³He polarization-dependent EPR frequency shifts of alkali-metal–³He pairs

We present temperature-dependent measurements of the EPR frequency shifts for Na, K, and Rb interacting with polarized ³He. K and Na frequency shifts were measured via comparison with Rb frequency shifts (well known at low temperatures) in Na-Rb-³He and K-Rb-³He spin-exchange cells. The lowered Rb vapor pressure of these “hybrid” spin-exchange cells also allowed us to extend the measured temperature dependence of the Rb EPR frequency shifts up to 350 °C. This work presents measurements of the EPR frequency shift for Na in ³He and significantly extends the temperature range of previous Rb and K EPR frequency shift measurements. These results are critical to the performance of accurate ³He EPR polarimetry in spin-exchange cells.