Crater and spallation shell formation by short laser pulse

Action of ultrashort laser pulses on opaque condensed plane targets is considered. The prehydrodynamical stage with supersonic electron heat conduction wave precedes to the hydrodynamical stage. At the prehydrodynamical stage near a boundary a heated layer with thickness $d_T$ is formed. An expansion of electron heat wave from a skin layer is studied. The expansion is accompanied by a gradual cooling of hot electrons due to electron-ion thermal relaxation. The analysis of a heat wave and relaxation allows to estimate dependence $d_T(F_{abs})$ of thickness of the heated layer on absorbed laser fluence $F_{abs} [{\rm J/cm}^2]$. For description of the hydrodynamical stage we use, first, A.A. Samarskii and Yu.P. Popov gasdynamical code and, second, multiprocessor (up to $10^3$ processors) molecular dynamics (MD) code. Massively parallel computations have allowed us to operate with very large amounts of atoms in MD simulations (${\sim}35\cdot 10^6$). This corresponds to experimental conditions. In MD calculations of other groups three order of magnitude smaller amounts of atoms are used (one processor approach).