Correlation between ablation efficiency, surface morphology, and multipass capability using a 100-W 10-MHz ultrafast laser

Nowadays the relevance and the robustness of ultrafast lasers are well established for many industrial applications. Indeed this laser technology combines the unique capacity to process any type of material with an outstanding processing precision and a minimal heat affected zone. The key issue is to combine high throughput, low residual thermal load and good processing quality. Thanks to high average power and high repetition rate it is possible to achieve high throughput providing that the operating parameters are precisely tuned to the application, otherwise heat accumulation and heat affected zone may appear, leading to detrimental effects such as burr, uncontrolled melting and metal oxidation. In this paper we report on high-throughput laser ablation of metals using a 100W- and 10MHz- ultrafast laser. Target materials were stainless steel, Copper, and Aluminum. Operating parameters such as fluence, repetition rate and scanning velocity have been considered. Results are discussed in terms of ablation efficiency, surface morphology, multipass and up-scaling capabilities. Different behaviors between materials are also discussed. We observe that pulse-to-pulse pitch and delay are key parameters that must be taken into account in order to define relevant process windows for each material. The use of polygon scanner instead of galvo scanner enables us to reduce the thermal load along the laser trajectory. The point is not to avoid heat accumulation but to take advantage of this phenomenon as long as the target material can stand the thermal load without detrimental effects on the processing quality.