We report on crater formation, line scribing and cavity milling experiments on Silicon, Copper, Aluminum and stainless steel with GHz bursts of femtosecond pulses. The intra-burst repetition rate has been varied between 0.88 and 3.52 GHz, the number of pulses per burst between 50 and 3200, the burst fluence between 8 and 80 J/cm². For these experiments, a 100-W femtosecond GHz-burst laser has been developed on an industrial laser basis, delivering a total burst energy up to 1 mJ at 100 kHz, with an adjustable number of pulses per burst. The results highlight the conditions to obtain high-ablation efficiency, show how to optimize the machining quality and point out the burst duration as the relevant parameter for femtosecond GHz machining.

We report on silicon ablation with a 20 W GHz amplified femtosecond laser source. This novel laser delivers burst energies up to 400 μJ, providing flexible intra-pulse repetition rates of 0.88 or 3.52 GHz, up to 200 pulses with $\sim 350\mathrm{fs}$ pulse duration. High-efficiency, high-quality ablation can be achieved through optimally determining the number of pulses, intra-pulse repetition, and average pulse energy within a burst. Due to such optimization, we demonstrate a specific ablation rate of $2.5{\mathrm{mm}}^3/\min /\mathrm{W}$ with a burst containing 200 pulses at 0.88 GHz, which is the highest one reported so far for fs laser ablation, to the best of our knowledge. GHz ablation is sensitive to the selection of laser parameters. We conceptually discuss the contributions of the pulses within a burst to heat-accumulation-based incubation and material ablation.

The authors report on a simple and easy-to-use GHz amplified femtosecond laser source. The laser source is based on a passively mode-locked oscillator with a near GHz repetition rate. GHz pulses are then selected, and the obtained bursts of pulses are further amplified in a high-power amplifier chain. The presented GHz femtosecond laser source is used with a galvanometric scanner to perform ablation experiments on copper, aluminum, and stainless steel. Specific ablation rates of 0.7, 2.3, and 1.4 (mm3/min)/W are reached. The role of the important experimental parameters, such as the number of subpulses in the burst, is highlighted. Thanks to a specific ablation scheme in the GHz mode, the ablation efficiency is then comparable to the case of single nanosecond pulses, but with the usual quality of femtosecond processing.

We report for the first time to our knowledge on top-down percussion drilling of high-quality deep holes in different glasses with femtosecond laser pulses in GHz-burst mode. We reveal the dynamics of the percussion drilling process by pump-probe shadowgraphy and thermal camera imaging demonstrating that the drilling process in GHz-burst mode is fundamentally different from single-pulse processing and confirming the presence of thermal accumulation. Moreover, we show a comparison to drilling by femtosecond single-pulses containing an equal laser fluence in sodalime, alkali-free alumina-borosilicate, fused silica, and sapphire.

The femtosecond GHz-burst mode laser processing has attracted much attention in the last few years. Very recently, the first percussion drilling results obtained in glasses using this new regime were reported. In this study, we present our latest results on top-down drilling in glasses, focusing specifically on the influence of burst duration and shape on the hole drilling rate and the quality of the drilled holes, wherein holes of very high quality with a smooth and glossy inner surface can be obtained. We show that a decreasing energy repartition of the pulses within the burst can increase the drilling rate, but the holes saturate at lower depths and present lower quality than holes drilled with an increasing or flat energy distribution. Moreover, we give an insight into the phenomena that may occur during drilling as a function of the burst shape.