ANALYSIS OF RAYLEIGH-PLESSET DYNAMICS FOR SONOLUMINESCING BUBBLES

Recent work on single-bubble sonoluminescence (SBSL) has shown that ma ny features of this phenomenon, especially the dependence of SBSL inte nsity and stability on experimental parameters, can be explained withi n a hydrodynamic approach. More specifically, many important propertie s can be derived from an analysis of bubble wall dynamics. This dynami cs is conveniently described by the Rayleigh-Plesset (RP) equation. He re we derive analytical approximations for RP dynamics and subsequent analytical laws for parameter dependences. These results include (i) a n expression for the onset threshold of SL, (ii) an analytical explana tion of the transition from diffusively unstable to stable equilibria for the bubble ambient radius (unstable and stable sonoluminescence), and (iii) a detailed understanding of the resonance structure of the R P equation. It is found that the threshold for SL emission is shifted to larger bubble radii and larger driving pressures if surface tension is increased, whereas even a considerable change in liquid viscosity leaves this threshold virtually unaltered. As an enhanced viscosity st abilizes the bubbles to surface oscillations, we conclude that the ide al liquid for violently collapsing, surface-stable SL bubbles should h ave small surface tension and large viscosity, although too large visc osity (eta(l) greater than or similar to 40 eta(water)) will again pre clude collapses.