Experimental observations of bubble response and light intensity near the threshold for single bubble...

Single bubble sonoluminescence in an air-water system has been shown to occur along a unique surface in the acoustic pressure-ambient radius-gas concentration parameter space where the bubble is stable both in shape and in (average) size. In this paper, we show how the bubble deviates from the expected path (traced by the shape-instability threshold as a function of pressure) in order to reach the observed stability. We also present measurements of the expansion ratio (R(max)/R(0)) for bubbles near the threshold for light emission. The results suggest that maximal bubble radial response is an insufficient criterion for the onset of light emission, and we present data for the dependence of the emitted light on several parameters.