Abstract:
Now that the exciting measurements of picosecond flash widths, clocklike emission, broadband ultraviolet light, and the role of noble gas doping have generated substantial interest and theories for sonoluminescence, it is time to take a more sober look at the experimental difficulties that stand in the way of the next round of insights. Parameters which control the steady-state motion of the bubble have not yet been elucidated. For instance, measurements of the dipole component of the sonoluminescence (SL) indicate that the bubble collapse can choose states with different ellipticity. Hydrogenic bubbles glow for periods ranging from 30 s to 5 min and are very sensitive to as yet unknown impurities. Tiny amounts of organic impurities dramatically alter the light emission. There is also concern that impurities may partly account for the different spectra observed in light and heavy water. Precise temperature control can be essential to prevent the bubble from hopping between different stable states. [Work supported by the NSF.] [sup a)]Current address: UC, Santa Barbara, CA.