Orientational Pair Correlation, Polar Order Parameter and Temporal Stability in the Second Harmonic Generation of Amorphous Polymers

Abstract : Measurements of the second harmonic generation (SHG) signal were made on the DAN/PMMA guest/host system as a function of the nonlinear optical (NLO) chromophore concentration and the poling field strength. The temporal stability of the SHG signal, after the poling field was removed, was also investigated. The polar orientational order parameters, L(sub 33) and L(sub 31) (see text for definition), were deduced from the second order nonlinear susceptibility. Both of the polar orientational order parameters and the relaxation time of the nonlinear susceptibility were found to increase with increasing NLO chromophore concentration. The concentration dependence was interpreted as due to the anisotropic intermolecular interaction, particularly the dipole-dipole interaction. The anisotropic intermolecular interaction introduces the orientational pair correlation function which enhances the polar order as well as the temporal stability of the NLO effect.