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arXiv:2610.32795

A Compact Single-Beam Optically Pumped Magnetometer Based on Absorption Detection

Jia-You Liou, Yi‐Hsuan Chen, Hsiang-An Chuang, Chih-Hsuan Huang, Zong-Hsin Liu, I-Chiao Tsai, Kai-Hsin Peng, Yi-Hsin Chen

Published Oct 23, 2026• 0 citations
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Abstract

We demonstrate a compact single-beam optically pumped magnetometer (OPM) employing a pure 87Rb microfabricated vapor cell with 500 Torr buffer gas. The residual magnetic field is actively minimized to below 400 pT through a combination of mu-metal magnetic shielding and internal compensation coils. We systematically characterize the OPM response as a function of laser detuning and optical intensity, and derive the magnetic-field sensitivity from the signal slope and noise amplitude spectral density. A best sensitivity of 11 fT/Hz^1/2 is achieved near the resonance transition at an optimal optical intensity, using a small cell volume of only 0.027 cm^3. Furthermore, a miniaturized OPM prototype was developed using a folded flexible printed circuit board (FPCB) to integrate the vapor cell, a compact heater, and magnetic-field coils into a cubic sensing head. Two coil configurations patterned directly on the FPCB were investigated. Under optimized operating conditions, the OPM prototype achieved a sensitivity of 66 fT/Hz^1/2. These results demonstrate that high-buffer-pressure single-beam OPMs can achieve excellent sensitivity, establishing a pathway toward compact and scalable arrays.

