In-situ analysis of laser-induced breakdown spectra for online monitoring of femtosecond laser machining of sapphire

Laser-induced breakdown spectroscopy (LIBS) is widely used for elemental analysis. However, its application for monitoring and analyzing a laser machining process by examining the changes in spectral information warrants further investigation. In this study, we investigate the effect of laser parameters on the spectra, variations in the time-resolved plasma emission spectra, and the relationship between the morphology of craters and plasma plume evolution during the femtosecond (fs) laser ablation of sapphire. The Boltzmann plot method and Stark’s broadening model are employed to estimate the temporal temperature and electron density of the plasma plume, revealing the process of plasma evolution. This study aims to demonstrate the feasibility of LIBS for online monitoring of laser processing through experimental data and theoretical explanations.