Sonoluminescence produced by steady cavitation

Abstract

Sonoluminescence (SL) is generally attributed to the radiative recombination of hydroxyl free radicals produced by the high temperatures and pressures associated with cavitation bubble collapse. Therapeutic ultrasound systems are known to produce large numbers of free radicals in water and biological fluids and thus present a possible health risk. In an examination of light produced by acoustic standing wave configurations at various frequencies ranging from 20 kHz–1 MHz, steady light emissions have been observed from the cavitation field indicative of violent bubble pulsation rather than cavity collapse. In many cases, multiple flashes occur each cycle, always maintaining a fixed phase with respect to the driving acoustic pressure. This “steady” cavitation is attributed to violent bubble pulsation, and an explanation of this phenomenon will be attempted in terms of numerical studies of bubble dynamics. [Work supported in part by the ONR and the NIH.]