High-repetition rate ultrafast burst laser processing of copper and silicon up to 15 GHz

Ultrafast lasers are widely used in microfabrication due to their precision and minimal thermal damage, but their throughput is often limited. Processing with bursts of pulses with GHz repetition rates aims to enhance ablation efficiency. However, recent results have shown strong dependencies on the number of pulses within the burst. The present work focuses on the pulse repetition rate. We report ultrafast laser ablation in copper and silicon at unexplored intra-burst repetition rates, from 1 up to 15 GHz, in both single and multi-burst processing. High-resolution scanning electron microscopy is used to characterize ablation volumes and crater morphology. Our results demonstrate a benefit in the ablation efficiency at very high repetition rates in the case of copper. It also shows that optimal processing for silicon and copper is observed with very different parameter configurations. This difference is attributed to the different thermal diffusivities. In addition, the crater morphologies across the different studied configurations strongly suggest a dependency on the viscosity of the liquid phase, providing insight into the varying temperatures reached during ablation.