Bubble Shape Oscillations and the Onset of Sonoluminescence

An air bubble trapped in water by an oscillating acoustic field undergoes either spherical or nonspherical pulsations depending on the strength of the forcing pressure. Two different instability mechanisms (the Rayleigh-Taylor instability and parametric instability) cause deviations from sphericity. Distinguishing these mechanisms allows an explanation of many features of recent experiments on single bubble sonoluminescence, and suggests methods for finding sonoluminescence in different parameter regimes.