A hybrid model is developed to study the dynamics of laser plume expansion in vacuum or into a background gas. The method takes advantages of both continuous and microscopic simulation approaches. As a result of the combination of two different numerical methods, such as, large particles and direct Monte Carlo simulation, the model describes high-rate laser ablation for a wide range of background pressures (from zero to hundreds Pa). The model is used to investigate laser plume interaction with background gases. Particularly, the plume-gas mixing and energy exchange are taken into account. The dynamics of the laser plume expansion is investigated. Snowplow effect is observed at sufficiently high pressures. At smaller pressures, strong plume-gas mixing takes place near the contact surface. The simulation results explain experimentally obtained spatial maps of the reaction products formed during the plume expansion into a reactive background gas. (C) 2002 Elsevier Science B.V. All rights reserved.