Laser-Induced cavitation bubble interaction with Surface-Attached bubbles

• Laser-induced cavitation enables hydrogen bubble removal from surfaces. • Bubble removal extends to 2–3 times cavitation radius, exceeding prior observations. • Dual mechanism: shockwave induced disturbance followed by sustained flow fields. • Surface bubble density dominates in removal process over standoff distance effects. • Repetitive pulses progressively expand cleaned radius through cumulative effects. We study the interaction of laser-induced cavitation bubbles generated atop an electrode covered with hydrogen bubbles. The bubbles respond to the shock wave from laser-induced breakdown and the flow field of expanding and collapsing cavitation bubbles. High-speed imaging reveals that both the shock wave and subsequent flow contribute to bubble detachment and electrode clearance. Clearance occurs within an approximately circular area exceeding 3 times the maximum bubble radius, with partial clearance extending to 5 times this radius, which is considerably larger than reported for particulate or liquid contaminant removal. The initial shock wave propagates as a void fraction wave upon reaching the bubbles, producing radially propagating bubble disturbance with velocities ranging from 490 m/s at low bubble concentrations to 50 m/s at high concentrations. These speeds are within the range expected for linear waves in bubbly liquids according to Wood’s formula. Bubble removal persists for 10 ms, approximately 100 times longer than the cavitation bubble lifetime, which is attributed to long-lasting vortical flow generated by non-spherical cavitation bubble collapse. The findings may help to improve the removal of particulate contaminants as well as reducing ohmic loads in electrolyzers.