基于温度迭代校正自吸收效应的激光诱导击穿光谱定量分析方法

Quantitative analysis method of laser-induced breakdown spectroscopy based on temperature iterative correction of self-absorption effect

激光诱导击穿光谱(laser-induced breakdown spectroscopy,LIBS)是一种理想的实时在线检测合金中微量元素的方法.然而在激光诱导击穿产生的高密度等离子体中,自吸收通常是一种不期望出现的效应,它降低了谱线的真实强度,使谱线强度随目标物质含量增长呈非线性,从而严重影响对目标中元素含量测量的准确性.本文提出了一种基于温度迭代校正自吸收效应的方法,借助等离子体热平衡辐射模型,对等离子体电子温度(T)和辐射粒子数密度乘以吸收路径长度(Nl)这两个参数进行迭代计算和校正,消除自吸收对谱线强度的影响,最终提高定量分析的准确性.对合金钢样品中Mn元素的实验测量结果表明,该方法有效地提高了Boltzmann平面图的线性度及元素含量的测量精度.该方法模型简单,计算效率高,且与Stark展宽系数的可用性和准确性无关,可以直接获得辐射粒子数密度和吸收路径长度参数,因此在提高LIBS定量分析能力的同时,还可以实现对等离子体状态的诊断.

(T)Laser-induced breakdown spectroscopy(LIBS)is an ideal real-time on-line method of detecting minor elements in alloys.However,in the case of laser-produced high-density plasma,the self-absorption is usually an undesired effect because it not only reduces the true line intensity,leading the line intensity to become nonlinear with the increase of emitting species content,but also affects the characterization parameters of the plasma,and finally affects the accuracy of quantitative analysis.Since the plasma electron temperature,radiation particle number density and absorption path length(Nl)determine the degree of self-absorption and affect the corrected spectral line intensity,a new self-absorption correction method is proposed based on temperature iteration.The initial T is obtained by using this method through spectral line intensity,and the self-absorption coefficient SA is calculated based on the initial Nl parameter to correct the spectral line intensity.Then a new T is obtained from the new spectral line intensity and the new SA is calculated to further correct the spectral line intensity.Through continuous calculation and correction of these two parameters,selfabsorption correction is finally achieved.The experimental results of alloy steel samples show that the linearity of Boltzmann plot is increased from 0.867 without self-absorption correction to 0.974 with self-absorption correction,and the linear correlation coefficient R2 of the single variable calibration curve for Mn element increases from 0.971 to 0.997.The relative error of elemental content measurement is improved from 4.32%without self-absorption correction to 1.23%with self-absorption correction.Compared with the commonly applied self-absorption correction methods,this method has obvious advantages of simpler programming,higher computation efficiency,and its independence of the availability or accuracy of Stark broadening coefficients.Moreover,this method can directly obtain the radiation particle number density and absorption path length,which is beneficial to the diagnosis and quantitative analysis of plasma.