Appl Phys A DOI 10.1007/s00339-011-6702-8 Numerical simulation of process dynamics during laser beam drilling with short pulses Karl-Heinz Leitz · Holger Koch · Andreas Otto · Michael Schmidt Received: 26 October 2011 / Accepted: 15 November 2011 © Springer-Verlag 2011 Abstract In the last years, laser beam drilling became in- creasingly important for many technical applications as it allows the contactless production of high quality drill holes. So far, mainly short laser pulses are of industrial relevance, as they offer a good compromise between precision and ef- ficiency and combine high ablation efficiency with low ther- mal damage of the workpiece. Laser beam drilling in this pulse length range is still a highly thermal process. There are two ablation mechanisms: evaporation and melt expulsion. In order to achieve high quality processing results, a basic process understanding is absolutely necessary. Yet, process observations in laser beam drilling suffer from both the short time scales and the restricted accessibility of the interaction zone. Numerical simulations offer the possibility to acquire additional knowledge of the process as they allow a direct look into the drill hole during the ablation process. In this contribution, a numerical finite volume multi-phase simu- lation model for laser beam drilling with short laser pulses shall be presented. The model is applied for a basic study of the ablation process with μs and ns laser pulses. The ob- tained results show good qualitative correspondence with experimental data. K.-H. Leitz ( ) · H. Koch · M. Schmidt Chair of Photonic Technologies and Erlangen Graduate School in Advanced Optical Technologies (SAOT), University of Erlangen–Nuremberg, Paul-Gordan-Str. 3, 91052 Erlangen, Germany e-mail: karl-heinz.leitz@lpt.uni-erlangen.de A. Otto Institute for Production Engineering and Laser Technology, Vienna University of Technology, Gusshausstrasse 30, 1040 Vienna, Austria 1 Introduction Generally, the quality of laser drilled holes gets better with shorter pulse length, mainly due to the reduced formation of melt. However, efficiency decreases as well (see Fig. 1). Single pulse drilling using ms and μs pulses allows the pro- duction of many holes within a short time. As there is quite a big amount of melt involved in the process, the quality and reproducibility of the holes is rather low. If higher pre- cision is needed, short and ultrashort pulses in combination with adequate drilling strategies are applied. In this pulse length range, only a small amount of melt is involved in the process, which means that high accuracy can be achieved. However, in the past the medium laser powers of ultrashort- pulsed systems were not sufficient to fulfil industrial effi- ciency requirements. Besides, studies have shown that even with ultrashort pulses the generation of melt cannot be pre- vented completely [1–7]. Only recently first attempts for the application of ultrashort laser pulses in industrial produc- tion have been reported [8, 9]. However, so far in many in- dustrial applications Q-switched laser systems in the micro- and nanosecond range are still widely common because they can deliver high medium laser power and allow a good com- promise between precision and efficiency. As in these pro- cesses, there is still a certain amount of melt involved, the choice of the right process parameters and the most suitable drilling strategy is of extreme importance in order to achieve the requested quality [10]. When a laser pulse hits the material, within a short time a multitude of highly dynamic coupled physical processes take place (see Fig. 2). The laser beam is absorbed on the surface of the material, and due to the high intensities of pulsed laser radiation, nearly instantly surface temperatures of some thousand Kelvin are reached, leading to an abrupt evaporation, ionisation of the material and the occurrence of