NMR calibration of optical measurement of nuclear polarization in 3He

We have performed precise NMR measurements in order to calibrate a standard optical technique for measuring the polarization of 3He nuclei. This optical technique requires knowledge of the pressure-dependent relationship between the nuclear polarization and the degree of circular polarization of the 668-nm light emitted from a 3He discharge. We determined the nuclear polarization by comparing the adiabatic fast-passage NMR signal from samples of polarized 3He at pressures between 0.1 and 5 torr to an identical sample of water. For water, the polarization is known from statistical mechanics. The 3He is polarized using the metastability exchange technique for optical pumping of 3He. The accuracy of the calibration is ±2%, which is required for applications in nuclear physics