Scientists were intrigued but found it was too difficult to study in detail the unwieldy mass of short-lived bubbles. In 1989, however, Lawrence Crum, then a professor at the University of Mississippi, and his graduate student, Felipe Gaitan, were able to induce sonoluminescence in a single bubble trapped within a sound field inside a cylinder of water. Since then, scientists have been able to study the phenomenon more closely. For example, the flash of light lasts an incredibly short time, a few tens of trillionths of a second. Also, the phenomenon is extremely sensitive to the nature, purity and temperature of the liquid and to the presence of dissolved gases in it.
Sound waves passing through the liquid cause the bubble to compress and expand repeatedly.
At its largest point, the bubble's diameter is about that of a human hair. Scientists believe the sound energy is concentrated during the bubble's compression phase, then is released as light near the point where its size is smallest. But the exact mechanism has remained a mystery. In his new paper, Prosperetti says it is unlikely that shock waves within the shrinking bubble trigger sonoluminescence because the bubble would need to maintain a near-perfect spherical shape. In a sound field, there is a very well-defined mechanism that will prevent this from happening.