Nonlinear Effect Analysis and Sensitivity Improvement in Spin Exchange Relaxation Free Atomic Magnetometers

In this study, the influence of the nonlinear magneto–optical rotation effect on a spin-exchange relaxation-free (SERF) atomic magnetometer is analyzed. The nonlinear effect is described by saturation parameters obtained from the density matrix model considering the Rabi oscillation of the probe light. For better sensitivity, the nonlinear effect is suppressed, and larger output signals are achieved. Based on the nonlinear effect analysis, the relationship between the probe sensitivity and light power density is obtained, and the optimal probe light power density is measured with best probe sensitivity. The best probe sensitivity improves by ≈6 times at the optimal probe light power density compared with that in the conventional linear optical rotation detection. The proposed method can be applied to SERF magnetometers, co-magnetometers, and atomic spin gyroscopes.