Selection rules and line strengths of Zeeman-split dark resonances

In a weak magnetic field coherent dark resonances in cesium vapor are split into up to 15 resolved components, depending on field direction and laser polarizations. We find that the selection rules are different for vapor cells with and without buffer gas due to a change in multipolarity of the two-photon coupling. At low laser intensities or sufficiently high buffer-gas pressure optical pumping between different dark resonances can be neglected so that a simple model allows one to calculate the relative line strengths, giving complete agreement with the experimental spectra.