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Kidney stones are a common and painful affliction, but fortunately physics offers some relief: Sound can be used to break up the stones, without invasive surgery. Efficacy of this ``lithotripsy'' treatment, however, depends strongly on cavitation, which can both attenuate the sound waves and provoke significant tissue damage. In this collaboration between a physicist, engineers, and materials scientists, our understanding of this process is advanced through measurements and modeling, providing insight into the relations between bubble dynamics and lithotripsy effectiveness.

The interaction of a lithotripter shock wave (LSW) with laser-generated single vapor bubbles in water is investigated using high-speed photography and pressure measurement via a fiber-optic probe hydrophone. The interaction leads to nonspherical collapse of the bubble with secondary shock wave emission and microjet formation along the LSW propagation direction. The maximum pressure amplification is produced during the collapse phase of the bubble oscillation when the compressive pulse duration of the LSW matches with the forced collapse time of the bubble.