Neat word, WW. I was wondering if the sono-- referred to sound, and I found:
An intense field of ultrasound in a fluid can trap a sub-millimeter radius gas bubble and make it emit light. This phenomenon is called sonoluminescence. The mechanisms that convert sound into light still remain unexplained despite many various theoretical approaches. A gas bubble is created into a flask filled with fluid. For example degassed, purified water and air are an excellent pair for the phenomenon. A coherent beam of ultrasound makes the bubble cavitate, i.e. to expand and compress in phase with the sound wave. Typical frequency for the sound wave is 25 kHz. While violently imploding in each cycle, the bubble emits light quanta.
Worth going to the site, imo, to see the figures illustrating Motion of the sonoluminescence bubble as a function of time. Notice the supersonic velocity of the radius at the time of imploding.
http://focus.hut.fi/annrep/1996/node33.html