Kinetic Theory Analysis of Laser Ablation of Carbon

Abstract

The paper presents a 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 momentum solution of the Boltzmann equation for arbitrary strong evaporation. The effects of laser intensity and ambient pressure on the ablated mass flux and parameters of vapor plume are studied. It is shown that most of the time the ablation rate is restricted by the kinetic theory limitation on the maximum mass flux that can be attained in a phase-change process. This fact makes the model tolerant of possible inaccuracies in calculating the saturation pressure of carbon vapor.