EXPRESS: Fractional–Rational Calibration for Laser-Induced Breakdown Spectroscopy (LIBS) Analysis of Steels with High Matrix Variability

The results of an original calibration methodology that accounts for interelement influences in the analysis of alloyed steels using laser-induced breakdown spectroscopy (LIBS) are presented. The results were obtained from a dataset of spectra provided for the regression competition at the LIBS 2022 conference and available online. The dataset includes spectra from 41 steel samples with known concentrations of major alloying elements (chromium, nickel, manganese, molybdenum, carbon, silicon, copper) and 15 samples with unknown compositions for model validation. The concentration of alloying elements varies over a wide range, with iron content ranging from 98% to 41%. To reduce spectral line position instability, we applied a preprocessing method that maximizes the correlation of each spectrum with the first spectrum in the dataset. The implementation of the developed calibration methodology led to an improvement in the mean square error of the analysis, with reduction factors ranging from two (for nickel and molybdenum) to five (for manganese and chromium) when compared to classical calibration.