Optical Emission Analysis of Triple-Fold Plume Formed at Pulsed IR Laser Ablation of Graphite

Abstract

A sheet of sintered graphite was ablated by a pulsed Nd:YAG laser in He gas and air at 1 atm. Triple-fold plumes were produced in both gases. The time-resolved emission spectrograms of the plume were measured and the plume was analyzed as follows. The plume is generated near the target surface and expands while separating into three because of different expansion speeds of its components. The fastest component is gas plasma mainly composed of carbon ions in the He atmosphere, and nitrogen and oxygen ions in air. The second fastest component is very hot and compressed neutral molecules of the gas, that is, the shock wave. The slowest component is radical vapor of the graphite target.