FREQUENCY DETUNING EFFECT ON THE COMPLEX NONLINEAR REFRACTIVE-INDEX OF AZO-DYE-DOPED POLYMER-FILMS

The optical frequency detuning characteristics of the magnitude and ph ase of the 3rd-order complex nonlinear refractive index were investiga ted in azo-dye-doped polymer thin films, and the experimental data wer e compared with the theoretical result of the two-level model. For the methylorange-dye-doped PVA thin film, we found that the phase of the 3rd-order complex nonlinear refractive index decreased as the optical frequency detuning increased, as was anticipated from the two-level mo del. Also, it was found that the magnitude of the 3rd-order complex no nlinear refractive index decreased with decreasing optical frequency d etuning because of the depletion in the number of trans parallel-to mo lecules. The phase of the 3rd-order complex nonlinear refractive index for methylred-dye-doped PMMA thin film was found to decrease with inc reasing optical frequency detuning, similar to the behavior of the met hylorange-dye-doped PVA thin film. However, we obtained different resu lts in the behavior of the magnitude of the 3rd-order complex nonlinea r refractive index compared to that expected from the two-level model.