GHz bursts in MHz burst(BiBurst) enabling high-speed femtosecond laser ablation of silicon due to prevention of air ionization

For the practical use of femtosecond laser ablation, inputs of higher laser intensity are preferred to attain high-throughput material removal. However, the use of higher laser intensities for increasing ablation rates can have detrimental effects on ablation quality due to excess heat generation and air ionization. This paper employs ablation using BiBurst femtosecond laser pulses, which consist of multiple bursts(2 and 5 bursts) at a repetition rate of 64 MHz, each containing multiple intra-pulses(2–20 pulses) at an ultrafast repetition rate of 4.88 GHz, to overcome these conflicting conditions. Ablation of silicon substrates using the BiBurst mode with 5 burst pulses and 20 intra-pulses successfully prevents air breakdown at packet energies higher than the pulse energy inducing the air ionization by the conventional femtosecond laser pulse irradiation(single-pulse mode). As a result, ablation speed can be enhanced by a factor of23 without deteriorating the ablation quality compared to that by the single-pulse mode ablation under the conditions where the air ionization is avoided.

Enhanced ablation efficiency for silicon by femtosecond laser microprocessing with GHz bursts in MHz bursts(BiBurst)

Ultrashort laser pulses confine material processing to the laser-irradiated area by suppressing heat diffusion,resulting in precise ablation in diverse materials.However,challenges occur when high speed material removal and higher ablation efficiencies are required.Ultrafast burst mode laser ablation has been proposed as a successful method to overcome these limitations.Following this approach,we studied the influence of combining GHz bursts in MHz bursts,known as Bi Burst mode,on ablation efficiency of silicon.Bi Burst mode used in this study consists of multiple bursts happening at a repetition rate of 64 MHz,each of which contains multiple pulses with a repetition rate of 5 GHz.The obtained results show differences between Bi Burst mode and conventional single pulse mode laser ablation,with a remarkable increase in ablation efficiency for the Bi Burst mode,which under optimal conditions can ablate a volume4.5 times larger than the single pulse mode ablation while delivering the same total energy in the process.