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Sonoluminescence is a little-understood phenomenon whereby light is emitted by tiny bubbles suspended in a liquid subjected to intense acoustic fields. The aim of this work was to construct apparatus to enable the observation of single-bubble sonoluminescence, to investigate its basic properties, and leave a kit and instructions to form the basis of a future final-year undergraduate experiment. It was found that despite the apparent simplicity of the setup, to obtain successful and repeatable sonoluminescence required great care in the selection and tuning of system components, and a good degree of patience. The precision and stability of the signal generator was found to be particularly critical, and (if not building your own as I did) a modern digital piece of instrumentation is highly recommended. The widely-reported increase in bubble brightness at low temperatures was readily confirmed, and a simple Mie scattering arrangement configured to monitor the bubble size gave results consistent with those already published.
Sonoluminescence was first observed in an ultrasonic water bath in 1934 by H. Frenzel and H. Schultes at the University of Cologne, an indirect result of wartime research in marine acoustic radar. This early work involved very strong ultrasonic fields and yielded clouds of unpredictable and non-synchronous flashing bubbles, now termed “multi-bubble sonoluminescence”. Such a chaotic phenomenon did not lend itself to detailed scientific investigation. Study of sonoluminescence then made little progress until 1988, when D. Felipe Gaitan succeeded in trapping a stable sonoluminescing bubble at the centre of a flask energised at its acoustic resonance – single-bubble sonoluminescence (SBSL). However their interest soon waned, and the research was subsequently taken up by Dr S. Putterman et. al., at UCLA, California.
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