Sonoluminescence and phase diagrams of single bubbles at low dissolved air concentrations.

We studied experimentally the dependence of light emission and phase space boundaries of air bubbles in water on the level of degassing down to low partial pressures of 15 mmHg. We found that the maximum obtainable light intensity increased monotonically by lowering the concentration of dissolved air in water. We also present a new technique to obtain the acoustic pressure (P(a)) and ambient radius (R0) parameters, based on the information provided by the timing of the flashes in the acoustic cycle. Using this technique we give phase diagrams of the bubble in the (R0,P(a)) and (P(a), gas concentration) space, and discuss the parametric dependence of the light intensity. The resulting power-law dependence of the relative intensity normalized by the ambient volume of the bubble on the expansion ratio indicates that more extreme conditions are attainable inside a bubble at dissolved air concentration of 15 mmHg than at 150 mmHg.