Magnetoencephalography using a compact multichannel atomic magnetometer with pump-probe configuration

Optically pumped atomic magnetometers operating in the spin exchange relaxation free (SERF) regime play increasingly important roles in magnetoencephalography measurements. In this application, a multichannel arrangement is necessary. A method to construct the multichannel system is to arrange multiple individual sensor modules, where each sensor module is designed in the one-beam configuration with the necessary magnetic modulation. However, such an arrangement restricts the spatial resolution, affects the uniformity of the sensor characteristics, and increases the system complexity. To address these issues, we developed a compact multichannel pump-probe configuration magnetometer based on a single vapor cell. Each channel of the multichannel system shares the same vapor cell. As a result, the influence of different cells is eliminated. Further, a two-beam configuration with an independent pump and probe beam is introduced. Compared with the one-beam configuration, the two-beam magnetometer achieves a higher sensitivity and does not require extra magnetic modulation. And then the magnetic field crosstalk between adjacent channels can be avoided. A sensitivity of 10 fT/Hz1/2 at 2 Hz is achieved for all channels. Using the compact multichannel magnetometer, an auditory evoked response is clearly observed. If more channels are required, the arrangement based on the single vapor cell configuration can be easily expanded by applying the photodiode with more than four quadrants.