Analysis and suppression of light shift error for NMR co-magnetometers

The nuclear magnetic resonance (NMR) co-magnetometers have become one of the directions for future gyroscope development due to its potential for small volume and high-precision measurement. The light shift is an important phenomenon in alkali atom optical pumping, whose equivalent magnetic field is an important error source of the NMR co-magnetometers. In this paper, based on the signal model of the NMR co-magnetometers, the light shift error in the NMR co-magnetometers is analyzed. In order to suppress the light shift error caused by pump laser intensity fluctuation, this paper proposes a method to measure the light shift equivalent magnetic field based on the locking Rb transverse magnetic moment and the free induction decay signal. Using this method, we directly measure the light shift equivalent magnetic field as a function of pump laser frequency. This enables accurate tuning of the pump laser to minimize the intensity dependence of the Rb atom spin frequency. Compared with the traditional optical absorption method, the proposed magnetic moment locking method reduces the laser intensity dependence of the phase-locked magnetic field and the y-axis residual magnetism by 20.8% and 19.6%, respectively.