Sonoluminescence: the star in a jar

The curious phenomenon of sonoluminescence has puzzled theorists and experimentalists alike. Seth Putterman explains how the rapid pulsations of a gas-filled bubble can transform sound into light.

Sound into light

The acoustics lab at the University of California in Los Angeles has seen a dramatic change in the past eight years. The transducers, microphones and amplifiers that are normally used for studying sound have now been joined by spectrometers, femtosecond lasers, the fastest oscilloscopes and photomultiplier tubes, as well as the most accurate time-interval meters. Equally important, but of a lesser technology, there is also equipment to purify water, and manifolds to prepare and control the gas content of fluids.

The phenomenon that demands this unusual confluence of equipment is sonoluminescence: the transformation of sound into light by the extraordinarily nonlinear pulsations of a gas bubble trapped in a fluid. Although sonoluminescence can be produced with equipment costing a couple of hundred dollars and can be detected by the eye for free, its measurement requires a set-up costing hundreds of thousands of dollars.

In this month's Physics World magazine (information), Seth Putterman of the Physics Department, University of California, Los Angeles, reports on sonoluminescence.