Methods and systems for fast field zeroing for magnetoencephalography (meg)

A magnetic field measurement system, comprising:

• an optically pumped magnetometer (OPM) comprising
• a vapor cell comprising a housing and a vapor of atoms disposed in the housing,
• a light source,
• a detector, and
• a magnetic field generator;
• and
• a processor coupled to the OPM and configured to perform actions comprising
• directing a light beam from the light source through the vapor cell of the OPM;
• applying RF excitation to the atoms to cause spins of the atoms of the vapor to precess;
• measuring a frequency of the precession by observing the light beam after passing through the vapor cell;
• for each of a plurality of different axes relative to the vapor cell,
• directing a light beam from the light source through the vapor cell,
• applying a magnetic field through the vapor cell along the axis,
• applying RF excitation to the atoms to cause spins of the atoms of the vapor to precess, and
• measuring a frequency of the precession in the applied magnetic field by observing the light beam after passing through the vapor cell;
• determining magnitude and components of an ambient background magnetic field along the axes using the measured frequencies;
• and
• applying a magnetic field based on the components around the vapor cell to counteract the ambient background magnetic field to facilitate operation of the OPM in a spin exchange relaxation free (SERF) mode.