Dynamics of laser-induced cavitation bubbles near an elastic boundary

The interaction of a laser-induced cavitation bubble with an elastic bounda ry and its dependence on the distance between bubble and boundary are inves tigated experimentally. The elastic boundary consists of a transparent poly acrylamide (PAA) gel with 80% water concentration with elastic modulus E = 0.25 MPa. At this E-value, the deformation and rebound of the boundary is v ery pronounced providing particularly interesting features of bubble dynami cs. It is shown by means of highspeed photography with up to 5 million fram es s(-1) that bubble splitting, formation of liquid jets away from and towa rds the boundary, and jet-like ejection of the boundary material into the L iquid are the main features of this interaction. The maximum liquid jet vel ocity measured was 960m s(-1). Such high-velocity jets penetrate the elasti c boundary even through a water layer of 0.35 mm thickness. The jetting beh aviour arises from the interaction between the counteracting forces induced by the rebound of the elastic boundary and the Bjerknes attraction force t owards the boundary. General principles of the formation of annular and axi al jets are discussed which allow the interpretation of the complex dynamic s. The concept of the Kelvin impulse is examined with regard to bubble migr ation and jet formation. The results are discussed with respect to cavitati on erosion: collateral damage in laser surgery, and cavitation-mediated enh ancement of pulsed laser ablation of tissue.