Kaduchak G, Marston P L
Appl Opt. 1994 Jul 20;33(21):4697-701. doi: 10.1364/AO.33.004697.
Previous observations of oblate drops of water illuminated perpendicular to their axis of symmetry exhibit catastrophe patterns near the primary-rainbow scattering angle [see, e.g., Appl. Opt. 30, 3468 (1991). The present research concerns observation of diffraction catastrophes near the secondary-rainbow scattering angle under similar experimental conditions. Illumination with laser light exhibits similar caustic structures in the secondary rainbow including the hyperbolic umbilic focal section and the E(6) or symbolic umbilic focal section. The range of drop aspect ratios explored includes aspect ratios as small as those found for freely falling drops in air as well as highly flattened drops. The new features of the secondary rainbow occur for highly flattened drops.
先前对垂直于其对称轴照明的扁球形水滴的观察表明，在主虹散射角附近会出现突变图案[例如，见《应用光学》30, 3468 (1991年)]。本研究关注在类似实验条件下二次虹散射角附近衍射突变的观察。用激光照明在二次虹中呈现出类似的焦散结构，包括双曲脐焦点截面和E(6)或符号脐焦点截面。所探索的水滴纵横比范围包括与空气中自由下落水滴一样小的纵横比以及高度扁平的水滴。二次虹的新特征出现在高度扁平的水滴中。
