Atomic magnetometers with magnetic field modulation have emerged as pivotal sensors for biomagnetic measurements. However, challenges such as crosstalk between adjacent modulation fields and the complexity of signal circuitry become increasingly serious in the development of array-based equipment with the magnetometers, especially in the miniaturized atomic magnetometer. This paper proposes an all-optical, fully integrated fiber-coupled atomic magnetometer that employs pump beam modulation. A miniaturized atomic magnetometer with a volume of 10 cm³ has been designed, incorporating an active measurement area of 3 × 3 × 3 mm3. The magnetometer operates in the spinexchange relaxation-free (SERF) regime with an 87Rb vapor cell. An amplitude-modulated pump beam directly modulates the rubidium atomic ensembles, rather than the magnetic field modulation. The optical rotation angle is detected by an unmodulated probe beam oriented orthogonally to the pump beam. In light of the discontinuous pumping characteristics, we developed a modified theoretical model to clarify the output response of the proposed atomic magnetometer. The experimental results demonstrate that the new design achieves the same sensitivity as conventional magnetometer configurations with a smaller volume and without crosstalk of the magnetic field. This research highlights the significant potential for advancing the development of highly sensitive, miniaturized atomic magnetometers, making them particularly suitable for applications in magnetocardiography (MCG) and magnetoencephalography (MEG).
Optically pumped gradiometers have emerged as a promising tool for measuring extremely weak magnetic fields generated by nearby bio-magnetic sources, providing remarkable advantages such as high sensitivity, compact footprint, and the ability to operate in unshielded environments. However, existing gradiometer configurations often employ fixed baseline distances, which hinders the optimization of parameters such as baseline distance when dealing with magnetic sources of different sizes. Moreover, there is a lack of universal conclusions in current research regarding the optimal selection of baseline distance, measurement distance, and other parameters for various magnetic source types. To address this issue, we construct a dual-channel spin-exchange relaxation-free (SERF) gradiometer with an adjustable baseline ranging from 5 mm to 60 mm to investigate the relationships between the baseline distance of the gradiometer, the size of the magnetic field source, and the measurement distance, as well as their impact on the signal-to-noise ratio (SNR). By employing circular coils of different radii to simulate magnetic field sources, we measure the SNR of the gradiometer under the distance ranging from 40 mm to 95 mm and present normalized SNR curves that illustrate the relationship between the baseline distance, field source radius, and measurement distance. To ensure universal applicability, the specific distances are converted into multiples of the source radius. The results demonstrate that positioning the gradiometer closer to the source enhances its SNR, regardless of the source size. However, the optimal baseline distance varies depending on the source size, with smaller sources requiring relatively longer baselines to achieve better performance. We believe these findings can offer reliable evidence for optimizing gradiometer configurations in bio-magnetic measurements and other applications involving sources of different sizes
An in situ simultaneous measurement of magnetic coil constants and nonorthogonal angles method is proposed using the atomic magnetometer. Based on the transient response of the atomic spin polarization under the different magnetic fields, we establish the corresponding measurement model of magnetic coil constants and nonorthogonal angles through the relationship between the Larmor precession frequency and the external magnetic field. By this model, we experimentally obtained the coil constants of x , y, and z axes are, respectively, 9.04 ± 0.10, 8.94 ± 0.07, and 4.34 ± 0.02 nT / V in our system. The nonorthogonal angles are 89.04 deg between x axis and y axis, 88.60 deg between y axis and z axis, and 91.15 deg between z axis and x axis. This method can be used to simultaneously measure magnetic coil constants and nonorthogonal angles without relying on external instruments, which provides a basic guarantee for the accurate calculation sensitivity of spin-exchange-relaxation-free atomic magnetometers, especially for miniaturized atomic magnetometers.
Laser heating of alkali metal vapor cells of atomic magnetometers is applied owing to its none magnetic field interference and little energy consumption, compared to heating by hot air and heating by AC electrical current. The development of laser heating technology, including the attachment of optical filters for better heat absorption, has expanded its usage from small chip-scale cells to relatively large cells, and from heating of single magnetometer to heating of an array of magnetometers. This paper offers a review of the evolution of laser heating in atomic magnetometers, introduces the different configurations of laser heating in experiments and points out the next possible target of the application of laser heating.
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