High-quality surface treatment using GHz burst mode with tunable ultrashort pulses

The authors report on a solid state GHz amplified laser source capable of varying the pulse duration in the range of 270 fs to 10 ps and generating a pulse train with an intra-burst pulse repetition rate of 5 GHz (pulse-to-pulse time interval approx. 200 ps). In this study, a laser radiating at 1030 nm wavelength is used to investigate the ablation and surface quality on stainless steel, cemented tungsten carbide and silicon with different pulse numbers per burst between one pulse and 25 pulses. As a consequence of shielding effects by the laser-induced plasma or by the ablation cloud, no material tends to be ablated in burst mode for all tested pulse durations at this intra-burst pulse repetition rate. Compared to the non-burst regime, a reduction of the surface roughness by a factor of four could be accomplished depending on the number of pulses per burst. Thus, the actual advantage of the GHz burst regime in terms of the obtainable surface quality could be established.