Generalized rainbows of oblate water drops in air recorded using a TinyLev ultrasonic levitator

The generalized rainbow caustics in the scattering of laser light by acoustically levitated oblate water drops in air [Marston and Trinh, Nature 312, 529-531 (1984)] display relationships between optical wavefields and the shape of wavefronts. The shape of the scattered optical wavefront depends on the drop shape controlled by the levitator. The present investigation demonstrates that an alternative array-based ultrasonic levitator design known as "TinyLev" can be used to trap drops for the purpose of recording generalized rainbows. The hyperbolic umbilic focal section was viewed. The TinyLev combined with CCD-based imaging may make investigations of generalized rainbows more accessible.