Abstract:
The origin of sonoluminescence, the conversion of acoustic energy into ultraviolet/visible radiation in liquids, has remained elusive. It is proposed that the emission arises from electrons confined to voids in the hot, dense fluid formed during the final stages of bubble collapse. Such electrons are produced by high-temperature ionization of the bubble constituents. A hard sphere-based model was developed for the fluid structure, thermodynamics, and confined electron emission. The model is consistent with the observed spectral distributions, power output, and time scale associated with emission from single cavitating rare gas bubbles. Effective temperatures during emission in the 200- to 700-nm spectral window are predicted to range from 20 000 to 60 000 K. The consistency of the confined electron model for single bubble sonoluminescence with the observed dynamics of bubble collapse is also explored. The key aspect of this approach is the treatment of the collapsed bubble as a true fluid. The hydrodynamics of bubble collapse are modeled with a modified Rayleigh--Plesset equation using improved formulations for the equation of state and specific heat ratio. Results are presented for the rare gases and related to experimental observations.