The Bell‐Bloom‐Type Optically‐Pumped FID Rubidium Atomic Magnetometer With a Multi‐Passing Probe Beam and Two Counter‐Propagating Pump Beams

ABSTRACT The Bell‐Bloom‐type optically‐pumped atomic magnetometers are well‐suited for weak geomagnetic field detection. However, conventional single‐beam pumping introduces an atomic spin polarization gradient, which limits the measurement accuracy and sensitivity. To address this issue, this paper proposes and experimentally demonstrates a Bell‐Bloom‐type rubidium FID magnetometer scheme integrating orthogonally polarized counter‐propagating pumping and multi‐pass probe detection. This design homogenizes the atomic spin polarization distribution and suppresses light shifts and power broadening. This uniform polarization, in turn, allows the five‐pass probe configuration to achieve a significantly larger signal amplitude. Experimental results reveal that, compared with the traditional single‐beam pumping and single‐pass detection scheme, the proposed magnetometer achieves a remarkable improvement in magnetic field measurement accuracy, and the magnetic field sensitivity is improved from 18.9 to 3.1 pT/. Notably, the two techniques work synergistically, yielding a 6.1‐fold sensitivity enhancement that far exceeds their individual gains. This work provides an effective technical approach and reference for optimizing the performance of atomic magnetometers and their applications in precision measurement fields.