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Heat input and accumulation for ultrashort pulse processing with high average power

: Finger, J.; Bornschlegel, B.; Reininghaus, M.; Dohrn, A.; Nießen, M.; Gillner, A.; Poprawe, R.


Advanced Optical Technologies 7 (2018), No.3, pp.145-155
ISSN: 2192-8584
ISSN: 2192-8576
Journal Article
Fraunhofer ILT ()

Materials processing using ultrashort pulsed laser radiation with pulse durations <10 ps is known to enable very precise processing with negligible thermal load. However, even for the application of picosecond and femtosecond laser radiation, not the full amount of the absorbed energy is converted into ablation products and a distinct fraction of the absorbed energy remains as residual heat in the processed workpiece. For low average power and power densities, this heat is usually not relevant for the processing results and dissipates into the workpiece. In contrast, when higher average powers and repetition rates are applied to increase the throughput and upscale ultrashort pulse processing, this heat input becomes relevant and significantly affects the achieved processing results. In this paper, we outline the relevance of heat input for ultrashort pulse processing, starting with the heat input of a single ultrashort laser pulse. Heat accumulation during ultrashort pulse processing with high repetition rate is discussed as well as heat accumulation for materials processing using pulse bursts. In addition, the relevance of heat accumulation with multiple scanning passes and processing with multiple laser spots is shown.