Time dependent ablation and liquid ejection processes during the laser drilling of metals

A self-consistent time dependent model for the laser drilling of metals is provided, including the analysis of ablation mechanisms, liquid ejection and heat conduction. The energy balance relation assumed to be valid at the ablation front links all the various interacting phenomena involving the absorption of laser light within the vapour. Two liquid ejection mechanisms are identified and discussed, the first of them taking place at the beginning of the process in the form of a sudden blast. The second mechanism occurs with laser beam profiles where the intensity declines with radial distance (e.g. Gaussian beams), and operates locally after the first one has vanished. In addition, experimental results are presented which quantify the ratio of material removed by liquid ejection under practical single pulse drilling conditions. This ratio is determined by the direct collection and weighing of the ejected melt on a glass slide of known mass. The dynamics of the ejection process are also investigated using a high speed digital camera capable of operating at 40,500 frames per second. © 2001 Elsevier Science B.V.