Optical pumping of Rb in the presence of high-pressure 3He buffer gas.

A cryogenic technique has been used to produce polarized $^{3}\mathrm{He}$ targets of up to relative density p=12 atm (\ensuremath{\approxeq}3\ifmmode\times\else\texttimes\fi{}${10}^{20}$ $^{3}\mathrm{He}$ atoms/${\mathrm{cm}}^{3}$; p=1 atm corresponds to 760 Torr or 101.3 kPa pressure at 273 K). In these targets $^{3}\mathrm{He}$ nuclei are polarized by spin-exchange collisions with optically pumped rubidium atoms. From transmission measurements at wavelengths of 790\char21{}800 nm, we have determined pressure shifts, linewidths, and line-shape asymmetries for the Rb 5${\mathit{S}}_{1/2}$\ensuremath{\rightarrow}5${\mathit{P}}_{1/2}$ D1 transition. The Rb spin-destruction rate was found to exhibit a quadratic increase versus $^{3}\mathrm{He}$ pressure, which indicates the importance of Rb${\mathrm{\ensuremath{-}}}^{3}$He${\mathrm{\ensuremath{-}}}^{3}$He collision processes. The transmission results for circularly polarized light are well described by a model that predicts the dependence of the average Rb polarization on Rb density, $^{3}\mathrm{He}$ pressure, light intensity, and cell geometry. The Rb${\mathrm{\ensuremath{-}}}^{3}$He spin-exchange cross section, 〈${\mathrm{\ensuremath{\sigma}}}_{\mathrm{SE}}$v〉=6.1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}20}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, was found to be independent of $^{3}\mathrm{He}$ pressure up to p=12.1 atm. Maximum $^{3}\mathrm{He}$ polarizations of 72\char21{}79% were observed with cells of 17 ${\mathrm{cm}}^{3}$ volume that contained $^{3}\mathrm{He}$ at p=6\char21{}9 atm.