Self-consistent coupling of cavitation bubbles in aqueous systems

The dynamics of an ensemble of cavitation voids initiated by laser-produced stress waves in aqueous systems is considered. Aqueous systems have large similarity to soft tissues. Laser-initiated stress waves are reflected from tissue boundaries, thereby inducing a tensile stress that is responsible for tissue damage. The early stage of damage is represented by an ensemble of voids or bubbles that nucleate and grow around impurities under stress wave tension. For impurity densities larger than 105 cm−3 the bubbles growth reduces the tensile wave component and causes the pressure to oscillate between tension and compression. For impurity densities below 108 cm−3 the bubbles grow on a long time scale (∼10 μs) relative to the wave interaction time (∼100 ns). For bubble densities above 108 cm−3 the bubble lifetime is greatly shortened because of the reduced tensile component. On a long time scale the growing bubbles cause a significant reduction in the liquid average compression pressure below the ambient atmospheric pressure. This effect increases the bubble lifetime by almost a factor of 2 relative to the low impurity density case when the bubbles are growing independently, in agreement with experiment [Paltauf and Schmidt-Kloiber, Appl. Phys. A: Mater. Sci. Process. 62, 303 (1996)]. As the collapse stage starts, small bubbles collapse first and the compression pressure screening becomes less effective, thereby accelerating the collapse of the larger bubbles and reducing the spread of the bubble lifetimes.