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arXiv:1510.00885

Polarization measurement of Cs using the pump laser beam

Jiancheng Fang, Rujie Li, Lihong Duan, Wenfeng Fan, Liwei Jiang

Published Oct 3, 2015• 0 citations
arXivHTMLPDF

Abstract

In the optical pumping systems based on the pump-probe arrangement, the spin polarization of the atoms is generally monitored utilizing the probe laser beam, in which way an extra perturbation must be introduced and thus affects the normal operation of the sensors. By investigating the absorption rate of the circularly polarized pump laser, here we demonstrate the feasibility of extracting the electron-spin polarization from the transmitted pump laser intensity. We experimentally validate the method in a spin-exchange relaxation free (SERF) magnetometer and the results are in excellent agreement with the theory. The scheme operates in a silent mode and features a real-time observation. We also study the corresponding magnetic field response of the SERF magnetometer and a term arising from the diffusion effects has been added to the original model to explain the discrepancy of the response.

DOI
10.48550/arxiv.1510.00885

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In the optical pumping systems based on the pump-probe arrangement, the spin polarization of the atoms is generally monitored utilizing the probe laser beam, in which way an extra perturbation must be introduced and thus affects the normal operation of the sensors. By investigating the absorption rate of the circularly polarized pump laser, here we demonstrate the feasibility of extracting the electron-spin polarization from the transmitted pump laser intensity. We experimentally validate the method in a spin-exchange relaxation free (SERF) magnetometer and the results are in excellent agreement with the theory. The scheme operates in a silent mode and features a real-time observation. We also study the corresponding magnetic field response of the SERF magnetometer and a term arising from the diffusion effects has been added to the original model to explain the discrepancy of the response.
In the optically pumped systems, the spin polarization of the atoms is generally derived by employing additional modulations, in which way an extra perturbation will be introduced and thus affect the normal operation of the sensors. By investigating the absorption principle of the circularly polarized pump laser, here, we demonstrate the feasibility of extracting the electron-spin polarization from the transmitted intensity of the pump beam. This scheme can detect real-time polarization without disturbing the normal operation of the sensor, and the experimental result agrees well with the theory. This research is of value to the research and development of optically pumped systems, especially the magnetometer, and the comagnetometer operated in the spin-exchange relaxation free regime.
A laser beam with left-/right-handed circular polarization is generally used to create the oriented atomic spins for precision measurements in a spin-exchange relaxation-free (SERF) co-magnetometer. The fluctuation of laser polarization interferes with the spin polarization of alkali metal atoms, leading to the system performance degradation. Here, we report a method for real-time polarization state measurement by using the transmitted light intensity of the pump beam passing through the vapor cell. Based on the principle of circular dichroism, the optical absorption model of polarized alkali metal atoms is established. The simulation results of the transmittance of the pump laser with different polarization states through the alkali metal vapor cell are given and verified by experiments. The experimental results show that the circularly polarized beam has the weakest absorption, while the linearly polarized laser beam is absorbed the strongest. The achieved measurement accuracy stands at an impressive 98.83 %. This work provides a simple and easy-to-use way to measure the polarization state of the laser beam used in the vapor cell devices, particularly the microfabricated prototypes with limited space.
Abstract Spin-exchange relaxation-free (SERF) co-magnetometers have promising applications in both inertial navigation and fundamental physics experiments. However, the fluctuation in the spin polarization caused by the probe beam has a non-negligible influence on the co-magnetometer signal. In this paper, a theoretical model containing three parameters of the probe beam is established by extending the coupled Bloch equation. Based on this model, the influence of probe power density on the transient and steady-state response of the SERF co-magnetometer is analyzed. According to the transient response model, a new measurement method for transverse optical pumping of the probe beam is proposed. Then, for the steady-state response model, a steady-state error suppression method is suggested by adjusting the degree of circular polarization of the probe beam. Eventually, the suppression method is used to refine the SERF co-magnetometer, achieving a suppression rate of 70.31% in transverse electron spin polarization fluctuations, thus improving the co-magnetometer to a stability of 0.0079∘ h−1. To our knowledge, this is better than what has been reported so far.
A novel method to determine the spin polarization and its distribution for a spin-exchange relaxation-free (SERF) atomic magnetometer are proposed in this paper. The Larmor precession frequency is measured using the fast Fourier transform (FFT) analysis result of the transient response of the magnetometer under the excitation of a series of the step-changed magnetic field. The spin polarization is extracted from the slow-down factor of the precession frequency. The variation of the spin polarization with different pump light intensities and the distribution of the spin polarization along the direction of the pump light are analyzed, and the experimental results are well consistent with the theoretical predictions. The expanded uncertainties of the experimental results vary from 2% to 11% with the increase of the spin polarization and the reason for this variation is analyzed. The advantage of this method is that it allows the accurate measurement of the spin polarization in the pump beam direction within the SERF regime operating state, and it is unaffected by the large optical depth of the vapor cell.
The magnitude of the electron spin-relaxation rate Rrel of the atomic ensemble directly affects the sensitivity of the spin-exchange relaxation-free (SERF) atomic magnetometer (AM). The rapid and in-situ characterization of Rrel is of great importance. In this work, a fast extraction method of Rrel is proposed with a measurement period shorten to 0.5 s, merely detecting the transient response of SERF AM to a transverse DC excitation magnetic field after switching off the pump beam. In contrast to the conventional methods based on the measurement of the magnetic resonance linewidth, this method circumvents the involvement of optical pumping rate, and enables monitoring Rrel under arbitrary polarization, which is expected to improve the authenticity of Rrel measurement in a more convenient way.
This paper presents a method for measuring the spin polarization of spin-exchange relaxation-free (SERF) atomic magnetometers at extremely large optical depths. Owing to the slowing-down effect, the spin polarization can be extracted by measuring the slowing-down factor extracted from the precession frequency. However, this technique is limited by a significant error in the regime of extremely large optical depths, where the pump beam intensity for achieving the optimized spin polarization of alkali atoms is significantly increased. We observed that the instantaneous precession frequency measured in the regime where the spin-exchange rate is not much larger than the Larmor frequency was no longer a constant but varied with the pump beam intensity. Thus, a method for measuring spin polarization based on the ratio of the precession frequency to the measured instantaneous precession frequency is proposed. Based on the proposed method, the spin polarization at a temperature of 473K and optical depth of 64 is measured. The measurement results were accordant with theoretical analysis. The expanded uncertainties of the experimental results varied between 1.8% and 9.6%. The proposed method is also applicable to other atomic devices operated in the SERF regime with extremely large optical depths, such as co-magnetometers and atomic spin gyroscopes.