A model is proposed to compute the salient optical caustic partitions occurring in the primary rainbow for oblate spheroidal drops. By computing the boundary limits of outgoing rays, the optical caustic structures (termed rainbow and hyperbolic umbilic fringes) for tilted drops are calculated and compared with those for aligned (untilted) drops. The curvature of the rainbow fringe and the shifts of cusp caustics are discussed as well. The observed properties of the caustics can potentially be used for drop measurements. The model could also be applied to compute the optical caustics for drops with arbitrary shape, arbitrary orientation, and shaped beam illumination.

中文翻译：

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用于根据倾斜的球状滴剂计算主彩虹的光学苛性分区的模型

提出了一个模型来计算在主要彩虹中出现的用于扁球形球滴的显着光学苛性分区。通过计算出射光线的边界限制，可以计算出倾斜液滴的光学腐蚀性结构（称为彩虹和双曲线脐带），并将其与对准（未倾斜）液滴的光学腐蚀结构进行比较。还讨论了彩虹条纹的曲率和尖顶苛性碱的偏移。所观察到的苛性碱性质可潜在地用于液滴测量。该模型还可以用于计算具有任意形状，任意方向和成形光束照明的墨滴的光学焦散。