High-speed ablation of ultradeep channels by a phase-conjugate dynamically controlled passively<i>Q</i>-switched Nd:YAG laser

Parameters of high-speed ablation of ultradeep channels by controlled pulse trains from a single-mode phase-conjugate dynamic cavity Nd:YAG laser emitting 20–200-ns, 70–250-mJ pulses at a pulse repetition rate in a train of 40–250 kHz are studied. The optimal parameters of ablation are found, for which a long-lived region of a hot rarefied gas was maintained in the ultradeep channel, which suppressed the shielding action of the surface plasma. The control of the lasing process during ablation optimises not only the heating and plasma formation, but also the removal of the processed material in the pause between laser pulses. Adaptive regulation of lasing parameters during ablation made it possible to obtain ultradeep channels of length 8–27 mm and diameters 80–300 μm of the input and output holes in metals (aluminium, steel and Inconel 718 nickel superalloy) and ultrahard ceramics (Al2O3, AlN, SiC).