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 phas e collisions on the evolution of a gas cloud desorbed by a pulsed lase r 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 p rescribed temperatures. This allows us to assess qualitatively the eff ect of an ionic component (hot particles) on the evolution of a neutra l gas cloud (cold particles). We find that an admixture of hot particl es 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 per centage of desorbed particles is scattered back towards the surface. T his deteriorated jet structure is due to the spatial segregation betwe en hot and cold particles in the desorbed gas cloud, such that cold pa rticles are found predominantly in its near-surface part.