Time-resolved study of the plasma-plume emission during the nanosecond ablation of lithium fluoride

Abstract

The properties of the plasma-plume accompanying the pulsed laser ablation of lithium fluoride (LiF) at medium-vacuum conditions (4Pa) were studied by a combination of spatially and temporally resolved optical emission spectroscopy. The laser-induced plasma at CO2 laser intensities ranging from 0.18 to 4.7GW×cm−2 was found strongly ionized in F+, Li+, F2+, and F3+ species and rich in neutral lithium and fluorine atoms. The temporal behavior of excited Li atoms and ionized excited species F+, Li+, F2+, and F3+ is reported. The results show a faster decay of the continuum emission and Li+, F3+, and F2+ ionic species than in the case of F+ and neutral Li atoms. The velocity distributions of atomic and ionic species are obtained from time-of-flight measurements. Electron density and excitation temperature in the laser-induced plasma were estimated from the analysis of spectral data at various delay times from the CO2 laser pulse incidence. From the intensity decay of Li+, F+, F2+ and F3+ with the delay time, we have estimated the three-body electron–ion recombination rate constants for these species.