Zero field servo-controlled magnetometer with low frequency filtering of the compensation field

A method for servo-controlling, in a zero field, a magnetometer that measures an ambient magnetic field having a frequency range of interest, the magnetometer including:

• an optical pumping source arranged to emit a light beam in the direction of a cell filled with an atomic gas, wherein the light beam is linearly polarised in a polarisation direction,
• a parametric resonance excitation circuit configured so as to induce in the cell a radiofrequency magnetic field having two components orthogonal to the polarisation direction and each oscillating at its own oscillation frequency,
• a parametric resonance detection circuit configured to perform synchronous detection, at an inter-harmonic of the oscillation frequencies, of an electrical signal outputted by a photodetector arranged to receive the light beam having passed through the cell,
• a zero-field servo-control circuit configured to generate from the performed synchronous detection of said electrical signal a compensation magnetic field opposite to a component of the ambient magnetic field oriented in the direction of polarisation,
• wherein the method includes a step consisting in controlling the generation of the compensation magnetic field so that it is attenuated within the frequency range of interest.