ABSTRACT
The coupling of electron spin and nuclear spin through spin-exchange collisions compensates for external magnetic field interference in the spin-exchange relaxation-free (SERF) comagnetometer. However, the compensation ability for magnetic field interference along the detection axis is limited due to the presence of nuclear spin relaxation. This paper aims to enhance the self-compensation capability of the system by optimizing the pressure of the noble gas during cell filling. Models are established to describe the relationships between the nuclear spin polarization, the polarizing magnetic field of nuclei, the magnetic field suppression factors, and the pressure of the noble gas in the K-Rb-21Ne atomic ensemble. Experiments are conducted using five cells with different pressure. The results indicate that in the positive pressure area, the nuclear spin polarization decreases while the equivalent magnetic field experienced by the noble gas increases with increasing pressure. The magnetic field suppression factor for transverse fields increases as the pressure increases, leading to a decrease in the ability to suppress low-frequency magnetic field interference. Moreover, at the cell temperature of 180°C and a transverse residual field gradient of 4.012 nT/cm, the system exhibits its strongest capability to suppress transverse magnetic field interference when the pressure of 21Ne is around 0.7 atm.
ABSTRACT
The magnetic field gradient affects the improvement of sensitivity and magnetic field suppression ability of the spin-exchange relaxation-free co-magnetometer. This paper proposes a response model of a co-magnetometer considering magnetic field gradient based on state-space method. The effects of transverse and longitudinal magnetic field gradients on the system's scale factor, bandwidth and magnetic field response are analyzed. The analysis shows that transverse gradient affects the whole frequency band of system response, including steady-state and dynamic performance, while longitudinal gradient only affects steady-state response. With the increase of the gradient, the effect becomes more significant. The test results are in agreement with the theory, proving the accuracy of the theoretical analysis. The rotational sensitivity at 1 Hz decreases from 6.51 ×10-6 °/s/Hz1/2 to 5.05×10-5 °/s/Hz1/2 in the presence of a magnetic field gradient of -40 nT/cm, so the effect of the magnetic field gradient is critical. This work provides an accurate model for evaluating the effects of magnetic field gradients and provides a method for suppressing gradients using gradient coils, which are important for improving the sensitivity and accuracy of co-magnetometers.
ABSTRACT
The misalignment error of the pumping laser in the atomic comagnetometer (ACM) dramatically diminishes the efficiency of the optical pumping process (characterized by the polarization of the hybrid atomic spin ensembles containing electron spins and nuclear spins) and deteriorates the performance of the ACM (characterized by the Allan standard deviation). In this work, a steady-state response model considering the misalignment error of the pumping laser is established and an in-situ evaluation method for this error is proposed. Based on the evaluation method, the influence of this misalignment error on the pumping efficiency and the performance of the ACM is quantitatively analyzed. Furthermore, a pumping laser alignment method based on the second harmonic of a single-beam magnetometer is then proposed, whose effectiveness is verified by experiments. The experimental results show that compared to the original ACM with the severely misaligned pumping laser, the polarization of the hybrid atomic spin ensembles of the ACM with the pumping laser aligned by the proposed method is increased by about 19%, and the corresponding Allan variance at 100s is reduced by about 40%.
ABSTRACT
The ferrite magnetic shield is widely used in ultra-high-sensitivity atomic sensors because of its low noise characteristics. However, its noise level varies with temperature and affects the performance of the spin-exchange relaxation-free (SERF) co-magnetometer. Therefore, it is necessary to analyze and suppress the thermal magnetic noise. In this paper, the thermal magnetic noise model of a ferrite magnetic shield is established, and the thermal magnetic noise of ferrite is calculated more accurately by testing the low-frequency complex permeability at different temperatures. A temperature suppression method based on the improved heat dissipation efficiency of the ferrite magnetic shield is also proposed. The magnetic noise of the ferrite is reduced by 46.7%. The experiment is basically consistent with the theory. The sensitivity of the co-magnetometer is decreased significantly, from 1.21 × 10-5°/s/Hz1/2 to 7.02 × 10-6°/s/Hz1/2 at 1 Hz. The experimental results demonstrate the effectiveness of the proposed method. In addition, the study is also helpful for evaluating the thermal magnetic noise of other materials.