Micromachining using pulse bursts: Influence of the pulse duration and the number of pulses in the burst on the specific removal rate

The today available ultra-short pulsed laser systems offer average power in the range of 100 W or even more resulting in high pulse energies. In contrast to treat metals only moderate peak fluences are required to work at the well-known optimum point, where the ablation process is most energy efficient. In a standard setup the laser beam is deflected by a galvo scanner. The achievable scan speed is limited and therefore also the usable repetition frequency and average power. The use of pulse bursts instead of single pulses is a possibility to further increase the ablation rate, i.e. using higher average power. This further increase is crucial for the usage of the ultra-short pulses in industrial applications. It was shown in previous publications that the number of pulses in the burst have a significant influence on the specific removal rate in case of ps pulses. It was observed, that the second pulse of a 2-pulse burst is shielded by the particle plume of the first pulse of the burst. It is believed that the shielding effect depends on the particle density of the plume, thus the effect should be stronger if more material is ablated. As already known, a decrease of the pulse duration to a few hundreds of fs leads to an increase of the specific removal rate for single pulses. In this work we investigate the influence of pulse bursts on the specific removal rate as well as the pulse duration on the ablation process using pulse bursts.