Monte Carlo simulation of the laser-induced plasma-plume expansion under vacuum and with a background gas

The plasma-plume created above a copper target irradiated by a pulsed KrF laser beam (wavelength = 248 nm, pulse duration = 20 ns, fluence = 17 J/cm(2)) is investigated by means of a Monte Carlo simulation. The plume expansion under both vacuum and background gas is followed in time by simulating particle motion and collisions in the gas phase. The expansion under vacuum of laser-ablated particles is dominated by the laser energy absorption by the evaporated particles during the laser pulse. A comparison between simulated time-of-flight curves and experimental curves obtained by spectroscopic time-of-flight measurements has shown that about 6% of the incoming laser energy was contributing to the expansion process through the time-delayed recombination of this energy into kinetic energy. The plasma-plume expansion under a residual argon pressure greater than 50 Pa has been found to be very much affected by collisions between laser-ablated and ambient gas particles. The compression of the ambient gas particles by the ejected particles in the leading edge of the plume (snowplow effect) is clearly observed. (C) 1999 Elsevier Science B.V. All rights reserved.