Orbital Angular Momentum in Nanoplasmonic Vortices

In the past decade, optical orbital angular momentum (OAM) has entered the field of plasmonics in the form of surface-confined vortices, generating vast interest. Here we give an overview of the field, starting with the pioneering analytic and experimental investigations of plasmonic OAM. We describe the advances leading to the study of suboptical cycle dynamics in time-resolved experiments and the investigation of angular momentum light-matter interactions through the mixing of circularly polarized light with plasmonic vortices. We describe how additional degrees of freedom can be controlled with metasurfaces and other design techniques leading to the complete spatial and temporal modularization of surface-confined OAM. We review maturing applications of plasmonic vortices, such as plasmonic tweezers for the selective trapping and rotation of microparticles and broadband multiplexing of angular momentum light beams for high-capacity optical communications. The major advances in the field, from the first observation to complete modularization, position the controlled surface-confined OAM at the forefront of light-matter science.