Light shift cross-sectional distribution measurement and suppression in SERF atomic magnetometers

Spin-exchange relaxation-free (SERF) atomic magnetometers (AMs) are widely used in biomagnetic sensing and precision measurements in fundamental physics. Nevertheless, off-resonant circularly polarized pump light induces a light shift, that is equivalent to a fictitious magnetic field. This introduces additional spin relaxation, broadens the magnetic linewidth, and degrades the performance of AMs. The nonuniform cross-sectional distribution of the light shift presents a significant challenge to its effective suppression. This study presents a detailed investigation of the cross-sectional distribution of the fictitious magnetic field, which is measured by precisely controlling the beam position. Experiments indicate that substantial residual fields remain after compensation, resulting from the nonuniform light shifts. Furthermore, the limitations of the conventional light shift measurement and suppression methods are analyzed based on the spatial dependence of the response from the AM. We overcome these limitations by introducing a suppression method which identifies an optimized spatial point for fictitious magnetic field measurement to determine the compensation value. This aims to reduce the residual fields. Compared with the conventional suppression method, experimental validation reveals that the proposed method achieves a 34% spatially averaged reduction in residual fictitious magnetic fields, a 9% narrowing in the average magnetic linewidth, and an 18% increase in the average scale factor. Thus, the proposed method provides an effective approach to enhance the performance of SERF AMs, particularly for multi-channel configurations.