The Orbital Angular Momentum of Light

by Miles Padget

Aula Rasetti (Dipartimento di Fisica - Ed. G.Marconi)

Aula Rasetti

Dipartimento di Fisica - Ed. G.Marconi

Parte I° It is 15 years since Les Allen et al. recognised that light beams could be made in the laboratory that carried an Orbital Angular Momentum (OAM). This OAM is independent of, and additional to, the spin associated with circular polarisation. Beam carrying OAM usually have helical phase-fronts and an associated phase singularity leading to line of zero optical intensity along their optical axis. Since the recognition of laboratory OAM much of my own groups work has been the exploration of this phenomenon, ranging from optical spanners and rotational frequency shifts to an angular form of Heisenbergs uncertainty principle. These lectures will, however, concentrate upon two of my current interests, 1) The familiar observation of laser speckle comprises many black specs, each of which is actually a phase singularity around which the local phase front is helical. But what patterns do these lines map out, what does their topology tell us? how can it be controlled? 2) The role that orbital angular momentum plays in understanding the intricacies and possible applications of quantum entanglement; ranging from new forms of ghost imaging to increased bandwidth quantum cryptography.