Detection of sulfur in the reinforced concrete structures using a dual pulsed LIBS system

In concrete structures, an excessive amount of sulfate ions can cause severe damage to the strength and the stability of the building structures and hence a sensitive and reliable technique for sulfate ion detection in concrete is highly desirable. Laser-induced breakdown spectroscopy (LIBS) is one of the most reliable and sensitive techniques to identify the presence of potentially dangerous sulfur in the concrete structure. The atomic emission lines of sulfur lying in the 200–900 nm region are mostly singly ionized states and hence inherently very weak. In order to enhance the sensitivity of the conventional LIBS system, we employed a dual pulsed LIBS system for detection of weak spectral line of sulfur in concrete using the S II peak at 545.38 nm as a marker for quantifying sulfur content in the concrete. The 1064 nm fundamental and 266 nm fourth harmonic of the Nd:YAG laser in conjunction with Spectrograph/gated ICCD camera are the core factors in improvement of sensitivity. Furthermore, the dual pulsed LIBS system and the fine maneuvering of the gate parameters and interpulse delay yielded improvement in the sensitivity, and resulted in a systematic correlation of the LIBS signal with the concentration of sulfur in the concrete sample. In order to quantify the sulfur content in concrete, a calibration curve was also drawn by recording the LIBS spectra of sample having sulfur in various concentrations. The limit of detection achieved with our dual pulsed LIBS system is approximately 38 μg/g.     

Laser-induced breakdown spectroscopy: technique,new features,and detection limits of trace elements in Al base alloy

Laser-induced breakdown spectroscopy (LIBS) has proven to be extremely versatile, providing multielement analysis in real time without sample preparation. The principle is based on the ablation of a small amount of target material by interaction of a strong laser beam with a solid target. The laser must have sufficient energy to excite atoms and to ionize them to produce plasma. We aimed to improve the LIBS limit of detection (LOD) and the precision of spectral lines emitted from the produced plasma by optimizing the parameters affecting the LIBS technique. LIBS LOD is affected by many experimental parameters such as interferences, self-absorption, spectral overlap, signal-to-noise ratio, and matrix effects. The plasma in the present study is generated by focusing a 6-ns pulsed Nd–YAG laser at the fundamental wavelength of 1,064 nm onto the Al target in air at atmospheric pressure. The emission spectra are recorded using an SE 200 Echelle spectrometer manufactured by the Catalina Corporation; it is equipped with an ICCD camera type Andor model iStar DH734-18. This spectrometer allows time-resolved spectral acquisition over the whole UV-NIR (200–1,000 nm) spectral range. Calibration curves for Cu, Mg, Mn, Si, Cr, and Fe were obtained with linear regression coefficients around 99 % on the average in aluminum standard alloy samples. The determined LOD has very useful improvements for Cu I at 521.85 nm, Si I at 288.15 nm, Mn I at 482.34 nm, and Cr I at 520.84 nm spectral lines. LOD is improved by 83.8 % for Cu, 49 % for Si, 84.3 % for Mn, and 45 % for Cr lower with respect to the previous works.     

复合肥中磷元素的激光诱导击穿光谱多元非线性定量分析

采用激光诱导击穿光谱技术对复合肥中磷元素含量进行了定量分析。通过分析特征谱线的激发能级、跃迁概率和干扰情况,确定255.3和844.6 nm分别为磷元素、氧元素的分析线。实验中对18个复合肥样品进行了测量分析,用14个样品建立磷元素的定标曲线,相关系数r仅为0.83,因此采用多元非线性回归方法进行定量分析,提高测量的准确性。与传统定标曲线相比,在考虑氧元素特征谱线的影响时,LIBS测量值与参考值的相关系数r提高到0.98,测量的相对误差大大减小,仅为0.38%～1.70%。实验结果表明,LIBS技术具有快速分析复合肥中磷元素的潜力。     

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.     

