Density grating time dependence

For readers interested in the quantitative description of the time-dependent magnetization processes, the magnetization grating , that occurs in Mims ENDOR using the density operator formalism, which leads to the experimental behavior described earlier, the reader is referred to other sources by authors infinitely more qualified than the present... 

A spectroscopic method has been recently developed to determine the trap density in C6o-sensitized PR polymers [33], It monitored the extinction coefficient increase due to the increase in number density of C6o anion traps with irradiation time, and it was found that the measured concentration of C60 anion and that of the traps determined by the spectroscopic method and PR grating formation experiments, respectively, agree with each other to within a factor of three. The study also revealed that the trap density is not constant but history-dependent and varies with both light intensity and electric field, which is in contrast to the assumption of constant trap density in the standard model. 

The order parameter fluctuations in the isotropic phase are a weak optical effect which is not directly significant in the thermal grating diffraction. Therefore, again there is no direct relation between the optical and ultrasonic relaxation. In the isotropic phase the refractive index change is due to density change Ap therefore rj a Ap. Nematic correlation in the isotropic phase will influence the relaxation time observed in the optical experiment. However the weak temperature dependence of r implies that this is not substantial. 

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