Avoiding Self-Reversed D Lines in Laser-Induced Breakdown Spectroscopy of Trace-Level Sodium in Soil

Abstract

Self-reversed sodium D lines in laser-induced plasmas generated from soil samples with a sodium trace concentration of 42.3 ppm was examined using laser-induced breakdown spectroscopy (LIBS). The inverse pulse-energy dependence as well as spatially resolved behaviors of self-reversal were investigated using a pulsed Nd:YAG laser (532 nm, 7 ns) and a spectrograph with an ICCD camera. As pulse energy increases, the degree of self-reversal first augments then rapidly diminishes. The mechanism behind this lies in the separation of emission and absorption centers in wavelength, coupled with the fact that the central and outer layers of the plasmas were heated up equally with higher pulse energies. This indicates the possibility of avoiding self-reversal in an active manner.