Parametric study of a fiber-optic laser-induced breakdown spectroscopy probe for analysis of aluminum alloys

Abstract

In the present work we demonstrate a fiber-optic laser-induced breakdown spectroscopy (FO LIBS) system for delivering laser energy to a sample surface to produce a spark as well as to collect the resulting radiation from the laser-induced spark. In order to improve the signal/background (S/B) ratio, various experimental parameters, such as laser energy, gate delay and width, detector gain, lenses of different focal lengths and sample surface, were tested. In order to provide high reliability and repeatability in the analysis, we also measured plasma parameters, such as electron density and plasma temperature, and determined their influence on the measurement results. The performance of FO LIBS was also compared with that of a LIBS system that does not use a fiber to transmit the laser beam. LIBS spectra with a good S/B were recorded at 2-μs gate delay and width. LIBS spectra of six different Al alloy samples were recorded to obtain calibration data. We were able to obtain linear calibration data for numerous elements (Cr, Zn, Fe, Ni, Mn, Mg and Cu). A linear calibration curve for LIBS intensity ratio vs. concentration ratio reduces the effect of physical variables (i.e. shot-to-shot power fluctuation, sample-to-surface distance, and physical properties of the samples). Our results reveal that this system may be useful in designing a high-temperature LIBS probe for measuring the elemental composition of Al melt.