Investigation of copper sulfate pentahydrate dehydration by terahertz time-domain spectroscopy

Copper sulfate pentahydrate is investigated by terahertz time-domain spectroscopy. It is shown that the terahertz absorption coefficients are correlated with the particle size of the samples, as well as the heating rates of the ambient temperature. Furthermore, the water molecules of copper sulfate pentahydrate can be quantitatively characterized due to the high sensitivity of the terahertz wave to water molecules. Based on such results, the status of water incorporated in mineral opal is also characterized using terahertz time-domain spectroscopy. It indicates that terahertz technology can be considered as an efficient method to detect the dehydration of minerals.

Terahertz Time-Domain Spectroscopy method for optical parameter extraction of plastic materials

A method for extracting optical parameters of plastics materials based on terahertz time domain spectroscopy is presented. The transmission-type Terahertz Time-Domain Spectroscopy(THz TDS) system is adopted to detect the refractive index and extinction coefficient on different plastic materials. Then the corresponding spectral information is obtained by Fourier transform of the terahertz time domain waveform of the sampling points, including the corresponding amplitude and phase information of the waveform. The optical parameter extraction model is built. By using the simplex optimization method, the curves of the refractive index and extinction coefficient for the plastic material are obtained. The experimental samples are made of different plastic parallel plate materials. The experimental results show that the optimization of optical parameters can improve their extraction accuracy, and the error of refractive index is ±0.005. Extraction technology with the simplex optimization method of optical parameter based on THz TDS can help to extract the optical parameters of engineering plastics. It is of great significance for the research of terahertz nondestructive testing.

Far-infrared conductivity of CuS nanoparticles measured by terahertz time-domain spectroscopy

This paper reports that terahertz time-domain spectroscopy is used to measure the optical properties of CuS nanoparticles in composite samples. The complex conductivity of pure CuS nanoparticles is extracted by applying the Bruggeman effective medium theory. The experimental data are consistent with the Drude-Smith model of conductivity in the range of 0.2 1.5 THz. The results demonstrate that carriers become localized with a backscattering behaviour in small-size nanostructures. In addition, the time constant for the carrier scattering is obtained and is only 64.3 fs due to increased electron interaction with interfaces and grain boundaries.

The Research of Connection between Degree of Polymerization and Frequency Domain Dielectric Spectroscopy Characteristics during Oil-Paper Insulation Aging

In order to study the linkage effects between degree of polymerization and frequency domain dielectric spectroscopy characteristics of oil-paper insulation, the frequency domain dielectric response test platform of oil-paper insulation is set up. Complex permittivity of oil-paper insulation respectively composed by new or aged oil and insulation paper with different DP are tested, and complex permittivity of oil-paper insulation respectively composed by insulation respectively composed by new oil and insulation paper with different DP and low or high moisture content are tested. The test results are analyzed, and the analysis results show that the degree of polymerization of insulation paper has an influence on complex permittivity of oil-paper insulation though influencing the distribution of moisture and acids between oil and paper.

Guest Editorial TTA Special Section on Applications of Terahertz Time Domain Spectroscopy

Terahertz （THz） radiation, whose frequency ranges from 0.1 THz to 10.0 THz, has rich science, but limited technology. It has long been considered the last remaining scientific gap in the electromagnetic spectrum. Far from being fully exploited, it offers great opportunities in science, innovation, new technology, and potential applications. THz science and technology enables fundamental research directly impact our lives, from industrial quality control,

The transmission enhancement of a THz pulse through an Ag/Ag_2 O layer detected by terahertz time-domain spectroscopy

This paper reports a new way to detect the enhanced transmission of a THz electromagnetic wave through an Ag/Ag2O layer by THz-TDS （time-domain spectroscopy）. As the THz beam illuminates the sub-wavelength Ag particles gained by Ag2O thermal decomposition, the evanescent wave is generated. The evanescent wave is coupled by a 500μm-GaAs substrate, which attaches behind the Ag/Ag2O layer, and then it transmits to the far field to be detected. The experimental results indicate that the transmitting amplitude is enhanced, as well as the frequent shifting and spectra broadening.

Investigation of solid-state reaction by terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy(THz-TDS)was utilized to investigate the solid-state reaction between L(+)-Tartaric acid and sodium hydrogen carbonate.Solid sodium hydrogen L(+)-tartrate monohydrate was synthesized efficiently by mechanical grinding,which is particularly sustainable and environmentally benign.Distinct THz absorptions were observed for pure reactants and the proposed product.The reaction process could be clearly visualized by THz spectral patterns of the reaction mixtures at different grinding time.The observed results were further confirmed by synchrotron radiation X-ray powder diffraction(SRXRPD)and Fourier transform infrared (FT-IR)spectroscopy.The study demonstrates that THz-TDS is an effective novel tool to monitor solid-state reactions in pharmaceutical industry.

