Theoretical and experimental results of optically pumped sodium atoms

Abstract

Optical pumping is a process that produces a nonthermal Zeeman sublevel population distribution. It plays an important role in alkali-metal magnetometers for two uses, constructing the sub-Doppler features to lock the laser frequency and providing the spin-polarized atoms to precess around the magnetic field. To comprehensively study the properties of sodium (Na) magnetometer, we present the detailed theoretical analysis of the saturated absorption spectroscopy (SAS) and the magneto-optical resonance signal in sodium D2 line. Accordingly, we have implemented two experimental schemes, the counter propagating pump-probe SAS of thermal Na vapor and the remote sensing Bell-Bloom magnetometry based on the Larmor precession frequency. In the first experiment, sub-Doppler features of D2 consist of two velocity selective optical pumping (VSOP) resonances located at the D2a and D2b transitions and a crossover (CO) resonance located between the VSOP resonances are observed. In the second experiment, an estimated intrinsic magnetometric sensitivity of δBint=286 pT in a 1 Hz bandwidth, is achieved by demodulating the recorded fluorescence signal of the resultant magneto-optical resonance near the 300 kHz Larmor precession frequency. Both kinds of experimental results are in good agreement with our theoretical calculations.