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Optics Young Scientist Summit (OYSS)

Biaxial zero-field atomic magnetometer with a multi-passed probe light

Yibo Qi, Shuying Wang, Nuozhou Xu, Xihui Ye, Xiaoyan Gao, Jixi Lu

Published Jan 22, 2025• 0 citations
Publisher

Abstract

Multi-passed probe light can enhance the signal of atomic magnetometers by increasing the effective optical path length between the alkali metal atomic ensemble and the probe light, thereby strengthening the sensitivity. In recent years, multi-passed probe light has become an important method for improving the response signal and sensitivity of atomic magnetometers. To achieve biaxial magnetic field measurement while maintaining high sensitivity, a biaxial measurement spin-exchange relaxation-free (SERF) atomic magnetometer with a multi-passed probe light is proposed in this paper. The theoretical model and experimental advantages of using multi-passed probe light in longitudinal magnetic field modulation (Z-mode) SERF atomic magnetometers are analyzed. In this paper, a new model of output response of the Z-mode SERF atomic magnetometer based on multi-passed probe light is established, a compact reflective optical path is designed to increase the optical path between the probe light and the polarized alkali metal atomic ensemble, enhance the signal response, and achieve the suppression of low-frequency 1/f noise through longitudinal magnetic field modulation. Experimental results confirmed that the magnetic field sensitivity in the x- and y-axis of the multi-passed probe light configuration improved by 29% and 18%, respectively, compared to the single-pass configuration.

DOI
10.1117/12.3055148

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Multi-passed probe light can enhance the signal of atomic magnetometers by increasing the effective optical path length between the alkali metal atomic ensemble and the probe light, thereby strengthening the sensitivity. In recent years, multi-passed probe light has become an important method for improving the response signal and sensitivity of atomic magnetometers. To achieve biaxial magnetic field measurement while maintaining high sensitivity, a biaxial measurement spin-exchange relaxation-free (SERF) atomic magnetometer with a multi-passed probe light is proposed in this paper. The theoretical model and experimental advantages of using multi-passed probe light in longitudinal magnetic field modulation (Z-mode) SERF atomic magnetometers are analyzed. In this paper, a new model of output response of the Z-mode SERF atomic magnetometer based on multi-passed probe light is established, a compact reflective optical path is designed to increase the optical path between the probe light and the polarized alkali metal atomic ensemble, enhance the signal response, and achieve the suppression of low-frequency 1/f noise through longitudinal magnetic field modulation. Experimental results confirmed that the magnetic field sensitivity in the x- and y-axis of the multi-passed probe light configuration improved by 29% and 18%, respectively, compared to the single-pass configuration.
Miniaturized high-sensitivity atomic magnetometers play a crucial role in biomagnetic measurements. The utilization of multipass cells enhances the sensitivity of atomic magnetometers. This study explores the benefits of employing a multipass cell in spin-exchange relaxation-free (SERF) atomic magnetometers through theoretical and experimental analysis. A signal-to-noise ratio (SNR) model was established by accounting for the optimal detuning frequency of the probe light and low-frequency 1/f noise. This enabled the optimal number of probe light passes through the vapor cell to be determined. Additionally, compact and symmetric reflective optical paths were designed to mitigate polarization gradients in atomic magnetometers with high atomic number density. Experimental results confirmed that the magnetic field sensitivity of the triple-pass configuration (1.8 fT/Hz1/2^{1/2}1/2) was 1.89 times that of the single-pass configuration (3.4 fT/Hz1/2^{1/2}1/2), consistent with the theoretical analysis. This study provides valuable theoretical guidance for analyzing the SNR performance of SERF atomic magnetometers and demonstrates the potential of multipass cells in enhancing their magnetic field sensitivity. The utilization of multipass cells presents a viable approach toward the realization of highly sensitive and portable miniaturized SERF atomic magnetometers.
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.
The spin-exchange relaxation-free (SERF) atomic magnetometers exhibit ultrahigh sensitivity for the magnetic field measurement, and their performance is further enhanced through zero-field parameter modulation. However, this modulation introduces additional parameter coupling that limits the performance of magnetometers in multi-axis measurement. In this paper, we develop a modified dual-axis output equation based on the nonlinear interaction between the optical pumping rate and modulation field amplitude, mediated by the spin-exchange relaxation and polarization. We employ a multi-objective optimization algorithm incorporating the implicit constraints among these parameters to enable efficient, simultaneous optimization of both the pump rate and modulation amplitude. Experimental results show that under optimal parameters obtained by the algorithm, the dual-axis signal responses improve by approximately 20% and 30% over conventional optimization methods, achieving 2.5 fT/Hz1/2magnetic measurement sensitivities for the y-axis and 4.0 fT/Hz1/2for the x-axis, respectively.
SERF atomic co-magnetometer offers high sensitivity and navigation-grade potential. However, the performance of traditional single-pass detection methods is limited due to insufficient Faraday rotation signals. To address this issue, this paper proposes a vertical-reflection multi-pass detection method. By introducing hollow roof mirrors and half-wave plates, the optical interaction path is significantly extended while ensuring strict orthogonality between the pump and probe beams. This compact square shaped optical path design effectively amplifies the Faraday rotation effect, suppresses cross-axis coupling, and significantly improves the signal-to-noise ratio and measurement sensitivity. Through theoretical modeling analysis, this approach enhances the rotation signal while extending the optical path, thereby improving the system response. Experimental results demonstrate that the multi-pass structure improves the signal-to-noise ratio by several times compared to single-pass detection, and the design offers excellent integration potential, providing a feasible technical path for high-performance SERF quantum sensors for navigation and high-precision physical research
Ultra-sensitive multi-channel optically pumped atomic magnetometers based on the spin-exchange relaxation-free (SERF) effect are powerful tools for applications in the field of magnetic imaging. To simultaneously achieve ultra-high spatial resolution and ultra-high magnetic field sensitivity, we proposed a high-resolution multi-channel SERF atomic magnetometer for two-dimensional magnetic field measurements based on a digital micro-mirror device (DMD) as the spatial light modulator for a single vapor cell. Under the optimal experimental conditions obtained via spatial and temporal modulation of the probe light, we first demonstrated that the average sensitivity of the proposed 25-channel magnetometer was approximately 25fT/Hz 1/2 with a spatial resolution of 216µm. Then, we measured the magnetic field distribution generated by a gradient coil and compared the experimentally obtained distributions with those calculated via finite element simulation. The obtained g value of 99.2% indicated good agreement between our experimental results and the theoretical calculations, thereby confirming that our proposed multi-channel SERF magnetometer was effective at measuring magnetic field distributions with an ultra-high spatial resolution.
Abstract We propose a signal- and sensitivity-enhanced spin-exchange-relaxation-free atomic magnetometer utilizing a multi-pass cell with a highly spatially homogeneous optical pumping scheme. The relationship between the magnetometer’s performance and the number of probe beam passes is measured. The optical rotation angle exhibits a linear correlation with the number of passes, achieving 89 mrad nT−1 for a quadruple-pass cell. However, the sensitivity does not increase linearly when further increasing the optical length due to the noise limit. This work provides a method to study the enhancement performance of the magnetic response and sensitivity in atomic magnetometers by using multi-pass cells.