The trillionfold concentration of sound energy by a trapped gas bubble
, so as to emit picosecond flashes of ultraviolet light, is found to b
e extremely sensitive to doping with a noble gas. Increasing the noble
gas content of a nitrogen bubble to about 1% dramatically stabilizes
the bubble motion and increases the light emission by over an order of
magnitude to a value that exceeds the sonoluminescence of either gas
alone. The spectrum also strongly depends on the nature of the gas ins
ide the bubble: Xenon yields a spectral peak at about 300 nanometers,
whereas the helium spectrum is so strongly ultraviolet that its peak i
s obscured by the cutoff of water.