Femtosecond Laser Drilling of High-Density Micro-Holes on Metals Using MHz Burst Mode

The pressing need from various technological sectors, e.g.aerospace, automotive and microfiltration, for higher drilling throughput at increasingly lower cost has propelled the continuous commercial development of ultrashort lasers offering very high average powers.Although such laser sources provide a huge potential for production upscaling, it is still challenging to fully utilise their output.The problem relates to unwanted thermal effects that degrade the overall process performance, especially in laser drilling of metal foils.Therefore, effective solutions are still required to exploit these new advances in ultrashort laser technology.Herein, we study throughput upscaling by utilising a 120 W femtosecond diode-pumped solid-state laser in both single-pulse and MHz burst modes for percussion drilling of 300 m thick stainless-steel foils.The influence of critical laser processing parameters was investigated for maximum drilling efficiency and best hole quality.Heat accumulation effects induced by MHz burst mode in high-density hole drilling were analysed and compared with those of nanosecond laser pulses of similar total temporal length.The results demonstrate new capability using MHz burst mode processing to improve drill rate and hole quality compared to single-pulse.Despite that, MHz burst mode showed similar heat-related issues with a nanosecond laser in high-density drilling operations.