Interaction between reflected shock waves and laser-induced cavitation bubbles.

This study experimentally investigates the interaction between acoustically reflected shock-wave echoes and laser-induced cavitation bubbles confined within cylindrical tubes. In these macroscopic experiments, the tube radius was systematically varied to control the timing and amplitude of reflected shocks relative to the bubble lifetime. Time-resolved high-speed imaging captured the bubble's expansion and collapse dynamics, revealing that early reflected echoes, returning within microseconds after the initial breakdown, strongly influence the collapse symmetry and morphology. Depending on their timing and intensity, these echoes compress the bubble along the tube axis, leading to prolate deformations and extended collapse durations. To complement these findings at the nanoscale, molecular dynamics (MD) simulations were performed to examine the interaction between plasma-induced shock waves and nanobubbles within cylindrical confinement. The simulations show that higher-energy pulses generate strong rebound shocks that induce prolate deformation and secondary growth-collapse cycles. Together, the experimental and atomistic results reveal a consistent physical mechanism across scales, where confinement-induced shock reflections modulated bubble dynamics through the timing and amplitude of early reflected waves. These findings provide new insight into echo-driven cavitation in confined geometries, with potential implications for ultrasonic cleaning, biomedical cavitation, and focused acoustic applications.