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

Xiaoxu Zhang,Xingqiao Ma,Hua Zhao,Yiping Chen,Qiongying Ren

doi:10.1063/5.0002064

Abstract

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.

Highlights

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
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
By solving the rate equations of the single Na atom, we find that the transient solutions of Zeeman populations would not reach the steady-state and the pump time becomes an important factor for population distributions

Summary

Introduction

Scalar optically pumped magnetometers (OPMs) based on the Larmor precession of spin-polarized alkali atoms (K, Rb, and Cs) have been fully researched.1–3 In particular, the micro-fabricated buffer-gas-filled K, Rb, and Cs vapor cells have become prevalent in miniaturized magnetometers.4–6 Their sensitivity approaches the femtotesla range and can even surpass the sensitivity of superconducting quantum interference devices (SQUIDs).7–10 magnetometers using the Na vapor have not been fully investigated owing to the lack of a commercial narrow-band tunable laser for the Na resonant D-line11,12 and its relatively low vapor pressure.13–15 In recent years, remote magnetometry utilizing the mesospheric sodium layer has gained considerable attention for geophysical applications.16–19 Researchers have demonstrated the feasibility of this technique but found the magnetic resonance signals of the Na magnetometer is weaker by many orders of magnitude compared to conventional Rb or Cs magnetometers.20,21 In this paper, we have proposed a theoretical model of optically pumped 23Na and 87Rb atoms to explain this result and optimize the inefficient optical pumping for the purpose of a highly spin-polarized Na atomic medium. 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.

Results

Conclusion