Femtosecond laser ablation by bibursts in the MHz and GHz pulse repetition rates.

Here, to the best of our knowledge, for the first time we report an in-depth experimental study of high ultrafast laser ablation efficiency for processing of copper and steel with single-pulses, MHz, GHz, and burst-in-the-burst (biburst) regimes. The comparison of burst, biburst, and single-pulse ablation efficiencies was performed for beam-size-optimised regimes, showing the real advantages and disadvantages of milling and drilling processing approaches. Highly efficient ultrashort pulse laser processing was achieved for ∼1 µm optical wavelength: 8.8 µm/µJ for copper drilling, 5.6 µm/µJ for copper milling, and 6.9 µm/µJ for steel milling. We believe that the huge experimental data collected in this study will serve well for the better understanding of laser burst-matter interaction and theoretical modelling.