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arXiv:2510.16159 · Optics Letters

Light shift suppression in a CPT magnetometer using linear polarization and double frequency interrogation

Mario Alberto González Maldonado, Yang Li, James McKelvy, Andrey B. Matsko, Irina V. Novikova, Eugeniy E. Mikhailov, John E. Kitching, Ying Ju Wang

Published Dec 8, 2025• 3 citations
arXivHTMLPDF

Abstract

We demonstrate a suppression of the light shift in a Coherent-Population-Trapping (CPT) atomic magnetometer by using linearly polarized light and a differential measurement between magnetic resonances. The radio frequency that creates the optical sidebands for CPT quickly switches between two magnetic sensitive transitions, and the magnetic field is extrapolated from the difference of the center frequencies of the magnetic resonances. Light shifts and common drifts like collisional shifts can be suppressed through careful choice of measured resonances, and we show the light shift reduction by more than a factor of 20 compared to excitation with circularly-polarized light. Various limitations of the method are discussed.

DOI
10.1364/ol.580190

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We demonstrate a suppression of the light shift in a Coherent-Population-Trapping (CPT) atomic magnetometer by using linearly polarized light and a differential measurement between magnetic resonances. The radio frequency that creates the optical sidebands for CPT quickly switches between two magnetic sensitive transitions, and the magnetic field is extrapolated from the difference of the center frequencies of the magnetic resonances. Light shifts and common drifts like collisional shifts can be suppressed through careful choice of measured resonances, and we show the light shift reduction by more than a factor of 20 compared to excitation with circularly-polarized light. Various limitations of the method are discussed.
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We report a laser-pumped 4He atomic magnetometer with light shift suppression through the atomic sensor itself. A linearly polarized light is used to optically align the 4He metastable atoms and we monitor the magneto-optical double resonance (MODR) signals produced by the left- and right-circularly orthogonal components. It is shown that light shift leads to the atomic alignment to orientation conversion effect, and thus, the difference between the two MODR signals. One of these two MODR signals is locked at the Larmor frequency and is used to measure the ambient magnetic field, while the differential signal is, simultaneously, fed back to suppress the light shift. The scheme could be of the advantage to the design of compact magnetometers by reducing the systematic errors due to light shift.
The light shift is an important error source for atomic magnetometers. It would vanish if the frequency of the circularly polarized light is tuned to the optical resonance center. For high-density alkali-metal atomic magnetometers, the vapor cell has a large optical depth near the resonance, resulting in the difficulty in obtaining the exact resonance center by measuring the optical absorption line. In order to solve this problem, we propose a method to tune the pump light to a frequency where the shift is minimum based on the magnetic field zeroing technique. In addition, we also compare our results with the fitting center of the optical absorption line based on the measurement data far detuned from the resonance. The experimental results show that our method achieves a better suppression result of the light shift.
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The light shift in a spin-exchange relaxation-free (SERF) atomic magnetometer (AM) generated by detuning of circularly polarized pump light, results in deviations of orthogonality measurement and attenuation of magnetometer response. In this paper, we propose and systematically investigate a dual-axis method to suppress light shift based on a self-developed single-beam compact SERF AM capable of measuring magnetic field components along two orthogonal sensitive axes. By sequentially observing the non-sensitive axis response and applying a magnetic field along the pump light direction, the virtual magnetic field induced by light shift is compensated and is rigorously demonstrated as a dominant component in this direction. Experimental results show a significant reduction in crosstalk between the dual sensitive axes, improving accuracy in resonant frequency determination of87Rb atoms and orthogonality evaluation of triaxial coils. Furthermore, the performance of dual-axis measurement in the SERF AM is tested, showing a more notable enhancement than that of single-axis measurement.
Single-beam optically pumped atomic magnetometers (OPAMs) represent promising candidates for applications in geomagnetic field monitoring, biomedicine, and various other precision sensing domains owing to their exceptional sensitivity, high measurement accuracy, and cost-effectiveness. However, in orientation-based OPAMs utilizing circularly polarized light (CPL) pumping, the off-resonant light introduces light shift. The light shift acts as an additional magnetic field, reducing the measurement accuracy of OPAMs. Moreover, the dependence of the light shift on light intensity and frequency facilitates the conversion of light noise into magnetic noise, thereby degrading the sensitivity of OPAMs. In this study, we propose an optical pumping scheme based on space division multiplexing light (SDML) to suppress the light shift in OPAM. The approach employs two orthogonally polarized linearly polarized beams with a controlled phase difference to generate a spatially periodic distribution of left- and right-handed CPL. Optical pumping with the SDML induces oppositely directed light shifts in distinct spatial regions that effectively cancel each other. Finally, it is verified by experiments that the light shift is greatly suppressed based on SDML. Under detuned SDML pumping, both the light shift and light intensity noise are suppressed by over 50%, while maintaining a sensitivity comparable to that achieved with conventional CPL pumping. The proposed method demonstrates significant potential for magnetometers in light-noise-prone environments, and it can be generalized to other orientation-based magnetometers that rely on CPL pumping.