Pulsed laser evaporation: equation-of-state effects

Theoretical study of laser ablation is usually based on the assumption that the vapor is an ideal gas. Its flow is described by gas dynamics equations [1,2]. The boundary conditions at vaporization front are derived from the solution of the Boltzmann equation that describes the vapor flow in the imm ediate vicinity of the vaporizing surface (so-called Knudsen layer) [1]. Th is model is applicable within the range of temperatures much lower than the critical temperature of target material. In the present work, a general ca se is considered when the temperature of the condensed phase is comparable to or higher than the critical temperature. The dynamics of both condensed and gaseous phases can be described in this case by the equations of hydrod ynamics. The dynamics of vaporization of a metal heated by an ultrashort la ser pulse is studied both analytically and numerically. The analysis reveal s that the flow consists of two domains: thin liquid shell moving with cons tant velocity, and thick low-density layer of material in two-phase state.