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Physical Review A

Highly polarized 3He by spin exchange with potassium

Guodong Wang, Wenjin Shao, E. W. Hughes

Published Dec 22, 2003• 7 citations
Publisher

Abstract

We report on measurements of the polarization for ${}^{3}\mathrm{He}$ using optically pumped potassium vapor. We achieve a ${}^{3}\mathrm{He}$ polarization greater than 40% in a mid-sized double-chamber glass target cell filled with ${}^{3}\mathrm{He}$ gas using a single Ti:sapphire laser. Applied to the production of polarized ${}^{3}\mathrm{He}$ as an atomic beam source for colliders, these developments could have significant impact on future studies of neutron spin structure. The results also motivate the development of high power diode lasers tuned to the appropriate potassium wavelengths.

DOI
10.1103/physreva.68.065402

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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.

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•Jan 1, 1991•0 citations
We report on measurements of the polarization for 3He{}^{3}\mathrm{He}3He using optically pumped potassium vapor. We achieve a 3He{}^{3}\mathrm{He}3He polarization greater than 40% in a mid-sized double-chamber glass target cell filled with 3He{}^{3}\mathrm{He}3He gas using a single Ti:sapphire laser. Applied to the production of polarized 3He{}^{3}\mathrm{He}3He as an atomic beam source for colliders, these developments could have significant impact on future studies of neutron spin structure. The results also motivate the development of high power diode lasers tuned to the appropriate potassium wavelengths.
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.
The use of high-power ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$Alx{\mathrm{Al}}_{\mathit{x}}Alx​As diode laser arrays for optical pumping of Rb vapor has been examined both theoretically and experimentally. Our studies show that large atomic polarizations can be obtained using the broad spectral output of a diode laser array if the Rb resonance line is collisionally broadened by several atmospheres of a buffer gas. The objective was to study the effectiveness of diode laser arrays as light sources for optically pumped spin-exchange polarized 3He^{3}\mathrm{He}3He targets. The average Rb polarization was deduced at three different Rb vapor pressures using the polarization induced in the 3He^{3}\mathrm{He}3He buffer gas. The largest 3He^{3}\mathrm{He}3He polarization observed was 53% using a 20-W diode array with 1.9-nm full width at half maximum spectral width in 10.5 amagat of 3He^{3}\mathrm{He}3He. This result compares favorably with other light sources for this target. The measured average Rb polarizations are compared to theoretical calculations.
We have studied the efficiency of spin-exchange optical pumping (SEOP) in cells that contain either pure rubidium, mixtures of rubidium and potassium, or pure potassium. Optical pumping was performed with spectrally narrowed diode array lasers operating at either the wavelength of the Rb $5{s}_{1∕2}\ensuremath{-}5{p}_{1∕2}$ transition (795nm)(795\phantom{\rule{0.3em}{0ex}}\mathrm{nm})(795nm) or the K $4{s}_{1∕2}\ensuremath{-}4{p}_{1∕2}$ transition (770nm)(770\phantom{\rule{0.3em}{0ex}}\mathrm{nm})(770nm). Calculations of the expected efficiency are shown for practical conditions and compared to measurements. We have measured the vapor density ratio in Rb-K mixture cells using absorption of white light. Our focus is on the conditions that are relevant for neutron spin filters, but the results are relevant to all applications of SEOP. We find that both Rb-K and pure K cells yield improvements in the spin-exchange efficiency, and each approach has its own advantages. Overall, the best results for high polarizing rate with high polarization were obtained with mixture cells with K-Rb vapor density ratios between 2 and 6.
Optical pumping is an efficient method for creating nuclear polarization M in a gas of 3He. M is first achieved in the metastable 23S state and then transfered to the ground state. Polarized 3He has numerous applications: quantum fluids, precision magnetometry, nuclear targets, etc. Much progress in achieving high values of M has resulted from the development of efficient IR lasers capable of exciting the 23S–23P3He transition at 1.08 μm. Using a novel lamp pumped LNA laser delivering 5 W cw, we have achieved M >85% for samples in the torr pressure range. To measure M we have developed an accurate technique based on the change as a function of M of the ratio between σ and π polarized light absorbed from a weak; probe beam by the 23S metastable atoms. The probe was delivered by a single mode tunable diode pumped LNA laser that was frequency modulated by using an étalon mounted on a galvoplate. M was also measured by monitoring the circular polarization of the 668 nm line emitted by the dis charge. Experimental and theoretical results on the optimization of the pumping will be presented, and the laser systems will be discussed.
We demonstrate spin-exchange optical pumping of 3He^{3}\mathrm{H}\mathrm{e}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^{3}\mathrm{H}\mathrm{e}3He atoms then transfer the angular momentum to the 3He^{3}\mathrm{H}\mathrm{e}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 1/41/41/4, 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.
Recent progress in the performance of laser-driven source of polarized deuterium is described. Optical pumping of potassium atoms followed by spin exchange scattering with deuterium atoms in a high magnetic field and RF transitions in a medium field was found to produce an intense, highly spin-polarized beam of deuterium atoms. In particular, the atomic polarization of deuterium was determined to be 73{plus_minus}3% at an intensity of 2.1 {times} 10{sup 17} Atomsis. The RF transition efficiency was measured and found to be 92{plus_minus}5%.