A plateau in the sensitivity of a compact optically pumped atomic magnetometer

Natsuhiko Mizutani,Tetsuo Kobayashi,Akira Terao,Kazuhiro Ban,Sunao Ichihara,Kazuhisa Okano

doi:10.1063/1.4880498

Abstract

In a compact optically pumped atomic magnetometer (OPAM), there is a plateau in the sensitivity where the dependence of the sensitivity on pumping power is small compared with that predicted by the uniform polarization model. The mechanism that generates this plateau was explained by numerical analysis. The distribution of spin polarization in the alkali metal cell of an OPAM was modeled using the Bloch equation incorporating a diffusion term and an equation for the attenuation of the pump beam. The model was well-fitted to the experimental results for a module with a cubic cell with 20 mm sides and pump and probe beams with 8 mm diameter. On the plateau, strong magnetic response was generated at the regions that were not illuminated directly by the intense pump beam, while at the same time spin polarization as large as 0.5 was maintained due to diffusion of the spin-polarized atoms. Thus, the sensitivity of the magnetometer monitored with a probe beam decreases only slightly with increasing pump beam intensity because the spin polarization under an intense pump beam is saturated. This plateau, which is characteristic of this type of magnetometer using a narrow pump and probe beams, can be used in arrays of magnetometers because it enables stable operation with little sensitivity fluctuation from changes in pump beam power.

Highlights

In a compact optically pumped atomic magnetometer (OPAM), there is a plateau in the sensitivity where the dependence of the sensitivity on pumping power is small compared with that predicted by the uniform polarization model
The analysis of the OPAM is valid with the Bloch equation including a classical diffusion term, while the pumping and relaxation rates are used as substitutes for quantum mechanical details of optical pumping
We extended the analysis of the spin polarization inhomogeneity by coupling the Bloch equation including diffusion term, and an equation for attenuation of the pump beam in an optically dense alkali cell

Summary

Introduction

In a compact optically pumped atomic magnetometer (OPAM), there is a plateau in the sensitivity where the dependence of the sensitivity on pumping power is small compared with that predicted by the uniform polarization model. The distribution of spin polarization in the alkali metal cell of an OPAM was modeled using the Bloch equation incorporating a diffusion term and an equation for the attenuation of the pump beam.

Results

Conclusion