In this study a single laser pulse spatially shaped into a ring is focusedinto a thin water layer, creating an annular cavitation bubble and cylindricalshock waves: an outer shock that diverges away from the excitation laser ringand an inner shock that focuses towards the center. A few nanoseconds after theconverging shock reaches the focus and diverges away from the center, a singlebubble nucleates at the center. The inner diverging shock then reaches thesurface of the annular laser-induced bubble and reflects at the boundary,initiating nucleation of a tertiary bubble cloud. In the present experiments,we have performed time-resolved imaging of shock propagation and bubble wallmotion. Our experimental observations of single-bubble cavitation and collapseand appearance of ring-shaped bubble clouds are consistent with our numericalsimulations that solve a one dimensional Euler equation in cylindricalcoordinates. The numerical results agree qualitatively with the experimentalobservations of the appearance and growth of dense ring-shaped bubble clouds atthe smallest laser excitation rings. Our technique of shock-driven bubblecavitation opens novel perspectives for the investigation of shock-inducedsingle-bubble or multi-bubble sonoluminescence phenomena in thin liquids.
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