Ablation efficiency of high average power ultrafast laser

Nowadays, the relevance of ultrashort laser is well established for many medical or industrial applications. Indeed, the ultrashort laser technology has reached a high level of robustness which makes it compatible with the needs of industry. This laser technology combines the unique capacity to process any type of material with an outstanding precision and a minimal heat affected zone. Thanks to high average power and high repetition rate it is possible to achieve high throughput providing that the operating parameters are finely tuned to the application, otherwise heat accumulation and heat affected zone may appear. In this paper, the authors report on high throughput single pass ablation of stainless steel with a high average power Yb-doped fiber ultrashort pulse laser which is tunable in pulse duration from 350 fs to 10 ps and in repetition rate from 200 kHz to 2 MHz. The influence of pulse duration, repetition rate, fluence, energy dose, and scanning velocity will be discussed in terms of ablation efficiency and processing quality. These results will be compared to those previously obtained on aluminum, copper, and molybdenum. The authors will see that the effect of these parameters is strongly material dependent. The ablation behavior of stainless steel is very sensitive to these parameters meanwhile it is not the case for aluminum in the investigated process window. The authors observe an intermediate behavior for copper and molybdenum. Moreover, the authors will demonstrate that engraving of metals without melt formation is possible even at high average power (20 W) and high repetition rate. Furthermore, best ablation efficiency and quality are obtained at low fluencies. Scaling up from 2 to 15 W implies to use high repetition rate and high deflection velocity.