Catastrophe Atom Optics: Fold and Cusp Caustics in an Atom Laser.

Typically discussed in the context of optics, caustics are envelopes of classical trajectories (rays) where the density of states diverges, resulting in pronounced observable features such as bright points, curves, and extended networks of patterns. Despite the apparent complexity of such patterns, they are based on just a small number of fundamental forms described by the theory of catastrophe optics. Here, we demonstrate caustics in the matter waves of an atom laser, extending catastrophe optics to catastrophe atom optics. We showcase the generic forms of fold and cusp caustics, and exploit internal state manipulation to trace the flow of atoms. Atom optics affords new perspectives for fundamental science, metrology, atom interferometry and nano-fabrication techniques. Exploring the role of caustics in this context may lead to innovation as the generation of caustics is inherently robust, and leads to a variety of pronounced and sharply delineated features.