All-optical and isotropic magnetometer

An optical pumping magnetometer comprising:

• a cell filled with a gas;
• a laser source emitting a laser beam;
• a polarization module adapted to linearly polarize the laser beam and to rotate a polarization such that the laser beam is polarized in a polarization direction;
• a photodetector receiving the polarized laser beam after the polarized laser beam has passed through the cell and outputting an electrical signal;
• first slaving means to keep a constant angle between the polarization direction and a magnetic field to be measured, wherein the first slaving means includes modulation means to modulate at least a first part of the laser beam so as to generate a pump beam modulated by a modulation frequency (fm);
• second slaving means to keep said modulation frequency equal to a Larmor frequency of the gas or one of a plurality of harmonics of the Larmor frequency, a value of the magnetic field to be measured being obtained from said modulation frequency;
• and
• a frequency synthesizer that generates the modulation frequency (fm), based on a measurement signal generated by the second slaving means, and sends the modulation frequency (fm) as feedback to the modulation means,
• wherein the modulation means make an intensity modulation at the Larmor frequency and at twice a frequency of the Larmor frequency,
• the magnetometer comprises an optical separator on an input side of the polarization module to form a first part and a second part of the laser beam, the pump beam (P) being obtained by modulating the first part of the laser beam by said modulation means, the second part of the laser beam forming a probe beam (S) not modulated by said modulation means, the electrical signal resulting from conversion of the probe beam being input to the first and to the second slaving means, and
• the probe beam and the pump beam are parallel and are separated by a distance less than a diffusion length of gas atoms in the cell.