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 crystal 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 fluence 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 overheated liquid drives a collective ejection of a significant volume of irradiated material. (C) 1999 Elsevier Science B.V. All rights reserved.