2D modeling of laser-induced plume expansion near the plasma ignition threshold

An axisymetric two-dimensional modeling of laser-induced plume dynamics near the plasma ignition threshold in the ambient gas is carried out to provide a better understanding of the pulsed laser deposition process. In our modeling the ionization process is absent and the plume consists of neutral gas. The numerical investigations are performed with initial conditions close to an irradiance of about 100 MW/cm2. This model takes into account different initial conditions in the plume just after the ablation pulse and follows the hydrodynamic behaviour of the subsequent plume expansion. The hydrodynamics induced by the plume expansion are governed by the two-dimensional unsteady Euler equation which are solved with the numerical method, based on a finite difference scheme associated with a flux corrected transport algorithm LCPFCT. The modeling was able to account for many important features of the gas plume dynamics. In particular, it is shown that the hydrodynamic behaviour and thermal relaxation of the gas plume are strongly dependent on the initial gradient of pressure and density between gas plume and background gas. Reversed flow of particles moving toward the target at certain distances along the R axis is clearly observed at a late expansion stage (> 2 μs).