M V Berry et al 2005 J. Opt. A: Pure Appl. Opt. 7 685 doi:10.1088/1464-4258/7/11/011
M V Berry1, M R Jeffrey1 and M Mansuripur2
Show affiliationsThe angular momentum Jinc of a light beam can be changed by passage through a slab of crystal. When the beam is incident along the optic axis of a biaxial crystal, which may also possess optical activity (chirality), the final angular momentum J can have both orbital (Jorb) and spin (Jsp) contributions, which we calculate paraxially exactly for arbitrary biaxiality and chirality and initially uniformly polarized beams with circular symmetry. For the familiar special case of a non-chiral crystal with fully developed conical-refraction rings, J is purely orbital and equal to Jinc/2, reflecting an interesting singularity structure in the beam. Explicit formulas and numerical computations are presented for a Gaussian incident beam. The change in angular momentum results in a torque on the crystal, along the axis of the incident beam. An additional, much larger, torque, about an axis lying in the slab, arises from the offset of the cone of conical refraction relative to the incident beam.
Issue 11 (November 2005)
Received 19 July 2005, accepted for publication 5 September 2005
Published 18 October 2005
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