Demonstration of fold and cusp caustics with a quasi-continuous atom laser

The invention of the laser revolutionized modern scientific methods, creating a versatile tool used for a variety of applications. The demonstration of the "atom laser" two decades ago further established tabletop ultracold atomic systems as exceptional playgrounds for building quantum analog systems. In our experiment, we investigate the intriguing dynamics of a quasi-continuous atom laser when a repulsive or attractive potential is positioned into the coherent atom stream. From this, we observe sharply delineated features, as well as clear indications of fold and cusp caustics, that are strongly dependent on the shape, strength, and sign of the potential. This direct observation of caustics in terms of atomic matter waves opens up the field of "catastrophe atom-optics" where multiple potentials can be introduced to generate intricate patterns and potentially higher-order caustic effects.