The dynamic properties of shock-waves formed during laser ablation at sub-atmospheric pressures

The Sedov-Taylor-von Neumann (STN) theory has been shown to accurately describe the dynamic properties of shock-waves generated during pulsed-laser ablation of solid aluminium targets at visible wavelengths (510/578 nm) with 40 ns pulses with energies up to 3.5 mJ. A ballistic pendulum is used to measure the integrated recoil pressure in various inert atmospheres (He, Ne, Ar, Kr, Xe, N-2, CO2, SF6) with pressures of 10(-2)-10(3) mbar. This recoil momentum is found to scale linearly with the background gas pressure P-1 and with the square root of the molecular weight M-1. More interestingly, the scaling with the ratio of heat capacities 7 is verified to be a monotonically increasing function dependent on the form factor of the shock-wave. The validity of a modified STN theory which accounts for the piston mass is assessed.