离焦量对空气中纳秒激光打孔效率的影响

Effect of Deviation Distance to Focal Spot on Nanosecond-Pulsed-Laser Drilling Rates in Air

用波长1.06μm,脉冲半峰全宽(FWHM)约10 ns的Nd∶YAG激光照射在薄铜靶上,研究了打孔效率同离焦量之间的关系。实验中脉冲能量分别为26 mJ,52 mJ,85 mJ,204 mJ和274 mJ,在各脉冲能量下,改变离焦量,测出相应的打孔效率。结果表明,离焦量是影响打孔效率的重要因素;实际打孔过程中,采用较低的激光功率密度和+3^+4 mm的离焦量是合理的选择。当离焦量d<0时,打孔效率主要由激光照射产生的热烧蚀、等离子体屏蔽两个物理机制决定;当离焦量d>0时,打孔效率是激光照射产生的热烧蚀、等离子体屏蔽和焦斑处空气等离子体辐射的促吸收效应共同作用的结果。

The effects of deviation distance from the focal spot to the target surface （d） on nanosecond-pulsed-laser drilling rates under different pulse energy were experimentally studied. The laser operated at a wavelength of 1.06 μm and pulse width of 10 ns （full width at half maximum）. Pulse energy of 26, 52, 85, 204 and 274 mJ was used respectively. The drilling rate was measured under different pulse energy and d value. The experimental results show that d is one of the important aspects affecting laser drilling rate, and that it is a reasonable choice of using relatively low intensity laser pulses and d at ＋3-＋4 mm. When d 〈 0, the drilling rate is mainly determined by laser-induced thrermal ablation and shielding of plasma. And when d 〉 0, the drilling rate is mainly determined by thermal ablation, shielding of plasma and promoting absorption induced by irradiation from the plasma at the beam waist.