Among the various debated models of the state of plasma in a sonoluminescing (SL) bubble, a key parameter in question is the degree of opacity. Interaction between an SL plasma and a laser provides a direct experimental investigation of the opacity. We have achieved strong interaction between a nanosecond laser pulse and a 70 micron radius SL bubble in a liquid hammer tube. The overall response of the system results in a factor of 2 increase in temperature as determined by its spectrum. Images of the the interaction reveal that light energy is absorbed and trapped in a region smaller than the SL emitting region of the bubble facing the incoming laser. We interpret this lower bound measurement of opacity as demonstrating that SL bubbles can be over 1000 times more opaque than follows from Saha equation of statistical mechanics in the ideal limit. We conclude that the effects of strong Coulomb interactions are an essential component of a first principles theory of sonoluminescence.

Furthermore, we provide detailed measurements of evolving light emission from our liquid hammer bubbles which are highly reproducible. Analysis of SL evolution demonstrates that the light emission is greatly reduced by a jet introducing liquid particles in the bubble. Spectral analysis demonstrates that the absence of atomic lines from the dim spectra is due to suppression of excited atomic states in a dense plasma. Finally, we show that a comparison of the collapse radius to the emission radius from a blackbody fit is a good indicator of the blackbody fit validity.