Direct in-situ measurement of the ablation rate in short pulse laser percussion drilling of metal targets

We demonstrate that a non-invasive sensing technique based on optical feedback interferometry is capable to instantaneously measure the ablation front displacement and the removal rate during ultrafast laser percussion drilling of metallic plates. The sawtooth-like modulation of the interferometric signal out of the detecting sensor has been analyzed to reveal the time dependence of the removal depth with sub-micrometric resolution. Various dynamic factors related to the influence of laser pulse duration and peak energy have been assessed by in-situ spatial- and time-dependent characterization all through the ablation process. The importance of realtime measurement of the ablation rate is crucial to improve the basic understanding of ultrafast lasermaterial interactions. Moreover, the detection system results high-sensitive, compact, and easily integrable in most industrial workstations, enabling the development of on-line control to improve the ablation efficiency and the quality of laser micromachining processes.