Steady-State Production of High Nuclear Polarization inHe3-He4Mixtures

Abstract

We demonstrate a new technique for producing high, steady-state nuclear polarization in liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixtures. Polarization of 56% has been obtained in a 4% ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-in-${}_{}{}^4{}_{}{}^{}\mathrm{He}$ mixture at 200 mK, roughly 3 times that achieved to date by other means. Polarization loss due to spin relaxation is compensated for by driving a constant circulation of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ between the liquid sample and a room-temperature optical pumping volume. The weak binding properties of cesium are used both to inhibit surface relaxation and to prevent refluxing ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ vapor from confining ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ atoms to the low-temperature part of the cell.