Abstract
Ultrashort pulse laser, capable of varying pulse duration between 210 fs and 10 ps and producing a burst of pulses with an intra-burst pulse repetition rate of 64.5 MHz (time distance between pulses 15.5 ns), was used to investigate the ablation efficiency of the copper. The study on ablation efficiency was done for various numbers of pulses per burst between 1 and 40. The increase in the ablation efficiency by 20% for 3 pulses per burst compared to a non-burst regime was observed. The comparison was made between the beam-size optimised regimes. Therefore, the real advantage of the burst regime was demonstrated. To the best of our knowledge, we report the highest laser milling ablation efficiency of copper of 4.84 µm3/µJ by ultrashort pulses at ~1 µm optical wavelength.
Highlights
Ultrafast laser pulses are already widely used in material processing due to high flexibility and precision, but for competitive industry the processing throughput must always grow[1]
When ablation optimisation is done by changing the size of the beam, the ablation rate and ablation efficiency are optimised together
We demonstrate that further increase, leading to the highest ever published laser milling ablation efficiency, can be done by the beam-size-optimisation
Summary
Ultrafast laser pulses are already widely used in material processing due to high flexibility and precision, but for competitive industry the processing throughput must always grow[1]. One of the most successful studies demonstrated that bursts of high repetition rate pulses could increase ablation efficiency by introducing ablation-cooled material removal[2]. The study reveals that the ablation-cooled regime for copper starts somewhere between the intra-burst pulse repetition rate of 27 MHz and 108 MHz. The burst regime was employed to enhance the laser modification efficiency of the transparent materials via accumulation effects[3]. The similar increase of copper ablation efficiency for the 3 pulses per burst regime compared to a single pulse regime was demonstrated by the pulse energy optimisation at a fixed beam size and reached improvement of 13%8 and 15%15. We demonstrate that further increase, leading to the highest ever published laser milling ablation efficiency, can be done by the beam-size-optimisation. The optimal processing parameters were used for laser milling of complex 3D surfaces
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