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.
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.
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.
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.
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.
A miniature wide-range three-axis vector atomic magnetometer under spin-exchange relaxation-free regime has been developed. With a cylindrical vapor cell of size 10 mm in diameter and length, we have constructed a single-beam configuration through a polarization-maintaining fiber carrying the laser beam to the sensor and a multimode fiber guiding the transmitted light field to the photodiode. A rotating field on the plane perpendicular to the direction of propagation of the laser and another modulation field in the pump direction, which are generated in the field programmable gate array using direct digital synthesis to measure the three components of the magnetic field simultaneously. The spin-exchange relaxation is suppressed in zero field controlled by a feedback system, thus a wide range and excellent accuracy of three-axis vector atomic magnetometer response is obtained. Consequently, the transverse magnetic field sensitivity of 350 fT/Hz1/2and longitudinal field sensitivity of 3pT/Hz1/2are achieved with a dynamic range of 60000 nT. This sensor with compact size, wide range and high sensitivity is particularly suitable for geomagnetic observatory and space exploration.
Atomic magnetometers operated in spin-exchange relaxation-free (SERF) have the potential to replace superconducting quantum interference devices (SQUIDs) in the field of biomagnetism. Here, we demonstrate the dual-axis closed-loop control of a single-beam SERF magnetometer that allows sensing of two orthogonal magnetic fields simultaneously and independently with suppressed cross-talk effect, achieved by applying a rotating modulation field and using of the negative feedback. Operating in the dual-axis closed-loop mode with a miniature 4 × 4 × 4 mm 87Rb cell, we achieve magnetic field sensitivity of 20 fT/Hz1/2 and a bandwidth of 1.8 kHz. In addition to the experimental study of the sensitivity and bandwidth, we perform a theoretical analysis to the dual-axis response and develop an effective decoupling method. The implementation of closed-loop control enables the magnetometer to be robust against the disturbance of the ambient field, which could enlarge the dynamic range, enhance the systematic stability, and suppress the cross-talk effect. Such a simple, yet high-performance SERF magnetometer could be suitable as a promising candidate in the field of biomagnetism, allowing for a denser sensor array and opening up new possibilities for the noninvasive biomagnetic imaging.
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.