Twelve years of single bubble sonoluminescence: A review

Single bubble sonoluminescence occurs when an acoustically trapped and periodically driven gas bubble collapse so strongly that the energy focusing at collapse leads to light emission. Detailed experiments have demonstrated the unique properties of this system: the spectrum of the light emission tends to peak in the ultraviolet and depends strongly on the type of gas dissolved in the liquid; small amounts of trace noble gases or other impurities can dramatically change the amount of light emission; small changes in the operating parameters (forcing pressure, dissolved gas concentration, liquid temperature, etc.) can lead to large changes in the light emission. This talk reviews experimental and theoretical efforts for understanding this phenomenon. The present understanding is that the bubble is adiabatically heated at collapse, leading to partial ionization of the gas inside the bubble and eventually to thermal bremsstrahlung. After presenting a brief historical review of single bubble sonoluminescence, we describe the major areas of research: First, we describe the classical theory of bubble dynamics, as developed by Rayleigh, Plesset, Prosperetti and others. Then we summarize the research on the gas dynamics inside the bubble. Shock waves inside the bubble do not seem to play a prominent role in the process. Next we discuss the hydrodynamic and chemical stability of the bubble. Sonoluminescence requires that the bubble must be shape stable and diffusively stable which determines the parameter space where light emission occurs. A summary of experiments and models addressing the origin of the light emission follows. The final part of the talk presents an overview of what is known and unknown, and outlines some directions for future research.