A highly-sensitive automatic transient laser-induced breakdown spectroscopy system with high temporal and spatial resolution

A highly-sensitive automatic transient laser-induced breakdown spectroscopy(LIBS) system is designed and integrated.It successfully avoids the delay time selecting problem in the conventional LIBS system,and realizes the LIBS data acquisition with high spatiotemporal resolution automatically.Multiple transient spectra can be obtained in each measurement,which will provide more information for spectral research.The water-vapour and liquid-water Raman scattering spectra are captured by this system,and the comparison of experimental water-vapour Raman scattering spectrum with theoretical data verifies the reliability of the LIBS system.Based on this system,the air laser induced air breakdown spectra are captured and analysed.The system is also useful for the research on water-vapour Raman Lidar remote sensing.     

激光诱导击穿光谱与拉曼光谱技术在危险物检测中的研究进展

炸药、生物及化学危险物检测在反恐和公共安全领域具有重要应用价值,也是目前亟需解决的问题。激光诱导击穿光谱技术利用高能激光脉冲诱导材料产生等离子体,通过探测等离子体辐射光谱从而分析其组成成分。拉曼光谱技术是基于非弹性光散射的一种光谱检测方法,可以反映分子的振动信息。由于它们都具有快速和非接触遥测的优点,成为最有发展潜力和应用前景的危险物检测技术。介绍了激光诱导击穿光谱、拉曼光谱以及二者联合探测技术在危险物检测中的国内外发展现状,并对各自的优缺点进行了分析。激光诱导击穿光谱信号强、实时性好,但重复性差、基底效应影响显著,在判别组成元素相同而分子结构不同的危险物和干扰物时面临巨大挑战。拉曼光谱能够提供被测物的分子信息,适合于鉴别有机危险物,但信号弱、受荧光干扰大、检测低浓度样品及分析混合物的能力弱,外场使用时受周围杂散光以及环境变化的影响大。将这两种光谱探测技术相融合,发挥各自的优点,可以有效地提高探测危险物的准确度。但两种光谱联合探测系统结构和数据处理复杂,成本高,还有许多技术难点亟需解决。文章最后,对危险物激光诱导击穿光谱和拉曼光谱研究的前景进行了展望。     

Na_2SO_4溶液激光拉曼/激光诱导击穿光谱联合探测

光谱技术应用于海底极端环境下多参数、多相态、无接触探测已成为深海化学传感器发展的一个重要方向,尤其是水下激光拉曼光谱技术和水下激光诱导击穿光谱技术正成为目前研究开发的热点。该工作旨在探索一项水下激光诱导击穿光谱与激光拉曼光谱(LIBS-LRS)联合探测技术,以实现LIBS和拉曼两种检测技术在检测系统上的整合,在信息获取上的互补。在实验室搭建了一套LIBS-LRS联合探测装置,该装置对于拉曼和LIBS采用同样的激发光源、光谱仪和探测器,前置光路分为两部分:拉曼光路和LIBS光路,分别收集Na_2SO_4溶液的拉曼信号和LIBS信号。前置光路收集的拉曼和LIBS信号由Y型光纤导入光谱仪,分别在面阵CCD不同区域进行探测。利用该装置对配置的Na_2SO_4溶液进行探测,同时获得了Na元素的LIBS信号和SO~(2-)_4拉曼信号。另外,随着激光能量的提高,在532nm脉冲激光能量超过3.6mJ时,在拉曼光路同时获得了Na元素的LIBS信号和SO~(2-)_4拉曼信号,这样采用同一光路即可实现两种光谱技术的联合,然而实验发现,随着激光能量的增加,激光在溶液中击穿产生的轫致辐射造成了光谱探测基线整体的抬升,对拉曼光谱弱信号的探测是不利的。实验结果初步证明了在拉曼和LIBS在水下联合探测的可行性。     

