Comparative study on microstructuring of steel using pico-and femtosecond laser pulses

Abstract

Results of investigations on microstructuring of steel using pico-and femtosecond laser pulses will be presented. For the experiments, lasers with high repetition rates in the 100 kHz range, but relatively small pulse energies were used. The pulse durations were 15 ps and 180 fs, respectively. Experiments showed that the volume of material ablated per pulse is always larger with femtosecond laser pulses compared to picosecond laser pulses using the same fluences and repetition rates, which suggests that the photons of femtosecond pulses are used more effectively for ablation. Moreover, the volume ablated per pulse using femtosecond laser pulses is from the beginning independent of the number of crossings used, whereas it increases at first with increasing number of crossings with picosecond pulses till a constant value is reached after 100 crossings of the laser beam over the structured area. The average roughness RA of comparatively deep structures produced with the femtosecond laser was generally found to be lower than with the picosecond laser. Thereby, the roughness increased with increasing depth of the structures, i.e. with increasing total number of laser pulses used, with both lasers. First investigations using burst mode with the picosecond laser have shown, however, that the quality of the structures with respect to surface roughness and also the ablation rates can be improved significantly by using this mode.