扫描速度对于太赫兹时域光谱系统信号品质的影响

太赫兹时域光谱技术是太赫兹技术的一个重要研究方向,较低的扫描速度一直是限制其应用的瓶颈。对比了不同扫描速度下太赫兹时域系统光谱系统信号的品质。发现信号品质因扫描速度提高而恶化,其程度和锁相放大器的时间常数密切相关。实验结果发现,系统中噪声主要是从电路中引入的。     

太赫兹时域频谱信噪比分析与规范性研究

基于飞秒激光的太赫兹脉冲时域光谱技术,已经成为诸多科学领域研究中有效的新手段。文章分析了太赫兹时域系统频谱采集方式的特点,提出标准信噪比的概念,使不同的太赫兹时域频谱仪可以在同一标准下进行量化评价。在研究了信噪比特点的基础上,给出了太赫兹时域频谱信噪比的简单获取方法。并采用这种方法对几个著名太赫兹研究小组的时域频谱系统的信噪比进行了比对。该方法让使用者只须获取单次测量数据就能换算出系统的标准信噪比,给用户评价太赫兹时域频谱系统带来了极大便利。     

A method for removing etalon oscillations from THz time-domain spectra

We present a simple algorithm for removing or reducing spurious oscillations in the THz spectra which result from secondary reflection peaks in samples or optical elements. The algorithm utilizes the fact that a THz time-domain trace containing secondary peaks can be represented as a convolution of the primary peak and two or more delta functions. The algorithm is applicable for samples which are sufficiently thick that the reflection peak does not overlap with the primary peak, and that do not have strong absorption or dispersion.     

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...     

Precisely optical material parameter determination by time domain waveform rebuilding with THz time-domain spectroscopy

We offer an innovative optical material parameter extraction algorithm for Terahertz time-domain spectroscopy (THz-TDS). Unlike previously reported extraction algorithms in frequency domain, which have to be compromised between amplitude and phase, or the real part and imaginary part of the transfer function, we calculate material parameters by minimizing the difference between the measured sample waveform and the rebuilt one in time domain. The new method is effectively verified by different samples, and can be used either in transmission mode or in reflection mode for THz-TDS.     

超薄金属膜在太赫兹波段的光学特性研究

超薄金属膜在太赫兹波段的探测器、反射镜、波导器件以及太赫兹量子级联激光器中得到了广泛应用。超薄金属膜的光学常数不仅是这些器件设计中不可缺少的参数,而且是开发新型光电材料的一个重要依据。文章运用太赫兹差分时域光谱技术对超薄金属铬、镍和钛膜的光学特性研究,获得其在太赫兹波段的折射率和消光系数,并根据菲涅尔公式计算入射介质为高阻GaAs时,GaAs/Metal界面的反射谱,三种金属在0.3～1.5THz的波段范围内的平均反射率均超过80%。研究超薄金属膜在太赫兹波段的反射特性,为设计性能优良的太赫兹辐射源、探测器及太赫兹光学元件奠定基础。     

用太赫兹时域光谱法检测沙粒中的微量原油

由于太赫兹波对极性物质有很高的灵敏度,因此可以利用太赫兹时域光谱技术检测沙粒中含有的微量原油。将微量的原油浓度与太赫兹衰减系数之间建立起线性模型。同时引入有效介质理论来证实太赫兹介电常数与原油含量低于200 ppm之间的线性关系。结果表明,太赫兹时域光谱技术可以成为检测沙粒中微量原油泄漏的有效方法。     

A novel method to measure dielectric properties of materials in terahertz spectroscopy

We present a simple method to obtain the optical and dielectric properties of samples without reference measurement in the reflection-type terahertz time-domain spectroscopy. The dielectric properties of the samples of silicon and gallium arsenide were examined. The optical and dielectric properties of the samples were measured through only simple configuration, without the misplacement error. The obtained dielectric functions of the samples in reflection geometry are in good agreement with that predicated by the theory. The main advantage of this method over other methods is its simplicity and accuracy and ease for application of the reflection systems with different incident angle.     