激光诱导击穿光谱对农药气溶胶的在线监测

作为现代农业的重要工具,农药凭借其高效的灭病虫害能力在农业生产中应用广泛,然而其灭杀虫害的同时对大气环境和人体健康等方面也会造成危害。使用激光诱导击穿光谱（LIBS）技术对农药的气溶胶喷雾进行了在线探测,研究了使用LIBS技术对农药使用过程的实时监测。首先检测了清洁环境下的空气LIBS光谱,在空气的光谱中探测到大量的氮（N）、氧（O）原子发射谱,这个结果与空气成分是相吻合的;同时还观察到了氢（H）的两条巴尔默系原子谱线,这主要是来源于空气中的水蒸气。值得注意的是,在空气谱中还发现了两条氩（Ar）的原子谱线,这也表明LIBS技术在微量元素检测方面有着重大潜力。选用农药敌杀死作为研究对象,对其有效成分溴氰菊酯（C₂₂H₁₉Br₂NO₃,CAS: 52918-63-5）进行了LIBS检测。在溴氰菊酯的LIBS光谱中观察到了卤素元素溴（Br）的存在,标记出了两条Br的原子发射谱线（827.294和833.470 nm）。对农药样品进行探测时也发现了包括CN分子发射谱与C₂分子发射谱等大量空气光谱中没有检测到的特征谱线;同时还检测到了空气谱中没有观测到的元素纳（Na）以及钙（Ca）;尤其是Ca,农药中不仅仅检测出了Ca的存在,而且相比于溴氰菊酯光谱中Ca谱线的能量以及数量都有着非常明显的上升。最后,实验中对CN分子的温度进行了研究;拟合得到溴氰菊酯与农药的CN分子的振动温度分别为8 800和6 200 K,转动温度分别为8 600和5 500 K。以上结果表明了使用LIBS技术对农药的在线监测是可行的,是有发展前景的。     

钢液中多元素的LIBS实时定量分析

将激光诱导击穿光谱(LIBS)技术直接应用于钢液成分的检测.研究结果表明,氩气作为保护气不仅可以避免钢液表面的氧化,同时可以增强等离子体信号强度.在氩气氛围下,钢液表面被聚焦成高功率密度的脉冲激光击穿形成等离子体,利用耦合CCD的多通道光纤光谱仪探测等离子体在冷却过程中发射的光谱信号,得到钢液组分的相关信息.根据分析谱线选取原则,确定了主要合金元素Mn,Si和Cr的特征谱线,并建立了相应元素的定标曲线,曲线的线性拟合度均在0.925以上,对应的质量浓度检测限分别为75.7,23.8和724.5 μg·g-1.     

激光诱导击穿光谱用于NaCl溶液中Na元素含量分析

为了研究Na元素在水中的检测灵敏度,采用激光诱导击穿光谱检测NaCl溶液中的Na元素。选择NaⅠ589.0 nm和NaⅠ589.6 nm作为分析谱线,利用配置的六种浓度的NaCl溶液,采用外标法、内标法以及小波变换降噪法,给出了NaCl溶液中Na元素的定标曲线。发现通过内标法获得的定标曲线的线性相关系数r达到0.998,优于外标法（r=0.985）,并且优于小波降噪后外标法（r=0.986）。相对外标法而言,小波变换降噪法有效降低了LIBS光谱中的连续背景光谱噪声,使LIBS的RSD从5.68%降至1.61%,从而使LOD值从50.8 μg·mL-1降至19.54 μg·mL-1, 内标法选择NaⅠ589.0 nm和NaⅠ589.6 nm钠原子谱线与内标参考谱线HⅠ656.2 nm氢原子谱线强度比值能有效的克服实验条件波动带来的影响,因此,内标法给出的NaCl溶液中Na元素的定标曲线的线性相关系数最大。而对于小波变换降噪处理方法,能够有效的降低LIBS光谱的连续背景带来的噪声,但不能克服实验条件波动对LIBS光谱信息的影响,因此小波变化降噪方法能够提高LIBS的RSD,但对降噪处理后的外标法给出的定标曲线的线性相关系数的提高影响不大。说明内标法有效的提高了检测灵敏度,减弱了实验条件波动带来的影响,定标曲线具有更好的线性相关性。而小波变换降噪处理后有效降低了LIBS光谱中的连续背景光谱噪声,实现LIBS检测限变低。谱线NaⅠ589.0 nm为分析谱线得到的RSD和LOD值小于以谱线NaⅠ589.6 nm为分析谱线的结果,NaⅠ589.0 nm和NaⅠ589.6 nm这两谱线的上能级分别为2.104和2.102 eV, 发现分析谱线的上能级对NaCl溶液中的Na元素的RSD和LOD值有影响,存在上能级大,而RSD和LOD值较小的现象。研究结果表明,LIBS技术可以实现溶液中元素的原位实时检测,并在水污染检测方面受到广泛关注。     

