Abstract

The optical glory, which is related to a weak focusing of backscattered light, is known to exist for spherical bubbles.¹ This caustic, however, is affected by small deviations from sphericity. Hydrodynamics causes freely rising air bubbles in pure water to become slightly spheroidal if the bubble diameter ≳ 250 μm. We modeled and photographed the near backward scattering from slightly spheroidal horizontally illuminated bubbles. Spherical bubbles produce backward-directed glory wavefronts having the local shape of a circular torus. Our model introduces the leading perturbation of those wavefronts resulting from a small deviation from sphericity. The cross-polarized scattering from a sphere¹ has a fourfold symmetric sin²2φ azimuthal dependence where φ denotes the azimuthal angle. For the spheroids, both the model and the observation give a twofold symmetric pattern. Detailed features of the modeled patterns are confirmed by the observations. This gives a specific example of broken symmetry resulting in an unfolding of a caustic which would otherwise have an infinite codimension.²

© 1986 Optical Society of America