Sonoluminescence

Small bubbles driven by an acoustic field in water glow. The properties of the light they emit seen? to suggest that it has a black body spectrum, wit h no features specific to the atomic properties of the gas within? the bubb le, and that it is emitted in short pulses. In this review: I describe expe riments which have been none to measure properties of the light emission an d the dynamics of the bubble wall. I concentrate on bubbles which contain n oble gases, and fit the experiments specific to a black body spectrum . Tes ts are shown to be generally good, and correspond to temperatures similar t o 25 000 K. I describe how a small bubble of noble gas can be expected to r adiate at this temperature, and shell that collisional excitation and press ure broadening can account for the observed spectrum, but that simple adiab atic compression of the gas tends to overestimate the source temperature, p articularlly 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 behaviou r can be important. The sensitivity of the gas motion to the bubble collaps e, and the ambiguities of the equations which describe the wall motion are discussed. I also give some details of an alternative theory based oil quan tum electrodynamics. Experiments on trapped helium ale identified as the mo st sample, and a calculation based on the ideas described in this article i s presented.