Relaxation mechanism of optically pumped Rb vapor of high density in strong magnetic fields

Abstract

The relaxation rates of the polarized rubidium (Rb) vapor were measured by using a chopped pumping laser to investigate the depolarization mechanism of a high density Rb vapor in a strong magnetic field. The measurement was carried out in a range of the magnetic field from 1 to 5 T and the Rb cell temperature from 90 to 130 °C which corresponds to the Rb vapor density from 0.2 to 2.0×10 13 at./cm 3 . The position dependence of the relaxation rates was also measured along the Rb cell axis. The experimental results showed that two components, i.e. a fast component with the relaxation rate of ∼ 65 ms −1 and a slow component with the relaxation rate of ∼ 1 ms −1 contribute. The observed relaxation rates were analyzed by the wall relaxation model, the effusion model and the radiation trapping model. It was found that the slow component was well explained by the wall relaxation and the effusion effect. On the other hand, the fast component is due to a formation of the localized Rb polarization around the pumping laser by a radiation trapping effect and a subsequent relaxation process due to an effusion.