Improvement of the taper degree of laser-drilled holes via a double-pulse train

Laser drilling has been widely used in various application fields because of advantages such as environmental friendliness, scalability, non-contact, etc. Nevertheless, it still has some drawbacks. One of the most concerning is the taper degree caused by the ablation process resulting from a laser Gaussian beam. In this study, we utilize a nanosecond double-pulse laser (at 532 nm) to experimentally acquire a series of holes on stainless thin plates. With the double-pulse train, the taper degree of a drilled hole becomes half of that drilled by using a single-pulse train. Different combinations of the power component of the two pulses for the double-pulse laser have been investigated to earn the optimum power ratio of the two pulses. For instance, by using a double-pulse laser train with a repetition rate of 5 kHz and a total power of 8 W, we observe that the optimized combination of the two pulses is 2 W and 6 W. Furthermore, we theoretically analyze the variations of the density, temperature, and pressure around the processing area during both the double-pulse and single-pulse laser processing based on a constrained interpolation profile procedure. The theoretical results show that drilled holes with smaller taper degree can be realized by using the double-pulse approach. Our results have great potential in laser drilling and precision laser machining.