In a nuclear spin co-magnetometer, it was found that the probe light parameters have a significant impact on the transverse residual magnetic field compensation. In this paper, we demonstrated that this effect is caused by the tensor light shifts of the linearly polarized probe light. This effect can be suppressed at a certain probe light polarization. We obtained this probe light polarization experimentally and reduced the impact of probe power on magnetic field compensation by 35 times. The impact of probe light frequency is also suppressed. Furthermore, the influence of the pump power, the static magnetic field, and the cell temperature on this optimized polarization was investigated. The tensor light shift can be suppressed at about 17° polarization under different conditions in our system. Moreover, the actual residual magnetic field in the magnetic shields can be obtained, which is useful for the magnetic field design of the co-magnetometer, and this method can also be extended to other atomic devices to suppress the tensor light shift.
In a nuclear spin co-magnetometer, it was found that the probe light parameters have a significant impact on the transverse residual magnetic field compensation. In this paper, we demonstrated that this effect is caused by the tensor light shifts of the linearly polarized probe light. This effect can be suppressed at a certain probe light polarization. We obtained this probe light polarization experimentally and reduced the impact of probe power on magnetic field compensation by 35 times. The impact of probe light frequency is also suppressed. Furthermore, the influence of the pump power, the static magnetic field, and the cell temperature on this optimized polarization was investigated. The tensor light shift can be suppressed at about 17° polarization under different conditions in our system. Moreover, the actual residual magnetic field in the magnetic shields can be obtained, which is useful for the magnetic field design of the co-magnetometer, and this method can also be extended to other atomic devices to suppress the tensor light shift.
Atomic magnetometers (AMs) are used in various fields, including magnetocardiography and magnetoencephalography. In AMs, accurately distinguishing and measuring the light-shift equivalent magnetic field generated by the pump beam from the remanent field within the central area of a magnetic shield has been a significant challenge. This paper presents a novel measurement method that addresses this issue using87Rb AMs. By exploiting the distinctive responses of the magnetometer to oscillating magnetic fields under different pump photon spin polarization vectors s and employing a fitting technique at the resonance peak, we determined both the residual field and light shift. Furthermore, we conducted comprehensive numerical simulations to analyze the light shift of the pump beam under various conditions, e.g., photon spin vectors, intensities, and frequency detuning. Additionally, experimental measurements were performed to investigate the pressure broadening effect on the D1 line of the cell. The proposed method allows precise measurement of remanent fields while eliminating the influence of light shift; thus, it is useful for high-precision atomic device measurements in diverse experimental settings.
The transverse light-shift can induce non-negligible polarization error in the output signal of spin-exchange relaxation-free (SERF) co-magnetometer. In this paper, a novel method for rapid measurement of transverse light-shift based on the error of steady-state response of co-magnetometer is proposed firstly, then the sources of transverse light-shift in a compact SERF co-magnetometer is modeled and analyzed from three aspects: the non-ideal linear polarization of probe laser, the circular dichroism of the atomic spin ensembles, and the stress-induced birefringence effect of the cell wall. Furthermore, the decoupling and suppression methods of transverse light-shift based on a degree of circular polarization (DOCP) regulation scheme is presented, to realize the decoupling measurement of the transverse light-shift introduced by the whole co-magnetometer cell, and cancel it out with the non-ideal linear polarization of the probe laser. Eventually, the DOCP regulation scheme suggested in this paper achieves more than a 67% suppression ratio in transverse light-shift, and the short- and long-term performance of SERF co-magnetometer are improved due to the reduction of the coupling effect between the probe laser power and transverse field. Moreover, the measurement, decoupling and suppression methods provided in this paper also have the potential to be applied to other atomic sensors, such as the SERF magnetometers and nuclear spin co-magnetometers.