利用LIBS技术实现钢液中多元素含量检测

在钢铁冶炼中,成分含量检测是保证冶炼质量的关键之一,激光诱导击穿光谱技术(LIBS)具有遥测的特点,非常适合于炉内钢水成分的检测。实验室搭建了一熔融合金LIBS检测实验系统,该系统由 Nd:YAG调Q激光器(重复频率10 Hz,波长1 064 nm,脉冲宽度10 ns,单脉冲能量约240 mJ),高频感应电炉(温度1 600 ℃),光谱仪(波长范围186～310 nm,光谱分辨率0.1 nm),激光聚焦和信号光收集系统组成。实现了对钢液中多元素的LIBS光谱检测,通过内标法建立了相应元素的定标曲线,并给出了系统的检测限。采用深紫外镀膜探测器的光谱仪和抗紫外曝光处理的光纤,在大气环境下得到的C,S,Mn和Cr元素定标曲线的线性相关系数优于0.96,检测限分别达到169,15,58.9和210 μg·g-1。对比发现,不同元素得到最佳定标曲线所需延时条件不同。     

铝合金焊前激光清洗的等离子体光谱在线检测

铝合金焊接技术在工业生产、制造和维修等领域有广泛的应用,焊缝内存在气孔导致焊接质量降低是铝合金焊接技术的常见问题。由于铝合金表面金属氧化物是导致气孔生成的主要来源,对激光清洗过程进行在线检测,不但可以实时分析表面氧化物的清洗状态,而且可以避免基体表面因为过度清洗造成损伤或二次氧化。提出采用激光诱导等离子体光谱(LIBS)在线检测铝合金焊前激光清洗过程,表征清洗后铝合金基体的表面状态。LIBS技术可以对多元素成分同时检测,拥有较低的检出限和较高的准确性。搭建基于Andor Mechelle 5000光谱仪的铝合金焊前激光清洗在线检测系统,剔除空气环境对实验结果的影响,测试6061铝合金表面氧化物和铝合金基体的LIBS光谱,分析两者独特的元素特征谱线,采用X射线能谱(EDS)测试结果验证元素特征谱线的准确性,并探讨激光清洗过程LIBS技术在线检测的可行性。实验测试等离子体光谱谱线强度与激光能量密度之间的关系,获得单次脉冲激光去除铝合金表面氧化物的损伤阈值,结合X射线能谱的检测结果研究激光损伤阈值的成因及影响。研究激光清洗过程等离子体光谱特征谱线与脉冲次数之间的关系,提出基于O/Al特征谱线强度比值作为在线检测清洗效果及二次氧化损伤的评判依据。为验证该评判依据的准确性,将O/Al特征谱线强度比值随清洗次数的变化趋势与X射线能谱测试获得的氧元素原子百分比变化趋势进行对比。实验结果表明:采用200~700 nm范围内激光诱导等离子体谱线特征分析激光清洗状态,可以剔除空气环境的影响;氧元素和铝元素特征谱线准确反映出表面氧化膜与铝合金基体的成分差异;X射线能谱检测元素成分和含量表明氧元素含量随着激光清洗能量密度先减后增,单次清洗铝合金的二次氧化损伤的激光能量阈值为11.46 J·cm-2,小于损伤阈值的激光能量密度对铝合金基体的多次清洗未造成损伤,等离子体光谱特征谱线强度与表面清洗状态相关, 656.5 nm(OⅡ)/396.2 nm(AlⅠ)谱线强度比值≤1.5%为激光清洗干净的依据。研究结果有利于铝合金的激光清洗实时控制技术和焊接装置集成化。     