LIBS-Raman光谱联合水下探测系统及初步试验

水下激光诱导击穿光谱技术(LIBS)和水下激光拉曼光谱技术(Raman)已在深海成功获得应用,这两种技术探测对象互补、器件类似,两者联合探测可更好的进行深海研究。针对此需求研发了一套LIBS-Raman光谱联合水下原位探测原理样机,整个系统集成于L790 mm×Φ270 mm的舱体内,在舱体前端有光学窗口和水密插头,舱体内部主要包括脉冲激光器、光谱仪、嵌入式计算机和供电转换装置,甲板控制终端通过水密电缆实现对系统的供电、控制和数据采集。该联合系统采用一台双波长脉冲激光器同时作为LIBS和拉曼光谱的激发光源,LIBS采用1 064 nm波长,拉曼光谱采用532 nm波长。双波长激光器发出的光束经分光镜分为两路,经过后向散射光路收集的两路信号分别进入两个小型光纤光谱仪进行分光探测,LIBS采用AvaSpec-ULS2048光谱仪,拉曼光谱采用QE 65000光谱仪。利用搭建的原理样机在青岛近海进行水下原位探测,在实验室开展了水中固体靶的探测,实验结果证明了LIBS-Raman联合光谱探测装置的可行性。下一步将优化系统并开展深海探测应用。     

LIBS和Raman光谱的VOCs在线探测

作为一种主要的大气污染物,挥发性有机物（VOCs）因其对大气环境极强的破坏性和生理毒性而受到广泛的关注,在线探测大气中挥发性有机物是一个极具挑战性的工作。将激光诱导击穿光谱（LIBS）与Raman光谱相结合,分别从原子发射光谱及分子结构信息角度对挥发性有机物进行了分析。在线原位检测得到的LIBS光谱观测到了Br元素特征谱线及N,O和H等空气所含元素特征谱线。实验成功探测到了挥发在空气中的邻氟溴苯,对于大气中溴的探测及其相关反应机理研究提供了支持。对于高能激光作用下产生的CN和C₂自由基分子,具体分析了二者产生机理。激光脉冲使空气中的氮气和邻氟溴苯的苯电离分解,邻氟溴苯中的碳原子与空气中的氮发生反应,会形成高温的等离子体,其中的碳氮原子再重新自由组合从而形成CN自由基并自发辐射,通过光谱仪可采集到该自由基的自发辐射的分子谱。待测样品邻氟溴苯分子含有苯环,分子中存在多个碳原子。在强激光作用下邻氟溴苯分子发生光解离,易于形成C₂自由基分子,并辐射产生C₂自由基光谱。实验验证了C₂自由基来自于邻氟溴苯样品里的苯环基团。为增加对挥发性有机物分子结构信息的了解,Raman光谱在线探测的引入很有必要。在样品Raman光谱实验结果的基础上,结合了密度泛函理论（DFT）对其振动模式及分布进行了计算拟合,对其振动产生的特征峰进行了标定并获得了其特征光谱指纹。强度较高的4个峰（310,833,1 036和1 244 cm-1）是C-Br键及C-F键振动表征,特别是前二者（310和833 cm-1）显示存在溴、氟原子位移,可作为该分子的特征光谱指纹对其进行识别。实验证明,LIBS与Raman光谱相结合应用至VOCs的在线探测具有很好的效果,对相关探测工作具有重要参考价值。     

Spectroscopic analysis using a hybrid LIBS-Raman system

A novel setup, combining two spectroscopic techniques, laser induced breakdown spectroscopy (LIBS) and Raman spectroscopy in a hybrid unit, is described. The work presented herein is part of a broader project that aims to demonstrate the applicability of the hybrid LIBS-Raman unit as an analytical tool for the investigation of samples and objects of cultural heritage. The system utilizes a nanosecond pulsed Nd:YAG laser (532 nm) for both LIBS and Raman analysis. In the Raman mode, a low intensity beam from the laser probes the sample surface and the scattering signal is collected into a grating spectrograph coupled to an intensified charge-coupled device (ICCD) detector, which records the Raman spectrum. In the LIBS mode a single high intensity pulse from the laser irradiates the sample surface and the time- and spectrally-resolved emission from the resulting laser ablation plume yields the LIBS spectrum. The use of a non-gated CCD detector was found to produce similar quality data (in terms of S/N ratio and fluorescence background) in the Raman mode, while in the LIBS mode spectral features were clearly broader but did not prevent identification of prominent atomic emission lines. Several model pigment samples were examined and the data obtained show the ability of the hybrid unit to record both Raman and LIBS spectra from the same point on the sample, a clear advantage over the use of different analytical setups. PACS 39.30.+w; 82.80.Dx; 82.80.Gk; 52.38.Mf     

