Optical nuclear polarization as a consequence of the non-crossing rule (level-anti-crossing)

The theory for Optical Nuclear Polarization (ONP) as a consequence of Level-Anti-Crossing (LAC) as outlined in the first part of this series, is extended by considering the influence of relaxation between the electron spin states Tx. Ty and Tz. Unselective relaxation as defined by equal rates of relaxation among the spin states, Tμ, in general reduces the nuclear polarization. In addition, it broadens the shape of the ONP as a function of the magnetic field. Similar destructive effects are found for selective relaxation with the exception of one specific type of selectiveness. It will be referred to as constructive relaxation, because it is even able to enhance ONP by LAC together with a more pronounced broadening of the field dependence. For instance when a polarizing field is taken in the z direction, a large relaxation rate Wxy (relaxation between Tx and Ty) enhances the effect. Large rates Wxz and Wyz would reduce the ONP. The constructive relaxation is treated analytically by perturbation theory. From the experimental ONP results one has to conclude that often of the three relaxation rates is considerably larger than the other two.