利用太赫兹反射式时域光谱系统测量有机溶剂的光学参数

采用太赫兹反射式时域光谱系统,测量了包括正己烷、液状石蜡、无水酒精和水在内的四种有机溶剂的反射式时域光谱,并根据实验模型设计了两种计算方法提取液体样品的光学参数.此外,还将反射算法得到的样品光学参数与透射算法的结果进行比较,验证了反射式系统对应算法结果的正确性,解决了透射系统无法准确测量和提取对太赫兹吸收很强的样品的光...     

玉米油光学参数的太赫兹波精确测定研究

利用太赫兹电磁波时域光谱（THz-TDS）技术对玉米油进行了测量.考虑容器对参数测量的影响,使用传输函数逼近方法来计算分析玉米油的折射率、吸收系数等重要的光学参数.与传统的太赫兹电磁波数值计算方法比较,传输函数逼近方法在分析玉米油的光学参数方面具有很高精度.结果表明,该测量分析方法对植物油品质检测具有重要指导意义. 关键词： 太赫兹时域谱 玉米油 光学参数 吸收系数     

基于太赫兹时域光谱技术的光学参数提取方法的研究进展

光学参数是宏观上表征材料光学性质的物理量,间接反映了材料的微观特性,对光学参数准确的提取可以研究材料的微观性质和机理。近年来,太赫兹时域光谱技术作为一种新兴的光谱分析手段已经成为研究的热点。由于太赫兹辐射能量低并且脉冲宽度窄(皮秒量级),太赫兹时域光谱技术在提取光学参数方面具有无损伤和高时间分辨率的特点。本文总结了基于太赫兹透射和反射时域光谱技术的光学参数提取方法的研究进展,着重阐述了几种经典方法,分析了每种方法的优缺点,并讨论了太赫兹时域光谱技术用于提取材料光学参数的挑战。研究结果表明,透射法适用于对太赫兹波吸收较弱的物质,而反射法则适用于对太赫兹波有强烈吸收的材料。     

太赫兹计量研究与标准研制进展

太赫兹作为新的技术手段在物质成分识别、高速通信、生物医学、安检成像和军事国防等领域具有重要的作用。太赫兹技术的各种应用都建立在对太赫兹本身及其与物质相互作用测量的基础上,因此准确的太赫兹参数测量及相关量值溯源是太赫兹应用的技术支撑和保障。介绍中国计量科学研究院在太赫兹辐射参数计量标准研究中形成的测量技术和溯源方法、研制的测量仪器和测量装置、制定的计量校准法规和建立的计量标准装置,对太赫兹辐射时域、频域、空域和强度等参数给出了量值溯源传递图并进行了测量不确定度分析。提出的太赫兹计量方法和标准装置可保障太赫兹技术研究和应用中的量值可靠,也可为其他太赫兹参数的测量提供参考。     

基于衰减全反射式太赫兹时域光谱技术的食用油光谱特性研究

食用油是人类营养和能量的重要来源,为人体提供必需的脂肪酸,研究食用油在太赫兹波段光学特性,对食用油成分分析及品质评价具有重要价值。衰减全反射式太赫兹时域光谱技术是一种新型的太赫兹时域光谱技术,通过样品与倏逝波的相互作用,获取样品的太赫兹光谱。与透射式或反射式太赫兹时域光谱技术相比,该技术能有效地避免测量食用油等液体样品时样品池对光学参数的影响,并能获得样品的精确光学参数。分别利用透射式太赫兹时域光谱技术和衰减全反射式太赫兹时域光谱技术测量了大豆油的吸收光谱。结果表明,与透射式太赫兹时域光谱技术相比,衰减全反射式太赫兹时域光谱技术能更有效地提取大豆油的吸收系数、吸收峰分布等光学特性。进一步利用衰减全反射式太赫兹时域光谱技术研究了大豆油、核桃油、葡萄籽油在太赫兹波段的光学特性,获得了三种食用油在1~1.8 THz范围内的折射率谱和吸收光谱。利用密度泛函理论计算了食用油中四种主要成分(软脂酸、硬脂酸、油酸和亚油酸)在太赫兹波段的振动、转动模式,理论计算结果同实验测量结果吻合较好。研究表明,在太赫兹波段食用油的吸收峰与所含脂肪酸分子种类与含量有关,其主要来源为脂肪酸分子的低频振动和转动。研究成果对食用油成分定性定量分析及品质检测等具有指导意义。     

