A simple explanation of light emission in sonoluminescence

Ultrasonically driven gas bubbles in liquids can emit intense bursts of light when they collapse. The physical mechanism for single-bubble sonoluminescence has been much debated. The conditions required for, and generated by, bubble collapse can be deduced within the framework of a hydrodynamic (Rayleigh-Plesset) analysis of bubble dynamics and stability, and by considering the dissociation and outward diffusion of gases under the extreme conditions induced by collapse. We show here that by extending this hydrodynamic/chemical picture in a simple way, the light emission can be explained too. The additional elements that we add are a model for the volume dependence of the bubble's temperature and allowance for the small emissivity of a weakly ionized gas. Despite its simplicity, our approach can account quantitatively for the observed parameter dependences of the light intensity and pulse width, as well as for the spectral shape and wavelength independence of the pulses.