Real-Time Measurement of Longitudinal Electron Spin Polarization in SERF Comagnetometers

This article presents an optical measurement method for real-time measurement of longitudinal electron spin polarization (LESP) in spin-exchange relaxation-free (SERF) comagnetometers and introduces a control strategy to stabilize LESP. The electron spins of alkali atoms with longitudinal polarization constitute the measurement foundation of the SERF comagnetometers. The proposed measurement method involves offline modeling of each class of optical loss and LESP within the cell and identification of the model parameters. Subsequently, the online measured incident and exit optical power data are utilized to accurately obtain the LESP state within the cell in real time. Finally, the LESP stabilization controller based on the proposed online measurement method is designed to improve the stability and anti-interference performance of LESP. Experimental results show that the controlled LESP effectively suppresses magnetic and thermal field interference compared to the uncontrolled LESP. The long-term stability of the controlled LESP, evaluated using Allan deviation, shows an improvement of approximately 170% compared to the uncontrolled LESP at a cluster time of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100~{\mathrm {s}}$ </tex-math></inline-formula>. Similarly, the long-term stability of the output signal of the SERF comagnetometer improves by approximately 500% at the same cluster time.