1. Hybrid K-Rb Spin Exchange Optical Pumping Cells for the Polarization of 3 He UNC/TUNL A.Couture, T.Daniels, C.Arnold, T.Clegg

2. Outline I. Motivations for Using Hybrid Cells II. Production of Hybrid Cells III. White Light Spectroscopy VI. Polarization Results

3. Motivation for Using Hybrid Cells The spin exchange efficiency for Rb- 3 He is about 2% under optimum conditions 50 photons to polarize a 3 He nucleus The spin exchange efficiency for K- 3 He is about 23% [Babcock, et.al, Phys. Rev Letter, Vol 91, Num. 12] Thus ~4 photons to polarize a 3 He nucleus

4. So Why Not Just Use Potassium? Pumping on the D2 line is bad Rb D1 and D2 are separated by ~15nm and absorption on the D2 has been observed Potassium’s D1 and D2 are located at 769.9 nm and 766.4 nm, respectively Directly pumping the D1 line of potassium without D2 absorption is currently not feasible.

5. Hybrid Cells Circumvent This Problem Optically pump Rb at 794.7 nm D1 resonance K-Rb spin exchange cross section is extremely large ~200 A 2 At densities of 10 14 cm -3, the spin-exchange rate can exceed 10 5 /s, compared to Rb- 3 He of ~10 -6 /s Thus any Rb polarization is nearly instantaneously transferred to K where the greater 3 He spin exchange efficiency may be realized [Babcock, et.al]

6. Production of Hybrid Cells Here is the final product. 3 inch diameter Pneumatic aluminum body ¼ in swagelok valve K-Rb with 8 amagat 3 He

7. The Initial Manifold Two cells are produced at once. Y-shaped retorts for separate introduction of K and Rb into manifold Place alkali ampules in manifold with nitrogen flowing then seal with a torch

8. The Baking Process

9. The day before baking is completed the alkali must be chased into the smaller retort. The larger retort is then removed with a torch. This distills the metal, removing impurities. Distillation

10. The alkali metals are then chased into the cells and the cells are removed. The optimum ratio of K:Rb is 30:1 in liquid form in the cells. This leads to vapor ratios of 10:1 at 250 C. We have as of yet not perfected this, only obtaining at best 2:1 in the vapor phase. Cell Filling

11. White Light Spectroscopy Standard 60 Watt white halogen bulb Oven at 200-250 C Ocean Optics Spectrometer

12. White Light Spectroscopy We then may examine the D1 and D2 absorption cross sections for Rb and K The following formula relates the absorption cross section to the alkali density: ResonanceWavelength ω Alk K-D1769.9.339 K-D2766.4.682 Rb-D1780.0.322 Rb-D2794.7.675

13. White Light Spectroscopy Thus we may compare either the D1 or the D2 cross sections for the two species to obtain:

14. White Light Spectroscopy Results for K-Rb pyrex cell Test performed at 200 C Ratio of K-Rb is 0.8±0.1

15. White Light Spectroscopy GE-180 K-Rb cell Test performed at 230 C Ratio of K:Rb is 2.2±0.3

16. Polarization Results Saturation polarization 35-40% Spinup time 2.3 hrs

17. Polarization Results Spindown time 14 hrs

18. Polarization Results Saturation polarization 35-40% Spinup time 9.2 hrs

19. Polarization Results Saturation Response Strength (polarization uncalibrated) 737 mV Spinup time 4 hrs

20. Polarization Results Saturation Response Strength (Polarization uncalibrated) 1350 mV Spinup time 9.2 hrs

21. References E. Babcock, I. Nelson, B. Driehuys, L. Anderson, F. Herman, and T. Walker, Phys. Rev Letters, 91, 12, 2003. Bastiaan Driehuys in the flesh.