An example of the complementarity of laser‐induced breakdown spectroscopy and Raman microscopy for wall painting pigments analysis

Laser‐induced breakdown spectroscopy (LIBS) and Raman microscopy were used for the identification of pigments in wall painting. Raman spectroscopy, which provides the molecular ‘fingerprint’ of the compound, is nowadays widely used by the archaeometry community, especially for pigment analysis. LIBS, which provides the elementary composition of samples, is a rapid noncontact method, enabling layer‐by‐layer analysis through a precise laser ablation of the sample. This work deals with the behavior of pigments after a LIBS analysis, by trying to identify the compounds before and after the laser shot. Six commercial pigments prepared with the fresco technique were investigated: ultramarine blue, red lead, charcoal, a yellow and a red ochre, and a green earth. Raman spectra, acquired on the sample surface and in the crater induced by LIBS analysis, were compared. The results show that these pigments are well recognized after a LIBS measurement. The analysis of green earth illustrates that the combination of these two techniques gives complete information from a sample. Copyright © 2007 John Wiley & Sons, Ltd.     

拉曼激发激光诱导电子荧光流场测量系统中标记过程的研究

研制了一套拉曼激光发激光诱导电子荧光空气流场测速系统,利用Nd:YAG激光器的二次谐波及其抽运的氧气受激拉曼散射作为标记光源,以ArF准分子激光作为荧光再现光源,并用像增强CCD摄像机（ICCD）记录荧光图像,成功地获得了纯氧及空气中的标记线的荧光图像,并进行了氧气喷流速度测量的初步研究。     

Technical Development of Raman Spectroscopy: From Instrumental to Advanced Combined Technologies

Abstract

Raman-based techniques have developed into excellent analytical tools in various research fields, primarily due to their noninvasive sampling capability, minimal sample preparation, and short analysis time. Major improvements in lasers, spectrometers, detectors, and holographic optical components have made Raman spectroscopy an effective tool for analyzing natural and synthetic materials. This article presents a short introduction to Raman spectroscopy and several recently related advances, including, Fourier transform (FT) Raman spectroscopy, micro-Raman spectroscopy, Raman sensing, and stand-off Raman spectroscopy techniques. Other topics discussed in this article are the importance of its combination with laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF).     

基于远程LIBS-Raman光谱的火星矿物成分分析方法研究

实现了一套实验室环境下的LIBS-Raman测试系统的设计,并验证激光诱导击穿光谱技术（LIBS）和拉曼（Raman）光谱技术在火星模拟环境下矿物样品的综合检测能力。该系统使用卡塞格林望远镜结构进行远程的LIBS激发,使用旁路反射光路进行远程脉冲Raman光谱的激发,其激发光源的波长分别为1 064和532 nm。之后统一使用卡塞格林望远镜进行二者光谱信号的收集。为了充分模拟火星表面矿物所处的物理条件,设计与实现了一套气体腔体,通过将样品放置在气体舱中,可以实现对火星表面条件进行最大程度的模拟。为了验证使用该LIBS-Raman系统进行火星矿物分析的能力,利用8种典型矿物(孔雀石、蓝铜矿、雄黄、雌黄、文石、方解石、硬石膏和石膏等)样品展开实验分析。在这些样品中存在巨大的元素和分子成分上的差异,其中孔雀石、蓝铜矿分子具有不同的价态和原子比例;雄黄、雌黄分子的各原子的个数均不相同;文石、方解石虽具有相同的分子式,但是晶体结构明显不同;硬石膏和石膏矿物的差异则体现在其分子有无含有结晶水上。利用LIBS和Raman技术对这些差异性进行研究,以此来验证在火星条件下使用此组合仪器分析矿物种类和成分的有效性,并研究激光诱导击穿光谱技术和拉曼光谱技术在物质成分分析中的优缺点。实验结果表明,该系统可以在火星条件下有效分析矿物种类和成分。该对比实验还验证了在分析火星物质中的特定矿物元素组成这一问题上,LIBS技术可快速区分元素种类,但针对分子信息探测存在明显局限性;Raman光谱技术则可以在一定程度上对这种局限性进行补偿。二者结合将有效提高极端条件下具有不同分子组成和结构的矿物的识别效能。该系统的成功验证可为进一步火星探测计划提供有力补充,并对实验室建立有价值数据库提供帮助。     

