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%.