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Sixth Symposium on Novel Optoelectronic Detection Technology and Applications

Vertical-reflection multipass detection method for enhancing SERF atomic spin measurement

Yi-an Xu, Jiale Quan, Haoran Xu, Yuxin Cong, Zhihong Wu, Haoying Pang, Zhuangsheng Zhu

Published May 11, 2026• 0 citations
Publisher

Abstract

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

DOI
10.1117/12.3109221

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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
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.
We introduce a novel, to the best of our knowledge, compact multipass cell design for spin-exchange relaxation-free (SERF) atomic magnetometers, replacing conventional reflective cavities with a dual-parallel plate configuration. This adjustable planar reflector setup achieves precise control of reflection optical paths and dramatically enhances signal response, resolving the complexity of cavity design and volume increase caused by multiple reflectors in existing schemes, while having high-temperature adaptability and minimizing size and complexity. Additionally, combined with a flat-top light pump to boost atomic polarization uniformity, our system achieves 1 fT/Hz½ sensitivity, delivering 260% improvement in signal and 200% in sensitivity over conventional designs. This streamlined, high-temperature-compatible architecture marks a significant step toward scalable, next-generation quantum sensors that unite exceptional sensitivity with practical miniaturization.
The single-beam comagnetometer working in the spin-exchange relaxation-free (SERF) state is being developed into a miniaturized atomic sensor with extremely high precision in rotation measurement. In this paper, we propose a reflective configuration for the single-beam SERF comagnetometer. The laser light simultaneously used for optical pumping and signal extraction is designed to pass through the atomic ensemble twice. In the optical system, we propose a structure composed of a polarizing beam splitter and a quarter-wave plate. With this, the reflected light beam can be separated entirely from the forward propagating one and realize a complete light collection with a photodiode, making the least light power loss. In our reflective scheme, the length of interaction between light and atoms is extended, and because the power of the DC light component is attenuated, the photodiode can work in a more sensitive range and has a better photoelectric conversion coefficient. Compared with the single-pass scheme, our reflective configuration has a stronger output signal and performs better signal-to-noise ratio and rotation sensitivity. Our work has an important impact on developing miniaturized atomic sensors for rotation measurement in the future.
Enhancing the light-atom interaction is a critical approach to improving the sensitivity of the spin-based quantum sensors. However, as the optical rotation increases, the output signal exhibits nonlinear characteristics that consequently impair the critical operation of the SERF comagnetometer, thereby negating the sensitivity gain. To address this issue, the nonlinear response model of the SERF comagnetometer is established, and the evolution of the coupled spin ensemble near the self-compensation state is analyzed based on this model. Based on the analysis of nonlinear responses under different nuclear spin self-compensation capabilities, a quasi-static parameter measurement method is proposed, which minimizes nonlinear response disturbance while decoupling probe light intensity noise, thereby enhancing measurement sensitivity. Experimental validation on a SERF comagnetometer with an integrated 14-pass cell confirms the accuracy of the nonlinear model. The self-compensation state was successfully determined under a 19.8-fold optical rotation amplification, and the suppression of probe laser intensity noise through frequency fitting achieving a 1.4-fold sensitivity improvement at 1 Hz. This study provides a significant advancement in light-atom interaction enhancement systems and enhances the sensitivity of SERF comagnetometers.
The Bell-Bloom-type optically pumped atomic magnetometers are well suited for weak geomagnetic field detection. However, conventional single-beam pumping introduces an atomic spin polarization gradient, which limits the measurement accuracy and sensitivity. To address this issue, this paper proposes and experimentally demonstrates a Bell-Bloom-type rubidium FID magnetometer scheme integrating orthogonally polarized counter-propagating pumping and multi-pass probe detection. This design homogenizes the atomic spin polarization distribution and suppresses light shifts and power broadening effects induced by the pump beam. Meanwhile, the five-pass probe configuration significantly enhances the signal amplitude. Experimental results reveal that, compared with the traditional single-beam pumping and single-pass detection scheme, the proposed magnetometer achieves a remarkable improvement in magnetic field measurement accuracy, and the magnetic field sensitivity is improved from 18.9 pT/\sqrt{Hz} to 3.1 pT/\sqrt{Hz}. This work provides an effective technical approach and reference for optimizing the performance of atomic magnetometers and extending their applications in integrated arrays.