A simple two-stage model for the formation and expansion of the plasma induced by high intensity nanosecond laser metal ablation in vacuum

A simple two-stage model for the formation and expansion of the plasma induced by high intensity nanosecond laser metal ablation in vacuum has been developed. To simulate the first stage of plasma formation and initial expansion within the laser pulse, the one-dimensional hydrodynamic equations are supplemented by a wide-range equation of state and solved numerically. For the second stage of plasma expansion after the end of laser pulse, a three-dimensional semi-analytical model is applied, the input of which comes from the output of the model in the first stage. In this way, a self-closed calculation is realized. This two-stage model is easy to apply and has very small computational cost. Although simplified and approximate, its predictions, however, are reasonably accurate, which has been shown by the good agreements between simulations and experimental measurements for the plasma front location, temperature and electron number density.