Dynamics of planar gas expansion during nanosecond laser evaporation into a low-pressure background gas

Abstract

A numerical study in a one-dimensional planar formulation of the dynamics of the neutral gas expansion during nanosecond laser evaporation into a low-pressure background gas is carried out using two different kinetic approaches: the direct simulation Monte Carlo method and direct numerical solution of the Bhatnagar–Gross–Krook equation. Results were obtained for a wide range of parameters: the background gas pressure, masses of evaporated and background particles, temperature and pressure of saturated vapor on the evaporation surface, and evaporation duration. They are in good agreement with the analytical continuum solution for unsteady evaporation into the background gas. The dynamics of the expansion is analyzed, and the characteristic times and distances that determine the main stages of the expansion process are established. General regularities are obtained that describe the dynamics of the motion of external and internal shock waves and the contact surface as well as the maximum density of evaporated particles and the characteristic temperatures of evaporated and background particles in the compressed layer. The obtained results are important for understanding and describing the change in the mixing layer during nanosecond laser deposition in a low-pressure background gas.