Halides formation dynamics in nanosecond and femtosecond laser-induced breakdown spectroscopy

Abstract

Abstract Laser-induced breakdown spectroscopy (LIBS) is an analytical technique based on the measurement of the emitted radiation coming from a laser-induced plasma (LIP) created after irradiation of a sample by a short-duration laser pulse. Research on molecular presence in LIPs has increased because the use of molecular emission has proven an encouraging way to improve LIBS abilities. LIPs are dynamic plasmas with fast time and spatial evolutions, in which atoms and molecules can follow different paths in their evolution and distribution. Molecular creation mechanisms within LIPs are still a challenging issue under investigation and the prevalence of some specific mechanisms are dependent on experimental conditions (sample nature, laser parameters, surrounding atmosphere…). In this work, different time and spatially solved experiments were carried out in ns- and fs-LIBS to investigate the dynamics of alkaline-earth (Ca) halide (F) diatomic molecule formation. Experiments were carried out on powdered CaF2 samples for both ns- and fs-LIBS. The effects of a gas flow (air, He, Ar) over the plume are investigated for ns-LIBS. Nebulization-modified ns-LIBS experiments in which the alkaline-earth element is externally added to the plasma plume as an aerosol were carried out on (C2F4) n samples. The spatial separation between atomic and molecular emission distribution was found to take place with and without external modifications over the ns-LIP. Behavior in fs-LIPs was determined to differ significantly from analogous experiments with nanosecond lasers, but temporal optimization remains the optimum method for molecular detection as spatial separation was not found to provide any remarkable advantage.