Surface Morphologies in Ultra-short Pulsed Laser Processing of Stainless-Steel at High Repetition Rate

Stainless-steel is ablated with femtosecond laser pulses at high repetition rate. A multi-pass, high spatial overlap laser scanning strategy is applied in order to cope with the requirements for large-scale machining of high aspect ratio structures. Topography of the processed surfaces is analyzed via Shear Force Microscopy scans, with the main aim to investigate morphology changes as a function of process parameters. Quantitative assessment of local height variations enables a detailed investigation of the produced features. Depending on the process parameters, in particular on laser fluence and repetition rate, a transition from small islands to large bumps is observed, explained in terms of feature coalescence.