Abstract:
Analytic solutions for a sonoluminescing gas bubble have been obtained, which provide density, pressure, and temperature distributions for the gas inside a bubble oscillating under the ultrasonic field. The solutions have revealed that sonoluminescence should occur just prior to the bubble collapse and its duration is less than 300 ps and that increase and subsequent decrease in the bubble wall acceleration induces the quenching of gas followed by the substantial temperature rise up to 100 000 K which can be regarded as a thermal spike. The gas temperature inside the bubble near collapse is determined primarily by the amount of radiation heat loss. Shock formation during the bubble collapse is questionable because gas density, as well as pressure at the bubble center, are much greater than those at the bubble wall during this stage. It also turns out that the number of electrons ionized, the ion species, and the kinetic energy of electrons affect the spectrum of light emission crucially. The spectral radiance calculated is in good agreement with the observed data qualitatively, which suggests that the origin of sonoluminescences is bremsstrahlung rather than thermal blackbody radiation. [Work supported by Korea Science and Engineering Foundation.]