激光诱导击穿光谱法定量分析水泥中的铜元素

为定量分析水泥中的铜(Cu)元素,根据激光诱导击穿光谱分析方法(Ll BS)的特点,建立了激光诱导击穿光谱分析系统。采用标准加入法为定标方法,制备了5个不同含铜量的水泥样品。根据LIBS谱图,以213.598 nm和219.958 nm作为分析线。应用Savitzky-Golary卷积平滑方法对光谱数据进行了预处理,比较了Guass、Lorentz和Voigt拟合方法对光谱曲线的拟合效果。对测量结果采用一元线性拟合建立了相应的定标曲线,213.598 nm和219.958 nm定标曲线的校正决定系数分别为0.994 8和0.986 4,平均相对误差分别为3.20%和5.78%。实验结果表明:213.598 nm作为分析线的准确度优于219.958 nm分析线,该方法能够满足水泥中Cu元素定量分析的要求。     

发射光谱研究氩气/空气混合气体介质阻挡放电能量传递过程

使用水电极介质阻挡放电装置,对比氩气与氩气/少量空气的混合气体以及空气与空气/少量氩气的混合气体放电的发射光谱,研究了氩气与空气相混合时气体放电中的能量传递过程。实验发现, 当氩气中加入少量的空气时,氩原子谱线均变弱,说明空气中的氮分子对氩原子的各激发态具有猝灭作用。并且随着空气含量的增加,各谱线变弱的速率不同。越是与氮分子的激发电位接近的氩原子的激发态被猝灭的作用越明显。另一方面,当空气中加入少量氩气时,发现氮分子第二正带系和氮分子离子第一负带系的谱线均被增强。说明在空气/少量氩气放电中,氮分子的激发由于亚稳态氩原子的潘宁激发传能而增强。因此在氩气/空气混合气体放电中,气体成分及比例影响放电的发光特性和能量传输特性。     

Elemental analysis in environmental land samples by stand-off laser-induced breakdown spectroscopy

The stand-off detection and analysis of environmental land samples have been demonstrated using laser-induced breakdown spectrometry. The samples of interest have included soils and vegetation powder. Elements Hg, As, Pb, Zn, Cd and Cr have been spectrally analysed with a focus on Hg as a trace contaminant in the samples. It is found that element Fe, usually contained in land samples, is a main source of spectral interference for Hg detection due to its ever present iron emission line at 253.68 nm that is closely adjacent to the strongest Hg emission line at 253.65 nm, and hence, a high resolution of spectral detection is necessary. The strong spectral signals from Bremsstrahlung emission in laser-induced plasma and atomic emission of Fe of high concentration caused a significant reduction in detection resolution in the use of image intensifier of an ICCD. The limit of detection at ~8 ppm for Hg detection in soil samples with iron as a minor constituent has been achieved, using an optical chopper and a CCD detector for laser-induced breakdown spectroscopy (LIBS) signal detection. Such detection method in LIBS system has shown a great advantage in determining trace elements from interfering elemental constituents in land sample matrixes.     

Role of Purging Gases in the Analysis of Polycarbonate With Laser-Induced Breakdown Spectroscopy

Polycarbonate is a strong, durable, and high-transparent material. It is being used extensively in electronics applications, eyewear lenses, exterior automotive components, construction industry, and manufacturing of containers. Laser-induced breakdown spectroscopy (LIBS) is a well-known and widely-used technique in quantitative and qualitative analysis of materials. The analysis is based on the spectra obtained in the LIBS process. We investigate the LIBS spectrum of polycarbonate (C₁₂H₁₈O₇)_n polymer in the presence of air, helium, argon, neon, and mixed-gas atmospheres using a Spectrolaser-7000 system. We investigate the peak intensities of hydrocarbon fragments like C₂, C, and CN in He, Ar, and Ne atmospheres. Moreover, we observe the CN molecular lines in the LIBS spectrum of polycarbonate in air only. We show that, in the He and Ne atmospheres, the peak intensity of the hydrogen (656 nm) line increases 1.85 and 4.5 times, and the peak intensity of the carbon (247 nm) line increases 1.46 and 2.6 times, respectively, as compared to that in air. These results are very useful and will help in the analysis and detection of polymers and bio-samples, which are mostly comprised of carbon and hydrogen.     

