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Optics Express

High-sensitivity operation of a single-beam atomic magnetometer for three-axis magnetic field measurement

Junjian Tang, Yueyang Zhai, Cao Li, Yaohua Zhang, Lin Li, Binbin Zhao, Binquan Zhou, Bangcheng Han, Gang Liu

Published May 3, 2021• 123 citations
Publisher

Abstract

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).

DOI
10.1364/oe.425851

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Journal of Physics D Applied Physics•Oct 24, 2022•22 citations
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).
In this paper, we propose a three-axis atomic magnetometer (AM), in which one light beam is divided into two orthogonal spatially separated pump beams by a lateral displacement polarized beam splitter and reflector mirrors; this scheme suppresses the three-axis crosstalk caused by the interaction between the two beams and atoms in the cell. When the AM operates in the direct-current (DC) mode, the three-axis crosstalk is significant. To solve this problem, three modulation fields with the same amplitudes, frequencies, and different phases are applied, which allow the AM operated in modulation mode to perform a highly sensitive synchronous and independent measurement of the three-axis magnetic field with low crosstalk. The experimental results showed that the three-axis crosstalk was less than 2%. In the modulation mode, the sensitivities were 22, 23, and 26 fT/Hz1/2 on the x-, y-, and z-axes, respectively. The 3-dB bandwidths of the three axes were 126, 124, and 112 Hz. In addition, we demonstrated a three-axis in-situ magnetic compensation method with a magnetic compensation accuracy of the pT level in the DC mode. The proposed triaxial AM can be easily miniaturised and used in biomedical applications, such as in magnetocardiography and magnetoencephalography.
The ultra-sensitivity magnetometer plays an important role in fundamental physics and applications, including magnetoencephalography (MEG) and magnetocardiography (MCG). The spin-exchange relaxation-free (SERF) atomic magnetometer (AM) has great sensitivity but is limited by the relatively complicated dual-beam structure for application, leading to the development of the compact AM based on one single laser beam. Compared with the single-beam optically pumped magnetometer (OPM) detecting the absorption of the circularly polarized beam, the SERF AM based on an elliptically polarized single beam detecting the optical rotation angle of polarization has a better response, lower laser power, and no need for signal modulation or demodulation. Here, we would like to report an elliptically-polarized single-beam SERF AM enhanced by reflecting the probe beam, increasing the light-atom interaction. Moreover, unlike the previous reflecting AM using the beam splitter, we used a D-shape mirror to extract the reflected beam, avoiding power losses of both incident and reflected beam and destruction of polarization. The sensitivity of our device in the reflecting scheme reaches 5 fT/Hz1/2 at 9–60 Hz, satisfying the need to measure the human MEG/MCG or search for the fifth force. Our research paves the way for developing the compact SERF AM for multiple future applications.
Spin-exchange relaxation free alkali-metal magnetometers typically operate in the regime of high optical density, presenting challenges for simple and efficient optical pumping and detection. We describe a high-sensitivity Rb magnetometer using a single elliptically polarized off-resonant laser beam. Circular component of the light creates relatively uniform spin polarization while the linear component is used to measure optical rotation generated by the atoms. Modulation of the atomic spin direction with an oscillating magnetic field shifts the detected signal to high frequencies. Using a fiber-coupled distributed feedback laser, we achieve magnetic field sensitivity of 7 fT/Hz7\text{ }\text{fT}/\sqrt{\text{Hz}}7 fT/Hz​ with a miniature $5\ifmmode\times\else\texttimes\fi{}5\ifmmode\times\else\texttimes\fi{}5\text{ }\text{mm}\text{ }\text{Rb}$ vapor cell.
Three-axis atomic magnetometers have great advantages for interpreting information conveyed by magnetic fields. Here, we demonstrate a compact construction of a three-axis vector atomic magnetometer. The magnetometer is operated with a single laser beam and with a specially designed triangular 87Rb vapor cell (side length is 5 mm). The ability of three-axis measurement is realized by reflecting the light beam in the cell chamber under high pressure, so that the atoms before and after reflection are polarized along two different directions. It achieves a sensitivity of 40 fT/Hz in x-axis, 20 fT/Hz in y-axis, and 30 fT/Hz in z-axis under spin-exchange relaxation-free regime. The crosstalk effect between different axes is proven to be little in this configuration. The sensor configuration here is expected to form further values, especially for vector biomagnetism measurement, clinical diagnosis, and field source reconstruction.
We investigate an all-optical scheme for high-sensitivity measurements of the Earth's scale magnetic field (BBB). The scheme is based on the Bell-Bloom technique with frequency-modulated light. A single elliptically polarized light beam is used both for pumping the alkali-metal atoms and probing Larmor precession of their spins under the external magnetic field. In contrast to many other high-sensitivity magnetometry schemes based on nonlinear polarization rotation of the light, the proposed approach enables the observation of magnetic resonance via changes in the light-beam ellipticity parameter. The approach has been validated in experiments with a vertical-cavity surface-emitting laser, irradiating a 0.1250.1250.125 cm3^33 cesium vapor cell filled with a buffer gas. In the current experimental conditions, the achieved sensitivity is estimated at 220220220 fT/√\surd√Hz under BBB ≈ \,\approx\,≈505050 μμμT, while the shot-noise floor corresponds to ≈ \approx\,≈202020 fT/√\surd√Hz. The bandwidth is estimated at ≈ \approx\,≈111 kHz. The proposed simple and robust single-beam scheme is well suited for miniaturization and is therefore particularly promising for the development of compact, highly sensitive, low-power-consumption atomic magnetometers for a wide range of applications in the geomagnetic field.
Abstract We display a single-beam triaxial spin-exchange relaxation-free (SERF) atomic magnetometer by utilizing two orthogonal transverse modulation fields perpendicular to the light. The magnetic field’s three-axis vector components can be extracted simultaneously and independently from the transmitted light by lock-in amplifiers with reference to the different demodulated frequencies. We find that the residual magnetic field is a significant factor that could affect triaxial coupling, and specially the influence of the z -axis remanence on xy -axis coupling is studied in detail. Under the optimal parameters, the three-axis sensitivities are 20 fT Hz − 1 / 2 in the x - and y - axis, and 230 fT Hz − 1 / 2 in the z -axis. Meanwhile, the three-axis bandwidths are 110 Hz, 138 Hz and 211 Hz in the x -, y - and z -axis, respectively. The proposed single-beam triaxial SERF atomic magnetometer could be used to construct a compact and low-cost atomic sensor that is particularly suitable for the vector measurement of the biomagnetic such as magnetoencephalography and magnetocardiography.