Supernumerary spacing of rainbows produced by an elliptical-cross-section cylinder. II. Experiment

We measured the supernumerary spacing parameter of the first- and second-or der rainbows of two glass rods, each having an approximately elliptical cro ss section, as a function of the rod's rotation angle. We attribute large f luctuations in the supernumerary spacing parameter to small local inhomogen eities in the rod's refractive index. The low-pass filtered first-order rai nbow experimental data agree with the prediction of ray-tracing-wave-front modeling to within a few percent, and the second-order rainbow data exhibit additional effects that are due to rod nonellipticity. (C) 2001 Optical So ciety of America.