若干低维材料的拉曼光谱学研究--2004年度国家自然科学二等奖获奖项目介绍

文章扼要介绍了2004年国家自然科学二等奖获奖项目：《若干低维材料的拉曼光谱学研究》．用拉曼光谱研究低维纳米材料,必须对传统拉曼光谱学进行改造,创建新的“低维拉曼光谱学”．该项目通过若干低维材料的研究,为创建低维拉曼光谱学作出了系统的创新性贡献,如最先鉴认出典型低维材料的拉曼指纹谱,发现拉曼光谱的两个基本特征出现“反常”,但证明拉曼散射基本原理在低维体系中依然成立．通过低维拉曼光谱和光发射谱的应用研究,发现了材料的许多新奇物性,如发现超晶格和碳纳米管是类缺陷结构,和极性半导体纳米晶材料具有非晶特性,并提出了多孔硅的“量子限制电化学”形成和“多源量子阱”光发射模型,促进了低维材料和半导体器件的制备．     

Detection of explosives with laser-induced breakdown spectroscopy

Our recent work on the detection of explosives by laser-induced breakdown spectroscopy (LIBS) is reviewed in this paper. We have studied the physical mechanism of laser-induced plasma of an organic explosive, TNT. The LIBS spectra of TNT under single-photon excitation are simulated using MATLAB. The variations of the atomic emission lines intensities of carbon, hydrogen, oxygen, and nitrogen versus the plasma temperature are simulated too. We also investigate the time-resolved LIBS spectra of a common inorganic explosive, black powder, in two kinds of surrounding atmospheres, air and argon, and find that the maximum value of the O atomic emission line SBR of black powder occurs at a gate delay of 596 ns. Another focus of our work is on using chemometic methods such as principle component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) to distinguish the organic explosives from organic materials such as plastics. A PLS-DA model for classification is built. TNT and seven types of plastics are chosen as samples to test the model. The experimental results demonstrate that LIBS coupled with the chemometric techniques has the capacity to discriminate organic explosive from plastics.     

Laser-induced plasma in methane and dimethyl ether for flame ignition and combustion diagnostics

In this paper we report the investigation of the laser-induced breakdown and ignition behaviour of methane/air and dimethyl ether (DME)/air mixtures. Moreover, the optical emission from the induced plasma is utilized for determining the mixture composition quantitatively by means of laser-induced breakdown spectroscopy (LIBS). To the best of the authors’ knowledge, LIBS and laser ignition of DME have not been reported in literature before. The technique under investigation is finally employed for combustion diagnostics in laminar as well as turbulent flames. In the laminar premixed and non-premixed flames the LIBS spectra allow spatially resolved measurements of the equivalence ratio and enable studying the mixing of gases provided through the burner with the surrounding room air. In addition, the breakdown threshold of the applied laser pulse energy yields an estimate for the local temperature. In the turbulent cases single-shot LIBS spectra are recorded at fixed position allowing the derivation of local statistical fluctuations of the equivalence ratio in partially premixed jet flames. The results show that laser-induced breakdowns have a strong potential for flame diagnostics and, under suitable conditions, for the ignition of combustible mixtures.     

单次冲击压缩下液态硝基甲烷的拉曼光谱

在单次冲击压缩实验中,运用高敏度瞬态拉曼光谱技术观测了液态硝基甲烷分子的拉曼光谱. 将该拉曼测量技术与二级轻气炮的实验平台结合起来,获得硝基甲烷分子振动模式的高压动态行为. 硝基甲烷被12 GPa压力冲击时的拉曼光谱可清晰探测,其拉曼振动峰仅仅发生了峰位蓝移和峰宽展宽的变化,未显示出化学变化产生的迹象.     

