Suppression of Heading Error in Bell-Bloom Atomic Magnetometer by Controlling RF Magnetic Field

The atomic magnetometers operated in Earth-scale magnetic field are susceptible to the nonlinear Zeeman (NLZ) effect, resulting in multiple resonance peaks and heading error, which restricts their practical applications. We introduce a spin-locking method based on magnetic field modulation to overcome the NLZ effect and thus suppress the heading error in atomic magnetometers. The suppression effect of spin-locking is proportional to the amplitude of the modulation field. However, an excessively high modulation field amplitude can lead to broadening of the measurement linewidth. A novel model characterizing the linewidth for the amplitude of modulated magnetic field under different environmental magnetic field is established by considering the NLZ effect. From the test results, the novel model can more accurately predict the linewidth under different environmental magnetic fields compared with traditional models. The optimized amplitude of modulated magnetic field is obtained based on the linewidth model, and the heading error is suppressed by about 80% within the magnetic field inclination angle of 28.76°. The theory and method presented here are important for the application of magnetometers in Earth-scale magnetic field, which can suppress the heading error while keeping the linewidth unchanged.