Laser-induced vaporisation of metal as a Riemann problem.

The process of vaporisation of a light-absorbing metal under laser irradiation will be 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 will be shown that the local sound velocity is an upper bound for the metal vapour velocity at the phase boundary. Furthermore it will be shown that for an absorbed intensity I sub a, which is greater than a certain threshold intensity I sub c, the vaporisation process is independent of the ambient gas. This intensity I sub c 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.