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Energy and angular distribution of pulsed-laser desorbed particles: the influence of a hot contribution on a cold desorbing species

Using a Monte Carlo simulation scheme, we model the effect of gas phase collisions on the evolution of a gas cloud desorbed by a pulsed laser beam from a target surface. As a special feature, we assume that the desorbed particles belong either to a cold or to a hot species with prescribed temperatures. This allows us to assess qualitatively the effect of an ionic component (hot particles) on the evolution of a neutral gas cloud (cold particles). We find that an admixture of hot particles has a deleterious influence on the ablation jet formed: it is less strongly peaked towards the surface normal and fast particles are not so strongly focused towards the jet axis. Simultaneously, a higher percentage of desorbed particles is scattered back towards the surface. This deteriorated jet structure is due to the spatial segregation between hot and cold particles in the desorbed gas cloud, such that cold particles are found predominantly in its near-surface part.