We demonstrate spin-exchange optical pumping of
3He using a ``hybrid'' K-Rb vapor mixture. The Rb atoms absorb light from a standard laser at 795 nm, then collisionally polarize the potassium atoms. Spin-exchange collisions of K and
3He atoms then transfer the angular momentum to the
3He with much greater efficiency than $\mathrm{R}\mathrm{b}\mathrm{\text{\ensuremath{-}}}^{3}\mathrm{H}\mathrm{e}$. For a K-rich vapor, the efficiency of the hybrid spin-exchange collisions approaches
1/4, an order of magnitude greater than achieved by pure Rb pumping. We present the first measurements of actual photon efficiencies (polarized nuclei produced per absorbed photon), and show that a new parasitic absorption process limits the total efficiencies for both hybrid and pure Rb pumping.
We report investigations of spin exchange between
21Ne nuclei and optically pumped Rb vapor. Polarization of 30% (
〈Kz〉=0.46) of 2\ifmmode\times\else\texttimes\fi{}
1019 atoms-${\mathrm{cm}}^{\ensuremath{-}3}$ has been achieved with a vapor pressure of 3\ifmmode\times\else\texttimes\fi{}
1014 atoms-${\mathrm{cm}}^{\ensuremath{-}3}$ of Rb. This high density of alkali metal can be efficiently optically pumped only when light trapping is suppressed by inclusion of at least 100 Torr of
N2. In addition, we have made the first accurate measurement of the binary-collision spin-exchange rate: $〈{\ensuremath{\sigma}}_{\mathrm{ex}}v〉=(4.66\ifmmode\pm\else\textpm\fi{}0.28)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}$
cm3-${\mathrm{s}}^{\ensuremath{-}1}$. Extension of these techniques to
3He has yielded 5% polarization of 2\ifmmode\times\else\texttimes\fi{}
1019 atoms-${\mathrm{cm}}^{\ensuremath{-}3}$ in a preliminary experiment.
We use accurate ab initio and quantum scattering calculations to demonstrate that the maximum ³He spin polarization that can be achieved in spin-exchange collisions with potassium (³⁹K) and silver (¹⁰⁷Ag) atoms is limited by the anisotropic hyperfine interaction. We find that spin exchange in Ag-He collisions occurs much faster than in K-He collisions over a wide range of temperatures (10-600 K). Our analysis indicates that measurements of trap loss rates of ²S atoms in the presence of cold ³He gas may be used to probe anisotropic spin-dependent interactions in atom-He collisions.
We present experimental studies on the spin-exchange optical pumping of 3He using alkali metal potassium vapor. High 3He polarizations are achieved using lower laser power than traditional rubidium-3He pumping studies. In addition, spin-exchange rate coefficient measurements for potassium-3He, rubidium-3He and cesium-3He pairs are reported. By spin-exchange optical pumping with potassium vapor, a high 3He polarization has been achieved in a mid-sized double-chamber glass target cell using only 5 watts of Ti:sapphire laser power. The spin-exchange rate coefficients of potassium-3He, cesium-3He and rubidium-3He pairs are measured and compared. The results are kSE = (4.0+/-0.3)E-20 cm3/sec for the potassium-3He pair, kSE = (6.5+/-0.4)E-20 cm3/sec for the rubidium-3He pair and kSE = (13.6 +/-1.3)E-20 cm3/sec for the cesium-3He pair. The results are consistent with theoretical predictions and confirm that the efficiency for spin-exchange polarization of 3He with potassium is significantly higher than with rubidium or cesium. The results motivate the development of high power diode lasers tuned to the appropriate potassium wavelengths. Applied to the production of polarized 3He as an atomic beam source for colliders, these developments could have significant impact on future studies of neutron spin structure. These studies may also have impact on magnetic resonance imaging using hyperpolarized 3He.
We experimentally study the Rb-Xe spin-exchange optical pumping process. The dependence of the spin-exchange rate on the intensity of the pumping light is measured at different temperatures under low magnetic fields. We demonstrate that the spin-exchange rate will decrease as the Rb spin polarization increases, which agrees well with the theoretical prediction. In our measurement, three spin exchange and spin relaxation mechanisms, namely, the spin exchange rates between Rb and Xe atoms caused by van der Waals molecule (${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{vdW}}$) and binary collision (${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{bin}}$) processes, and the spin relaxation rate due to the wall collision of Xe atoms (${\mathrm{\ensuremath{\Gamma}}}_{\mathrm{w}}$), have comparable magnitudes. These rates are extracted separately from the measured data with different Rb spin polarization at various temperatures. Our work provides a comprehensive confirmation of the physical picture of the spin-exchange optical pumping process.
A cryogenic technique has been used to produce polarized
3He targets of up to relative density p=12 atm (\ensuremath{\approxeq}3\ifmmode\times\else\texttimes\fi{}
1020 3He atoms/
cm3; p=1 atm corresponds to 760 Torr or 101.3 kPa pressure at 273 K). In these targets
3He nuclei are polarized by spin-exchange collisions with optically pumped rubidium atoms. From transmission measurements at wavelengths of 790--800 nm, we have determined pressure shifts, linewidths, and line-shape asymmetries for the Rb 5
S1/2\ensuremath{\rightarrow}5
P1/2 D1 transition. The Rb spin-destruction rate was found to exhibit a quadratic increase versus
3He 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,
3He 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{}${10}^{\mathrm{\ensuremath{-}}20}$
cm3 ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$, was found to be independent of
3He pressure up to p=12.1 atm. Maximum
3He polarizations of 72--79% were observed with cells of 17
cm3 volume that contained
3He at p=6--9 atm.