Sonoluminescence - the phenomenon whereby air bubbles caught in a liquid emit a flash of light under the action of acoustic waves - has been described by scientists for a long time. But its mechanisms are still poorly understood.
David Flannigan and Kenneth Suslick, of the University of Illinois at Urbana Champaign, took another step in understanding the process by successfully creating a single bubble of argon in a solution of sulfuric acid. Under the action of sound waves at frequencies above 18000 cycles per second, the bubble first expanded before reaching its limits and then quickly collapsed. It is during this last step that we observe the emission of light. Thanks to their work, the two researchers managed to obtain a spectrum 3000 times brighter than previous experiments. This allowed them to make a more detailed analysis of the event. According to their measurements, the local temperature reached 15000 Kelvin, which is several times the temperature on the surface of the Sun. Most notable, however, was the detection of highly energetic ionized argon and oxygen atoms during the experiment.
A result that traditional chemical and thermal reactions are not sufficient to explain and that the authors of the research therefore attribute to the collision of atoms with electrons and ions of very high energies in the form of very hot plasma formed in the nucleus of the bubble. If these data were confirmed, they would constitute the first direct detection of a plasma associated with sonoluminescence.
NYT 15 / 03 / 04 (Tiny bubbles implode with
the heat of a star) http://www.nytimes.com/2005/03/15/science/15soni.html