Influence of pressure on aluminium plasma expansion produced by a nanosecond laser pulse: a numerical study

摘要

This work deals with a numerical study of the expansion and extinction phase of an aluminium plasma, created by nanosecond laser ablation into air. Two series of pressures are considered: (150 mTorr, 300 mTorr, 600 mTorr) and (1.3 Torr, 3 Torr, 10 Torr). The plasma expansion is studied by means of a two-dimensional numerical model over a time interval of 10 μs. The resolution of the Navier-Stokes equations shows that in general the plasma dynamics in the presence of a gas follows three successive stages, appearing after the laser pulse: (1) a rapid expansion stage of the ablated particles, (2) a deceleration stage due to the interaction with the ambient gas, and (3) a stopping stage dominated by particle diffusion on the long term. In this paper, we study the effect of the pressure of the ambient air on the behaviour, size, and mean temperature of the plasma. The calculation results are in overall agreement with experiments.