Optical glory of small freely rising gas bubbles in water: observed and computed cross-polarized backscattering patterns

Light scattered from spherical bubbles in water manifests an enhancement in the backward direction analogous to the well-known optical glory of a drop. Unlike the glory for water drops, in which the rays travel partially on the drop's surface, the glory for bubbles is due to rays that are refracted and multiply reflected within the scatterer and is an example of a transmitted wave glory. Photographs of glory scattering for freely rising air bubbles in water are displayed for bubbles having diameters of less than 300 ym. A physical-optics model for backscattering is developed for spherical bubbles. Computed glory patterns from both Mie-series calculations and the physicaloptics model agree with the observed patterns. The patterns of freely rising air bubbles having a diameter of S300 ,am are essentially those predicted for a spherical scatterer. The interference of different classes of glory rays is more clearly seen for bubbles in water than for the previously studied case of bubbles in oil.