术提取了2种转基因油菜种子和一种非转基因油菜种子的太赫兹吸收谱,朴素贝叶斯算法、基于朴素贝叶斯的自适应提升算法、主成分分析结合随机森林算法、主成分分析结合支持向量计算法被应用于转基因油菜种子的太赫兹吸收谱的分类识别。通过实验对比,基于朴素贝叶斯的自适应提升算法获得了高达96.6%的检测准确率。该研究为运用太赫兹光谱技术手段开展转基因作物的快速检测提供方法参考。     

Terahertz Absorption Characteristics of NiCr Film and Enhanced Absorption by Reactive Ion Etching in a Microbolometer Focal Plane Array

Nano – scale metallic films have been proven to be an effective terahertz (THz) absorption layer in uncooled infrared (IR) microbolometers operated in THz spectral range. Optimized absorption can be achieved by adjusting the thickness of metallic film. Nickel – chromium (NiCr) thin films are deposited on the diaphragms of 320 × 240 VO_x – based infrared focal plane arrays (IRFPA). Absorption measurements of the diaphragms with different thicknesses of NiCr (5 to 40 nm) agree reasonably well with the predicted absorption. To improve THz absorption further, a reactive ion etching (RIE) process applied to the dielectric support layer is first suggested, which generates nano – scale surface structures and increases the effective surface area of NiCr absorption film. This provides an effective way which is easy to accomplish and compatible with the manufacturing process of microbolometer IRFPAs to improve THz absorption and detection sensitivity.     

太赫兹光谱数据库的建立和使用

为了将太赫兹光谱分析技术应用于物质识别领域,需要建立太赫兹波段的光谱数据库,并研究合适的数据库使用方法,以鉴别未知物质。光谱获取采用自行搭建的太赫兹时域光谱测量系统,通过小波变换去除基线和噪声等干扰信息,建立起含有20种典型有机物的光谱数据库。使用该数据库识别未知物质时,分成两步:1)用径向基函数神经网络算法判断未知物质是否在数据库中;2)若在数据库中,采用基于纠错输出编码的支持向量机多类算法鉴别物质种类。测试结果表明,对库内物质识别率为96.7%,对库外物质也有较好的预测和推断能力,识别率为93.2%。提出的太赫兹光谱数据库建立和使用方法,对系统噪声等干扰因素有很好的抑制作用,可以应用到实际场合。     

基于多重体全息光栅的光谱器件的研究

提出了一种新型的基于多重体全息存储的光栅光谱仪。在光折变晶体Fe:LiNbO3中的同一位置采用角度与波长混合复用的方法记录多个光栅，它们对相应波长的光具有光谱色散功能；采用布喇格角度与波长补偿的方法，它们还可以通过单一波长的激光器进行记录。给出了该器件的工作原理和参数设计，并在实验上制作了10通道的光谱间隔为10nm的光谱器件，实验结果表明，该光谱器件具有设计灵活、光谱范围宽、光谱分辨率高和衍射效率高等优点。     

植物延迟荧光与光合能力相关性的理论与实验研究

从理论推导出利用延迟荧光强度表征光合能力的相关条件及数学模型,以玉米叶片和紫薇叶片为样品,用自制的延迟荧光探测系统与光合速率测量仪LI-6400进行了延迟荧光强度与光合速率的对比测量.实验结果表明,两者具有良好的线性相关性,与理论推导的结果一致;延迟荧光测量时间在10 s内,而LI-6400的稳定测量结果需要5～10 min.因此,延迟荧光技术是一种快速、准确的表征植物光合能力的方法.     

Nd∶KGW多波长激光晶体生长与光谱特性

采用顶部籽晶熔盐法 (TSSG)生长出掺钕钨酸钾钆Nd∶KGd(WO4 ) 2 (Nd∶KGW)多波长激光晶体。XRD分析了晶体结构 ,通过X射线荧光分析 ,检测到晶体中含有W ,K ,Gd和Nd元素。测试了晶体的红外、拉曼和紫外可见吸收光谱 ,计算了晶体中Nd3+ 离子的吸收截面积     

Nd:KGW多波长激光晶体生长与光谱特性

采用顶部籽晶熔盐法(TSSG)生长出掺钕钨酸钾钆Nd:KGd(WO4)2(Nd:KGW)多波长激光晶体.XRD分析了晶体结构,通过X射线荧光分析,检测到晶体中含有W,K,Gd和Nd元素.测试了晶体的红外、拉曼和紫外可见吸收光谱,计算了晶体中Nd3+离子的吸收截面积.     

微小型光谱仪光谱带宽及象元分辨力的讨论

微小型光谱仪是光谱分析仪器发展的一个重要方向。以典型光 仪为基础,对微小型光谱仪的主要性能指标光谱带宽及象元分辨力与结构参数的关系进行了较深入的分析讨论,为实现其结构优化设计提出了综合协调微小型光谱仪性能指标与结构参数关系的理论依据。     

平板压电扬声器的理论和实验研究

提出了平板压电扬声器声学性能的量化描述方法,制备了多层压电陶瓷用于平板压电扬声器样品,并建立了样品的简化模型.阐述了声压级的有限元分析方法,进而取得了样品的声压级-频率曲线.通过声学测量设备Audio Precision得到的实验结果与仿真结果基本吻合,即最低谐振频率相差约150 Hz,平均声压级相差约2.5 dB,标准方差相差约0.9 dB,证明了这种仿真方法的有效性.     

乙酸的光谱学及其特性的研究

采用光栅光谱仪获得了波长为 2 5 4nm(Δλ1 /2 4nm)的紫外光激励乙酸溶液的紫外吸收光谱和不同浓度溶液的荧光光谱 ,并对其产生机理和谱线特性进行了研究。实验结果和理论分析表明 ,波长为 2 5 4nm的紫外光诱导乙酸分子发出的荧光是由乙酸分子上的荧光团 -C =O -产生的 ,其量子转换效率可达 5 0 %以上 ;乙酸溶液的荧光量子产额将随浓度发生明显的变化。研究乙酸的紫外光谱和荧光光谱及其特性可为其作为溶剂和催化剂时对其他有机大分子光谱特性的影响提供参考