超大长宽比U型开口谐振器的太赫兹调控特性

近年来,金属亚波长结构由于在负折射材料方面存在巨大应用价值,及可作为太赫兹波段的光学限制器等器件应用,引起了研究者们的广泛关注。本文采用电子束曝光离子束刻蚀的方法在金膜上制备了亚波长的超大长宽比U型开口矩形谐振器阵列结构,利用时域有限差分方法(FDTD)和太赫兹时域光谱技术(THz-TDS)对U型阵列结构的太赫兹波透射光谱响应进行了测量和分析,讨论了透过率对结构几何参数的依赖特性和异常透射的物理机制。通过这种U型开口谐振器能够实现太赫兹波的强局域和场增强,可将太赫兹波局域在波长千分之一的尺寸上,从而实现了太赫兹的异常透射现象,这种超大长宽比的U型开口谐振器可在太赫兹探测、太赫兹成像及其他光学器件的设计上得以应用。     

基于高斯混合模型的液体电磁参数太赫兹测量方法

针对使用透射式测量系统难以提取太赫兹波段高吸收样品电磁参数的难题,采用反射式时域光谱系统分别测量了极性液体和非极性液体的时域光谱。通过时域有限积分算法对太赫兹波在样品中的传播特性进行建模,并使用高斯混合模型重新构建反射光谱,从噪声中恢复了原始的太赫兹时域信号,解决了反射式系统信号易受干扰导致的电磁参数发生伪波动的问题。实验结果表明,使用恢复信号计算得到的水和液体石蜡在0.4 THz～2 THz波段的折射率和消光系数,与使用原始信号计算得到的结果相比,有效地消除了波动现象,去趋势波动分析（detrended fluctuation analysis, DFA）标度指数较之原始信号计算值分别上升了7%、3%、29%、31%,验证了该方法的有效性和正确性。     

太赫兹源发散角测量技术研究

发散角是太赫兹源光束特性的重要衡量指标,是太赫兹光学系统设计的重要参数。研究了太赫兹源发散角测量原理,设计了一种由精密弧形导轨、斩波器、狭缝组件、太赫兹高莱探测器、锁相放大器和计算机系统组成的测量装置,设计了一种由自准直仪、光学角规和CCD相机组成的发散角测量装置标定模块,对太赫兹肖特基倍频源和太赫兹雪崩固态源的发散角进行了测量。此外,对测量结果不确定度进行了评定,其不确定度水平达到U_(rel)=3.2%(k=2)。太赫兹源发散角的准确测量为深空探测、战术通信、反隐身、战场隐蔽目标识别等领域提供了有力的支撑。     

皮肤含水量对太赫兹光谱参数的影响规律研究

太赫兹时域光谱技术已经用于皮肤癌、皮肤烧伤以及皮肤疤痕治疗效果的诊断和过程监测,通常采用太赫兹时域和频域光谱参数作为区分皮肤组织不同状态的诊断参量.目前最常用的皮肤活体反射式太赫兹测量装置需将皮肤放置于介质窗上来提高测量的准确性,这使得皮肤表层水分含量因为阻塞而发生变化,从而影响太赫兹诊断皮肤的精确性.随着太赫兹生物应...     

