Experimental investigation on multiple breakdown in water induced by focused nanosecond laser.

Multiple breakdowns in liquids still remains obscure for its complex, non-equilibrium and transient dynamic process. We introduced three methods, namely, plasma imaging, light-scattering technique, and acoustic detection, to measure the multiple breakdown in water induced by focused nanosecond laser pulses simultaneously. Our results showed that linear dependence existed among the cavitation-bubble lifetime, the far-field peak pressure of the initial shock wave, and the corresponding plasma volume. Such a relationship can be used to evaluate the ideal size and energy of each bubble during multiple breakdown. The major bubble lifetime was hardly affected by the inevitable coalescence of cavitation bubbles, thereby confirming the availability of light-scattering technique on the estimation of bubble size during multiple breakdown. Whereas, the strength of collapse-shock-wave and the subsequent rebound of bubbles was strongly influenced, i.e., the occurrence of multiple breakdown suppressed the cavitation-bubble energy being converted into collapse-shock-wave energy but enhanced conversion into rebound-bubble energy. This study is a valuable contribution to research on the rapid mixing of microfluidics, damage control of microsurgery, and photoacoustic applications.