When a light beam is circularly polarized, each of its photons carries a Spin Angular Momentum (SAM) of , where is the reduced Planck constant and the sign is positive for left and negative for right circular polarizations (this is adopting the convention from the point of view of the receiver most commonly used in optics). This SAM is directed along the beam axis (parallel if positive, antiparallel if negative).
The above figure shows the instantaneous structure of the electric field of left () and right () circularly polarized light in space. The green arrows indicate the propagation direction.
The mathematical expressions reported under the figures give the three electric-field components of circularly polarized plane wave propagating in the direction, in complex notation.
Born, M. & Wolf, E. (1999). Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light (7th ed.). Cambridge: Cambridge University Press. ISBN 0-521-64222-1.
Allen, L.; Barnnet, Stephen M. & Padgett, Miles J. (2003). Optical Angular Momentum. Bristol: Institute of Physics. ISBN 978-0-7503-0901-1.
Torres, Juan P. & Torner, Lluis (2011). Twisted Photons: Applications of Light with Orbital Angular Momentum. Bristol: Wiley-VCH. ISBN 978-3-527-40907-5.
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