On the natures of the spin and orbital parts of optical angular momentum

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Barnett, Stephen M and Allen, L and Cameron, Robert P and Gilson, Claire R and Padgett, Miles J and Speirits, Fiona C and Yao, Alison M (2016) On the natures of the spin and orbital parts of optical angular momentum. Journal of Optics, 18 (6). 064004. ISSN 2040-8978 (https://doi.org/10.1088/2040-8978/18/6/064004)

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Abstract

The modern field of optical angular momentum began with the realisation by Allen et al. in 1992 that, in addition to the spin associated with polarisation, light beams with helical phase fronts carry orbital angular momentum. There has been much confusion and debate, however, surrounding the intricacies of the field and, in particular, the separation of the angular momentum into its spin and orbital parts. Here we take the opportunity to state the current position as we understand it, which we present as six perspectives: (i) We start with a reprise of the 1992 paper in which it was pointed out that the Laguerre-Gaussian modes, familiar from laser physics, carry orbital angular momentum. (ii) The total angular momentum may be separated into spin and orbital parts, but neither alone is a true angular momentum. (iii) The spin and orbital parts, although not themselves true angular momenta, are distinct and physically meaningful, as has been demonstrated clearly in a range of experiments. (iv) The orbital part of the angular momentum in the direction of propagation of a beam is not simply the azimuthal component of the linear momentum. (v) The component of spin in the direction of propagation is not the helicity, although these are related quantities. (vi) Finally the spin and orbital parts of the angular momentum correspond to distinct symmetries of the free electromagnetic field and hence are separately conserved quantities.

ORCID iDs

Barnett, Stephen M, Allen, L, Cameron, Robert P ORCID logoORCID: https://orcid.org/0000-0002-8809-5459, Gilson, Claire R, Padgett, Miles J, Speirits, Fiona C and Yao, Alison M ORCID logoORCID: https://orcid.org/0000-0002-6260-5852;
  • Item type:Article
    ID code:55898
    Dates:
    Date
    Event
    21 April 2016
    Published
    11 March 2016
    Accepted
    Subjects:Science > Physics
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:15 Mar 2016 13:39
    Last modified:02 Dec 2024 01:17
    Related URLs:
    URI:https://strathprints.strath.ac.uk/id/eprint/55898
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