Spectroscopic analysis of signals from LIBS experiments

摘要

In the LIBS experiences (Laser Induced Breakdown Spectroscopy), in particular those carried out at atmospheric pressure, the observed atomic lines present a high absorption which is a setback in order to employ the measured line intensities to calibrate the element concentration in the samples. Absorption mainly occurs in the strongest lines of the spectrum and, consequently, those with the biggest probability of detection in a multi-element plasma. With the goal of quantifying some element in a laser-induced plasma several procedures are used. The most widely known is constructing calibration curves. In contrast, free-calibration methods are already available. The latter requires knowing plasma parameters and equilibrium (LTE) and optically thin plasma conditions are assumed. In both cases the experimental measurement of absorbed lines leads to errors in the concentration calculus. In this paper, working methods under optically thick inhomogeneous plasma conditions are studied. Considering information deduced from the optical thickness of the measured spectral lines quantification of trace elements in the samples is achieved. The optical thickness is responsible of line saturation. It is related to the emitting species density, the electronic temperature and concerned spectral line.