Terahertz Time-Domain Spectroscopy and Its Applications

The terahertz time-domain spectroscopy （THz-TDS） system and the related technology and the applications in Capital Normal University are presented. The most often used THz-TDS system as a spectroscopic measurement setup in our lab is introduced in detail, including the THz radiation source, the THz detection method and its measurement, and the control system. THz spectra of various materials is summarized and discussed. These materials include but not limited to two kinds of typical matter-the illegal drugs and explosives. The biological macro-molecules, cosmetics and fine chemical materials, edible pigments and food additives, homocysteic acid and related compounds, heavy ions in soil, Chinese medicines, tobacco and crops, oil and chemical products, carbon nanotubes, superconductors, and various semiconductors and their heterojunctions, are presented. THz emissions from the InAs and InN semiconductors surface are compared. THz spectral investigation of metallic mesh structures is summarized. Finally, an outlook of THz spectroscopic applications is given.

Temperature and Pressure Effects on Terahertz Time-Domain Spectroscopy of Crystalline Methedrine by Molecular Dynamics Simulation

In this study, the terahertz time-domain spectroscopy (THz-TDS) of crystalline methedrine, which is one of the illegal drugs, is performed using molecular dynamics simulation by the Fourier transform of time derivative auto-correlation functions of the dipole moment. In order to accurately detect the drugs from samples, it is necessary to build a complete database for terahertz spectra under different external conditions from theoretical calculation, which are hardly obtained from the experiments directly. Our results show remarkable consistency with the available experimental data in the frequency range of 10 - 100 cm-1 indicating that the presented method has significant capability to simulate terahertz spectra at various conditions. We investigated the effects of temperature and pressure on THz-TDS by simulating the system at temperature range between 78.4 K and 400 K at pressures up to 100 atm. Results show the spectral features of THz-TDS both in intensity and profile are highly sensitive to the variation of temperature and with a lower magnitude to the variation of pressure. The vanishing, rebuilding and shifting of spectral peaks are due to the complex mechanisms such as the anharmonicity, shifting in the vibration energy levels, formation and destruction of hydrogen-binding and the deformation of the potential energy surface during the environment changing. This improved our understanding for complicated THz-TDS of crystalline methedrine and would be useful for assignment of the practical measurements.

Electronic states of domain walls in commensurate charge density wave ground state and mosaic phase in 1T-TaS_(2)

Domain walls(DWs)in the charge-density-wave(CDW)Mott insulator 1T-TaS_(2)have unique localized states,which play an important role in exploring the electronic properties of the material.However,the electronic states in DWs in 1TTaS_(2)have not been clearly understood,mostly due to the complex structures,phases,and interlayer stacking orders in the DW areas.Here,we explored the electronic states of DWs in the large-area CDW phase and mosaic phase of 1T-TaS_(2)by scanning tunneling spectroscopy.Due to the different densities of DWs,the electronic states of DWs show distinct features in these phases.In the large area CDW phase,both the domain and the DWs(DW1,DW2,DW4)have zero conductance at the Fermi level;while in the mosaic phase,they can be metallic or insulating depending on their environments.In areas with a high density of DWs,some electronic states were observed both on the DWs and within the domains,indicating delocalized states over the whole region.Our work contributes to further understanding of the interplay between CDW and electron correlations in 1T-TaS_(2).

太赫兹光谱技术在食品污染检测中的研究进展

随着新的食品加工技术及新型食品材料的不断涌现,食品污染问题也越来越多,国际食品安全事件频繁爆发,食品污染造成的食源性疾病对人民生命健康造成严重威胁,如何把控好食品质量成为人们关注的焦点问题。太赫兹技术作为一项新兴的检测技术,其反映样品的物理结构、性质及化学成分的同时,也获取样品在太赫兹波段的时域和频域信息作为物质“指纹”谱,用于无损检测和识别领域并取得了一定的成果。相较于传统的检测手段,太赫兹技术安全性高、透视性好以及波谱分辨能力强等优势使其在食品污染检测领域具有极大的应用潜力和应用前景。文章简述了太赫兹光谱技术的基本原理,以其中最为常用的太赫兹时域光谱技术为主要研究重点,对该技术在食品生物性污染、化学性污染、物理性污染检测方面的应用研究工作进行了重点归纳总结,最后聚焦于太赫兹技术在食品污染检测领域的实际应用现状,讨论其发展趋势和应用前景,并分析目前研究仍存在的问题,以期为太赫兹技术在食品安全检测领域未来的进一步发展提供参考。

