Measuring system and measuring cell for making magnetic field measurements

Claim 3

An apparatus according to claim 1, further comprising: an emission device making it possible to emit a linearly polarized light beam propagating along a given propagation axis, said ferrimagnetic material plate aligned in accordance with the light beam and permitting, in its interior, a guided propagation of the beam, as well as a rotation of the beam polarization direction during its propagation, means for measuring the polarization rotation associated with the plate along the light beam axis, receiving the beam after pasing through the associated plate and supplying a polarization rotation measurement signal; a solenoid placed around the ferrimagnetic material so as to be able to induce a magnetic field along the light beam axis, and wherein said first and second means comprise supply and control circuits making it possible, during a time corresponding to said first predetermined time period to supply said solenoid with a high amplitude alternating current so that the induced field saturates the plate and then during said second time corresponding to the second stage to progressively reduce the alternating current supply level for the solenoid and simultaneously supply it with a feedback direct current as a function of the polarization rotation measurement signal supplied by the measuring means, to make it possible to offset a continuous magnetic field existing along the axis of the beam.

Claim 4

An apparatus according to claim 2, wherein said supply and control circuits comprise: a supply circuit having first, second and third control inputs and multiple outputs for supplying current to said solenoid in accordance with the signals received on said supply circuits three inputs, a gate circuit connected to the third input of hte supply circuit for transmitting thereto a polarization rotation measurement signal received from measuring means, a time base circuit connected to the first and second inputs of the supply circuit, as well as to the gate circuit which supplies for a predetermined time corresponding said first predetermined time a first signal to the first input of the supply circuit in order to control the supply of the solenoid with the aid of a high amplitude modulating alternating current and then for a time corresponding to the second time a second signal to the second input of the supply circuit and also for producing a signal which controls the progressive reduction of the modulating alternating current and which further supplies this signal to said gate circuit so as to make said gate circuit conductive, while permitting the transmission of the polarization rotation measurement signal to the third input of the supply circuit, such that the the third input controls the supply of the solenoid with the aid of a feedback current inducing a magnetic field, which cancels out the effect of the magnetic field to be measured.

Claim 5

A measuring cell according to claim 1, wherein the ferrimagnetic material coating has an elongated shape and is deposited in such a way that the light beam passes through it along its small dimensions.