Two-dimensional model for laser-induced materials damage: Effects of assist gas and multiple reflections inside the cavity

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Abstract
A two-dimensional axisymmetric model for materials removal during laser irradiation is presented by taking into account the reflections of the laser beam at the wall of the laser-induced cavity. Also, the liquid metal flow due to the shear stress at the interface of the assist gas and the liquid metal is studied in this paper. The vaporization of the liquid metal and the melting of the solid substrate at the liquid-vapor and the solid-liquid interfaces, respectively, are modeled by applying the Stefan condition at various points on the interfaces. Maximum drilling rate is determined by considering that the laser energy is used only to melt and vaporize the material. The effects of various process parameters such as the laser power, laser beam radius, and the laser pulse-on time on the cavity depth, the recast layer thickness, and the cavity tapering are examined in this study. It is found that the laser-induced materials removal process can be described in terms of a single parameter called the ‘‘gross’’ laser intensity.