Dynamics of a Laser-induced Bubble Near a Convex Free Surface*

This paper experimentally documents the behavior of a laser-induced bubble near a convex paraboloidal free surface with different vertical radius of curvatures, generated in a rotating cylindrical water flask. Due to the strong influence of the free surface, the bubble forms a microjet outwards the free surface when it collapses. And the nondimensional bubble collapse time, T_c/T_c’, is smaller than 1, where T_c is the bubble collapse time and T_c’ is the Rayleigh time of bubble collapse with an equivalent maximum radius. As the relative distance between the bubble center and the free surface, h/R_max, decreases, T_c/T_c’ decreases, which is different with the bubble behavior near a flat rigid boundary, where h is the distance between the bubble center and the flat free surface or the convex free surface center, R_max is bubble equivalent maximum radius. Meanwhile the convex free surface provides a focusing mechanism to the splash on the free surface when bubble collapses. The splash gets a higher velocity when r_s/R_max decreases.