Ultrafast Laser Machining of Micro Grooves on Stainless Steel with Spatially Optimized Intensity Distribution

Femtosecond laser processing enables the machining of micro-grooves by translating the focused femtosecond beam on the sample surface.Most of the time, the spatial intensity distribution on the sample is nearly Gaussian with a circular symmetry.The micro-grooves machined this way show 'classic' cross sectional profile with a 'v' shape.We present here a technique to modulate the cross sectional profile of the micro-grooves in a single laser scan.The technique relies on advanced spatial beam shaping where the intensity distribution is designed to spatially modulate the pulse overlapping during the scanning process.The corresponding exposure gradient enables to control the cross sectional profile of the micro groove.We present machining results on stainless steel using ultrashort pulses (120fs, 800nm at a repetition rate of 5kHz) where calculations based on the ablation rate clearly match the cross sectional profile of the machined micro grooves.