Measurement of pressure and density inside a single sonoluminescing bubble

The average pressure inside a sonoluminescing bubble in sulfuric acid has been determined by two independent techniques: (1) plasma diagnostics applied to Ar atom emission lines, and (2) light scattering measurements of bubble radius vs time. For dimly luminescing bubbles, both methods yield intracavity pressures ∼1500 bar. Upon stronger acoustic driving of the bubble, the sonoluminescence intensity increases 10000-fold, spectral lines are no longer resolved, and radius vs time measurements yield internal pressures >3700 bar. Implications for a hot inner core are discussed.