Author: Greenland P. T.
Source: Contemporary Physics, Volume 40, Number 1, 1 January 1999 , pp. 11-30(20)
Publisher: Taylor and Francis Ltd
Abstract:Small bubbles driven by an acoustic field in water glow. The properties of the light they emit seem to suggest that it has a black body spectrum, with no features specific to the atomic properties of the gas within the bubble, and that it is emitted in short pulses. In this review I describe experiments which have been done to measure properties of the light emission and the dynamics of the bubble wall. I concentrate on bubbles which contain noble gases, and fit the experimental spectra to a black body spectrum. The fits are shown to be generally good, and correspond to temperatures ~ 25 000 K. I describe how a small bubble of noble gas can be expected to radiate at this temperature, and show that collisional excitation and pressure broadening can account for the observed spectrum, but that simple adiabatic compression of the gas tends to overestimate the source temperature, particularly for Ar and Xe. The significance of new experimental results on the pulse duration is stressed. I discuss theories of the collapse of the bubble, and describe calculations which show that non-uniform gas behaviour can be important. The sensitivity of the gas motion to the bubble collapse, and the ambiguities of the equations which describe the wall motion are discussed. I also give some details of an alternative theory based on quantum electrodynamics. Experiments on trapped helium are identified as the most simple, and a calculation based on the ideas described in this article is presented.
Document Type: Research article
Publication date: 1999-01-01