Optically pumped magnetometer and magnetoencephalograph

An optically pumped magnetometer comprising:

• a cell configured to be filled with alkali metal vapor;
• a pump light incidence unit configured to cause pump light for pumping alkali metal atoms constituting the alkali metal vapor to be incident on a sensitivity region inside the cell in a first direction;
• a probe light incidence unit configured to cause probe light for detecting change in electron spins in a pumped state of the alkali metal atoms to be incident on the sensitivity region in a direction intersecting the first direction;
• a bias magnetic field coil configured to apply a bias magnetic field in the first direction to the inside of the cell and determine a resonance frequency of the electron spins;
• a gradient correction coil configured to correct a gradient of the bias magnetic field applied through the bias magnetic field coil;
• an electron spin tilting unit configured to tilt a rotation axis direction of the electron spins in a direction perpendicular to the first direction;
• an optical sensor configured to detect the probe light having passed through the sensitivity region;
• and
• a magnetic field measuring unit configured to measure a magnetic field strength related to the sensitivity region based on an output of the optical sensor,
• wherein the gradient correction coil corrects the gradient of the bias magnetic field such that a relaxation time of free induction decay obtained from an output of the optical sensor becomes longer than a first time when correction by the gradient correction coil is not performed, and
• wherein the gradient correction coil corrects the gradient of the bias magnetic field such that the relaxation time of free induction decay obtained from an output of the optical sensor becomes the longest.

An optically pumped magnetometer comprising:

• a cell configured to be filled with alkali metal vapor;
• a pump light incidence unit configured to cause pump light for pumping alkali metal atoms constituting the alkali metal vapor to be incident on a sensitivity region inside the cell in a first direction;
• a probe light incidence unit configured to cause probe light for detecting change in electron spins in a pumped state of the alkali metal atoms to be incident on the sensitivity region in a direction intersecting the first direction;
• a bias magnetic field coil configured to apply a bias magnetic field in the first direction to the inside of the cell and determine a resonance frequency of the electron spins;
• a gradient correction coil configured to correct a gradient of the bias magnetic field applied through the bias magnetic field coil;
• an electron spin tilting unit configured to tilt a rotation axis direction of the electron spins in a direction perpendicular to the first direction;
• an optical sensor configured to detect the probe light having passed through the sensitivity region;
• and
• a magnetic field measuring unit configured to measure a magnetic field strength related to the sensitivity region based on an output of the optical sensor,
• wherein the gradient correction coil corrects the gradient of the bias magnetic field such that a spectral peak after fast Fourier transform regarding a relaxation time of free induction decay obtained from an output of the optical sensor becomes steeper than when correction by the gradient correction coil is not performed, and
• wherein the gradient correction coil corrects the gradient of the bias magnetic field such that the spectral peak after fast Fourier transform regarding the relaxation time of free induction decay obtained from an output of the optical sensor becomes the steepest.