The damage potential of near-wall shock waves from cavitation bubbles investigated via total internal reflection fluorescence imaging.

This study establishes total internal reflection fluorescence (TIRF) imaging as a diagnostic method for investigating shock waves generated by collapsing laser-induced cavitation bubbles near a solid-liquid interface. TIRF was combined with synchronized short-pulse transillumination to capture both near-wall shock signatures and conventional bubble dynamics. A temperature-compensating Rhodamine 6G/Rhodamine B mixture made fluorescence variations primarily sensitive to density- and refractive-index changes. By tuning the laser incidence angle relative to the critical angle, the evanescent-field depth and density sensitivity were controlled, enabling robust detection of shock-wave footprints at the wall. Bubbles of 1-1.5 mm radius at moderate stand-off distances γ=1.0-1.6 were examined. The second collapse consistently produced the strongest shock activity, and the shock-originating event was observed to lead to microcrack formation. During the second collapse, the shock velocities of 1490-1971 m/s corresponded to peak pressures of 5-464 MPa. To our knowledge, this is the first fluid-dynamic measurement to provide physically reasonable pressure estimates for the second-collapse cavitation shocks at moderate stand-off distances, showing that the damage-producing shocks can reach or exceed the yield strength of technically relevant steels.