Polarisation nucléaire de 3He gazeux par pompage optique laser

Abstract

2014 Une polarisation nucléaire élevée, de l'ordre de 70 %, a été obtenue par pompage optique dans 3He gazeux grâce à l'utilisation d'un laser à centres colorés (F+2* dans NaF) fournissant plusieurs centaines de milliwatts à la longueur d'onde 03BB = 1,08 03BCm.

Optical pumping in 3He with a laser

“…Let us remark that the values of the ratio derived from these fits are compatible in all cases with the assumption : made in § 1.4.1 for calculating formula (21). (See the values of r ' /2 ~D given in appendix B).…”

“…At low laser power, i.e. for low P, the results do not depend on ntn/nm; this is not surprising since in such a case one can make use of a linearized model, such as that developed in [1], in which the relevant parameter for the pumping power is the average pumping time for a ground state atom, namely which does not depend on (see formula (21)). In con-trast, at high pumping power, the orientation P increases with the number nm of metastable atoms effectively pumped This comes from the non-linearities in the orientation coupling between photons and ground state atoms through the nm metastable atoms.…”

“…The present work is a generalization of that of Timsit and Daniels [8], who considered optical pumping with circularly polarized resonance radiation from a 4He discharge light source. Such a generalization is justified by the much higher flexibility offered by a laser which can be tuned on any of the components of the A = 1.08 03BC line [9]. Moreover, the present calculations include stimulated emission, which was not the case in previous studies.…”

“…For other time constants occurring in equations (25) to (28), such as Te, T, and we performed additional experiments with our 'He optical pumping set-up, which is described elsewhere [21]. Te is related to ~e by equations (1) and (2) which involve nm, the total density of metastable atoms.…”

Spin rotation effects and spin waves in gaseous 3He↑

“…Instead of creating strong gradients of magnetization over the sample, we have studied a situation where the atoms explore all the volume available inside the container before being significantly affected by the applied magnetic gradient (motional averaging condition [20,21]); clearly, this is possible only if the walls of the gas container have only a very weak relaxation effect. In this kind of situation, the effects of spin waves can be simply and completely described [22] [25,26].…”