This paper investigates the performance optimization of optically pumped magnetometers under zero-field parametric modulation. Based on the analytical solutions of the Bloch equation, both longitudinal and transverse modulations are studied experimentally. To estimate the nonuniform polarization distribution of alkali-metal atoms in the vapor cell, an average pumping rate model is proposed. Furthermore, the accuracy of this model and the measurement of the transverse relaxation rate are verified via the agreement between experimental and theoretical values. The results indicate that optimal performance can be achieved by employing a suitable modulation field, the selection of which is related to the modulation index $u$ in the Bessel series and the pump-light intensity. Although both operating modes show similar responses to weak magnetic fields, their effects on pump-light intensity are different due to the means of detecting atomic polarization. An optimal value of the pump-light intensity on the response strength exists in longitudinal modulation. However, with regard to transverse modulation, the sensitivity under weak pump-light intensity is better. This research has far-reaching significance for cases when the parametric modulation is manipulated.

Spin-exchange relaxation-free gyroscope (SERFG) is a promising rotation sensor, and the bias error is one of its most important characteristics. It is identified that rotation measurement noise induced by thermal magnetization fluctuations inherent in the ferrite shield in a SERFG limits its bias stability. The root cause of this error lies in the low-frequency magnetic field sensitivity dominated by the nuclear spin relaxation rate. In this paper, the steady state response model of a SERFG is modified considering the non-negligible nuclear relaxation rate and the pressure-dependent magnetic field sensitivity is experimentally studied. Our results show that reducing nuclear spin relaxation is an effective method to suppress the bias error induced by thermal magnetization fluctuations. Finally, in case of Pneon=1 atm, it is estimated that a bias stability limit of 5×10-4 deg/h is set by the lowest thermal magnetization noise of 4.4f-1/2 fT ever reported in a ferrite shield.

Nuclear spin co-magnetometer operated in spin-exchange relaxation-free (SERF) regime is a promising tool for long-term navigation application for its abilities to sense inertial rotation and to suppress environmental magnetic field disturbance. The magnetic field response model of a K-Rb-21Ne nuclear spin co-magnetometer is derived based on the state space method and the model is experimentally validated on a tabletop SERF co-magnetometer. Theoretical and experimental results indicate that the relaxation rate of the nuclear spins limits the field-suppression ability. The results here not only give insight into the nature of self-compensate characteristic, but also provide a precise model for the estimation on magnetic noise induced rotation measurement error in SERF co-magnetometer.

This paper investigates the laser polarization error in the optical rotation detection system (ORDS) of an atomic comagnetometer (ACM), which will seriously degrade the long-term performance of the ORDS. We first establish an optical transmission model of the ORDS by using Jones matrix concerning the optical imperfection of polarizers. Then, we analyze the polarization error based on this model and propose a novel error suppression method. Finally, we experimentally test the long-term performance of the ORDS and the ACM before and after the polarization error suppression to verify the effectiveness of the proposed method. The experimental results show that the long-term performance of the ORDS and the ACM can be improved by approximately 3.4 times with the proposed polarization error suppression method.

The coupling between the transverse magnetic field and the angular velocity in atomic spin gyroscopes (ASGs) makes it difficult to achieve high-precision in situ closed-loop control, which seriously affects the long-term stability of the gyroscopes. This article innovatively proposes a transverse magnetic field closed-loop control method based on high-frequency modulation and transient response. A steady-state response model for the electron spin–nuclear spin coupling ensemble based on high-frequency modulation is established, enabling high-precision in situ measurement of the transverse magnetic field. A method for decoupling the transverse magnetic field and angular velocity based on transient response is proposed. Based on the above, a transverse magnetic field closed-loop control scheme is designed, achieving high-precision in situ closed-loop control in the ASGs for the first time. Experimental results demonstrate that the sensitivities of in situ transverse magnetic field measurements reach 50 and 110 fT/Hz$\mathbf {^{1/2}}$, respectively. The inertial sensitivity of the ASGs is improved by 23.8$\%$ to $\mathbf {6.30 \times {10^{ - 6}}}^{\circ }$/s/Hz$\mathbf {^{1/2}}$, and the bias instability is reduced by 31.3$\%$ to $\mathbf {9.04 \times {10^{-3}}}^{\circ }$/h. This approach is of great significance for improving the anti-interference capability of ASGs and broadening their application range.