Restricted diffusion of polarised 3He gas in aerogels

Polarised He-3 is used to non-destructively probe by NMR the structure of silica aerogels. Using laser optical pumping large spin-echo signals are obtained with small amounts of gas, even at low magnetic field. Attenuation induced by applied field gradients is measured for equivalent He-3 pressures ranging from 5 mbar to 3 bar. Systematic diffusion studies are performed by NMR on custom-made (98% porous) and commercial (97% porous) aerogels used by research groups to study quantum fluids in confined geometries. The observed pressure dependence suggests a non-uniform structure of both aerogel samples on length scales up to tens of microns. (C) 2003 Elsevier Science B.V. All rights reserved.