MONTE-CARLO SIMULATION OF THE LASER-INDUCED PLASMA PLUME EXPANSION UNDER VACUUM - COMPARISON WITH EXPERIMENTS

The laser induced plasma plume expansion in vacuum is studied by a Mon te Carlo simulation. An original method, which allows the simulation w ith no size restrictions on laser spot width or ablated depth, is pres ented. The global shape of the plume created above a copper target is followed in time by using a three-dimensional algorithm. Particles eva poration from the sample surface during the laser pulse duration is do ne by taking into account a radial distribution of laser energy and th e influence of vapor pressure on surface temperature. The simulation i ndicates that, when much more than few monolayers are ablated, the las er energy absorption by the evaporated particles has dominant effects on the plume shape during the expansion process. An approximation of t hese effects has been done by considering that a fraction of the recom bination of ionic and excited species leads to a delayed kinetic energ y transfer in the plume. II was found that this contribution has a sig nificant effect on the angular and kinetic energy distributions of the evaporated particles. Results of Monte Carlo simulations are compared with experimental results obtained by spectroscopic time of flight me asurements and fast photography of the luminous component of the plume , a particular good agreement is obtained for kinetic energy distribut ions of particles. (C) 1998 American Institute of Physics.