散射在太赫兹吸收谱定量分析中的应用研究

基于太赫兹光谱的物质成分定量分析是太赫兹技术重要的应用方向之一。但是当太赫兹波入射样品时,会与样品颗粒在微观尺度下发生散射效应,造成太赫兹波强度的衰减。因此实验测得的样品的太赫兹吸收谱主要由两部分组成,即样品本身对太赫兹波的吸收以及由散射效应造成的衰减。尤其是当样品的颗粒尺寸与太赫兹波的波长接近或可相比拟时,散射效应更为明显。在以往的太赫兹定量分析领域,往往仅考虑了Lambert-Beer定律,即物质对光的吸收与其浓度成线性变化的关系,而忽视了散射效应的作用,导致定量分析的准确度受到了限制。在对混合物样品的太赫兹波段散射效应进行分析的基础上,采用类比的方法,提出了混合物的太赫兹吸收谱模型,并通过一系列定量分析实验验证了该模型的有效性。在对多组混合物样品的定量分析实验中,定量分析误差普遍小于3%,较之仅考虑Lambert-Beer定律而言准确度得到了大幅提高,表明研究散射效应对提高太赫兹定量分析的准确度具有重要作用。     

基于THz光谱技术的1,3-二硝基苯挥发气体检测方法研究

针对工业生产过程中1,3-二硝基苯挥发气体突发性泄露等情况的发生,设计了一种基于太赫兹(THz)特征光谱吸收技术的检测方法,该方法可通过1,3-二硝基苯在THz波段的特征波长对痕量剧毒有害气体进行检测。系统设计了双气室结构,为THz波提供差分数据,一组为标准空气,另一组为待测样气。由1,3-二硝基苯在THz波段的四个主吸收带0.635,0.912,1.095和1.435THz可根据对应吸收带吸收系数的比例关系得到对应波长上的吸收幅值,最终反演气体浓度。经过对两种传统检测方法的实验分析和对THz吸收检测方法的仿真研究可知,色谱法检测速度无法实现实时检测,红外吸收法对环境湿度要求很高,需经干燥处理,而THz吸收法对环境湿度要求较低,且具备实时性,更适合于实际应用。     

基于太赫兹时域谱分析的爆炸物检测方法研究

采用太赫兹时域谱分析技术测量了在氮气和空气环境下四种典型爆炸物的太赫兹光谱,并分别利用均值平滑、傅里叶低通滤波以及小波分解与重构三种方法来消除空气中由水蒸气吸收引起的光谱振荡现象。实验结果表明:四种爆炸物的太赫兹光谱具有可分辨的特征,能够作为识别的依据;通过研究水蒸气的影响,使得利用太赫兹时域谱分析技术检测爆炸物向实用化迈进了一步。     

2005年物理科学一处评审工作综述

2005年国家自然科学基金的各项评审工作已经基本结束,我们在此向所有关心和支持物理科学一处工作的广大科研工作者表示衷心的感谢！年底将至,我们将就科学处全年的评审工作情况向大家做一个汇报,对在评审中发现的一些问题提出一些建议,希望能对下一年度的项目申请有所帮助.     

THz光谱技术在炸药及其相关材料检测中的应用进展

太赫兹（THz）光谱技术近年来在航空航天、生命科学、安全检测等领域的应用进展迅速.由于许多炸药及其相关材料在THz波段具有特征吸收,许多非金属、非极性材料对THz 波是透明的,且THz波具有低能性,THz光谱技术在安检中具有巨大的应用潜力.文章介绍了国际上THz光谱技术在炸药及其相关材料研究中的现状和进展及文章作者在炸药及其相关材料THz光谱研究方面的成果,讨论了THz技术应用于安全检测领域面临的挑战.     

太赫兹波段豆油光谱的优化测量

太赫兹时域光谱技术是基于飞秒超快激光技术的有效的光谱检测技术,太赫兹波独特的优势使其成为一种有效的无损检测手段,并被广泛地应用到各个领域。然而在样品检测尤其是液体样品检测过程中,由于Fabry-Perot效应的存在,太赫兹波在样品、样品容器、以及光学元件之间的多次反射,使时域信号产生回波,样品的吸收光谱在频域内产生振荡,有可能会隐藏一些重要的吸收特征。为了解决这一问题,对解卷积算法进行改进,在传统计算模型的基础上,考虑系统中液体池窗片和光学元件对太赫兹波的非线性吸收,将包含回波的太赫兹时域信号描述为太赫兹主脉冲与一系列冲击信号和非线性传递函数的卷积。通过分析,有效去除回波引起的频谱振荡,进一步提高太赫兹波段豆油光学参数的测定精度。实验对比了改进前后0.2～2 THz波段豆油的频谱及吸收谱,实验结果证明,与传统的主脉冲截取法相比,本算法不仅能有效去除回波引起的频谱振荡,且在相同检测条件下,可将太赫兹波段豆油样品的频率分辨率由50 GHz有效提高至10 GHz。该算法不受被测对象参数的影响,同样适用于其他液体的太赫兹时域光谱测量。最后对吸收谱中残余的频谱振荡进行了深入分析。     

