Energy conversion and momentum coupling of the sub-kJ laser ablation of aluminum in air atmosphere

Energy conversion and momentum coupling using nano-second 1-μm-wavelength pulse laser irradiation on an aluminum target were measured in air and nitrogen gas atmospheres over a wide range of laser pulse energies from sub-J to sub-kJ. From the expansion rate of the shock wave, the blast-wave energy conversion efficiency, ηbw, was deduced as 0.59 ± 0.02 in the air atmosphere at an ambient pressure from 30 to 101 kPa for a constant laser fluence at 115 J/cm2. Moreover, the momentum coupling of a circular disk target was formulated uniquely as a function of the dimensionless shock-wave radius and the ratio of the laser spot radius to the disk radius, while ηbw could be approximated as constant for the laser fluence from 4.7 to 4.1 kJ/cm2, and the ambient pressure from 0.1 to 101 kPa.