Electron states and electron Raman scattering in semiconductor double cylindrical quantum well wire

The differential cross section for an electron Raman scattering process in a semiconductor GaAs/AlGaAs double quantum well wire is calculated,and expressions for the electronic states are presented.The system is modeled by considering T = 0 K and also with a single parabolic conduction band,which is split into a subband system due to the confinement.The gain and differential cross-section for an electron Raman scattering process are obtained.In addition,the emission spectra for several scattering configurations are discussed,and interpretations of the singularities found in the spectra are given.The electron Raman scattering studied here can be used to provide direct information about the efficiency of the lasers.     

激光诱导击穿空气等离子体光谱及半经验理论模拟

利用Nd∶YAG激光器输出的1 064 nm激光进行了激光诱导击穿空气光谱实验,测量了空气等离子体的时间分辨光谱。基于局域热动力学平衡模型,建立了模拟激光诱导击穿光谱的方法。对700~900 nm波段的空气等离子体光谱进行了模拟。通过模拟结果与实验结果的比较,进一步估算出了空气中氮、氧和氩的相对含量。     

ZnO晶体的偏振拉曼散射的深入研究

利用拉曼选择定则,设计了ZnO单晶的直角偏振几何配置。在室温下测量了ZnO单晶的各种振动模式的偏振拉曼散射光谱。与原先的文献相比较,初步讨论了各种振动模式的线宽和强度的变化原因。除ZnO晶体中包括非极性和极性拉曼基频振动,准横光学和准纵光学模式和振动属性被指认外,它们的高阶拉曼散射模式首先被确定。本研究结果为深入了解ZnO晶体和薄膜的宏观性质和微观结构提供了依据。     

低频声子谱拉曼测试腔的设计与研制

根据一些物理原理，对低能声子（≤０．０２５ｅｖ）的拉曼测试提出了一套设计思想，免除了空气中氮、氧分子对低频区（≤１８０ｃｍ￣（－１））的干扰影响，从而开拓了Ｒａｍａｌｏｇｓｙｓｔｅｍ中１４０３双单色仪探究低频声子的能力，使该范围内的拉曼结果赋有可信性和科学性     

指纹光谱病原菌快速检测研究进展与趋势

病原菌检测对于保障饮用水和食品安全,应对突发公共卫生事件至关重要。现行检测标准或方法存在操作耗时费力,成本高等缺陷,难以满足现代社会高时效性要求,因此开发操作简单、低成本的病原菌快检技术迫在眉睫。近年来,随着激光技术和光电探测技术的高速发展,能够快速获取微生物指纹信息的激光光谱引起了研究者的广泛关注,其中表面增强拉曼光谱（SERS）和激光诱导击穿光谱（LIBS）由于具有快速、原位无损或微损检测等优点,在病原菌快速检测领域广受关注。SERS作为一种分子振动光谱技术,是在常规拉曼（Raman）光谱中引入具有光学信号放大作用的贵金属纳米结构,实现Raman信号数量级的提升同时能够猝灭荧光,因此可以快速获取目标分子的指纹光谱信息。然而受贵金属纳米粒子的材质、形貌、大小等自身属性,以及与待测物距离等多种因素的影响,重现性仍然是SERS在细菌检测中的一大瓶颈。LIBS作为一种新兴的原子发射光谱技术,具有多元素实时检测的能力,可以快速获取样品包括微量和痕量元素在内的所有元素信息。LIBS进行细菌分类和鉴别时,为了降低基底、共存基质的元素干扰,需采集大量纯培养细菌的光谱数据,不仅增加了检测周期,同时带来定性定量难两全的局面。结合SERS和LIBS技术在病原菌快检领域的研究现状,综述了两类方法各自的优势和局限性,并对其在病原菌快速检测领域的发展趋势进行了展望,为开发基于激光光谱的病原菌快检技术提供参考意见。     

用拉曼光谱测定CCl_4散射介质的温度

作者发展了测量散射体温度的拉曼光谱方法,选用CCl4液体做散射介质,对它的217、315和459等三个散射带进行观测,分别记录它们的Stokes和AntiStokes分量的光谱强度,测量得到CCl4液体散射体的温度。实验结果显示,这种非接触光谱测量法具有重要的实用价值。