Pump-probe imaging for process control and optimization in high-speed laser micro machining

Sebastian Kraft; Joerg Schille; Stefan Mauersberger; Lutz Schneider; Udo Loeschner

doi:10.1117/12.2545021

12 March 2020 Pump-probe imaging for process control and optimization in high-speed laser micro machining

Sebastian Kraft, Joerg Schille, Stefan Mauersberger, Lutz Schneider, Udo Loeschner

Proceedings Volume 11268, Laser-based Micro- and Nanoprocessing XIV; 112681H (2020) https://doi.org/10.1117/12.2545021
Event: SPIE LASE, 2020, San Francisco, California, United States

Abstract

The recent developments in high-speed laser machining combine high-average power lasers with ultrafast beam deflection systems.1 However, when using ultrashort pulses at megahertz pulse repetition frequencies the incoming laser beam may interact with the plasma/particle ablation plume that is due to the very short time intervals between the impinging megahertz-repetitive pulses. Thereby, the subsequently irradiated pulses will either be reflected, absorbed and/or scattered by the still existent plasma/particle plume as induced by the previously irradiated pulse(s). This shielding of the incoming laser beam is adversely affecting material ablation and can potentially be avoided when the beam is ultrafast moving in front of the emerging plasma/particle plume. For the real-time analysis of such fairly unknown processing regimes, a pump-probe shadowgraph imaging technique was used to visualize laser materials interaction in high-speed ultrashort pulse laser machining. The pump laser source supplied a beam of λ=1030 nm, ƬH =600 fs and 48MHz maximum pulse repetition frequency for material ablation. A diode laser system provided the probe beam of λ=688 nm and ƬH =13 ns. The pump and the probe beam could be electronically delayed within a time frame of up to 10 µs. Sequences of shadowgraphs will be presented to visualize plasma/ablation plume expansion for providing unique insights into high-pulse repetition frequency ultrashort pulse laser materials interactions at ultrafast laser beam movements above 250m/s. The shadowgraphs reveal that the form of the emerging plasma/particle plumes is influenced by the laser beam moving speed. The plumes vary in their density and structure from clearly distinguishable at highest speed, through smoothly detached to be turbulent. In addition, it is shown on the shadowgraphs material ejection takes place at the time when the ultrafast scanned laser beam moved away from the initial irradiation area.

Citation Download Citation

Sebastian Kraft, Joerg Schille, Stefan Mauersberger, Lutz Schneider, and Udo Loeschner "Pump-probe imaging for process control and optimization in high-speed laser micro machining", Proc. SPIE 11268, Laser-based Micro- and Nanoprocessing XIV, 112681H (12 March 2020); https://doi.org/10.1117/12.2545021

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