Kinetic theory analysis of laser ablation of carbon: Applicability of one-dimensional models

The paper discusses the applicability of a one-dimensional approximation in a recently proposed model of ablation of carbon by a nanosecond laser pulse that considers the kinetics of the process. The model approximates the process as sublimation and combines conduction heat transfer in the target with the gas dynamics of the ablated plume which are coupled through the boundary conditions at the interface. The ablated mass flux and the temperature of the ablating material are obtained from the conservation relations at the interface derived from the moment solution of the Boltzmann equation for arbitrarily strong evaporation. It is shown that in the one-dimensional approximation the surface pressure and the ablation rate are too low and that the ablation rate is restricted most of the time by the kinetic theory limitation on the maximum mass flux that can be attained in a phase-change process. As a consequence, the model overpredicts the surface temperature and the duration of the process. However, it predicts the total ablated mass with good accuracy.