Analysis of the Shadow-Sausage Effect Caustic

We analyze the optical caustic produced by light refracted at the curved meniscus surrounding a cylindrical rod standing partially out of a liquid-filled container. When the rod is tilted from the vertical or when light is diagonally incident, the caustic is a fourcusped astroid with two of its cusps obscured by the rod ’s shadow. If a portion of the flat end of the rod is raised above the water level, the caustic evolves into a pattern of five interlocking cusps. The five cusps result from symmetry breaking of a threecusped surface perturbation caustic. [Optical Society of America ]