DOI
10.48550/arxiv.2610.32795

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We demonstrate a compact single-beam optically pumped magnetometer (OPM) employing a pure 87Rb microfabricated vapor cell with 500 Torr buffer gas. The residual magnetic field is actively minimized to below 400 pT through a combination of mu-metal magnetic shielding and internal compensation coils. We systematically characterize the OPM response as a function of laser detuning and optical intensity, and derive the magnetic-field sensitivity from the signal slope and noise amplitude spectral density. A best sensitivity of 11 fT/Hz^1/2 is achieved near the resonance transition at an optimal optical intensity, using a small cell volume of only 0.027 cm^3. Furthermore, a miniaturized OPM prototype was developed using a folded flexible printed circuit board (FPCB) to integrate the vapor cell, a compact heater, and magnetic-field coils into a cubic sensing head. Two coil configurations patterned directly on the FPCB were investigated. Under optimized operating conditions, the OPM prototype achieved a sensitivity of 66 fT/Hz^1/2. These results demonstrate that high-buffer-pressure single-beam OPMs can achieve excellent sensitivity, establishing a pathway toward compact and scalable arrays.
Optically pumped atomic magnetometers (OPAMs) offer high sensitivity at room temperature and are increasingly considered for portable magnetic sensing in geomagnetic-field environments. Here, we report a handheld-scale, single-beam scalar 87Rb OPAM with a sensor-head volume of approximately 110 ml. The device operates in an all-optical Bell–Bloom configuration and uses digital lock-in, dispersive tracking of the 87Rb Larmor resonance, implemented with a hybrid electronics stack that combines in-house control hardware with commercial modules. A single frequency-modulated laser beam performs both pumping and probing without RF coils. All signal processing is realized in Python on a single-board computer paired with a commercial off-the-shelf data-acquisition module, enabling immediate deployment without dedicated signal-processing hardware. The magnetometer has an intrinsic in-band field sensitivity of approximately 21 pT/Hz, estimated from the lock-in dispersion slope, over a 0.1–30 Hz closed-loop in-band region with a digital-output rate of 200 samples/s. In an unshielded Earth-field deployment, we detect repeatable transient magnetic signatures from a controlled elevator motion sequence and quantify standoff observability over sensor-elevator distances from 1.25 m to 10 m. These results show that compact scalar OPAMs can provide bandwidth and range-resolved event sensitivity suitable for field-deployable magnetic anomaly detection and infrastructure monitoring in realistic geomagnetic environments.
A scalar magnetic field sensor based on a millimeter-size Rb87 vapor cell is described. The magnetometer uses nearly copropagating pump and probe laser beams, amplitude modulation of the pump beam, and detection through monitoring the polarization rotation of the detuned probe beam. The circularly polarized pump laser resonantly drives a spin precession in the alkali atoms at the Larmor frequency. A modulation signal on the probe laser polarization is detected with a lock-in amplifier. Since the Larmor precession is driven all-optically, potential cross talk between sensors is minimized. And since the pump light is turned off during most of the precession cycle, large offsets of the resonance, typically present in a single-beam Bell–Bloom scheme, are avoided. At the same time, relatively high sensitivities can be reached even in millimeter-size vapor cells: The magnetometer achieves a sensitivity of 1 pT/Hz1/2 in a sensitive volume of 16 mm3, limited by environmental noise. When a gradiometer configuration is used to cancel the environmental noise, the magnetometer sensitivity reaches 300 fT/Hz1/2. We systematically study the dependence of the magnetometer performance on the optical duty cycles of the pump light and find that better performance is achieved with shorter duty cycles, with the highest values measured at 1.25% duty cycle.
Magnetic field imaging is a valuable resource for signal source localization and characterization. This work reports an optically pumped magnetometer (OPM) based on the free-induction-decay (FID) protocol, that implements microfabricated cesium (Cs) vapor cell technology to visualize the magnetic field distributions resulting from various magnetic sources placed close to the cell. The slow diffusion of Cs atoms in the presence of a nitrogen (N 2 ) buffer gas enables spatially independent measurements to be made within the same vapor cell by translating a 175 μ m diameter probe beam over the sensing area. For example, the OPM was used to record temporal and spatial information to reconstruct magnetic field distributions in one and two dimensions. The optimal magnetometer sensitivity was estimated to be 0.43 pT/Hz within a Nyquist limited bandwidth of 500 Hz. Furthermore, the sensor’s dynamic range exceeds the Earth’s field of approximately 50 μ T, which provides a framework for magnetic field imaging in unshielded environments.
The most efficient way to improve the sensitivity of an optically pumped magnetometer (OPM) is to maximize the spin-polarization lifetime of the atoms. The spin exchange relaxation-free (SERF) OPM that operates in zero field environment is one of the most sensitive magnetic sensors. This paper proposes a new three-axis magnetic field compensation method for the single-beam OPM, which zeroes the magnetic field around the sensor to make it work in SERF regime. The method simultaneously employs two modulation magnetic fields and two low-frequency sweeping magnetic fields along two directions perpendicular to the laser beam during the compensation process. The output signal of the photodiode is demodulated at different frequencies, resulting in two outputs that reflect the three components of the magnetic field. This method does not require iterate to tune the three-axis field, which increases the speed of the compensation process significantly. The magnetic field resolutions of the method for the x-axis, y-axis and z-axis are 0.6 pT, 0.6 pT and 5 pt, respectively. A compact OPM with noise density about 20 fT / Hz1/2@10 Hz is developed and tested, demonstrating the feasibility of the method.
Abstract We present a design for a multi-channel optically pumped zero-field magnetometer utilizing a 200-μm-thick Rubidium vapor cell. The vapor cell and its housing are designed to reduce the minimal distance between a magnetic sample and the sensing volume to about 1 mm, to optimize the effective spatial resolution. The thin vapor cell, filled with 2 atm of nitrogen as a buffer gas reduces the volume across which the magnetic field is averaged. The vapor cell is fully illuminated by a single laser beam, and the transmitted light is imaged onto a 4 x 4 photodiode array, allowing for simultaneous measurement of a magnetic field distribution with up to 16 channels. The performance of the magnetometer is studied for all channels. It is shown that the sensor can operate in the spin-exchange relaxation-free regime with a projected photon-shot noise limited noise floor of about 1 pT/Hz1/2 for a sensitive voxel size of approximately 600 μm x 600 μm x 200 μm.
We demonstrate a single-beam atomic magnetometer (AM) capable of measuring a three-axis magnetic field with high-sensitivity, achieved by applying a small DC offset field and a high frequency modulation field. To satisfy the miniaturization demand of AMs, an elliptically polarized light detuned by 50 GHz from the resonance transition center is employed. The circularly polarized component is used to polarize the alkali-metal atoms, while the linearly polarized light is used to detect the dynamics of the polarized spin under a magnetic field. Based on theoretical analysis, parameters that significantly affect the performance are optimized, and a sensitivity of 20 fT/Hz 1/2 in x -axis, 25 fT/Hz 1/2 in y -axis, 30 fT/Hz 1/2 in z -axis is achieved with a miniature 4 × 4 × 4 mm 87 Rb vapor cell. Moreover, we also verify that the operation principle of AMs can be used to null background magnetic fields in-situ with isotropic compensation resolution of 6.7 pT, which provides an effectively precise method for zeroing ambient magnetic field. The high-sensitivity operating of an elliptically-polarized-laser-based magnetometer provides prospective futures for constructing a compact, low-cost AM, which is particularly applicable for non-invasive bio-magnetic imaging such as array-based magnetoencephalography (MEG) and magnetocardiography (MCG).