Sound and light

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Science  30 May 1997:
Vol. 276, Issue 5317, pp. 1309
DOI: 10.1126/science.276.5317.1309d

Gas bubbles in water, when hit by ultrasonic waves, can produce bright flashes of visible and ultraviolet light, an effect called sonoluminescence (SL). Such experiments have not been simple to understand and have spawned numerous theories. Moss et al. (p. 1398; see the Perspective by Crum and Matula, p. 1348) present a model of bubbles undergoing SL that can account for its chemical specificity (the bubbles need to contain some noble gas) and the lack of afterglow from these picosecond light pulses. The collapsing bubble produces a shock wave that creates a thermally conducting, partially ionized plasma of ions and electrons. Electrons produce the SL flash, and changes in transparency of the plasma limit the pulse duration. The dynamics are sensitive to bubble size, which could explain the variability of experimental results.

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