Femtosecond laser material ablation in the GHz-burst mode has attracted much attention in the last few years and was controversially discussed. The crucial parameters determining whether the burst mode is beneficial or detrimental for the ablation efficiency are the number of pulses within a burst and thus, the burst length, as well as the energy of the pulses within the burst. In this contribution, we show new possibilities of femtosecond GHz-burst laser processing for top-down percussion drilling in alkali-free alumina-borosilicate. We show that deep high-quality holes can be drilled, however the inter-burst repetition rate is limited due to heat accumulation. Furthermore, we present time-resolved in-situ imaging of the drilling process. As laser source, a 100 W average power industrial femtosecond laser is used with a GHz oscillator. Thanks to its flexibility, this source allows for optimizing many process parameters such as burst energy, number of pulses within the burst and burst repetition rate.
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