Two-dimensional model for melting and vaporization during optical trepanning

Annular laser beams provide a drilling mechanism that can be referred to as optical trepanning. In this paper an analytical two-dimensional model is developed for optical trepanning. The analysis accounts for conduction in the solid, vaporization, and convection due to the melt flow caused by an assist gas. Based on the model, the influences of pulse duration, laser-pulse length, pulse repetition rate, intensity profiles, and beam radius are investigated to examine their effects on the recast layer thickness, hole depth, and taper. Deeper cavity depth, thicker recast layer, and larger taper are obtained with the increase in the laser intensity. By using different types of intensity profiles, the nature of the hole taper can be modified, i.e., convergent or divergent holes can be produced. The effects of the inner radius of annular beams are more significant than other laser parameters. An increase in the inner radius reduces the hole taper and produces thinner recast layer and deeper cavity depth.