Laser microprocessing in a gas environment at a high repetition rate of ablative pulses

The parameters of laser ablation of channels in steel are studied in a wide range of nanosecond pulse repetition rates f (5 Hz ≤ f ≤ 200 kHz). It is found that for f ≥ 4 kHz, the results of ablation in air are identical to those obtained under the action of single laser pulses in vacuum. The experimental data as well as the estimates of the parameters of laser plasma and the gas environment in the region of the laser action lead to the conclusion that there exists a long-lived region of hot rarefied gas, known as a fire ball in the theory of explosions. The emerging rarefaction reduces the screening effect of the surface plasma formed under the action of subsequent pulses. This makes it possible to use lasers with a high pulse repetition rate for attaining ablation conditions close to the conditions in vacuum without complicating the technology of microprocessing by using vacuum chambers and evacuating pumps.