Measurement and Suppression of Transverse Optical Pumping in a Spin-Exchange Relaxation-Free Co-Magnetometer

The transverse optical pumping (TOP) introduced by a probe beam can result in a polarization error in the output signal of a spin-exchange relaxation-free (SERF) co-magnetometer. In this article, a model capable of quantitatively evaluating TOP in a SERF co-magnetometer is established based on three characteristics of the probe beam. According to this model, a novel fast measurement method for TOP based on steady-state response output signals and longitudinal polarization information is proposed. Furthermore, a method of suppressing TOP based on counter-propagating beam is suggested, and the circular polarization-induced TOP is effectively reduced by finely adjusting the amount of phase retardation of an octantal waveplate. Eventually, the counter-propagating beam scheme achieves a 22.74% TOP suppression ratio. The stability of both the short- and long-term outputs of the SERF co-magnetometer is improved and the lowest point of the Allan variance is
$0.006~^{\circ }$
/h better than the original. Moreover, the coupling effect between the probe beam power fluctuation and output signal bias of the SERF co-magnetometer is decreased.