Conservation of angular momentum for light propagating in a transparent anisotropic medium

When light propagates through a transparent medium, both the orbital and spin angular momenta of the light may change. It is shown by explicit calculation that the change in the angular momentum of the light is exactly equal and opposite to the change in the internal angular momentum of the atoms in the transparent medium. The centre-of-mass motion of the atoms does not play any significant role in this interchange of angular momentum.