A simplified cavity analysis for estimating energy coupling during laser ablation and drilling of solids - experiment

The theory for a general departure function, f, for laser-irradiated caviti es was previously developed to estimate laser energy coupling to an opaque solid target as a function of heat transfer and the cavity shape and size. In this article, a specific form of f is calculated for ultraviolet (UV) la ser ablation of copper (Cu) and aluminum (Al) targets. Methods are also giv en for calculating the geometric factor, a, and experimentally determining the heat transfer parameter, nu, which is shown for this form of f to be th e intensity-dependent effective reflectivity of the material. Experimental results for different gauges of laser energy coupling with a solid target a re given and compared to calculations of net absorbed energy based on f and the incident laser energy. Using the simplified cavity analysis, the resul ts demonstrate that the experimental values for f fall within the limits pr edicted by the theory, and that energy coupling can be predicted to within a mean of 2% of experimental gauges. Neglecting the factors in f from calcu lations of energy coupling can lead to large errors for laser-irradiated ca vities, establishing that both cavity shape and treat transfer should be si multaneously considered. In addition, a first-order sensitivity analysis ba sed on f shows that the initial rate of change in material removal strongly increases with reflectivity, which can lead to runaway cavity formation fo r highly reflective materials. (C) 1999 Elsevier Science B.V. All rights re served.