Paramagnetic resonance and optical pumping magnetometer in the near zero magnetic field-range

Abstract

Abstract Magnetometer for measuring steady magnetic fields of steady direction in the range of the nanogauss field intensities. The apparatus is generally used for measuring weak fields in a limited region of the inside of a magnetic shield envelope and comprises a paramagnetic resonance cell, three direct current pairs of Helmholtz coils the axis of which form a threedimensional rectangular coordinate system, the origin point of which lies in said resonance cell, and a pair of alternating current Helmholtz coils having its axis coinciding with one selected axis among those of the direct current coils. DC currents are applied to the direct current coil pairs and are adjusted to obey approximately compensate the field in said region except in the direction of said selected axis, along which exact compensation is aimed at, trihedral and an alternating current is applied to the alternating coil pair and produces an alternating magnetic field colinear with the steady field to be measured. The cell is filled with atoms of alkaline metals in vapor state or with 4He in the state 23S1. Pumping light is applied to the cell perpendicularly to the field to be measured and the light transmitted through the cell in the same direction as that of the pumping beam is collected on a photomultiplier. The signal delivered by the photomultiplier is filtered at the frequency of the alternating current and synchronously detected. When exact compensation of the steady field component to be measured along said selected axis is reached, the intensity of the light transmitted through the cell reaches a maximum value, and, in the light intensity modulation caused by the alternating field, the odd harmonic components pass through the zero value. The frequency of the alternating current is chosen much higher than the product of the gyromagnetic ratio of the material inside the cell by twice the direct current field variation on either side of the zero value that would reduce the light intensity change caused by the latter field to half its maximum value, and; the amplitude of the alternating field is given an optimum predetermined value. The value of the steady field component to be measured is calculated from the direct current intensity in the coil having said selected axis, while the direct current intensities in the other coils are so adjusted that the variation of said light intensity modulation as a function of the value of the latter current intensity be as sharp as possible.

Inventors

• 👤 Marie-Anne Bouchiat
• 👤 Jean Brossel
• 👤 Claude N Cohen-Tannoudji
• 👤 Jacques A Dupont-Roc
• 👤 Serge Haroche
• 👤 Alfred H Kastler
• 👤 Jean-Claude Lehmann

Bibliographic Details