Sonoluminescence, so to say, a wonderful natural phenomenon caused by bubbles suspended in a liquid, has kept scientists puzzled over the decades. However, the actual explanation of the phenomenon has not been given till now, though many theories exist. So, let's see what this interesting phenomenon holds.
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| Sonoluminescence |
Sonoluminescence, as the name suggests, refers to the emission of light by using sound energy or to say material waves which are used to implode a bubble suspended in a liquid, raising the temperature of the bubble high enough to produce light.
The inception of study of bubble dynamics dates back to early 20th century when Lord Rayleigh was employed by Royal Navy to explain degradation of ship propellers, the reason behind which was found out to be collapsing bubbles. However, sonoluminescence was first discovered(accidentally) at the University of Cologne, in the process of a work on SONAR, in 1934. Study of sonoluminescence got an impetus only in 1989, however, when Felipe Gaitan and Lawrence Crum succeeded in producing stable single bubble sonoluminescence(SBSL).
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| Studying Sonoluminescence |
Single bubble sonoluminescence(SBSL) is more easier to study than multi-bubble sonoluminescence(MBSL) as SBSL emits more light than any individual bubble in MBSL, also it is easier to study acoustic cavitation in SBSL as only a single bubble collapses. Many theories have been proposed to explain the photon-emission process in the phenomenon, which include Bremsstrahlung radiation, quantum explanations like Hawking radiations, nuclear reactions(due to elevated temperatures, initiating thermonuclear fusion), proton tunneling, corona discharges, molecular recombination etc.
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| Process of Sonoluminescence |
The inertia of cavitating bubble produces high temperatures and pressures, capable of ionizing a fraction of the gas. Recently it has been measured that temperatures reach as high as 20,000 K in SBSL, which is in favor of many of the above stated theories. However, more accurate measurements of the bubble properties are required to get a conclusion as to what is the actual reason behind photon-emission. The light flashes from the bubbles occurring for very short time(a few hundred picoseconds), and the extremely small size of the bubble( 1 micrometer in diameter) during photon emission adds up to the challenge in taking measurements, which are mainly taken on basis of models of bubble dynamics.
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| Pistol Shrimp |
Moreover, apart from the ideal laboratory conditions for sonoluminescence, it is interesting to note that biosonoluminescence is also observed in pistol shrimp. This is produced from a collapsing bubble caused by quickly snapping a specialized claw. The light produced is of low intensity, and wouldn't be detected by naked eye. Upon its discovery in 2001, it has been dubbed as shrimpoluminescence as it was the first instance when animals producing light using cavitating bubbles was discovered.
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