Ablation efficiency of laser drilling of thin metal foils with ultrashort pulses in MHz bursts

In burst mode, a single pulse is replaced by a packet of multiple pulses of the same energy. Recently, various research groups have conducted numerous experiments on the processing of metals using the GHz burst mode, while the less expensive and more accessible MHz burst mode has been little explored. Therefore, in this study, we investigate the extent to which it is possible to achieve the advantages of GHz burst laser machining by using MHz burst laser (wavelength 1030 nm, intra-burst repetition rate of 40 MHz, repetition rate of 333 kHz, and pulse duration between 300 fs - 10 ps) on metals. We measure the ablation efficiency as the volume removed per energy (dV/dE) when drilling stainless steel foils with different thicknesses (25 μm, 50 μm and 75 μm). The ablation efficiencies are compared for different ultrashort pulse durations (300 fs - 10 ps), for ns pulses, and for a different number of pulses within the burst (at constant burst energy). The results show that a MHz burst mode can be a cost-effective alternative to the GHz burst mode for a broader implementation of burst-mode laser processing in various industrial applications.