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.

A novel method to control the light intensity stability and modulate the probe light polarization using a liquid crystal variable retarder (LCVR) to detect atomic spin precession simultaneously in a K-Rb-²¹Ne gyroscope is reported. A sinusoidal driving voltage is applied to drive the LCVR and is skillfully used to produce a high-frequency modulation for the probe light. The modulation helps to avoid electronic detection noise appearing at low frequencies and allows for phase-sensitive detection. The coefficient of rate ramp can be reduced from 1.31 (deg/h)/h to 0.05 (deg/h)/h (Allan deviation), and the bias instability of about 0.08 deg/h at the averaging time of 200 s is achieved. Therefore, the long-term stability of the angular velocity measurement can be improved and other optical modulators can be replaced to facilitate the miniaturization of the gyroscope by using this intensity modulation detection method. This optical rotation detection method also can be applied to other miniaturized atomic sensors, such as atomic magnetometers.

This study presents the development of a SERF atomic co-magnetometer with a magnetic shielding system. The shielding system includes multiple cylindrical passive magnetic shield and active magnetic compensation coils. The multilayer shield, which adopts a structural style comprising a barrel body and end cover, is applied to attenuate the external magnetic field to less than 10 nT or ideally close to zero. For the purpose of degaussing, pumping, and probing light paths, several openings must be made on the magnetic shield. A hybrid approach combining theoretical calculations and the finite element method is proposed to analyze the shielding properties, considering the influence of openings. To evaluate the shielding properties of the magnetic shield, two different simplified finite element models are established and analyzed. The simulation results are compared with theoretical and experimental data, and the results are in good agreement. The modeled results show that the openings bear a considerable influence on the shielding performance, and thus, their effect cannot be ignored. The axial magnetic shielding factor with several openings is roughly 4.4×104, which is about two orders of magnitude lower than that without openings. Further, a rotation sensitivity of 5.86×10–7rad·s–1·Hz–1/2 is obtained with the open-hole magnetic shield. This sensitivity corresponds to a magnetic sensitivity of 27.8 fT/Hz1/2. Based on the results, possible improvements are suggested for future designs.