Plasma Energy Transfer to Metal Surfaces Irradiated by Pulsed Lasers

Abstract

Recent experimental data have indicated that when highly reflective metal targets are irradiated by pulsed lasers in an air environment, a larger fraction of the incident laser energy is coupled into the target when a plasma is ignited above the surface than when plasma formation does not occur. Models of the plasmadynamics and subsequent energy transfer to the surface by radiation and conduction are constructed in order to predict the thermal coupling coefficient (coupled energy/laser energy) for pulsed laser irradiation of a metal target. It is found that the largest fraction of the incident laser energy is coupled into the target when a laser-supported combustion wave is ignited in close proximity to the surface. Energy transfer is via reradiation from the absorbing air plasma. Techniques for obtaining maximum thermal coupling are suggested as a result of the theoretical models. Results are compared with both computer simulations of the plasmadynamics and existing experimental data.