Effect of Optical Nonorthogonality on Dynamic Response in Dual-Beam Atomic Magnetometer

In this article, we analyze the amplitude-frequency and phase-frequency responses of a spin-exchange relaxation-free (SERF) atomic magnetometer with the nonorthogonal angle between the pump and probe beam. The optical nonorthogonality leads to a change in the photon spin direction of circularly polarized pump light, which decides the polarization direction of the atomic ensemble, causing significant differences in dynamic responses to the magnetic field. We theoretically analyze relationships between dynamic response solutions of the Bloch equation with different pump lights and magnetic field directions based on which the equations are linearized. The equations are solved with the Fourier transform method, and three-axis dynamic responses are obtained under the influences of optical nonorthogonality and residual static magnetic field. In the experiment, we verify the linear superposition characteristics between different response components. According to the results, we propose a novel method to quickly calibrate the nonorthogonal angle, which could reduce the optical nonorthogonal angle by 20 times, reaching 0.54°, and effectively enhance the dynamic magnetic field response signal in atomic magnetometers.