Competitive mechanism of laser energy and pulses on holes ablation by femtosecond laser percussion drilling on AlN ceramics

In laser microstructure machining, results are derived through the action of multiple laser processing parameters (LPPs); therefore, multiple studies on the effect of LPPs on machining results are available. Further, few studies observed how competitive mechanism of each LPP affects machining results. As the most important LPPs, single-pulse energy and the number of pulses were varied to assess their effect on hole dimension and morphology. Additionally, competitive mechanism of LPPs on hole ablation was further explored. The study was based on femtosecond laser percussion drilling on aluminum nitride (AlN) ceramics surface. It was found that laser energy has a dominant role in initial ablation, determining both ablation and ablation mechanism. Additionally, it also determined hole inlet surface morphology and ablation mechanism remained the same regardless of increase in the number of pulses. Laser pulses assumed a dominant role after intersection point of LPPs acceleration rate and hole dimension acceleration rate. Hence, final hole dimensions and its sidewall morphology were defined. It was found that deep holes can be processed both in gentle ablation and strong ablation with lots of pulses. However, there are opposite mechanisms for inducing hole sidewall morphology; for example, in strong ablation, solidification effect is enhanced with increase of hole depth, while it is decreased in gentle ablation.