Effects of level degeneracy and spontaneous emission on deflection of an atomic beam by a standing light wave

We present a general formalism for describing the diffraction of an atomic beam by a nearly resonant standing light wave, containing the correlation between the acquired transverse momentum, the number of emitted fluorescent photons and the internal polarization state of the atoms. The formalism is applied in some special cases to yield explicit results for the momentum distribution. At the same time it is shown to give a unified description of various previous results for two-state atoms