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arXiv:2502.11512

Triaxial Alignment Magnetometer Utilizing Free-Spin Precession in the Geomagnetic Range

Jin, Ge, Tao Shi, Sheng Zou

Published Feb 17, 2025• 0 citations
arXivHTMLPDF

Abstract

In this paper, we present a triaxial alignment magnetometer based on free-spin precession deployed in the geomagnetic range. Existing vector measurement methods often require complex optical setups, heating structures, and laser modulation. This study addresses this challenge by employing a linearly polarized probe beam to induce atomic alignment and subsequently detecting the optical polarization rotation caused by the pulsed radio frequency field. The experiment is conducted in a paraffin-coated cell without buffer gas at room temperature, containing rubidium with natural abundance. We report triaxial measurements with a static magnetic field amplitude of approximately 50 $μ{\text{T}}$ (close to Earth's magnetic field), where the noise levels for each axis are approximately 5.3 ${\text{pT/}}\sqrt{\text{Hz}}$, 4.7 ${\text{pT/}}\sqrt{\text{Hz}}$, and 9.3 ${\text{pT/}}\sqrt{\text{Hz}}$ respectively. The proposed method demonstrates a simple structure suitable for cost-effective and versatile applications.

DOI
10.48550/arxiv.2502.11512

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We present an implementation of an atomic magnetometer based on free spin precession of optically pumped Rb 87 atoms. The design features a microfabricated vapor cell with an effective volume of 7.1 mm 3 containing isotopically enriched Rb 87 and nitrogen buffer gas. The magnetometer is designed to operate in the Earth-field range, exhibiting a magnetic noise floor of about 147 fT / Hz at field strengths comparable to Earth's magnetic field, i.e., around 50 μ T . This is in close agreement with the Cramér-Rao lower bound of 118 fT / Hz . The good sensitivity as well as the high dynamic range enables a wide range of applications, including magnetocardiography and geomagnetic measurements.
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Abstract High-sensitivity triaxial magnetic field measurements are crucial in various scientific and industrial applications, with spin-exchange relaxation-free (SERF) atomic magnetometers (AMs) standing out for their exceptional sensitivity. However, conventional methods for achieving triaxial measurements in SERF magnetometers typically involve multiple modulated magnetic fields, which introduce crosstalk challenges in array-based configurations. We propose a static bias magnetic field assisted optical modulation triaxial AM to address this limitation. In this configuration, the detuned circularly polarized light is utilized to achieve synchronous modulation of the fictitious magnetic field and pumping rate while incorporating a static bias magnetic field to generate a transverse projection component. We develop a comprehensive triaxial response model that fully considers the effects of the longitudinal spin polarization deflection. Building upon this model, we derive the relationship between the transverse spin component and the triaxial magnetic field and introduce parameter optimization methods to obtain optimal parameters, thus enabling triaxial measurements of 12 fT Hz −1/2 , 10 fT Hz −1/2 , and 15 fT Hz −1/2 along the x-, y -, and z -axes. Our approach offers significant advantages over existing methods, particularly in minimizing crosstalk and mitigating spin-exchange relaxation introduced by multiple modulated magnetic fields. Moreover, the effective detection of simulated magnetocardiography signals highlights the practical applicability and reliability of the proposed method in real-world scenarios.