Effect of Focusing on Charge-Induced Current and Spectral Emission in a Plasma Generated by a Nd: YAG Laser at Low Pressures

Abstract

The effect of laser focusing condition on the emission and charge-induced current characteristics of the copper plasma induced by a Q-switched Nd-YAG laser (37 mJ, 8ns) at reduced pressures of air has been studied to examine the excitation process of the ablated atoms in the secondary plasma. The charge-induced current measurement has been conducted by placing a partially transmitted nickel mesh in front of the sample surface at a certain distance. Also by using the rainbow interferometric technique, the density jump in the secondary plasma could be clearly observed. The relationship analysis on the secondary plasma emission intensity, the charge-induced current and the average velocity of the shock front as a function of laser irradiation focusing condition revealed clearly the role of the shock wave in the excitation mechanisms of the secondary plasma, proving the electron collision and the electronion recombination are not major processes.