Product Code: ICAL07_M805

Monitoring of the Micro-Drilling Process by Detection of Laser-Induced Shock Waves in Air
Andreas Michalowski, Institut für Strahlwerkzeuge; Stuttgart Germany
Dmitrij Walter, Forschungsgesellschaft für Strahlwerkzeuge mbH; Stuttgart Germany
Friedrich Dausinger, Forschungsgesellschaft für Strahlwerkzeuge; Stuttgart Germany
Roland Gauch, Forschungsgesellschaft für Strahlwerkzeuge; Stuttgart Germany
Presented at ICALEO 2007

This work presents a method for the determination of different stages of the micro-drilling process including the measurement of the hole depth and the detection of the completion of desired channel morphology. The experimental method utilizes the detection of shock waves generated during the interaction of the laser beam with the irradiated material. The propagation behaviour of shock waves is detected by a non-contacting optical method using shadowgraphic and schlieren photography techniques. The depth of the hole was derived from the size of the shock wave radius. This waves travelling from the bottom of the channel were measured at a fixed time delay after laser exposure of the target material. A linear dependence between both values was observed for a wide range of pulse durations (100 fs - 5 ps) and different materials. Furthermore we were able to investigate a correlation between the widening of the hole outlet and the shock wave size. The end of the drilling process, when no more ablation takes place, is detectable by means of the dramatic decay of the shock wave radius. The obtained results prove that the proposed method offers a good potential for in-situ diagnostics of laser drilling processes.

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