The issue of whether the optical orbital angular momentum of light can play any significant role in chiroptical interactions has seen a resurgence of interest in the past few years. Revising preliminary expectations, it has been shown both theoretically and experimentally that the topological charge can indeed play a decisive role in some chiroptical interactions, with the rates of these optical phenomena proving sensitive to the sign of the vortex charge ℓ. Using quantum electrodynamics, it is now revealed how the inclusion of molecular electric-quadrupole transition moments in both chiral and achiral anisotropic media produces such an effect. Specifically, for single-photon absorption it transpires that both the orbital and spin angular momentum must be engaged through a circularly polarized vortex beam. The chiroptical effect is identified as a manifestation spin-orbit interaction in light.
Kayn A. Forbes and David L. Andrews, "The angular momentum of twisted light in anisotropic media: chiroptical interactions in chiral and achiral materials," Proc. SPIE 10672, Nanophotonics VII, 1067210 (Presented at SPIE Photonics Europe: April 24, 2018; Published: 4 May 2018); https://doi.org/10.1117/12.2305723.
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