The sound waves cause the bubble to expand and contract, with short flashes of light being emitted the instant the bubble reaches its minimum radius. Single-bubble sonoluminescence was first observed in 1989 by the author as part of his PhD research at the University of Mississippi (see, for example, Physics World May 1998).

Most of the interest in sonoluminescence has focused on explaining how the light is produced, but to some scientists the remarkable stability of the bubble has been just as fascinating. How can the bubble expand to a size of up to 50 microns and then collapse to a radius of less than a micron, all within 50 µs or so, without dissolving or disintegrating? Recent experiments by Jeffrey Ketterling and Robert Apfel of Yale University in the US seem to confirm that chemical reactions are responsible for the remarkable stability of the bubble (Phys. Rev. Lett. 1998 81 4991).

In the March issue of Physics World, Felipe Gaitan from the University of Mississippi, US describes the latest research into sonoluminescence.