Orbital angular momentum 25 years on [Invited]

TLDR

Orbital angular momentum of light, once thought rare and limited to high‑order atomic transitions, is now known to be carried by every photon in a laser beam, enabling new optical effects and applications such as manipulation, imaging, quantum optics, and communications. This review surveys current research on orbital angular momentum and discusses potential future directions.

Abstract

Twenty-five years ago Allen, Beijersbergen, Spreeuw, and Woerdman published their seminal paper establishing that light beams with helical phase-fronts carried an orbital angular momentum. Previously orbital angular momentum had been associated only with high-order atomic/molecular transitions and hence considered to be a rare occurrence. The realization that every photon in a laser beam could carry an orbital angular momentum that was in excess of the angular momentum associated with photon spin has led both to new understandings of optical effects and various applications. These applications range from optical manipulation, imaging and quantum optics, to optical communications. This brief review will examine some of the research in the field to date and consider what future directions might hold.