In recent years, arrayed atomic magnetometers have been continuously applied in biomagnetic scenarios. However, the crosstalk between adjacent sensors introduced by the modulated magnetic fields significantly compromises the imaging accuracy of arrayed atomic magnetometers. To solve this problem, a detuned square-wave optical modulation zero-field atomic magnetometer configuration is developed and we provide an analytical solution of this method. In this scheme, the circularly polarized pump light is used to polarize alkali metal atoms longitudinally, and a beam of detuned square-wave modulated circularly polarized light is applied transversely to generate a light-shift modulation instead of the coil-generated modulated magnetic field. Then the transverse magnetic field is measured by the optical absorption method of longitudinally circularly polarized pump light. This scheme maintains the inherent advantage of high sensitivity in spinexchange relaxation-free (SERF) atomic magnetometers. Additionally, the all-optical configuration eliminates the need for additional modulated magnetic fields or radio frequency (RF) fields, thereby mitigating crosstalk issues associated with modulated magnetic fields in array applications. Consequently, this scheme exhibits great potential for arraying and is expected to be employed in magnetocardiography (MCG) and magnetoencephalography (MEG).
In recent years, arrayed atomic magnetometers have been continuously applied in biomagnetic scenarios. However, the crosstalk between adjacent sensors introduced by the modulated magnetic fields significantly compromises the imaging accuracy of arrayed atomic magnetometers. To solve this problem, a detuned square-wave optical modulation zero-field atomic magnetometer configuration is developed and we provide an analytical solution of this method. In this scheme, the circularly polarized pump light is used to polarize alkali metal atoms longitudinally, and a beam of detuned square-wave modulated circularly polarized light is applied transversely to generate a light-shift modulation instead of the coil-generated modulated magnetic field. Then the transverse magnetic field is measured by the optical absorption method of longitudinally circularly polarized pump light. This scheme maintains the inherent advantage of high sensitivity in spinexchange relaxation-free (SERF) atomic magnetometers. Additionally, the all-optical configuration eliminates the need for additional modulated magnetic fields or radio frequency (RF) fields, thereby mitigating crosstalk issues associated with modulated magnetic fields in array applications. Consequently, this scheme exhibits great potential for arraying and is expected to be employed in magnetocardiography (MCG) and magnetoencephalography (MEG).
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).
Abstract High-sensitivity triaxial magnetic field measurements are crucial in various scientific and industrial applications, with spin-exchange relaxation-free (SERF) atomic magnetometers (AMs) standing out for their exceptional sensitivity. However, conventional methods for achieving triaxial measurements in SERF magnetometers typically involve multiple modulated magnetic fields, which introduce crosstalk challenges in array-based configurations. We propose a static bias magnetic field assisted optical modulation triaxial AM to address this limitation. In this configuration, the detuned circularly polarized light is utilized to achieve synchronous modulation of the fictitious magnetic field and pumping rate while incorporating a static bias magnetic field to generate a transverse projection component. We develop a comprehensive triaxial response model that fully considers the effects of the longitudinal spin polarization deflection. Building upon this model, we derive the relationship between the transverse spin component and the triaxial magnetic field and introduce parameter optimization methods to obtain optimal parameters, thus enabling triaxial measurements of 12 fT Hz −1/2 , 10 fT Hz −1/2 , and 15 fT Hz −1/2 along the x-, y -, and z -axes. Our approach offers significant advantages over existing methods, particularly in minimizing crosstalk and mitigating spin-exchange relaxation introduced by multiple modulated magnetic fields. Moreover, the effective detection of simulated magnetocardiography signals highlights the practical applicability and reliability of the proposed method in real-world scenarios.
In spin-exchange-relaxation-free (SERF) atomic magnetometers (AMs), the attenuation of circularly polarized pump beam introduces spatial-dependent artificial magnetic fields in atomic spin polarization and light shift. In general, such a spatial-dependent effective magnetic field, especially prevalent in single-cell magnetometer arrays, cannot be uniformly compensated over the entire excitation region, resulting in a complex distributed compensation mask effect. In addition, any external effective-field-compensation methods inevitably complicate the final analysis of the unknown magnetic field measured. Here, we report a new excitation scheme that can substantially suppress spatial nonuniformity due to pump beam attenuation. Using counter-propagating pump beams with symmetrically red- and blue-detuning-paired frequencies, we demonstrate a significant reduction of spatial inhomogeneity in atomic spin polarization and light shift in comparison with the usual single-frequency unidirection and counter-propagating pump schemes. Employing this red-/blue-detuning-paired pump scheme, we construct a single-cell, four-channel SERF magnetometer array with high spatial homogeneity. We demonstrate ~10-fT/Hz1/2sensitivity in the 5–45-Hz band for all four channels, with a gradient sensitivity of 2 fT/Hz1/21/2/cm in the same band. This new scheme enables the development of single-vapor-cell, high-uniformity multichannel magnetic field mapping devices with potential applications in magnetoencephalography (MEG) and magnetocardiography (MCG), or in searching for exotic spin-dependent interactions.
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).
Emerging quantum sensing devices namely atomic magnetometers have become promising candidate for future biomagnetism imaging. However, the limitation of detection bandwidth exists a major drawback for devices of this kind. Conventional approaches, including transverse magnetic field modulation and close-loop control, have seen challenging tradeoffs between size, resolution and bandwidths. In this study, a wide bandwidth zero-field magnetometer with a miniaturized light source has been developed for alternating current (AC) magnetic field detection. A dual-beam Spin-Exchange Relaxation-Free (SERF) magnetometer employing a 4×4×4mm3 alkali metal vapor cell achieves a bandwidth of 188 Hz. This represents a threefold increase in bandwidth compared to non-modulated mode. The sensitivity under modulated mode demonstrated a sensitivity of 55fT/Hz1/2within the frequency range of 10-188Hz. Our results also demonstrated that the sensitivity is constrained by relaxation induced by the modulation of pumping source, so possible tradeoffs can be made based on various applications. The proposed method provides novel approach for bandwidth extension of atomic magnetometers which further pave the way for future applications including magnetoencephalography (MEG), particularly in reducing magnetic noise crosstalk and enhancing spatial resolution.