Multi-channel spin exchange relaxation free magnetometer towards two-dimensional vector magnetoencephalography.

Optically pumped atomic magnetometers based on spin exchange relaxation free regime have recently become a powerful tool in the field of magnetoencephalography measurements. For this application of magnetometers, simultaneous multilocation magnetic field measurements are desired. To fulfill the requirement, we develop a multi-channel sensor module based on a single large vapor cell. The probe beam passes through the vapor cell twice by reflection and then records the two-dimensional spatial magnetic field distribution with two 2 × 2 photodiode matrixes. Comparing with the previous multi-channel tangential magnetic field measuring sensors, our magnetometer is sensitive to the normal magnetic field by operating in the longitudinal parametric modulation mode. Measuring the normal component is considered more suitable for magnetoencephalography, because the normal component provides more information. The sensitivities of the channels are approximately 10 fT/Hz1/2 in the normal direction. The auditory evoked magnetic fields of the four adjacent locations perpendicular to the scalp are detected simultaneously. Our magnetometer can measure the normal and tangential magnetic fields simultaneously. The dual-axis vector measurement of magnetic field is very important for magnetoencephalography.