Influence of different interfaces on laser propulsion in water environment

The dynamics of laser-induced semispherical cavitation bubbles are investigated by means of an optical beam deflection method. The bubbles were generated in water in the vicinity of three different interfaces: including water–air, water–colloid and water–solid, and also in the bulk. Numerical simulation shows that the propelled surface obtains more energy and longer propulsion from the semispherical bubble than from the spherical bubble during the first expansion of the bubble. The collapse time of the quasi-semispherical bubble is significantly less than the Rayleigh collapse time of the spherical bubble for all the cases considered in this work. The influence of water–air or water–solid interfaces on the collapse time of a semispherical bubble is similar to that of a spherical bubble. As the bubble energy grows, the effect of the water–colloid interface changes gradually from that of the water–solid to that of the water–air interface. In other words, the energy of the bubble dictates whether the water–colloid interface behaves as a water–solid or a water–air interface.