Electron kinetic theory approach for sub-nanosecond laser pulse heating

Laser short-pulse heating initiates non-equilibrium thermodynamic processes in the surface vicinity of solid substrates that are subjected to the pulse heating. The Fourier heating model, however, overestimates the temperature rise in this region. Consequently, it becomes essential to consider a heating model employing a microscopic level energy exchange mechanism in the surface vicinity. In the present study, electron kinetic theory, Fourier theory (one-equation model) and a two-equation model are introduced for sub-nanosecond laser heating pulses. The effect of laser pulse intensity on the temperature rise is also considered. The equations resulting from the models are solved numerically for gold and chromium substrates. The predictions are validated for a triangular pulse and a silicon substrate. It is found that electron kinetic theory and a two-equation model both predict lower temperatures in the surface vicinity at early heating times. As the pulse heating progresses, the predictions of both models converge to the result of a one-equation model.