Temporal analysis of self-reversed Ag I resonant lines in LIBS experiment at different laser pulse energy and in different surrounding media

Abstract

In this work we studied the temporal evolution of the resonant emission lines of neutral silver (Ag I) at wavelengths328.9 nm and 338.2 nm, in different surrounding media (He, Ar, Xe and air) and at different laser pulseenergy (15 mJ, 30 mJ and 60 mJ), using a frequency triplicated Nd:YAG laser (355 nm).We observed that the self-reversal of the Ag lines, caused by the combined effect of self-absorption and plasmainhomogeneity, is strong when the plasma expands in molecular gases (N2 and O2 in air) while is negligible inatomic noble gases (He, Ar, Xe), independently on the mass of the atoms. From the experimental data, we alsoconclude that the shock wave generated during the breakdown may play an important role in generating theplasma inhomogeneities which are essential conditions for the occurrence of the self-reversal effect.