Improvement of the Pumping Efficiency in an Optically Pumped Cesium Beam Tube with a (σ + π)-Polarized Laser

We observed that atomic population was trapped in the ground state of cesium atoms when a σ-polarized laser was illuminated to the atoms under a weak static magnetic field in an optically pumped cesium beam tube. The population trapping could be removed by applying a (σ+π)-polarized laser which was made by superposition of both σ- and π-polarizations. The pumping laser with the (σ+π)-polarization increased the pumping efficiency even in the low magnetic field and accordingly, the background noise of the Ramsey spectrum was reduced by about four times and moreover, the Ramsey signal became more stable against the power fluctuation of the pumping laser.