基于BS结构的太赫兹光谱数据库的设计与实现

随着太赫兹技术中关键科学与技术问题的解决和有关仪器发展,其在各个领域的应用也备受人们的关注。由于太赫兹光谱技术具有一些独特优势,在快速无损检测技术的发展方面具有重要的应用前景,该技术与其他方法互补,可以解决许多原来难以解决的检测问题。进一步开发太赫兹光谱技术实际检测方法的关键之一就是需要具有一套较为完整和可靠的太赫兹光谱数据库。介绍了近期开发的一个基于浏览器/服务器(Browser/Server)的太赫兹光谱数据库系统。根据实际需要设计了太赫兹光谱数据库的结构和主要功能。该数据库目前包括240多条太赫兹光谱信息,其数据来源包括三个部分：(1)收集了部分国外太赫兹光谱数据库的信息;(2)从文献中收集部分光谱数据;(3)国内部分实验室测量的太赫兹光谱数据。着重介绍了建立BS结构的太赫兹数据库的基本结构和项目,介绍了BS结构太赫兹光谱数据库的功能与检索方法。该数据库具有计算样品的光学参数功能,可以根据输入的太赫兹时域光谱数据计算出样品的吸收系数,折射率等其他光学参数,以便于样品特征研究和谱库检索。检索系统能方便的提供注册用户收集、查询、显示谱图及其实验数据和分子结构图、数据匹配等功能。该数据库可以登录http://www.teralibrary.com进行查询和使用。该数据库是根据目前的太赫兹光谱数据信息建立的,以后会逐渐完善。希望该太赫兹光谱数据库能够为用户提供强大、方便和高效的服务功能,进而推进太赫兹技术在更多领域的应用。     

Characteristics of adsorption phase with water/organic mixtures at a surface of activated carbons possessing intraparticle and textural porosities

The behaviour of water and water/organic mixtures adsorbed onto activated microporous carbons or a carbon adsorbent with narrow intraparticle micropores and broad mesopores and macropores between nanoparticles was studied using low-temperature adsorption method and ¹H NMR spectroscopy with layer-by-layer freezing-out of liquids at 190-273 K. These investigations revealed concentration-dependent effects of benzene, DMSO, acetone, chloroform, methane and acetonitrile on the characteristics of adsorbed water and the influence of this water on the interfacial behaviour of adsorbed organics. The influence of organics causes the structural and energetic differentiations of adsorbed water. The latter can be displaced by organics from micropores into broader pores and/or form mixture with polar solvents in meso and macropores. Freezing of adsorbed water can affect the adsorbent structure because ice crystallites have a larger size than that of liquid water droplets that lead to changes in the behaviour of adsorbed water/organic mixtures observed by the ¹H NMR and adsorption methods.     

The reaction field contribution to the proton magnetic shielding of acetonitrile in some non-polar solvents

The gas-to-infinite dilution proton chemical shifts of acetonitrile in a series of non-polar, isotropic solvents have been measured. After allowance for the bulk susceptibility and van der Waals contributions, it is possible to to explain the observed shifts by the well-known reaction field theory. The existing level of experimental error in chemical shift measurement is sufficiently large that no justification exists in preferring the form of the theory based on an ellipsoidal cavity to that based on a spherical cavity. Some further observed results are given which demonstrate the existence of specific interactions between acetonitrile and each of several non-polar solvents including carbon tetrachloride.     

Structure and properties of 1,4-benzenedimethanethiol films grown from solution on Au(1 1 1): An XPS and NEXAFS study

Core level photoemission and X-ray absorption at the carbon C 1s edge are applied to the study of chemisorption of 1,4-benzenedimethanethiol molecules on Au(1 1 1) and to investigate the effect of the solvent used to prepare the organic films. 1,4-Benzenedimethanethiol films were prepared in polar and non-polar solvents, i.e. ethanol, methanol and n-hexane. 1,4-Benzenedimethanethiol molecules are anchored to the substrate through a single S-Au bond; the molecules in the films tend to assume an upright orientation, the aromatic ring resulting tilted towards the direction perpendicular to the substrate plane. The films present an effective thickness corresponding to more than a single layer. Only small differences are observed among behaviours in different solvents. It is concluded that the final properties and conformation of the 1,4-benzenedimethanethiol films are largely determined by the reciprocal interactions between the molecules and with the substrate.     

