Self-calibrating measurement of polarization-dependent frequency shifts from Rb−3He collisions

We have studied the frequency shift in the Rb electron-paramagnetic-resonance (EPR) line due to the presence of nuclear polarized ${}_{}{}^3{}_{}{}^{}\mathrm{He}$. By measuring the resonant frequency in a cylindrical cell oriented both parallel and perpendicular to an applied magnetic field, we determined the classical EPR shift due to long-range macroscopic fields. We thus calibrated the larger, geometry-independent shift, due to the Fermi-contact interaction between the Rb electron and the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ nucleus, to 2.5%. The EPR frequency shift can be used to determine the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ nuclear polarization.