Phase transition at low fluences in laser desorption of organic solids: a molecular dynamics study

Molecular dynamics of a short pulse laser irradiation of a molecular crysta l are performed to investigate the dependence of the mechanism of ejection on laser fluence. We find that at low laser fluences molecules are desorbed from a thin surface layer of solid sample. An increase in the laser fluenc e leads to the melting of the surface region and desorption occurs from an overheated melted state. An additional increase of the fluence leads to the ablation when the laser-induced pressure and phase explosion of the overhe ated liquid drives a collective ejection of a significant volume of irradia ted material. (C) 1999 Elsevier Science B.V. All rights reserved.