Phase change phenomena during high power laser-materials interaction

Abstract

This work investigates phase change phenomena due to high power pulsed laser irradiation. During high power laser heating, the intense radiation flux from the laser is transformed to the target material and raises the temperature of the target surface rapidly. When the laser fluence is high enough, melting and superheating of liquid are possible. At even higher laser fluences, the superheated liquid undergoes a phase explosion that turns the liquid into a mixture of liquid and vapor. In this paper, we describe theoretical, numerical and experimental studies of the materials’ response under nanosecond pulsed excimer laser irradiation. Experiments are performed in a laser fluence range between 2.5 and 10 J/cm 2 (between 100 and 400 MW/cm 2) on nickel specimens. The velocity of the laser-evaporated vapor, absorption of the laser energy by the laser-evaporated vapor, the threshold laser fluence for phase explosion, and the pressure and temperature at the target surface are determined. Results of these studies reveal phase change mechanisms during high power laser interaction with metal.