Quantitative interpretation of the nonlinear Faraday effect as a Hanle effect of a light-induced birefringence

Abstract

We present a simple quantitative description of the lowest-order nonlinear Faraday effect of an atomic vapor by modeling the effect as a Hanle-type precession of the quadrupole moment induced by optical pumping. This gives the medium the symmetry of uniaxial birefringence, and the Faraday rotation is expressed in terms of this birefringence. We obtain expressions for transitions between states of arbitrary angular momenta; the new expressions match results obtained earlier for the case of depopulation pumping. The novel aspects are that only level populations intervene and that no explicit use of sublevel coherences is made. We present experimental verifications of the equivalence of light-induced birefringence and the nonlinear Faraday effect.