Effect of the electrostatic interactions of chromophores on the macroscopic second-order nonlinear optical properties of the polymer films

The polyetherketone (PEK-c) guest-host system thin films doped with 3-(1,1- dicyanothenyl)-1-phenyl-4,5-dihydro-1H-pryazole (DCNP) were prepared. Their second-order nonlinear optical (NLO) coefficients chi(33)((2)) were measur ed by using Maker fringe method for the polymer films doped with different weight percents of DCNP. Experimental results indicate that the second-orde r NLO properties of the poled polymer films could decrease with the chromop hore loading increasing when the chromophore loading reaches a fairly high level. In this paper, the relationship between the macroscopic second-order NLO coefficient and the chromophore number density was modified under cons idering the role of the electrostatic interactions of chromophores in the p olymer film. According to the modified relationship, the macroscopic second -order NLO coefficient is no longer in direct proportion with the chromopho re number density in the polymer film. The effect of the electrostatic inte ractions of chromophores on second-order NLO properties was discussed. The attenuation of the macroscopic second-order NLO activity can be demonstrate d by the role of the chromophore electrostatic interactions at high loading of chromophore in the polymer systems.