Spin Polarized Helium-3, a Playground in Many Domains of Physics

This article gives a survey of the different methods which can be used to polarize the nuclear spin of helium-3. These techniques are particularly discussed in relation to the production of polarized helium-3 targets for nuclear physics experiments, such as electron or proton scattering and neutron spin filters. Some emphasis is given to the development of new powerful solid state lasers now used for helium optical pumping. .Applications to atomic physics and quantum statistics are also mentioned. A recent experiment is finally described which shows that the heat conductivity of the helium-3 gas at low temperature depends on the nuclear spin polarization. This is a consequence of the quantum indistinguishability of the particles which plays a large role in binary collisions, thus influencing the transport properties of the gas. I SEVERAL FIELDS OF PHYSICS MAKE USE OF SPIN POLARIZED HELIUM 1.1 In atomic ~hvsics In atomic physics the helium atom has been extensively studied in the last decades : it is one of the simplest existing atoms and the wavefunctions for a two electron particle are relatively well known [l]. Spectroscopic measurements of high accuracy, making use of optical pumping and magnetic resonance techniques, were performed on the ground state and the excited states of both helium-3 and helium 4 isotopes, providing a value for a, the fine structure constant [2j and several tests of Quantum Electrodynamics. This field was first revived by the use of single frequency tunable lasers and Doppler free spectroscopy methods. Enhanced precision is now expected from (1) Unit6 de recherche de 1'Ecole Normale Supkrieure et de 1'Universitk Paris 6, associee au