Air spark-assisted excitation to suppress the self-reversal effect in nanosecond UV laser-induced breakdown spectroscopy

Abstract

A self-reversal effect in plasma has affected the accuracy of laser-induced breakdown spectroscopy (LIBS). This effect becomes pronounced in a high-density and inhomogeneous plasma, which is commonly generated in UV LIBS due to efficient ablation of the sample by UV irradiation. Here we present a simple method to suppress the self-reversal effect in UV LIBS at atmospheric pressure utilizing an air spark-assisted excitation. We simultaneously generated the air spark and target plasma by adjusting the lens’ focal point position relative to the sample surface. The interaction between the air spark’s tail and target plasma helps reduce the number of cold ground-state atoms at the periphery of the target plasma. Under this condition, we significantly suppressed the self-reversal effect in the resonance lines of high-concentration aluminum. The time-resolved features show that the emission lines of Al I 394.40 nm and Al I 396.15 nm obtained using the proposed approach are free from self-reversal. These results indicate that the proposed technique can improve the plasma’s homogeneity and, therefore, the spectral quality of resonance lines of nanosecond UV LIBS.