Laser Induced Breakdown Spectroscopy for Comparative Quantitative Analysis of Betel Leaves from Pakistan

Laser induced breakdown Spectroscopy (LIBS) was applied for the elemental analysis and exposure of the heavy metals in betel leaves in air. Pulsed Nd∶YAG (1064 nm) in conjunction with a suitable detector (LIBS 2000+, Ocean Optics, Inc) having the optical resolution of 0.06 nm was used to record the emission spectra from 220 to 720 nm. Elements like Al, Ba, Ca, Cr, Cu, P, Fe, K, Mg, Mn, Na, P, S, Sr, and Zn were found to present in the samples. The relative abundances of the observed elements were calculated through standard calibration curve method, integrated intensity ratio method, and weight percentage LIBS approach. LIBS findings were validated by comparing its results with the results obtained using a typical analytical technique of Inductively Coupled plasma-optical emission spectroscopy (ICP-OES). Limit of detection (LOD) of the LIBS system was also estimated for heavy metals. The experience gain through this work implies that LIBS could be highly applicable for testing the quality and purity of food products.     

Spectral Characterization of Nitrogen in Farmland Soil by Laser-Induced Breakdown Spectroscopy

Nitrogen is one of the most important elements in farmland soil, and nitrogen content is one of the evaluation indicators of fertilizers. It is difficult to measure the nitrogen content in farmland soil because the chemical and physical properties of farmland soil are complex. Through the adoption of buffer gases to remove the influence of the nitrogen in air, this paper studied the laser-induced breakdown spectroscopy (LIBS) characteristics of nitrogen in soil to establish a foundation for in situ measurement of nitrogen in farmland soil. Three characteristic spectral lines have been found. Based on the precise controlling of laser power and triggering of delay time between laser generation and spectra collection, we have studied the effects of laser energy on LIBS spectral characteristics and the time evolution characteristics to supply the basis of parameter optimization for the measurement. In addition, we have studied the relationship between nitrogen concentration and LIBS spectral intensity. The results demonstrated that LIBS was an effective measurement method of nitrogen content in farmland soil with simple hardware structure, fast detection, and high precision.     

Stoichiometry analysis of titanium oxide coating by LIBS

In this work, laser induced breakdown spectroscopy (LIBS) is used to determine the composition of titanium oxide film produced by anodized of Ti6Al4V alloy. We have used Ti lines in the spectral region between 470–520 nm to determine temperature of the plasma generated on anodized surface of Ti6Al4V alloy for temperature determination by Boltzmann plot method. In order to measure the content of oxygen and titanium ratio on the surface the alloy, we have used the oxygen lines 777.194, 777.417 and 777.539 nm, and titanium lines 780.597 and 782.491 nm observed in an ambient of argon. Finally, we report the possibilities for the determination of the coating chemical composition using LIBS.     

应用激光诱导击穿光谱对土壤中多元素同时定量分析

土壤元素的丰缺是对土壤养分检测、农业按需种植和科学施肥的依据,是精准农业农情信息感知技术检测的关键点,更为农业生态、高效和优质生产提供理论指导。该研究运用激光诱导击穿光谱(LIBS)技术结合定标曲线法和偏最小二乘回归(PLSR)方法对土壤中的Al,Fe,Mg,Ca,Na和K多种元素同时进行定量分析。利用LIBS检测仪获取了五种标准土壤样品(国家编号： GBW07446,GBW07447,GBW07454,GBW07455和GBW07456)的LIBS数据之后,将每种土壤的多条谱线平均处理来消除试验误差。通过分析所获取的土壤LIBS谱线信息,选取了Al,Fe,Mg,Ca,Na和K元素的特征分析谱线和分析光谱区间,并利用谱线的峰值信息和分析光谱区间内的单个或多个谱峰的积分信息(峰面积)与对应元素浓度拟合并建立定标曲线。结果表明,基于谱峰的峰面积建立的定标曲线的线性关系优于利用峰值信息建立的定标曲线(Fe除外)。同时,针对所选的分析光谱区间和元素的浓度信息,运用PLSR建立定量分析模型,其结果明显要优于定标曲线的分析精度,这也表明LIBS技术结合化学计量学分析在未来光谱化学分析领域有很大应用前景。研究的结果不仅为现代农业的土壤养分空间分布检测和农田精准施肥技术的应用起指导作用,还为田间使用的便携式LIBS土壤检测仪的开发奠定了理论基础。     

