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IEEE Sensors Journal

Single-Beam Atomic Magnetometer Enhanced With Elliptically Polarized Reflected Light

An‐Ning Xu, Jin Peng, Yiran Yin, Bei Liu

Published Jun 27, 2024• 7 citations
Publisher

Abstract

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.

DOI
10.1109/jsen.2024.3417902

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Journal of Physics D Applied Physics•Oct 24, 2022•22 citations
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.
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).
Abstract The chip-scale hybrid optical pumping spin-exchange relaxation-free (SERF) atomic magnetometer with a single-beam arrangement has prominent applications in biomagnetic measurements because of its outstanding features, including ultrahigh sensitivity, an enhanced signal-to-noise ratio, homogeneous spin polarization and a much simpler optical configuration than other devices. In this work, a miniaturized single-beam hybrid optical pumping SERF atomic magnetometer based on a microfabricated atomic vapor cell is demonstrated. Although the optically thin Cs atoms are spin-polarized, the dense Rb atoms determine the experimental results. The enhanced signal strength and narrowed resonance linewidth are experimentally proven, which shows the superiority of the proposed magnetometer scheme. By using a differential detection scheme, we effectively suppress optical noise with an approximate five-fold improvement. Moreover, the cell temperature markedly affects the performance of the magnetometer. We systematically investigate the effects of temperature on the magnetometer parameters. The theoretical basis for these effects is explained in detail. The developed miniaturized magnetometer has an optimal magnetic sensitivity of 20 fT/Hz 1/2 . The presented work provides a foundation for the chip-scale integration of ultrahighly sensitive quantum magnetometers that can be used for forward-looking magnetocardiography (MCG) and magnetoencephalography (MEG) applications.
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.
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.
A reflected atomic magnetometer with single beam is described in this study. A single beam propagates forward for polarizing the atoms and backward for detecting Larmor precession after reflection. The feasibility of the system was studied theoretically and experimentally and compared with the single beam with ellipticity. In reflected scheme, high pump efficiency ensures a reduced power and more flexible operating wavelength considering the AC Stark shift, pump efficiency, and probe signal. The nonuniform optical rotation distribution along the cell was also analyzed. The wavelength of the system was optimized to 795.3 nm. The magnetic field sensitivity of the system is achieved to be 600 fT/Hz1/2and the experimental bandwidth was 17 Hz. The compact design enables new possibility of the atomic magnetometer for magnetoencephalography systems.
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.