We study the dynamics of laser-induced cavitation bubbles near the free surface of a viscoplastic fluid. Using controlled experiments, we examine how stand-off distance and fluid rheology govern the formation and evolution of cavitation bubbles. Our observations reveal four distinct regimes: swelling, trapped, bullet jet, and vapor jet. When the bubble is generated very close to the free surface, it remains anchored, producing gentle surface deformations. At intermediate distances, the competition between inertial and yield stress forces causes bubbles to either become trapped near the surface, producing confined jets, or alternatively give rise to more forceful bullet-like penetrations. At larger distances from the free surface, rapid bubble collapse produces intense vapor jets that pierce the fluid. To interpret these phenomena, we propose a simplified force-balance model that successfully captures the penetration dynamics in the trapped and bullet jet regimes, in close agreement with experimental observations. These insights contribute to a deeper understanding of cavitation processes, with potential applications ranging from drug delivery and biomedical therapies to advanced material processing.
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