Optical angular-momentum flux

S.M. Barnett

Research output: Contribution to journalArticle

202 Citations (Scopus)

Abstract

We introduce the angular-momentum flux as the natural description of the angular momentum carried by light. We present four main results: (i) angular-momentum flux is the flow of angular momentum across a surface and, in conjunction with the more familiar angular-momentum density, expresses the conservation of angular momentum. (ii) The angular-momentum flux for a light beam about its axis (or propagation direction) can be separated into spin and orbital parts. This separation is gauge invariant and does not rely on the paraxial approximation. (iii) Angular-momentum flux can describe the propagation of angular momentum in other geometries, but the identification of spin and orbital parts is then more problematic. We calculate the flux for a component of angular momentum that is perpendicular to the axis of a light beam and for the field associated with an electric dipole. (iv) The theory can be extended to quantum electrodynamics.
Original languageEnglish
Pages (from-to)S7-S16
JournalJournal of Optics B: Quantum and Semiclassical Optics
Volume4
Issue number2
DOIs
Publication statusPublished - Apr 2002

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angular momentum
light beams
orbitals
propagation
quantum electrodynamics
electric dipoles
conservation
geometry
approximation

Keywords

  • angular momentum
  • electromagnetic theory
  • photonics
  • optics

Cite this

Barnett, S.M. / Optical angular-momentum flux. In: Journal of Optics B: Quantum and Semiclassical Optics. 2002 ; Vol. 4, No. 2. pp. S7-S16.
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Optical angular-momentum flux. / Barnett, S.M.

In: Journal of Optics B: Quantum and Semiclassical Optics, Vol. 4, No. 2, 04.2002, p. S7-S16.

Research output: Contribution to journalArticle

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AB - We introduce the angular-momentum flux as the natural description of the angular momentum carried by light. We present four main results: (i) angular-momentum flux is the flow of angular momentum across a surface and, in conjunction with the more familiar angular-momentum density, expresses the conservation of angular momentum. (ii) The angular-momentum flux for a light beam about its axis (or propagation direction) can be separated into spin and orbital parts. This separation is gauge invariant and does not rely on the paraxial approximation. (iii) Angular-momentum flux can describe the propagation of angular momentum in other geometries, but the identification of spin and orbital parts is then more problematic. We calculate the flux for a component of angular momentum that is perpendicular to the axis of a light beam and for the field associated with an electric dipole. (iv) The theory can be extended to quantum electrodynamics.

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