Sonochemical reaction of selected cyclic C6Hx hydrocarbons in organic solvents

The rates and products of the sonochemical reactions of benzene, 1,4-cyclohexadiene, 1,3-cyclohexadiene, cyclohexene, and cyclohexane in selected organic solvents have been investigated. The sonochemical reactions of these educts in the investigated organic solvents follow first-order kinetics. Generally, they are sonicated more rapidly in polar than in non-polar solvent; higher volatility of the solute results in faster sonolysis in the organic solvents. However, the sonication of cyclohexane in n-decane and the sonication of benzene in n-propanol are exceptional cases. Since cyclohexane exhibits a much higher lipophilicity and benzene a much higher hydrophilicity than other educts, it might be more difficult to transfer either educt from the bulk liquid into the cavitation bubbles. In tetrachloroethylene, the reactivity of the tested educts with in situ generated chlorine as well as chlorine-containing radical intermediates can accelerate the rate of sonochemical reactions under the employed conditions. In n-propanol and n-decane, the pyrolysis during the collapse of the cavitation bubbles is the only reaction pathway of sonolysis. In tetrachloroethylene, the pyrolysis during the collapse of the cavitation bubbles and the free radical reaction in the bulk liquid may occur simultaneously. Except for the products generated from sonolysis, products formed from chlorine transformations (substitution or addition reactions) are detected. Benzene is hardly decomposed in tetrachloroethylene. However, when FeCl3 is added into the reaction system, benzene is sonoconverted rapidly, and the product chlorobenzene was detected. In organic solvents, the sonoreaction rates and the sonoproducts are dependent on the physicochemical properties of the solvents used, as well as the volatility, the polarity and the reactivity of educts.     

Effect of dielectric properties of solvents on the quality factor for a beyond 900 MHz cryogenic probe model

A previous report by Kelly et al. [J. Am. Chem. Soc. 124 (2002) 12013] indicated that the ionic conductivity of aqueous solution produces a significant contribution to the sensitivity loss in high-resolution NMR equipped with a cryogenically cooled probe. The loss in a sample solution contains two contributions: one from the ionic conductivity and the other from the dielectric loss; the latter is especially important at high frequencies such as above 900 MHz. Here, we investigated the effect of the dielectric conductivity on the quality factor of a 930 MHz cryogenic probe model; in particular, it deals with the ionic aqueous solutions and organic solvents commonly used for NMR in biological research and the chemistry of natural compounds. The sample quality factor, Qs, at first increases with the real part of the relative dielectric permittivity epsilon' and then saturates. In the case of polar organic solvents, the transverse electric field on the sample decreases with epsilon', resulting in an increase of Qs. In the case of non-polar organic solvents, the dielectric conductivity is so small that the gradient of the increase is steep, resulting in much larger Qs though the epsilon' is small. The effect of the transverse electric field is negligible if the epsilon' becomes large, thus the loss for ionic aqueous solution is mainly governed by a loop current induced in the sample solution. As the induced electromotive force is independent of the epsilon', the Qs is saturated at high values of epsilon'. Based on the Qs obtained with the cryogenic probe model, the sensitivity for the cryogenic probe is expected to be as follows: the loss in sensitivity by loading water is more than 66%, i.e., the effect of the dielectric conductivity of water is remarkable at high frequencies; polar organic solvent suffers much larger losses, which is due to the enhancement of the effective sample resistance by the effect of epsilon'; a non-polar organic solvent is nearly free of the sensitivity loss as the dielectric conductivity is negligible; the reverse micelle behaves similarly.     

