为了确定激光诱导击穿光谱(laser-induced breakdown spectroscopy, LIBS)的最佳探测时间,采用时间分辨LIBS研究了样品中4种元素Fe、Pb、Ca和Mg的4条 特征谱线峰值强度以及相应的连续背景辐射光谱强度的衰减特性,对特征谱线峰值强度和连续背景辐射光谱强度的比值求极值,获得了特征谱线最佳信 背比(signal-to-background ratio, SBR)所对应时间的计算值。连续背景辐射和特征谱线光谱强度均呈指数形式衰减,4条特征谱线衰减时间分 别为1.42, 1.95, 1.69, 1.65 μs,相应的连续背景辐射衰减时间分别为0.85, 0.93, 0.89, 0.87 μs。 4条特征谱线最佳SBR所对应时间的计算值分别为1.43, 1.77, 1.62, 1.80 μs,最佳SBR所对应的时间的实验测 量值分别为1.5, 2.0, 1.5, 1.5 μs,二者具有较好的一致性。特征谱线峰值强度和连续背景辐射光谱强度的演化规 律能够对最佳SBR出现的时间作出预测。以上研究结果表明,LIBS最佳探测时间与连续背景辐射和特征谱线的衰减规律密切相关,通过对光谱强 度的比值求极值,可以预测谱线最佳SBR出现的时间,此方法为确定LIBS技术探测和分析的最佳时间提供了依据。

In order to determine the optimal detection time of laser-induced breakdown spectroscopy(LIBS), time-resolved LIBS technique has been adopted to study the decay characteristics of peak intensity and spectral intensity of four elements Fe, Pb, Ca and Mg contained in the sample. The extreme value of ratio of peak intensity of characteristic lines and spectral intensity of continuous radiation is calculated, and the calculation value of time corresponding to the optimal signal-to-background ratio (SBR) of characteristic lines is obtained. The peak intensity of characteristic lines and spectral intensity of continuous radiation both decay in exponential form, the decay time of four characteristic lines are 1.42, 1.95, 1.69, 1.65 μs, and the corresponding decay time of continuous radiation are 0.85, 0.93, 0.89, 0.87 μs respectively. The calculation value of corresponding time of optimal SBR of four characteristic lines are 1.43, 1.77, 1.62, 1.80 μs, and experimental measurement value of corresponding time of optimal SBR are 1.5, 2.0, 1.5, 1.5 μs. They have a good consistency. The corresponding time of optimal SBR can be predicted by evolution law of peak intensity of characteristic lines and spectral intensity of continuous radiation. The results indicate that the optimal detection time of LIBS is closely related to decay law of continuous radiation and characteristic lines, and the corresponding time of optimal SBR of spectral lines can be predicted by evaluating extreme value of the ratio of spectral intensity. The method provides the basis for selecting the optimal time of LIBS detection and analysis.