Multichannel Optically Pumped Atomic Magnetometer With High Resolution and Femtotesla Sensitivity for Biomagnetic Field Measurement

In this paper, we propose a highly sensitive nine-channel optically pumped magnetometer (OPM) operated in the spin-exchange relaxation-free (SERF) regime designed to address the challenges of crosstalk arising from magnetic field modulation and low spatial resolution in multi-channel OPMs employed individual sensors. By introducing a flat-top beam shaper, the uniformity of atomic polarization within the vapor cell was improved, which enhanced the consistency across all channels. Additionally, we analyzed the atomic diffusion crosstalk by varying the beam spacing and measuring the scale factor deviations induced by adjacent channels. Following system optimization, we achieved high-precision magnetic field measurements with a spatial resolution of 3.25 mm and an accuracy quantified by a σ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>i</i></sub> value of 99.73 %. Meanwhile, the average bandwidth of the channels was measured at 93 Hz, with the single-channel sensitivity of approximately 11 fT/Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> and the gradient sensitivity reaching roughly 10 fT/cm/Hz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup>. Furthermore, an impressive common mode rejection ratio of 60 dB was realized. The nine-channel OPM was successfully demonstrated by comparing the simulated magnetocardiography (MCG) signals with the corresponding measured signals. With its potentially high spatial resolution and sensitivity, the nine-channel OPM offers a viable alternative to traditional superconducting quantum interference devices with compact and wearable advantages for MCG, magnetoencephalography (MEG), and magnetic particle imaging.