Pulsed‐CO2‐laser interaction with aluminum in air: Thermal response and plasma characteristics

Simultaneous target heating, plasma spectral emission, and time‐resolved plasma interferometry data were taken for the interaction of CO2 (λ=10.6 μm) laser pulses with aluminum targets in air. The laser spot area on the planar targets was 1.4 cm2, the pulse duration was 1.8 μs, and the maximum peak flux on target was 8×107 W/cm2. The target thermal response is analyzed to provide both the total energy deposited on target and the spatial distribution of the energy. The total energy deposited increases in direct proportion to the laser‐pulse energy, with a coupling coefficient of 18% above the plasma ignition threshold. The spatial maximum value of the energy‐deposition density, in contrast to the total energy, remains constant as the laser‐pulse energy increases, demonstrating that target heating takes place over an area increasing with the laser‐pulse energy. Even at the plasma ignition threshold, the area of energy deposition exceeds substantially the laser spot area. The spectroscopic measurements sugge...