Hybrid kinetic-continuum model for simulations of laser-induced plasma plumes*

A two-dimensional hybrid computational model is developed for simulations of plumes induced by irradiation of metal targets by short and ultrashort laser pulses. The model includes a thermal model of the irradiated target and kinetic-continuum model of plasma plume. The thermal model is based on the heat conduction for short pulses and two-temperature model, which accounts for finite time of electron-phonon coupling in metals, for ultra-short pulses. The kinetic model of plasma flow is implemented in the form of the direct simulation Monte Carlo (DSMC) method generalized for plasma flows. The DSMC method is combined with both equilibrium ionization model based on Saha equations and non-equilibrium model, when the molar fractions of ions are calculated based on kinetic rates of ionization and recombination. The absorption model accounts for multiphoton ionization and inverse Bremsstrahlung. The model is applied for simulations of plasma plumes induced by irradiation of copper targets to the range of laser parameters, when the non-equilibrium effects are important for predicting the plasma shielding effect in material processing applications.