The Acoustic Pressure Generated by the Non-Spherical Collapse of Laser-Induced Cavitation Bubbles Near a Rigid Boundary

In this paper we study the acoustic transients emitted during the collapse of a laser-induced cavitation bubble. A 150MHz bandwidth fiber optic probe hydrophone, resolves complex signals produced during the non-spherical collapse of the bubble near a rigid boundary. Simultaneous high-speed video recording up to 200,000 frames/s are correlated with the hydrophone trace. Additionally, we employ an intensified CCD-camera to record snapshots of the shock waves. The acoustic signal contains several pressure peaks with rise times as fast as 18 ns; they correspond to shock waves emitted as the bubble is reaching its minimum volume. For a limited range of standoff parameter values, 1.8 ≤ γ ≤ 5.0, the strength and time of emission of the first and the second emitted shock waves are related. The maximum radii of the bubbles tested are between 560 μm and 760 μm. We obtain peak pressures of up to 1 kBar during the collapse phase for the bubbles collapsing closes to the boundary.