Laser metal interaction in vacuum

We investigate the processes by which energy is exchanged when a laser pulse is incident on a metal surface, originally in vacuum. The thermal state of the metal is determined by numerical solution of the nonlinear heat transfer equations. A method is described for extrapolating data on material thermal properties which are usually given at lower temperatures. Results are compared with the predictions of a steady-state calculation. Kinetic equations describing the growth of a plasma in the ablated vapor are formulated to describe effects of importance in the early stages of the plasma evolution process, when strong longitudinal spatial gradients cause thermal diffusion effects to dominate hydrodynamic expansion. Numerical studies of these equations indicate several distinct periods, during each of which a different physical mechanism takes on primary importance. Features of the numerical results pertaining to the propagation of the discharge front are deduced from an analytic model of the breakdown process.