Sonoluminescence

Sonoluminescence is the emission of short bursts of light from imploding bubbles in a liquid when excited by sound.

The sonoluminescence effect was first discovered at the University of Cologne in 1934 as a result of work on sonar.H. Frenzel and H. Schultes put an ultrasound transducer in a tank of photographic developer fluid. They hoped to speed up the development process. Instead, they noticed tiny dots on the film after developing and realized that the bubbles in the fluid were emitting light with the ultrasound turned on. It was too difficult to analyze the effect in early experiments because of the complex environment of a large number of short-lived bubbles. (This experiment is also ascribed to N. Marinesco and J. J. Trillat in 1933, which also credits them with independent discovery). This phenomenon is now referred to as multi-bubble sonoluminescence (MBSL).

In 1960 Dr. Peter Jarman from Imperial College of London proposed the most reliable theory of SL phenomenon. The collapsing bubble generates an imploding shock wave that compresses and heats the gas at the center of the bubble to extremely high temperature.

In 1989 an experimental advance was introduced by D. Felipe Gaitan and Lawrence Crum, who produced stable single-bubble sonoluminescence (SBSL). In SBSL, a single bubble trapped in an acoustic standing wave emits a pulse of light with each compression of the bubble within the standing wave. This technique allowed a more systematic study of the phenomenon, because it isolated the complex effects into one stable, predictable bubble. It was realized that the temperature inside the bubble was hot enough to melt steel. Interest in sonoluminescence was renewed when an inner temperature of such a bubble well above one million kelvins was postulated. This temperature is thus far not conclusively proven; rather, recent experiments conducted by the University of Illinois at Urbana–Champaign indicate temperatures around 20,000 K (19,700 °C; 35,500 °F).

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