2D MODELING OF LASER-INDUCED PLUME EXPANSION NEAR THE PLASMA IGNITIONTHRESHOLD

An axisymetric two-dimensional modeling of laser-induced plume dynamic s near the plasma ignition threshold in the ambient gas is carried out to provide a better understanding of the pulsed laser deposition proc ess. Zn our modeling the ionization process is absent and the plume co nsists of neutral gas. The numerical investigations are performed with initial conditions close to an irradiance of about 100 MW/cm(2), This model takes into account different initial conditions in the plume ju st 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 differe nce 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 b ehaviour and thermal relaxation of the gas plume are strongly dependen t on the initial gradient of pressure and density between gas plume an d background gas. Reversed flow of particles moving toward the target at certain distances along the R axis is dearly observed at a late exp ansion stage (> 2 mu s).