激光诱导击穿光谱技术及应用综述

Laser-Induced Breakdown Spectroscopy and Its Application

元素的成分和含量对材料的性能起着至关重要的作用,常规的检测方法能够获取待测样品的类别和成分信息,但存在成本高、操作复杂、效率低等问题。应用领域的不断扩展对分析技术有了更高的需求,找寻一种更新、更快、适应性更强的检测技术成为当前的研究热点。激光诱导击穿光谱技术具有多元素同时检测、结构简单、检测速度快、不受样品形态影响等特点,在诸多领域展现出广阔的应用前景。基于此,综述了激光诱导击穿光谱技术的机理、装置类型、基础研究进展以及应用研究,并对其发展趋势进行了展望。

Significance The physical and chemical properties of materials are determined by their element compositions and contents.How to obtain the compositions and content information of materials quickly,accurately,and at low cost has always been the research direction of scholars.The existing methods for the analysis of elements in the materials can be divided into the chemical methods and the instrumental methods.Based on the law of chemical reactions,the chemical methods carry out the qualitative and quantitative systematic analysis on the chemical compositions of samples,including the gravimetric method,the volumetric method,and the colorimetric method.In contrast,the instrumental methods directly obtain the physical and chemical information of the unknown samples through the analytical instruments,such as the inductively coupled plasma mass spectrometry,the Raman spectrum,the near-infrared spectrum,the X-ray spectrometry,and the atomic absorption spectrometry.The above-mentioned methods can obtain the categories and composition information of the samples with high sensitivity and accuracy,but they present complex operation,high cost,and low efficiency.However,with the continuous expansion of application fields,there is a high demand for the analysis technologies.Looking for a newer,faster,and more adaptive detection technology has become a research hotspot.Laser induced breakdown spectroscopy(LIBS)is an element analysis technology,which uses a laser as the excitation source to ablate the sample and produce plasma.The emission spectrum of the plasma is then detected by a spectrometer to obtain the element category and the content information of the sample to be measured.Compared with other analytical technologies,the LIBS technology has the unique advantages of simultaneous detection of multiple elements,simple structure,fast detection speed,and being not affected by sample morphology.It shows great application prospects in many fields.Based on this,the mechanism,device types,basic research progress,and applications of LIBS are summarized.Progress The plasma characteristics and self-absorption effect of the LIBS instruments raise the most concerns.By studying the relevant characteristics of plasma,it is helpful to understand the generation mechanism of laserinduced plasma and solve the relevant problems encountered in the LIBS analysis.The self-absorption infulences the linear relationship between the original plasma emission spectral intensity and the concentration of related elements,and thus it reduces the accuracy of a quantitative analysis.To satisfy different analytical requirements,variable types of LIBS instruments are developed,including an LIBS in the laboratory(Fig.3),a stand-off LIBS(Fig.4),an on-line LIBS (Fig.5),and a portable LIBS (Fig.6).The LIBS in the laboratory has higher sensitivity and reproducibility,which is often used in the study of mechanism and exploratory applications.The stand-off LIBS can realize an in-situ detection of dangerous samples under harsh conditions on the premise of ensuring personnel safety.With the unique advantages of in-situdetection,real-time,fast,and no complex sample pretreatment,the on-line LIBS can quickly process numerous samples on the production line.The portable LIBS has the advantages of small volume,light weight,and convenient use,which has better applicability in industrial fields with harsh conditions.To improve the analytical performance of the LIBS technology,the signal enhancement methods and the methods for the qualitative and quantitative analysis have become the focus study.The signal enhancement methods mainly contain surface enhancement methods (Fig.7),inert-gas protection enhancement methods (Fig.9),confinement enhancement methods (Fig.10),and double-pulse enhancement methods (Fig.11).The surface enhancement method ablate the substrate and the sample to be measured at the same time.The high-temperature plasma generated by the substrate heats the sample which can improve the temperature and electron number density of the sample plasma.Using inert gas as ambient gas can prolong the life of luminous atoms in plasma and avoid the light signal from being absorbed by air.Confinement enhancement uses the confinement cavity or magnetic field to affect the external and internal conditions of the plasma and confine the plasma to achieve signal enhancement with the advantages of simplicity,economy,and high feasibility.The double-pulse technology uses the second laser pulse to excite and heat the plasma again,which can greatly increase the temperature of the plasma and enhance the spectral intensity.Various methods are carried out for the qualitative and quantitative analysis,including material identification,element detection,and quantitative analysis.Conclusions and Prospects With the specific advantages of the LIBS technology and the development of abovementioned methods,the LIBS technology has been successfully used in various fields,including space exploration(Fig.14),geological prospection (Fig.15),pollution monitoring(Fig.16),food safety(Fig.17),industrial metallurgy(Fig.18),and biomedicine (Fig.19).The rapid identification of sample category is the focus of current research,and good analytical results have been obtained.However,due to the change of experimental environments,surface dirt of samples,and the diversity of manufacturing processes and additives,the prediction accuracy of the LIBS technology for real samples is still low.Outlier screening,variable selection,scale transformation,and other spectral preprocessing methods,as well as the improvement and integration of algorithms,are effective ways to solve this problem.Due to the matrix effect,laser energy fluctuation,spectrometer resolution difference,detection environment limitation,and other reasons,the LIBS technology has a large deviation in the prediction of element contents in materials.Optimizing the LIBS instrument platform,studying the signal enhancement methods,and improving the analysis methods are the effective methods to improve the prediction accuracy of the quantitative analysis.The matrix effect is the most critical problem that limits the wide application of the LIBS technology.With the continuous development of the LIBS instruments and the corresponding components,this problem can be effectively solved,but it will take a long time.The improvement of the analytical chemistry method will be an effective way to improve the application performance of the LIBS technology.In order to realize the rapid and sensitive detection of massive materials,the development of an on-line LIBS device will be the development trend in the future.