Expansion of a laser plume from a silicon wafer in a wide range of ambient gas pressures

Expansion of the laser plume from a silicon wafer into surrounding gas is considered in the range of ambient gas pressure from 0.1 to 1 bar using a kinetic approach. The plume is generated by a nanosecond Gaussian laser pulse. Absorption of laser radiation and heating and melting of the target are described by a two-dimensional thermal model. Axisymmetric flow in the laser plume is calculated by the direct simulation Monte Carlo method. It was found that diffusion of mixture components is significant in the considered time scale, flow is non-equilibrium, and regions of high rarefaction temporally appear in the flow. In atmospheric pressure, the re-deposition of the silicon vapor was observed only in the vicinity of the laser spot.