Direct observation of period-doubled nonspherical states in single-bubble sonoluminescence.

We present direct observations of period doubling in the flash to flash pulse heights in single-bubble sonoluminescence. States involved are stable, spherically symmetry broken. Observations are made using seven detectors distributed in the equatorial plane of the bubble. Contrary to earlier experiments by Holt et al. [Phys. Rev. Lett. 72, 1376 (1994)], where period doubling was observed in the time intervals between flashes but not in the pulse heights, we observe period doubling in pulse heights, but no corresponding period doubling is seen in the time intervals. In parameter space the period doubling is observed below the n=2 shape instability boundary line where extinction is shown to take place.