Planar multi-channel measurements with optically pumped magnetometers based on pump beam modulation

Optically pumped magnetometers (OPMs) need to be multi-channel for biomagnetic-field measurements. Our group has been developing a multi-channel OPM with a hybrid cell by applying two methods, such as multi-channel photodetectors and modulated pump beams. In this study, we suggested a planar multi-channel OPM with a hybrid cell combining the two methods. We configured a six-channel OPM, which consists of three probe beams as well as two pump beams modulated with sine waves at different frequencies. We found that high modulation frequencies decreased the output signals. The sensitivities of three channels modulated with 43 Hz were 32, 37 and 30 pT/√Hz, and those modulated with 63 Hz were 24, 19 and 18 pT/√Hz. On the contrary, when modulated with 83 Hz and 123 Hz, even the signal with 120 pT could not be observed. Hence, it is necessary to further reduce the noise toward biomagnetic field measurements. © 2021, Japan Soc. of Med. Electronics and Biol. Engineering. All rights reserved.