高分辨太赫兹衰减全反射频域光谱系统

由于水对太赫兹(THz)波具有强烈的吸收,含水样本的太赫兹光谱检测面临重大挑战。为解决太赫兹光谱对含水样本的高灵敏检测问题,本文提出并实验验证了一种太赫兹衰减全反射(ATR)的高分辨频域光谱系统。该系统采用创新式光混频相干检测技术,获得了出色的动态范围和分辨力性能,在0.3~1.2 THz范围内,峰值动态范围超过100 dB,频率分辨力高达100 MHz。创新式的ATR架构有效提升了灵敏度,在对不同浓度α-乳糖水溶液的实验测量中,实现了对水溶液样本的直接、精确定量检测。

太赫兹时域光谱成像增强算法

低分辨率是扫描太赫兹时域光谱(THz-TDS)系统图像的一个重要缺点.本文提出了一种针对太赫兹时域光谱图像的超分辨率增强算法,该算法结合了多层感知机(MLP)和超分辨率卷积神经网络(SRCNN),创建了一个复合网络.本文算法针对太赫兹光谱图像的特点,通过引入新的目标函数,避免了传统机器学习算法需要采集或模拟生成大量训练集的弊端,实现了训练图像即目标图像的单幅光谱图像增强.为了实现这一目标,本文算法的基本原理是,让试件产生一个刚体位移,利用THz-TDS系统采集位移前后两幅三维(1个时间维,2个空间维)光谱图像作为输入数据.机器学习网络包括两部分:首先,利用一个MLP网络实现三维光谱图像到二维光强图像的转化;其次,采用传统针对二维图像的SRCNN网络获取一幅高分辨率图像,对位移前后图像处理后计算得到新的高分辨率图像的位移场,并将位移场方差作为目标函数,再通过机器学习算法,优化网络中的成像参数,实现太赫兹光谱图像的分辨率增强.典型验证性实验最终得到的峰值信噪比为42.65 dB,结构相似度为0.816,均比其他现有方法高,表明本文算法能获得良好的图像增强.

全光纤耦合式太赫兹近场探针光谱成像系统

通过对太赫兹光电导探针天线与飞秒倍频光路进行光纤模块化封装,并结合光纤耦合式太赫兹光电导天线辐射源,以及自主研制设计的光纤飞秒激光光源和光纤式高速光学延时线,开发了一种全光纤耦合式太赫兹近场探针光谱成像系统,其光谱范围覆盖0.1~2.0 THz,动态范围达到60 dB,光谱采样速度高达0.1 s/谱,近场成像分辨率优于20μm的全光纤耦合式太赫兹近场探针光谱成像系统。得益于整套系统的全光纤结构设计,太赫兹辐射源和探针式探测器之间可以根据测量需求灵活调节而不需要重新校准光路,极大地提高了系统的工作稳定性和使用方便性。该研究为太赫兹科学研究提供了一种高性能且实用性强的太赫兹近场光谱成像测量系统。

具有单晶到单晶转化的Cu(Ⅰ)配合物的发光性质

选用2-(N,N-双(二苯基膦基甲基))胺基吡啶(bdppmapy)为膦配体、二吡啶并[3,2-a∶2',3'-c]吩嗪(dppz)为氮配体、[Cu(CH_(3)CN)_(4)]BF_(4)为铜盐,在常温下进行反应,制备了3种新型Cu(Ⅰ)配合物,分别为[Cu(dppz)(bdppmapy)]_(2)(BF_(4))_(2)·H_(2)O (Cu BF_(4)-1)、[Cu(dppz)(bdppmapy)]BF_(4)(Cu BF_(4)-2)和[Cu(dppz)(bdppmapy)]BF_(4)(Cu BF_(4)-3)。获得了Cu BF_(4)-1和Cu BF_(4)-3的单晶,发现了单晶到单晶转化过程的现象,并探究了溶剂分子的存在对配合物结构和光物理性能的影响。通过单晶X射线衍射确定配合物Cu BF_(4)-1和Cu BF_(4)-3的结构,使用粉末X射线衍射(PXRD)、红外光谱(IR)和核磁共振氢谱/磷谱(~1H/^(31)P NMR)对合成的3个配合物进行结构表征。对配合物进行紫外可见吸收光谱(UV-Vis)、荧光光谱、荧光寿命及量子产率等光物理性质的表征和分析,比较了配合物发光性质的差异,探讨了溶剂分子对配合物结构和光物理性质的影响规律。太赫兹时域光谱对配合物的研究提供了帮助。

