Supersonic needle-jet generation with single cavitation bubbles

Collapsing cavitation bubbles produce intense microscopic flows. Here, in an aqueous environment, we seed single laser-induced bubbles (diameter about one millimeter) in proximity to a solid surface, in a regime that has not been well explored before in order to generate a "needle jet." The needle jet propagates at supersonic speed through the gas phase toward the solid. It reaches average velocities of more than 850 m s - 1 and thus is an order of magnitude faster than the regular jets that have frequently been observed in cavitation bubbles. The dynamics leading to the needle jet formation are studied with high speed imaging at five million frames per second with femtosecond illumination. This highly repeatable, localized flow phenomenon may be exploited for injection purposes or material processing, and it is expected to generate significantly larger water hammer pressures and may also play a role in cavitation erosion and peening.