Double-pulse technique for short pulse laser drilling

In order to improve the efficiency of short pulse laser drilling,a double-pulse technique is put forward. The double-pulse herein represents two neighboring nanosecond pulses with several tens of nanoseconds interpulse separation,acquired by temporal pulse shaping. In the experiments,laser beams from a Q-switched Nd:YLF laser was focused on steel workpieces 0.4mm～1.0mm thick. The influence of energy density,repetition rate and the ambient gas pressure on ablation rate was studied. The experimental results show a significant enhancement of ablation rates using double-pulse instead of conventional single-pulse under the same condition of energy density and pulse repetition frequency. The ablation mechanism of the double-pulse drilling, including material preheating,melt flow accelerating and quasi-vacuum environment,was discussed respectively. These results are important for practical efficient laser drilling.