He Targets Using Thermally Polarized Water

When using the NMR technique of adiabatic fast passage (AFP) to monitor the polarization of ³He targets polarized using spin-exchange optical pumping at low magnetic fields, the absolute calibration of the polarimetry system can be achieved by comparison with the AFP signals of thermally polarized water. In this talk we will talk about an ultra-low noise custom-made NMR system capable of measuring an AFP signal from a thermally polarized water sample in a single measurement at 36 Gauss. We will also be talking about some of the systematics associated with signal averaging when using thermally polarized water for the calibration of AFP-based NMR systems at low fields. When comparing AFP signals from ³He and water, it is important to account for the dissimilarities in the shape of the glass containers holding the two samples. We will present a method of capturing the shape of the containers using spherical harmonics and a way of making corrections to the signal size based on that information.