Frankfurt 2006 – wissenschaftliches Programm
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A: Atomphysik
A 20: Poster II: Atomare Systeme in starken Laserpulsen und statischen Feldern
A 20.18: Poster
Donnerstag, 16. März 2006, 16:30–18:30, Labsaal
Optical measurement of nuclear polarisation of 3He gas in arbitrary magnetic field — •Marion Batz1, Pierre-Jean Nacher2, Geneviève Tastevin2, and Werner Heil1 — 1Johannes Gutenberg-Universität Mainz, Institut für Physik, Staudingerweg 7, 55099 Mainz, Germany — 2Laboratoire Kastler Brossel, Département de Physique de l’E.N.S., 24 Rue Lhomond, 75231 Paris Cedex 05, France
Gaseous 3He can be spin polarised by metastability exchange optical pumping, through excitation of the ground state atoms into the 23S metastable state by a radiofrequency discharge, and pumping with a 1083 nm-laser on the 23S-23P transition. In other excited states populated in the plasma, hyperfine interaction transfers nuclear orientation to electronic angular momentum. Monitoring the circular polarisation of a selected He spectral line is a standard optical detection technique, but it is difficult to accurately calibrate and its sensitivity decreases with gas pressure and in high applied magnetic fields (above a few mT, due to hyperfine decoupling in the involved excited states). We present an optical method to measure the nuclear polarisation of 3He based on absorption measurements of a weak probe laser at 1083 nm. It relies on the fact that metastability exchange collisions enforce a spin-temperature-like distribution of populations in the probed metastable state sublevels that reflect the nuclear polarisation of the ground state. We have performed systematic measurements up to 30 mT in various conditions to assess the accuracy of this technique. Very high SNR (up to 10000) can be obtained, and the effects of an intense pumping laser and of the gas pressure have been studied.