LASER-INDUCED VAPORIZATION OF METAL AS A RIEMANN PROBLEM

The process of vaporisation of a light-absorbing metal under laser irradiation is investigated from a theoretical point of view. The tools are the Euler equations, the stationary heat-flow equation and the kinetic equations to calculate the gas dynamical properties of the edge of the Knudsen layer. Using the one-dimensional deflagration theory, it is shown that the local sound velocity is an upper bound for the metal vapour velocity at the phase boundary. Furthermore, it is shown that for an absorbed intensity Ia, which is greater than a certain threshold intensity Ic, the vaporisation process is independent of the ambient gas. This intensity Ic is calculated for aluminium and iron. On the assumption that a stationary limit of the vaporisation process is reached, the solution of the Euler equations is equivalent to the solution of a Riemann problem. © 1990 IOP Publishing Ltd.