In Situ Magnetic Field Compensation for High-Sensitivity Optically Pumped Magnetometers in Single-Beam Configuration

The Spin-Exchange Relaxation-Free (SERF) optically pumped magnetometer (OPM) is one of the most sensitive magnetic sensors, yet it needs to work in near-zero ambient magnetic fields. Triaxial magnetic field compensation is essential to achieve such a zero-field environment. Existing methods typically rely on complex and time-consuming iterative procedures to compensate for environmental magnetic field. To address this problem, this paper proposes an in-situ magnetic compensation method to improve compensation efficiency. The pre-compensation process eliminates most of the background magnetic field by reducing the fundamental frequency response of the SERF OPM. Subsequently, the precise compensation process further reduces residual magnetic fields through high-frequency magnetic field modulation. After compensation, the noise density of the OPM is about 20 fT/ √ Hz. The effectiveness of this compensation method is validated through theoretical analysis, numerical simulations, and experimental verification. This approach achieves fast compensation of large background magnetic fields, simplifies the operational procedure, and significantly enhances the practicality of single-beam SERF-OPMs. It provides critical technological support for emerging biomedical applications such as magnetocardiography (MCG) and magnetoencephalography (MEG), as well as other fields requiring high-sensitivity magnetic measurements.