What direction is the angular momentum of right hand polarized light points to? Is it vertical to its propagating direction? I want to recognize this in quantum theory.
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$\begingroup$ have a look at teachers.web.cern.ch/teachers/archiv/HST2008/teacherslab/… $\endgroup$– anna vMay 16, 2013 at 14:12
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2 Answers
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The spin of a right handed photon points in the direction of its momentum, while in a left handed photon it points in opposite way.
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$\begingroup$ This is the answer to a slightly different question than the one asked here. $\endgroup$– rob ♦Nov 12, 2021 at 14:43
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A “right-handed” photon has its spin parallel to its linear momentum; a “left-handed” photon’s spin is antiparallel to its linear momentum. The psuedoscalar product $\vec\sigma\cdot\vec p$ is sometimes called the “helicity.”
Beware that “right-circular polarized” light is made of left-handed photons, and vice-versa (because history is cruel). This is demonstrated conclusively in my favorite classic physics paper: Richard Beth, Mechanical detection and measurement of the angular momentum of Light, Physical Review 50 115 (1936). See this answer for a brief summary of Beth’s experiment.
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$\begingroup$ Is it not true that there are two conventions for defining what left- and right-polarized light is? It would seem that in one of the two conventions, RCP light comprises right-handed photons... $\endgroup$– garypAug 28, 2022 at 17:27
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$\begingroup$ According to an encyclopedia, the "helicity" convention is used by quantum physicists like me, radio astronomers, and the engineering society IEEE. Meanwhile the reversed "receiver-perspective" convention is used in optics textbooks (where I learned it), by the optics society SPIE, and by the chemists' society IUPAC. In conclusion, ugh. $\endgroup$– rob ♦Aug 28, 2022 at 18:10