同步双脉冲激光致声研究

利用高速摄像机拍摄了同步双脉冲激光聚焦击穿水介质产生激光空泡的运动过程。分析了该条件下产生的四种典型激光声信号特性，初步计算了光声能量转换效率。研究结果表明：通过调节脉冲激光的能量差，可以控制激光声信号峰值间隔，提高激光声信号脉宽；两空泡之间无量纲距离为1.5时，溃灭过程中出现融合现象，融合过程中空泡热力学能转化为机械能，融合后形成的单个空泡能量变大，其溃灭产生的激光声信号主频降低；同步双脉冲激光聚焦击穿情况下的光声能量转换效率为6%~10%。

Acoustic signals induced by synchronous double-pulse lasers

The movement process of bubbles produced by synchronous double-pulse lasers focusing into water and then breaking it down has been recorded by high-speed cameras. The characteristics of four typical laser-induced acoustic signals were analyzed, and opto-acoustic energy transferring efficiency was calculated. Experimental results show that intervals between peak values of laser-induced acoustic signals could be controlled through adjusting the energy difference of pulsed lasers, and that pulse width of laser-induced acoustic signals could be increased. When none dimensional distance between laser-induced bubbles is 1.5, the bubbles begin to fuse in the collapse process, through which the thermodynamic energy of bubbles converts into mechanical energy. The single bubble finally formed has more energy than any single bubble before fusing. The main frequency of laser-induced acoustic signals produced by collapsing of bubbles decreases. The opto-acoustic energy transferring efficiency is 6%-10%.