自润滑滑动轴承涂层厚度的太赫兹无损检测

[目的]自润滑轴承在服役过程中面临的恶劣工况会加剧涂层磨损,涂层一旦失效则可能发生重大事故,因此对涂层磨损量的检测就显得尤为重要.[方法]针对当前对轴承自润滑涂层磨损失效评价技术存在的精度低、可靠性不足等问题,本研究提出基于太赫兹时域光谱技术的高精度自润滑滑动轴承涂层厚度无损检测方法.在系统探究聚四氟乙烯(PTFE)型涂层材料在太赫兹频段的介电响应特性的基础上,对其厚度及磨损量进行精确测量,并重构涂层界面形貌.[结果]结果表明,太赫兹波对PTFE型涂层具有良好的穿透性和特征响应特性,其厚度检测的理论最大误差为4.69μm,相对误差为2.35%,并且能对1μm的磨损量进行检测.[结论]该方法可满足实际的工程检测需求,为发展更加适用于自润滑涂层的无损检测技术提供了新方案.

电气设备复合绝缘结构的太赫兹无损检测综述

在电气设备复合绝缘结构检测方面,基于声、光、电、磁等物理量、化学组分和微观特征的检测方法得到广泛应用,但难以实现无损可视化表征。相比之下,太赫兹检测技术利用太赫兹波的光学和电磁学特性可以有效反演出被测物的结构特征和介电特性,较传统检测方法具有无损可在线测量的明显优势。为此,该文总结了当前太赫兹无损检测技术在电气设备复合绝缘结构检测方面的研究现状。首先,系统介绍了太赫兹检测方法的原理及系统,并与传统检测手段进行了比较;其次,重点总结了太赫兹时域和频域光谱及其成像技术在复合绝缘材料老化和缺陷检测中的实际应用,包括缺陷的识别和定位、组分鉴定及老化状态评估等;最后,对太赫兹无损检测技术在该领域的发展前景进行了展望。希冀该综述可帮助相关研究人员快速了解太赫兹无损检测技术在电气设备状态诊断方面的研究和应用情况,并对同类问题提供解决思路。

太赫兹时域光谱成像系统的研究进展

太赫兹时域光谱成像技术具有穿透性、超快时间分辨能力、指纹光谱特性、安全无辐射电离等显著特点,在物质成分光谱分析、工业材料无损检测领域具有独特的应用价值,成为近些年来的研究热点。基于此,从成像体制和成像算法两个方向进行介绍。在成像体制层面,全面介绍了逐点扫描成像、太赫兹焦平面成像、太赫兹光电导阵列成像等二维的成像方式,以及突破衍射极限的太赫兹近场成像技术;在成像算法层面,介绍了飞行时间成像和断层扫描成像技术等三维成像方式。列举了太赫兹技术在生物医学、无损检测、安防检测等领域的应用。最后总结了当前太赫兹时域光谱技术所面临的问题。

太赫兹时域光谱技术在材料科学领域研究进展

太赫兹时域光谱技术是一种研究材料中载流子超快动力学过程及光电导率特性的重要实验手段。近年来,随着材料科学的飞速发展,人们应用太赫兹时域光谱技术研究了包括二维层状材料、钙钛矿材料和碳基低维材料等新型材料中光生载流子、激子和极化子等粒子及准粒子在皮秒时间尺度上的超快动力学过程及在太赫兹波段的光电导特性。本文主要介绍近5年来太赫兹时域光谱技术在材料科学领域取得的最新研究进展,并对太赫兹时域光谱技术在材料科学领域的应用做出展望。

太赫兹金属线波导传输特性实验研究及模拟分析

太赫兹波介于微波与红外之间,当前太赫兹波主要在自由空间中传输,金属线波导以低损耗、低色散等突出的传输特性被广泛关注.本研究首先根据太赫兹波在不同金属线表面的趋肤深度选择铜线作为研究对象,然后基于太赫兹时域光谱系统搭建可调节式金属线波导传输特性测试光路,采集到通过不同半径、不同长度、不同端口状态的单/双铜线传输的时域信号,最后利用有限元方法对不同半径、不同形变程度的单/双根铜线在空气域的传输特性进行仿真.实验结果表明,传输损耗会随着铜线长度的增加而增加,金属线越细传输速度越慢,端口形态对传输特性的影响不如长度变化对传输特性的影响明显,双金属线越粗传输速度越快.仿真结果表明,太赫兹波在单根金属线上传输时,电场主要分布在金属线表面,金属线越细表面等离激元的模场面积越小;当金属线形变成椭圆时,模场主要分布在长轴两端;当太赫兹波在双金属线中传输时,模场主要分布在两根金属线中间,且距离越远模场面积越小.本研究结合实验与仿真分析方法对单、双金属线的太赫兹传输特性进行研究,为后续开发高效太赫兹金属波导提供参考.