Role of Na-Xe molecules in spin relaxation of optically pumped Na in Xe gas

Abstract

A mixture of dense sodium vapor (number density [Na] ∼ ${10}^{13}$ ${\mathrm{cm}}^{-3\mathrm{}}$), and buffer gases helium, xenon, and nitrogen is optically pumped to a high degree of spin polarization using a single-frequency single-mode tunable dye laser. The relaxation in the "dark" of the variables $〈S_z〉$ and $〈\overrightarrow{I}·\overrightarrow{S}〉$ is studied as a function of [Na] and buffergas pressures. For lower helium pressures (46-torr helium and 2-torr Xe) the dominant contribution to the relaxation of $〈S_z〉$ in the presence of Xe comes from the "sticking" three-body collisions with He acting as the third body. This is further confirmed by studying the longitudinal magnetic field dependence of the spin-relaxation rate. At higher helium pressures (He 700 torr, and Xe 2 torr) the relaxation of $〈S_z〉$ in the presence of Xe is mainly due to the "sudden" binary collisions between the Na and Xe, and the relaxation rate of $〈S_z〉$ is independent of the longitudinal magnetic field. Significant hyperfine pumping is achieved by proper tuning of the laser. The temperature dependence of the relaxation of $〈\overrightarrow{I}·\overrightarrow{S}〉$ and $〈S_z〉$ is also discussed.