Développement d'un appareillage pour l'étude de la polarisation optique de l'hélium-3 et de sa relaxation par des surfaces

We have developed an apparatus to polarize 3He gas (at a few torrs pressure) by optical pumping from a 4He light source and to measure the evolution of the magnetic moment for relaxation studies. The magnetic moment is measured by applying a pulse of radio frequency magnetic field B1 transverse to the static magnetic field B0 and by amplifying the signal induced by the free precession of the magnetic moment. As the relative decrease of the magnetic moment involved in each measure is only 10-2 to 10-3, we can make ten to twenty measurements during the relaxation time. This time, which is of the order of between 103 to 104 sec, is measured with an accuracy of ±5%.