The spin exchange relaxation free (SERF) atomic magnetometer has been a research hotspot due to its ultra-high sensitivity. The SERF atomic magnetometer's sensitivity is subject to the accuracy of its compensating magnetic field and the calibration signal. These two processes need a tri-axial coil system to generate the required magnetic fields, which are directly affected by the non-orthogonality of the tri-axial coil system, especially the non-orthogonality between the x- and y-axes coils. In order to solve this problem, an ingenious and effective method for measuring the non-orthogonal angle between the x- and y-axes in a magnetic coil system has been demonstrated in this paper for the first time. This measurement method was only based on the dynamics of the SERF atomic magnetometer and did not need any additional calibration equipment. A large dc magnetic field Bywas applied to the y-axis, such that the magnetic field Byxprojected from Byon to the x-axis could be measured. By then solving the relevant trigonometric function, we could obtain the non-orthogonal angle. Using this method, we experimentally obtained the non-orthogonal angle of about 84.08° between the x- and y-axes saddle-shaped coils, with a variance of about 0.14°. Finally, the correctness of this method for calculating the non-orthogonal angle was analyzed.
The spin exchange relaxation free (SERF) atomic magnetometer has been a research hotspot due to its ultra-high sensitivity. The SERF atomic magnetometer's sensitivity is subject to the accuracy of its compensating magnetic field and the calibration signal. These two processes need a tri-axial coil system to generate the required magnetic fields, which are directly affected by the non-orthogonality of the tri-axial coil system, especially the non-orthogonality between the x- and y-axes coils. In order to solve this problem, an ingenious and effective method for measuring the non-orthogonal angle between the x- and y-axes in a magnetic coil system has been demonstrated in this paper for the first time. This measurement method was only based on the dynamics of the SERF atomic magnetometer and did not need any additional calibration equipment. A large dc magnetic field Bywas applied to the y-axis, such that the magnetic field Byxprojected from Byon to the x-axis could be measured. By then solving the relevant trigonometric function, we could obtain the non-orthogonal angle. Using this method, we experimentally obtained the non-orthogonal angle of about 84.08° between the x- and y-axes saddle-shaped coils, with a variance of about 0.14°. Finally, the correctness of this method for calculating the non-orthogonal angle was analyzed.
The calibration results of the triaxial coils affect the atomic magnetometer’s measurement sensitivity. For precise in situ calibration, we first studied the transient atomic dynamics of a dual-beam spin-exchange relaxation free (SERF) atomic magnetometer under alternating magnetic fields. We obtained the corresponding dynamic free-induction-decay (FID) curves by alternately applying square wave signals to thex-,y-, andz-axis coil, and then extracted the precession frequencies by fast Fourier transform (FFT) to achieve a decoupled calibration of the triaxial coil constants. Our calibration results were in better agreement under different experimental conditions than traditional parameter fitting methods with a relative error of less than 1.5% compared to conventional fluxgate calibration methods. Furthermore, we simultaneously measured nonorthogonal angles between each pair of axes: x–y, y–z, and z–x, respectively, which are used to correct the magnetic fields error. This method is suitable for coil calibration and nonorthogonal correction of integrated and miniaturized dual beam magnetometers.
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.
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.
In this study, we demonstrate a non-modulated triaxial magnetic field compensation method for spin-exchange relaxation-free (SERF) atomic magnetometers. We realize simultaneous compensation of the magnetic field along the pump and probe directions by maximizing the first order differential value of the zero-field resonance signal. The magnetic field perpendicular to the pump-probe plane is compensated by zeroing the DC response of the magnetometer. The zero-field resonance is obtained by applying a linearly changed magnetic field along the direction perpendicular to that of the pump-probe plane. The first order differential of the zero-field resonance is acquired using the second order central difference method in real time. Compared with the conventional compensation methods, this method does not involve modulation and demodulation. Therefore, it requires no lock-in amplifier, thus making it more applicable in miniature atomic devices. Moreover, this method compensates the magnetic field along the pump and probe directions using only one criterion. It avoids the cross-talk effect between the pump and probe directions in the presence of non-orthogonal coils. The experiment results show that the compensation resolution is 9 pT, 7 pT and 0.05 pT for the probe, pump, and direction perpendicular to the pump-probe plane, respectively.
The spin-exchange relaxation-free (SERF) atomic magnetometer has high sensitivity for magnetic field measurement, and is of great significance in frontier physics research, biomagnetic detection and other fields. In recent years, as one of the important development directions, its high spatial resolution and multi-channel magnetic field detection capabilities have been further extended. In this paper, based on the three-axis in-situ magnetic field zeroing method (MFZM), the accurate measurement of three-axis static magnetic field is realized, and the using of the digital micro-mirror device (DMD) further supports the measurement of two-dimensional three-axis magnetic field distribution in a specific area. Then, the experimental system was set up and realized the three-axis magnetic field measurement of 25 points within the 4 mm × 4 mm two-dimensional measurement range, and the resolution of each point is a square area with a side length of 0.8 mm. The proposed method based on the SERF atomic magnetometer can measure the triaxial magnetic field in the internal micro-regions in the magnetic field coil, magnetic shield, etc., helping the analysis and evaluation of the high-resolution magnetic field distribution.
The spin-exchange-relaxation-free (SERF) atomic magnetometer is an ultra-high sensitivity magnetometer, but it must be operated in a magnetic field with strength less than about 10 nT. Magnetic field compensation is an effective way to shield the magnetic field, and this paper demonstrates an in situ triaxial magnetic field compensation system for operating the SERF atomic magnetometer. The proposed hardware is based on optical pumping, which uses some part of the SERF atomic magnetometer itself, and the compensation method is implemented by analyzing the dynamics of the atomic spin. The experimental setup for this compensation system is described, and with this configuration, a residual magnetic field of strength less than 2 nT (±0.38 nT in the x axis, ±0.43 nT in the y axis, and ±1.62 nT in the z axis) has been achieved after compensation. The SERF atomic magnetometer was then used to verify that the residual triaxial magnetic fields were coincident with what were achieved by the compensation system.