A new and unusual phenomenon which we call light narrowing is reported and discussed in this paper. We discovered this effect in dense, spin-polarized cesium vapor optically pumped with a cw blue dye laser beam tuned to the second resonance
D1 line (4593 \AA{}). We observe a significant narrowing of the radio-frequency power-broadened magnetic resonance lines (linewidths narrow by as much as a factor of 2.5) when the intensity of the circularly polarized incident dye laser beam is increased by either focusing the beam or by the removal of attenuating filters from the focused beam. The magnetic resonance linewidths in spin-polarized cesium vapor were measured over a wide range of cesium number densities (5\ifmmode\times\else\texttimes\fi{}
1012 ${\mathrm{cm}}^{\ensuremath{-}3}$ \ensuremath{\le}[Cs]\ensuremath{\le}1\ifmmode\times\else\texttimes\fi{}
1016 ${\mathrm{cm}}^{\ensuremath{-}3}$). This corresponds to cesium spinexchange rates of 4.5\ifmmode\times\else\texttimes\fi{}
103 to 9\ifmmode\times\else\texttimes\fi{}
106 ${\mathrm{sec}}^{\ensuremath{-}1}$. For low cesium number densities (5\ifmmode\times\else\texttimes\fi{}
1012 [Cs]3\ifmmode\times\else\texttimes\fi{}
1014 ${\mathrm{cm}}^{\ensuremath{-}3}$) the light-narrowing effect is large (a factor of 2.5) and independent of [Cs]. In the region of 3\ifmmode\times\else\texttimes\fi{}
1014 to 1\ifmmode\times\else\texttimes\fi{}
1015 ${\mathrm{cm}}^{\ensuremath{-}3}$ in number densities, the light-narrowing effect decreases with increasing [Cs]. At high cesium number densities ([Cs]> 1\ifmmode\times\else\texttimes\fi{}
1015 ${\mathrm{cm}}^{\ensuremath{-}3}$) this light-narrowing effect almost completely disappears. In the limit of low-radio-frequency power the magnetic resonance linewidths for focused and unfocused dye laser beam are nearly the same. Experimental observations on this new effect are presented in detail. In the latter part of this paper a self-contained theoretical treatment of the light-narrowing effect is developed. Using Bloch equations in the presence of optical pumping, spin relaxation (diffusion, electron randomization), rapid spin exchange, and radio-frequency magnetic field, expressions for magnetic resonance line shapes are derived. In general, we find good agreement between our experimental results and the theory.
We present a detailed experimental analysis of Rb-polarization imaging in high-pressure gas cells. The Rb vapor in these cells is optically pumped by high-power diode-laser arrays. We present images for high (35 G) and low (4 G) magnetic fields and for different He and Xe buffer-gas mixtures. We demonstrate that high-field imaging provides an absolute measurement of the Rb-polarization distribution in the cell, based on the fact that a spin-temperature distribution of the hyperfine magnetic sublevels is established in high-pressure buffer gases. A survey of various mechanisms that broaden the Rb magnetic-resonance lines is presented. These broadening mechanisms determine the limits of the spatial resolution achievable for images of the Rb-polarization distribution.
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.
We present detailed images of the Rb polarization in a high-pressure optical pumping cell. Images taken at high magnetic field strengths (≈37 G) yield precise information on the relative occupation probability of the hyperfine Zeeman sublevels. Low-field (⩽4 G) images yield very high resolution (less than 1 mm) maps of the spatial distribution of the Rb polarization. For optical pumping in the presence of high-pressure buffer gases, the measured populations of the hyperfine magnetic sublevels are shown to be well described by a spin temperature, even though the Rb–Rb spin exchange rate is much smaller than the rates of optical pumping or electron-randomizing Rb–Xe collisions in the buffer gas.
Abstract The polarization of 129 Xe gas by spin exchange with optically pumped Rb vapor is examined in high magnetic field. Measurements of the Rb–Xe velocity averaged spin exchange cross section 〈 σ v 〉 and the 129 Xe relaxation time in the absence of Rb, T 1 Xe , are discussed. Comparison of these high field results to low field literature values for 〈 σ v 〉 show that this parameter is essentially field independent. T 1 Xe is also found to be significantly longer in high field. On the basis of these observations, it is shown that production of large amounts of spin polarized 129 Xe gas can be made more efficient by high field operation.