Abstract:
Attention is drawn to the fact that the very mechanism that traps a bubble in a standing acoustic wave causes it to execute an oscillatory translational motion in the direction of gravity. A bubble driven below resonance will move up during the collapse phase and down during the expansion phase. A bubble translating and collapsing develops a jet in the direction of motion. It is hypothesized that sonoluminescence is due to the collision of this jet with the other side of the bubble surface. The mechanism of light emission is a ``fracture'' process of the liquid that initially cannot respond by flowing due to the very short rise time of the applied pressure. The picosecond duration of the light flash is the time it takes for the microjet overpressure to be relieved by reflection from the microjet free surface. Several other observed features of sonoluminescence (such as noble gas and temperature sensitivity, anomalous mass loss process, effect of surfactants) can also be explained, at least qualitatively. [Work supported by the Office of Naval Research.]