基于多谱线内标法的不规则铜合金样品中 Pb元素成分检测研究

原位分析和在线检测是激光诱导击穿光谱(LIBS)技术的一大优势,但是,在野外环境中,人们无法对样品进行统一预处理,面对各种形态的待测样品如何保证LIBS的检测精度是函待解决的一大难题。提出一种多谱线内定标的方法来解决上述问题,即通过求解多条分析谱线的强度和与内标元素谱线的强度比值来建立定标曲线,进而降低光谱信号波动带来的误差,提高线性相关性和检测精度。实验中以铅黄铜合金样品为例,采用LIBS对厚度不一（最大变化值为±2 mm）的铅黄铜样品中的Pb元素进行了定量检测研究,并分别采用传统定标法和多谱线内定标法对这种不规则样品进行校正和建立定标曲线。实验发现,对于不规则样品,传统定标法的检测精度大大降低,定标曲线没有明显的线性关系。当采用单条谱线的内定标方法时,定标曲线线性相关度大大提高,校正决定系数达到0.724 89。而采用多条谱线内标方法（考虑多条分析谱线的相对强度总和）计算发现,当选取5条Pb谱线（Pb 261.42 nm,Pb 280.20 nm,Pb 368.35 nm,Pb 405.78 nm和Pb 520.14 nm）进行计算时,定标曲线线性拟合度达到0.984 6,由此可见该方法消除了样品不规则所带来的光谱强度波动误差,显著提高了测量精度。虽然继续增加分析谱线数目可以进一步提升线性相关度,但是也会增加计算的复杂度,所以选择合适的分析谱线是十分重要的。此外,通过多谱线内标法也能一定程度上消除基体效应和光谱干扰等影响,是一种简单有效且具备普适性的数据处理方法。当然,该方法也存在一定的局限性（如样品成分分布极不均匀、样品表面极不规则致使激光能量低于击穿阈值等）,不过通过调整和优化检测装置方案（例如增大激光能量、增大聚焦光斑、采用长焦距聚焦透镜等）可以更好的发挥该方法的优势。该研究内容可以为LIBS原位检测和在线检测的应用提供一种新思路。     

激光诱导击穿光谱技术对土壤中重金属元素Cr的定量分析

为促进LIBS技术在土壤微量重金属元素检测中的应用,提高特征谱线的光谱强度和信背比,对实验参数进行优化,并对Cr元素进行分析.首先对激光器激发能量、样品距透镜距离和光谱仪采集延时等实验参数进行优化.对比激光器能量从60 m J到110 m J的谱线强度和信背比,当选用90 m J的激发能量时可以得到最佳实验结果.其次,...     

铝合金中铬元素的时间分辨激光诱导击穿光谱高灵敏检测

为了消除在激光诱导击穿光谱(LIBS)信号检测时等离子体中强的轫致电子辐射对光电倍增管和前置信号放大器造成的不良影响,提高信号检测灵敏度,设计了一种基于CR110的门控端窗光电倍增管并用于LIBS中的微弱信号检测。该门控光电倍增管与前置信号放大器组合运用既可以成功抑制激光等离子体中强的轫致电子辐射的背景干扰,又可以进一步放大微弱的原子辐射信号,提高光谱分析的灵敏度。用LIBS分析铝合金标样中的微量铬元素,采用该门控光电倍增管时其检出限可以达到5.55 ppm,与采用普通光电倍增管的相比改善了近6倍,显示出该门控光电倍增管在时间分辨信号检测领域良好的应用效果。