Push-pull optical pumping on the Cs D1-transition

We report on preliminarily results of push-pull optical pumping (PPOP) on the D1-transition of cesium. PPOP is based on a coherent population trapping effect prepared with polarization-modulated bichromatic light coupling the two ground-state hyperfine levels, the light polarization being modulated at the microwave frequency. With a suitable choice of polarizations, a single specific coherent superposition (dark state) formed by the two m_F = 0 sublevels can be prepared under optimal conditions. This increase the contrast of the clock reference signal without significant line-broadening.