The spatial distribution of heating of aluminum targets by laser-ignited air plasmas

Abstract
Measurements of the heating of metal targets in air by laser pulses with plasma ignition have shown substantial enhancement of thermal coupling compared to simple infrared absorption. This heat is in some cases spread over an area much larger than the laser spot. We present direct measurements of the spatial distribution of aluminum target heating with a high‐energy (11 kJ, 40 μs) CO2 laser pulse. This observed distribution is compared to that calculated for a model of thermal coupling via thermal emission from a vertically propagating disk‐shaped plasma. This model yields a better fit to the data than is obtained for a model of coupling via thermal conduction from a hydrodynamically expanding plasma due to Robin.