Magneto-optical rotation in an atomic vapour

Abstract We give a brief account of a density matrix treatment of an atom in a dilute vapour subject to a magnetic field in the direction of propagation of a monochromatic plane electromagnetic wave, the frequency of which is close to that of an absorption transition with J (lower level)=1, J ′ (upper level)=0. Analytical solutions which include the effects of collisions are given for the case of a plane-polarized wave of arbitrary intensity. The treatment is based on our earlier account of the J=0→J′=1 case; the solutions differ significantly in that because of optical pumping effects the collisional destruction of orientation and alignment play a much more important role when the lower level is degenerate.