A novel method to compensate the residual magnetic field for an atomic magnetometer consisting of two perpendicular beams of polarizations was demonstrated in this paper. The method can realize magnetic compensation in the case where the pumping rate of the probe beam cannot be ignored. In the experiment, the probe beam is always linearly polarized, whereas, the probe beam contains a residual circular component due to the imperfection of the polarizer, which leads to the pumping effect of the probe beam. A simulation of the probe beam's optical rotation and pumping rate was demonstrated. At the optimized points, the wavelength of the probe beam was optimized to achieve the largest optical rotation. Although, there is a small circular component in the linearly polarized probe beam, the pumping rate of the probe beam was non-negligible at the optimized wavelength which if ignored would lead to inaccuracies in the magnetic field compensation. Therefore, the dynamic equation of spin evolution was solved by considering the pumping effect of the probe beam. Based on the quasi-static solution, a novel magnetic compensation method was proposed, which contains two main steps: (1) the non-pumping compensation and (2) the sequence compensation with a very specific sequence. After these two main steps, a three-axis in situ magnetic compensation was achieved. The compensation method was suitable to design closed-loop spin-exchange relaxation-free magnetometer. By a combination of the magnetic compensation and the optimization, the magnetic field sensitivity was approximately 4 fT/Hz(1/2), which was mainly dominated by the noise of the magnetic shield.
Abstract In a K-Rb- 21 Ne co-magnetometer, the Rb electron magnetic field which is experienced by the nuclear spin is about 100 times larger than that of the K in a K- 3 He co-magnetometer. The large electron magnetic field which is neglected in the K- 3 He co-magnetometer coupled Bloch equations model is considered here in the K-Rb- 21 Ne co-magnetometer to study the low frequency magnetic field suppression effect. Theoretical analysis and experimental results shows that in the K-Rb- 21 Ne spin co-magnetometer, not only the nuclear spin but also the large electron spin magnetic field compensate the external magnetic field noise. By comparison, only the 3 He nuclear spins mainly compensate the external magnetic field noise in a K- 3 He co-magnetometer. With this study, in addition to just increasing the magnetic field of the nuclear spins, we can suppress the magnetic field noise by increasing the density of the electron spin. We also studied how the magnetic field suppression effect relates to the scale factor of the K-Rb- 21 Ne co-magnetometer and we compared the scale factor with that of the K- 3 He co-magnetometer. Lastly, we show the sensitivity of our co-magnetometer. The magnetic field noise, the air density fluctuation noise and pumping power optimization are studied to improve the sensitivity of the co-magnetometer.
Quantum manipulation technology and photoelectric detection technology have jointly facilitated the rapid development of ultra-sensitive atomic spin magnetometers. To improve the output signal and sensitivity of the spin-exchange-relaxation-free (SERF) atomic spin magnetometer, the noises influencing on the output signal and the sensitivity were analyzed, and the corresponding noise suppression methods were presented. The magnetic field noises, including the residual magnetic field noise and the light shift noise, were reduced to approximately zero by employing the magnetic field compensation method and by adjusting the frequency of the pump beam, respectively. With respect to the operation temperature, the simulation results showed that the temperature of the potassium atomic spin magnetometer realizing the spin-exchange relaxation-free regime was 180 °C. Moreover, the fluctuation noises of the frequency and the power were suppressed by using the frequency and the power stable systems. The experimental power stability results showed that the light intensity stability was enhanced 10%. Contrast experiments on the sensitivity were carried out to demonstrate the validity of the suppression methods. Finally, a sensitivity of 13 fT/Hz(1/2) was successfully achieved by suppressing noises and optimizing parameters.
Ultrasensitive atomic comagnetometers (ACMs) are invaluable tools for both inertial measurement and fundamental physics research. However, the misalignment between the pump light and the main magnetic field affects the polarization characteristics of nuclear spins of the noble gas atoms, making it a significant source of noise. In this article, an atomic magnetometer response model with the optical-magnetic misalignment error is established, and the mechanism of the influence of optical-magnetic misalignment on nuclear spin polarization is analyzed. An in situ evaluation method and a suppression method of optical-magnetic misalignment error are proposed, and their effectiveness is verified through experiments with varying pump light incidence directions. The experimental results indicate that after optical-magnetic alignment using the proposed method, the spin polarization of the coupled atomic ensemble is enhanced by 20.7%, and the longitudinal relaxation rate of the nuclear spin is reduced by 6.9%. Additionally, the amplitude-frequency response (AFR) of the x-axis magnetic field is reduced by 33.2% at 1 Hz and by 53.1% at frequencies below 0.002 Hz. This indicates an improvement in the transverse magnetic field error suppression capability of the ACMs.