Suppressing Rubidium back-polarization in nuclear spin comagnetometer by radiation trapping assisted depolarization pumping.

Back polarization of Rb by noble gases causes a systematic error for determining the ratio of precession frequencies in noble gas \textasciicircum 3He-\textasciicircum 129Xe comagnetometer that is being developed in our group [1]. We investigate a new active depolarization scheme for Rb atoms using a linearly polarized laser tuned to the Rb D2 transition. The depolarization process is assisted by radiation trapping of D2 light in optically-thick Rb vapor in the absence of N2 quenching gas, which is typically used in most optical pumping experiments. Instead we use hybrid optical pumping with optically-thin K vapor to create a large Rb polarization when needed. We show preliminary results demonstrating active control of Rb polarization over a large dynamic range. [1] M. E. Limes, D. Sheng, and M. V. Romalis, Phys. Rev. Lett. 120, 033401, 2018