Computed optical emissions from a sonoluminescing bubble

A sonoluminescing bubble has been modeled as a thermally conducting, partially ionized plasma. The model is more complete than previous models, due to the inclusion of both plasma and normal molecular thermal conduction, vapor pressure, surface tension, the mixing of gas and water vapor in the bubble, and opacities. The model accounts for most of the observed experimental trends, including (i) the asymmetric pulse shape; (ii) the temperature and driving pressure dependence of the pulse width and intensity; and (iii) spectral shapes, in particular, the 300-nm peak in the spectrum of xenon sonoluminescence, which to our knowledge has not been explained by any previous model; and (iv) a hydrodynamic explanation of why water is the ``friendliest'' liquid in which sonoluminescence occurs. The agreement between the calculations and the data, as well as the model's predictions of almost every experimental trend, suggest strongly that the spectral and temporal properties of the emissions of a sonoluminescing bubble are due to adiabatic- or shock-initiated thermal emission from a cool dense plasma.