An improved method to experimentally determine temperature and pressure behind laser-induced shock waves at low Mach numbers

Abstract

Laser–matter interactions are frequently studied by measuring the propagation of shock waves caused by the rapid laser-induced material removal. An improved method for calculating the thermo-fluid parameters behind shock waves is introduced in this work. Shock waves in ambient air, induced by pulsed Nd : YAG laser ablation of aluminium films, are measured using a shadowgraph apparatus. Normal shock solutions are applied to experimental data for shock wave positions and used to calculate pressure, temperature, and velocity behind the shock wave. Non-dimensionalizing the pressure and temperature with respect to the ambient values, the dimensionless pressure and temperature are estimated to be as high as 90 and 16, respectively, at a time of 10 ns after the ablation pulse for a laser fluence of F = 14.5 J cm−2. The results of the normal shock solution and the Taylor–Sedov similarity solution are compared to show that the Taylor–Sedov solution under-predicts pressure when the Mach number of the shock wave is small. At a fluence of 3.1 J cm−2, the shock wave Mach number is less than 3, and the Taylor–Sedov solution under-predicts the non-dimensional pressure by as much as 45%.