Torque equations for spin and orbital angular momenta of radiation fields and Faraday effect |
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Authors: | Osamu Yamashita |
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Affiliation: | Materials Science, Co., Ltd., 5-5-44, Minamikasugaoka, Ibaraki, Osaka 567-0046, Japan |
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Abstract: | The spin angular momentum S of light has never been linked to the Faraday rotation of light traveling in an optically active medium possessing a rotational invariance of a crystal, because there was no helicity term associated with the phase shift in the previous torque equation for S. In order to relate the change in S with time to the Faraday rotation, therefore, we derived an exact torque equation for S. As a result, a magnetic helicity term appeared in a new torque equation for S, so that one-half of the phase shift derived from the helicity term was equivalent to the Faraday rotation angle. However, the orbital angular momentum L had no relation to the Faraday rotation. It was thus clarified that the change in S with time is related to the Faraday rotation angle of light traveling in an optically active medium, owing to the appearance of the helicity term without a rotational invariance around the optical axis. It was also demonstrated theoretically that the Faraday rotation is accompanied by a torque acting on the crystal so that the total angular momentum of light and matter is conserved. |
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Keywords: | PACS: 03.50.De 41.20.Jb 42.25.Bs 42.25.Ja 78.20.Ek |
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