For nearly 60 years following its 1933 discovery, sonoluminescence (SL)—the conversion of acoustic energy into optical energy by way of bubble cavitation—was exclusively a multibubble phenomenon. In a liquid subjected to a sufficiently intense ultrasound field, rarefaction would cause micron-sized gas bubbles to form and expand, then compression would cause them to collapse into a shimmering cloud of light. (See the articles in PHYSICS TODAY by Lawrence Crum, September 1994, page 22, and by Detlef Lohse, February 2003, page 36.) The bursts of light are a consequence of adiabatic compression, which heats the bubbles to temperatures approaching 5000 K—sufficient to dissociate molecules and excite bound electrons.
In 1990, Lawrence Crum and Felipe Gaitan (then at the University of Mississippi) generated SL in a lone, acoustically levitated bubble. In single-bubble SL, one bubble can survive millions of acoustic cycles, emitting a burst of light each time it nears maximum...
