Numerical analysis of the optical pumping process coupled with 23Na D2 manifold modeled as a partially resolved hyperfine structure

All magnetometers using alkali atoms rely on the monochromatic light driving the optical pumping process in the D1 or D2 line to create spin-polarized atoms. In the study of a sodium (Na) magnetometer, we find that 23Na exhibits the same hyperfine structure as exhibited by the 87Rb atom but differs from Rb in terms of level splitting. The narrowly split hyperfine levels of the 23Na 3P3/2 excited state are comparable to its natural broadening (9.8 MHz). We have modeled the nearly unresolved hyperfine structure as a partially resolved multilevel system in which the absorption at each photon detuning will induce adjacent allowed transition pathways simultaneously. Thus, the corresponding optical pumping processes of 23Na and 87Rb are governed by similar rate equations but result in different redistributed populations. By numerically solving the rate equations, we demonstrate that optically pumped 23Na has a much smaller spin polarization than that of 87Rb because the population imbalances between the ground state Zeeman levels of 23Na are very small. The inefficient optical pumping can explain why Na magnetometers are not studied extensively. The investigation into the optical pumping process of 23Na is helpful in preparing a highly spin-polarized atomic medium and optimizing the sensitivity of Na magnetometers.