Toroidal vortices of light

Toroidal vortices, also known as vortex rings, are whirling, closed-loop disturbances that form a characteristic ring shape in liquids and gases and propagate in a direction that is perpendicular to the plane of the ring. They are well-studied structures and commonly found in various fluid and gas flow scenarios in nature, for example in the human heart, underwater air bubbles and volcanic eruptions(1-3). Here we report the experimental observation of a photonic toroidal vortex as a new solution to Maxwell's equations, generated by the use of conformal mapping(4-7). The resulting light field has a helical phase that twists around a closed loop, leading to an azimuthal local orbital angular momentum density. The preparation of such an intriguing state of light may offer insights for exploring the behaviour of toroidal vortices in other disciplines and find important applications in light-matter interactions, optical manipulation, photonic symmetry and topology, and quantum informations(8-17).

Automated summary

Toroidal vortices, also known as vortex rings, are closed-loop disturbances that form a ring shape and propagate perpendicular to the plane of the ring. A photonic toroidal vortex, generated using conformal mapping, was experimentally observed and offers new insights for exploring toroidal vortices in other disciplines and potential applications in light-matter interactions and optical manipulation.