Frequency Response of Optically Pumped Magnetometer with Nonlinear Zeeman Effect

Rui Zhang,Hong Guo,Jingbiao Chen,Xiang Peng,Teng Wu

doi:10.3390/app10207031

Rui Zhang, Hong Guo + Show 3 more

Open Access

https://doi.org/10.3390/app10207031

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Abstract

Optically pumped alkali atomic magnetometers based on measuring the Zeeman shifts of the atomic energy levels are widely used in many applications because of their low noise and cryogen-free operation. When alkali atomic magnetometers are operated in an unshielded geomagnetic environment, the nonlinear Zeeman effect may become non-negligible at high latitude and the Zeeman shifts are thus not linear to the strength of the magnetic field. The nonlinear Zeeman effect causes broadening and partial splitting of the magnetic resonant levels, and thus degrades the sensitivity of the alkali atomic magnetometers and causes heading error. In this work, we find that the nonlinear Zeeman effect also influences the frequency response of the alkali atomic magnetometer. We develop a model to quantitatively depict the frequency response of the alkali atomic magnetometer when the nonlinear Zeeman effect is non-negligible and verify the results experimentally in an amplitude-modulated Bell–Bloom cesium magnetometer. The proposed model provides general guidance on analyzing the frequency response of the alkali atomic magnetometer operating in the Earth’s magnetic field. Full and precise knowledge of the frequency response of the atomic magnetometer is important for the optimization of feedback control systems such as the closed-loop magnetometers and the active magnetic field stabilization with magnetometers. This work is thus important for the application of alkali atomic magnetometers in an unshielded geomagnetic environment.

Highlights

Resolving measurements of weak signals in the Earth’s magnetic field are very important for applications that involve measurement of faint magnetic-field signals, such as geophysical exploration [1,2,3,4], bio-magnetic field detection in an unshielded geomagnetic environment [5,6], and ultralow-field nuclear magnetic resonance [7,8]
We set the biasing magnetic field to be around 1.15 μT, where the nonlinear Zeeman (NLZ) effect is negligible and the magnetic resonance can be viewed as a single Lorentz peak, and measure the response of the optically pumped magnetometers (OPMs) to magnetic-field modulations when the detuning δω = γB0 − ωM is set to a different value
We present a quantitative model to describe the influence of the NLZ effect on the frequency response of the OPM and experimentally verify this model with a Bell–Bloom cesium OPM

Summary

Introduction

Resolving measurements of weak signals in the Earth’s magnetic field are very important for applications that involve measurement of faint magnetic-field signals, such as geophysical exploration [1,2,3,4], bio-magnetic field detection in an unshielded geomagnetic environment [5,6], and ultralow-field nuclear magnetic resonance [7,8]. In the Earth’s field, alkali atoms based OPMs suffer from the nonlinear Zeeman (NLZ). In the case of a small amplitude of the magnetic field, the NLZ effect is much smaller than the magnetic resonance linewidth and the frequency response of the OPM is typically a first-order Butterworth low-pass filter [28,30]. When the magnetic field amplitude increases and the NLZ effect is comparable with the magnetic resonance linewidth, the OPM’s frequency response deviates from that of the first-order low-pass filter. We theoretically analyze the frequency response of the alkali atomic magnetometer for a non-negligible NLZ effect and experimentally verify the theoretical predictions with an amplitude-modulated Bell–Bloom cesium OPM. OPM is measured when the biasing magnetic field is 50 μT or 70 μT and the results are coincident with the theoretical predictions

Experiment Setup

Theory

Results and Discussions

Conclusions and Outlook