Sonoluminescence refers to the emission of light from bubbles suspended in water, when those bubbles are forced to vibrate by acoustic waves. This emission of light is fascinating because the energy required to produce the light suggests that the temperature inside the bubble exceeds 10,000 Celcius. Scientists are still debating the physics of Sonoluminescence. Although it is still not clear precisely what sequence of events creates the light, laboratory experiments have established several strong theories to explain this phenomenon.
The first known demonstration of sonoluminescence occurred in 1934 as an accidental by-product of a test involving underwater acoustic radar. Early experiments in sonoluminescence produced unpredictable results and the concept was not pursued for many years. In 1988, however, Professor Gaitan successfully produced a single, stable bubble that produced sonoluminescence as a result of acoustic resonance. Scientists still cannot explain why the sound is converted to light; however, scientists have developed standard scientific procedures for producing sonoluminescence. .
Those procedures involve trapping an air bubble in a flask by use of an acoustic standing wave that causes the flask to resonate at its natural frequency. For a 100mL flask, it would take around 25kHz of acoustic energy to cause the flask to resonate. Each flash from the bubble consists of approximately one million photons, which is a very small amount of light. As the poster accompanying this report illustrates, the standard theory explaining sonoluminescence is that the sounds waves applied to the flask and moving through the liquid to the bubble create a shock wave within the bubble. This shock wave compresses the bubble at a velocity of about Mach 1, causing the gas within the bubble to become so intensely hot that the gas ionizes. This ionization produces a plasma at a sufficient high temperature that the plasma emits light waves near ultra violet frequencies.