太赫兹时域光谱在邮件隐匿危险品检测中的应用

随着电子商务的快速发展,邮件数量剧增,在邮件中隐匿危险品已经成为犯罪分子重要的犯罪手段,威胁公共安全和社会稳定。邮件的安全检查变得尤为重要,而常规的检测技术不能准确识别危险品。太赫兹波是介于红外和微波之间的电磁波,邮件中隐匿的爆炸物、毒品和有害生物因子等在太赫兹波段存在特征吸收光谱,而邮件常用的非极性包装材料可以被太赫兹波穿透。太赫兹波还具有低能性、相干性等特性,这些特性使得太赫兹技术可以实现邮件隐匿危险品高灵敏度的无损检测。文章介绍了太赫兹技术的特性,太赫兹时域光谱系统的组成和获取光学常数的菲涅尔公式解析法。该方法通过样品透射或反射信号和参考信号来获取包括吸收光谱在内的材料参数。将样品的太赫兹特征吸收光谱和已建立的各种危险品的光谱特征数据库进行比对,可以判断是否为危险品以及危险品种类。对爆炸物、毒品在太赫兹波段的特征吸收光谱的研究成果,及在各种非极性材料遮挡下吸收光谱的特异性的研究进展进行了总结。获取吸收光谱的解析法适用于较厚样品,针对薄样品,还介绍了一种P-谱法。该方法不需要参考信号就能准确获取覆盖物下样品的吸收光谱。除直接利用吸收光谱做检测外,近些年还提出了很多其他识别危险品的方法,如光谱动力学分析法,化学计量学方法和基于太赫兹时域光谱的成像分析法等。其中,光谱动力学分析法可以很好的区分吸收频率有重叠的物质;化学计量学方法可以对混合物进行成分的定性和定量分析;光谱成像法可以完成较大面积的隐匿危险品识别。分析了太赫兹时域光谱技术识别有害生物因子的可行性,以及针对有害生物因子携带量小的特点,总结了太赫兹时域光谱技术在提高生物因子检测灵敏度方面的研究进展。探讨了太赫兹技术在邮件安检应用中一些有待解决的问题,如太赫兹功率有限、受环境因素影响较大、缺乏统一的标准等,展望了未来的发展趋势。     

Terahertz radiation from armchair carbon nanotube dipole antenna

This paper investigates the electromagnetic radiation characteristics of a metallic, large aspect ratio single walled carbon nanotube antenna in the terahertz frequency region below 12.5 THz. The key features of terahertz pulse have been revealed on the carbon nanotube antenna in comparison with conventional photoconductive switching. The terahertz waveforms, radiation power and their field distributions have been evaluated and are analysed. The Fourier transformed spectra over the whole frequency range demonstrate that the carbon nanotube antenna can be used as radiation source for broadband terahertz applications.     

四苯基卟啉锌-单壁碳纳米管复合薄膜的制备与光电特性研究

使用喷涂法制备了四苯基卟啉锌(ZnTPP)薄膜及ZnTPP-单壁碳纳米管复合薄膜。采用金相显微镜、扫描电子显微镜、台阶仪、四探针测试仪、紫外-可见光分光光度计、傅里叶红外光谱仪对薄膜的形貌、电学及光学性能等进行了系统的测量,研究了ZnTPP薄膜及ZnTPP-碳纳米管复合薄膜的太赫兹响应特性。结果表明,ZnTPP的太赫兹指纹谱峰为44,57,77,88,95和102 cm-1,与文献[3]报道的棕树叶中叶绿素的指纹谱峰基本一致。重要的是,通过与碳纳米管相复合的方法,不仅使ZnTPP有机薄膜的均匀性及致密性得到了改善,还使后者的导电性及在紫外到太赫兹波段的光吸收性能获得明显增强。此外,还发现了复合薄膜在47及66 cm-1处出现新的太赫兹吸收峰,证明了碳纳米管和ZnTPP之间存在的相互作用。这种作用使复合薄膜的综合性能得到提高。结果表明,通过加入碳纳米管,能够对ZnTPP的薄膜质量以及电学和光学性能等进行有效的改善,使之具有综合优良的物理性能、具备光电器件的应用前景。研究成果对促进有机物的太赫兹光谱研究以及寻找新型太赫兹有机敏感材料等具有重要意义。     

Spectroscopic method to measure the formation enthalpy of self-association of indolic molecules in non-polar solvents

Formation enthalpy of self-association of indoles in non-polar solvents is obtained from the behaviour of their fluorescence spectra areas with temperature. Formation enthalpy of skatole self-association thus obtained is in agreement with that found by another method. This supports the hypothesis that the spectral anomalies observed are due to self-association. The method can be extended to other molecules and it is independent of the spectral structure.