High performance micromachining of sapphire by laser induced plasma assisted ablation (LIPAA) using GHz burst mode femtosecond pulses

GHz burst-mode femtosecond (fs) laser, which emits a series of pulse trains with extremely short intervals of several hundred picoseconds, provides distinct characteristics in materials processing as compared with the conventional irradiation scheme of fs laser (single-pulse mode). In this paper, we take advantage of the moderate pulse interval of 205 ps (4.88 GHz) in the burst pulse for high-quality and high-efficiency micromachining of single crystalline sapphire by laser induced plasma assisted ablation (LIPAA). Specifically, the preceding pulses in the burst generate plasma by ablation of copper placed behind the sapphire substrate, which interacts with the subsequent pulses to induce ablation at the rear surface of sapphire substrates. As a result, not only the ablation quality but also the ablation efficiency and the fabrication resolution are greatly improved compared to the other schemes including single-pulse mode fs laser direct ablation, single-pulse mode fs-LIPAA, and nanosecond-LIPAA.