Shielding effects and re-deposition of material during processing of metals with bursts of ultra-short laser pulses

Investigations on the ablation of copper with ultra-short laser pulses using single pulses and bursts of two or three pulses are presented in this paper. On the basis of shadowgraphic experiments, it is shown that the material ablated by the first pulse is shielding the second pulse of a burst. In addition, material is re-deposited, which significantly counteracts the ablation process. Adding a third pulse to the burst again leads to ablation of material, but with an ablation cloud containing more material than the one generated by a single pulse. (C) 2018 Elsevier B.V. All rights reserved.