The spin-orbit decomposition of the angular momentum of free electromagnetic fields is artificial

  • H. H. Arnaut
  • G. A. Barbosa
Conference paper


In the standard decomposition of the total angular momentum (AM) J(ro)=L(ro)+S of a free electromagnetic field the vector S represents an intrinsic angular momentum also refered lIS the photon spin. In 1936 Beth [1] performed a famous experiment in which a intense beam of circularly polarized light reaching a quartz half-wave plate emerged on the opposite side with the inverse polarization. The mechanical torque on the plate could be measured in their apparatus and it coincides in sign and magnitude with what would be expected if one consider a variat ion of ±2ħ per photon due the polarization inversion. That experiment is sometimes referred to as the measurement of the spin AM of the photon. In atomic theory is very well know that a absorption or emission of a photon circularly polarized changes the z component of the atomic AM of ±ħ in perfect concordance with the image of a intrinsic AM carried for photons. The uncountable number of experiments carrying similar interpretations turned the concept of photon spin undisputable.


Angular Momentum Total Angular Momentum Plane Wave Expansion Intrinsic Part Paraxial Approximation 
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  1. [1]
    R. A. Beth, Phys. Rev. 48, 471 (1935); 50, 115–125 (1936).ADSCrossRefGoogle Scholar
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    S. J. Van Enk and G. Nienhuis, J. Mod. Opt. 41, 963–977 (1994).ADSCrossRefGoogle Scholar
  3. [3]
    H. H. Arnaut and G. A. Barbosa, Phys. Rev. Letters 85, 286–289 (2000)ADSCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2003

Authors and Affiliations

  • H. H. Arnaut
    • 1
  • G. A. Barbosa
    • 2
  1. 1.Departamento de FísicaUniversidade Federal de Minas GeraisBelo HorizonteBrazil
  2. 2.Center for Photonic Communication and Computing ECE DepartmentNorthwestern UniversityEvanstonUSA

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