Study by a Monte Carlo simulation of the influence of a background gas on the expansion dynamics of a laser-induced plasma plume

The expansion of a laser-induced plasma plume into a non-reactive backgroun d gas is investigated theoretically using a Monte Carlo simulation. The met hod allows the description of the collective motion of both laser-ablated a nd background gas particles. The influence of the background gas pressure o n the plume shape and on the ambient gas particles distribution within the plume of ejected matter is studied. The expansion dynamics under various am bient gas pressures and nature is also investigated. The compression of the ambient gas particles by the ejected particles in th e leading edge of the Flume (snowplow effect) is clearly observed for a res idual argon pressure greater than 50 Pa. The narrowing, or focusing, of the laser-induced plasma plume is also observed with increasing the ambient ga s pressure. The ambient gas particles are then preferentially located at th e edge of the plume of ejected matter, whereas the high-density region in t he plume appears to be deficient in background gas particles. The dynamics of the expansion of the plume under a high residual pressure appears to be different from low-pressure cases, with a stronger thermalization of the pl ume and an evidence of the oscillatory behavior of the plume expansion. The Monte Carlo simulation also predicts vortical flow formation at the plume periphery.