The effect of radiation trapping on a high field spin exchange optically pumped target

The effect of radiation trapping on an optically pumped spin exchange polarized atomic hydrogen or deuterium target operated in a high magnetic field is analyzed. It is shown that, if possible, it is desirable even in a high magnetic field to use an alkali density low enough that significant radiation trapping does not occur since fewer photons are needed on the average to polarize an atom. This permits one to obtain the maximum number of polarized hydrogen atoms per photon. Operation at a low alkali density requires both a high atomic hydrogen density and a low hydrogen polarization loss rate. It is also suggested that in a high magnetic field there may be advantages in using linearly polarized light for the optical pumping. (orig.)