Acoustic pressure generated from laser-induced bubble collapse near an elastic membrane

In this study, the acoustic pressure signals are measured and analyzed to investigate the characteristics of the shock waves generated from a laser-induced bubble collapsing near an elastic membrane. A high-speed shadowgraph imaging system is utilized to visualize bubble evolution, and a needle probe hydrophone is employed to detect the accompanying acoustic transients. The influences of dimension distance, γ, on the acoustic pressure and the collapse shock wave energy are examined. In each case, two notable peaks are observed in the acoustic pressure profile, corresponding to the shock waves emitted at the optical breakdown of the laser pulse and at the first collapse of the bubble when it reaches its minimum volume. Asymmetrical collapse of the bubble can lead to the emission of multiple shock waves and a decreased in the pressure peak. Moreover, the normalized shock wave energy in our experiments varies between 2.61 % and 13.65 %, initially decreasing and then increasing with the decrease of dimensionless distance.