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

Abstract

Laser-induced breakdown spectroscopy (LIBS) is an ideal real-time on-line method for the detection of minor elements in alloys. However, in the case of high-density plasma generated by LIBS, the self-absorption is usually an undesired effect because it not only reduces the true line intensity, introduces nonlinear effects in the growth of line intensity versus the content of the emitting species, but also affects the characterization parameters of the plasma, and finally affects the accuracy of quantitative analysis. Since the plasma electron temperature (<i>T</i>), radiation particle number density and absorption path length (<i>Nl</i>) determine the degree of self-absorption and affect the corrected spectral line intensity, a new self-absorption correction method based on temperature iteration is proposed. This method obtains the initial <i>T</i> through spectral line intensity, and calculates the self-absorption coefficient <i>SA</i> based on the initial <i>Nl </i>parameter to correct the spectral line intensity. Then a new <i>T</i> is obtained from the new spectral line intensity and the new <i>SA</i> is calculated to further correct the spectral line intensity. Through continuous calculation and correction of these two parameters, self-absorption correction is finally achieved. The experimental results of alloy steel samples showed that the linearity of Boltzmann plots was 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 increased from 0.971 to 0.997. The relative error of elemental content measurement has significantly 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 independency 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.