Sonoluminescence flashes can have a dipole shape

17 Jun 2002

Sonoluminescence (SL) is a process in which sound waves strike a tiny gas bubble, trapped in a liquid, causing the bubble to oscillate and emit picosecond pulses of light. An experiment at UCLA by Seth Putterman and his colleagues shows now that the SL light emission pattern can have a dipole shape. This implies that the collapse of the bubble is not spherically symmetric. Furthermore, the dipole pattern can persist for a period equivalent to 100 bubble cycles.

Scientists at MIT and the University of Marburg (Germany) have put forward a theory which addresses the new data. Michael Brenner and his collaborators assert that the large energy focusing of the SL process can be explained as the storage of acoustic energy over many oscillations (and not just one bubble cycle as in the standard shock theory of SL). In a paper in an upcoming issue of the Physical Review of Letters, the researchers posit the bubble is a storage tank, patiently soaking up acoustic energy before re-emitting the energy in the form of sharp light pulses. This model, the MIT researchers say, accounts for the persistence of the dipole pattern in the UCLA observations, and points to the possibility that successive light flashes may not be independent but actually correlated in some way.