ASA 124th Meeting New Orleans 1992 October

5pPA10. E[sub 6] diffraction catastrophe in light scattered near the rainbow region of an acoustically levitated spheroidal water drop.

Gregory Kaduchak

Philip L. Marston

Dept. of Phys., Washington State Univ., Pullman, WA 99164-2814

Light scattering by oblate acoustically levitated drops of water gives a method of exploring a variety of weak foci known as diffraction catastrophes. The present research concerns laser light observations of a formerly unidentified caustic exhibited by white light scattering of a highly oblate drop [H. J. Simpson and P. L. Marston, Appl. Opt. 30, 3468--3473 (1991), plate 16]. The scattering pattern exhibits a rich structure that changes rapidly over a narrow range of drop aspect ratio D/H. The caustic patterns are those predicted of an E[sub 6] catastrophe in the range of D/H explored [J. F. Nye, Proc. R. Soc. London (accepted for publication)]. The focal section of the E[sub 6] is observed though the E[sub 6] has a control space of five dimensions while the experiment explores only three dimensions. The observations illustrate how special symmetrics and geometries can constrain the caustics produced in far-field scattering from a penetrable spheroid. [Work support by ONR.]