Miniature quad-channel spin-exchange relaxation-free magnetometer for magnetoencephalography

A miniature quad-channel optically pumped atomic magnetometer (OPM) has been developed based on the spin-exchange relaxation-free (SERF) mechanism. With a vapor cell of size 8 mm×8 mm×8 mm, we have incorporated four SERF magnetometer channels, which provides sufficient spatial resolution for magnetoencephalography (MEG). The four channels share the same laser beam for the best cancellation of common mode noise due to laser fluctuations. With gradient measurement, the sensitivities of the four sensors are better than 6 fT/Hz^1/2, which is also good enough for MEG measurement. The vapor cell is heated to 160 °C by a novel nonmagnetic current-heating structure. Our sensor with high spatial resolution and compact size is particularly suitable for MEG systems.