THz光谱技术在炸药及其相关材料检测中的应用进展

太赫兹（THz）光谱技术近年来在航空航天、生命科学、安全检测等领域的应用进展迅速.由于许多炸药及其相关材料在THz波段具有特征吸收，许多非金属、非极性材料对THz波是透明的。且THz波具有低能性，THz光谱技术在安检中具有巨大的应用潜力．文章介绍了国际上THz光谱技术在炸药及其相关材料研究中的现状和进展及文章作者在炸药及其相关材料THz光谱研究方面的成果，讨论了THz技术应用于安全检测领域面临的挑战.     

The transmission enhancement of a THz pulse through an Ag/Ag2O 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.     

Accurate rotational spectroscopy of sulfur dioxide, SO2, in its ground vibrational and first excited bending states, v2 = 0, 1, up to 2 THz

Approximately 150 pure rotational transitions each have been recorded for SO₂, v₂ = 0 and 1, in selected frequency regions up to 2 THz. The J and K_a quantum numbers reach very high values: 92 and 23, respectively, for the ground vibrational state and 81 and 21, respectively, for the first excited bending state. The highest levels accessed are almost 3000 cm⁻¹ above ground. The relative experimental uncertainties Δν/ν are about 10⁻⁸ for several medium to strong, isolated lines, and generally better than 2.5 × 10⁻⁷. Improved spectroscopic parameters have been obtained for both states, particularly for the excited bending state. In fact, the accuracies with which the energy levels of the v₂ = 1 state are known depend essentially only on the accuracy with which the vibrational spacing is known from infrared spectroscopy.     

非极性有机溶剂光学参数的太赫兹波精确测量

利用太赫兹时域光谱技术对六种常用非极性有机溶剂进行了测量,其中包括正己烷、环己烷、石油醚、甲苯、四氯化碳和二硫化碳.由于这些非极性有机溶剂常用于溶解其他有机物,因此测量非极性有机溶剂的光学参数,有助于进一步研究其他有机物在太赫兹波段的各种特性.在提取有机溶剂光学参数的过程中,考虑了用于盛放液体的比色皿对太赫兹信号的影响...     

Plasma wave interactions in the microwave to THz range between carriers in a semiconductor 2DEG and interdigital slow waves

Traveling wave interactions between the plasma wave in a two-dimensional electron gas (2DEG) in the AlGaAs/GaAs high electron mobility transistor (HEMT) structure and the electromagnetic space harmonic slow waves produced by interdigital metal electrodes were investigated both theoretically and experimentally. By means of a TM mode analysis, a general expression for the ω- and k-dependent effective permittivity of the 2DEG plasma was derived. The two-terminal admittance was calculated by a Green’s function method from the microwave to the THz wave region. Occurrences of negative admittance were predicted, and its peak values increased with frequency to a very large value in the THz region due to the reduction in the number of collisions per cycle. Preliminary admittance measurements at microwave frequencies showed good agreement with calculations, confirming the existence of plasma wave interactions.     

Probing the sulfur content in gasoline quantitatively with terahertz time-domain spectroscopy

Terahertz time-domain spectroscopy(THz-TDS)was used for the quantitative detection of sulfur content in gasoline.Models of chemo metrics methods and partial least squares(PLS)were built to measure THz-TDS and the sulfur content.All of the samples were divided into two parts.One part was used for calibration and the other one for validation.In order to evaluate the quality of the models,the correlation coefficient(R)and root-mean-square errors(RMSE)of calibration and validation models were calculated.The value of R and RMSE were close to 1 and 0 within acceptable levels,respectively,indicating that the combination of THz-TDS and PLS is a potential method for further quantitative detection.