Counter-propagating Raman transitions with polarization-filtered sidebands

An atomic gravimeter based on Raman transitions requires two phase-locked counterpropagating beams with a frequency separation close to the hyperfine separation of the atoms. This type of beam can be generated using an electro-optical modulator, which automatically produces sidebands locked in phase to a carrier signal. However, when using this technique, more than one pair of Raman beams are generated that excite the same transition, giving rise to a modulation of the Rabi frequency throughout the gravimeter. Sending the beam through a calcite crystal, we rotate the polarization of the sidebands in a configuration in which they can be filtered in retro-reflection, thanks to the fact that it is a highly dispersive birefringent material. This configuration allows us to excite counter-propagating transitions with only one pair out of all possible ones, thus eliminating the Rabi frequency modulation problem. (author)