Improvement in linear and nonlinear optical-properties by blending poly(N-vinyl-2-pyrrolidone) with an electro-optic polymer

Poly(N-vinyl-2-pyrrolidone) (PVP) has been blended with a urethane–urea copolymer (UU); this resulting electro-optic polymer was thought to improve the linear and nonlinear optical properties. Transparent films without scattering were obtained from the mixed solutions of PVP and UU with a wide mixture ratio. The refractive indices and absorption coefficients of the films decreased with the nonlinear optical (NLO) chromophore concentration. The optical nonlinearity, which was evaluated by the d-coefficient for second harmonic generation, was enhanced by blending 10–20 w/w% PVP with UU in spite of a decrease in the NLO chromophore concentration. No noticeable lowering of the temporal stability of the nonlinearity was observed in the blended film containing 10–20 w/w% PVP. The improvement induced by the addition of a small amount of PVP could not be explained by the interaction between the NLO chromophore and PVP but between UU and PVP. The blended films containing 10–20 w/w% PVP showed an improvement in temporal stability at 100°C by additional heating during corona poling. The blending of polysulfone (PSF) with UU was examined, and the blended film containing 10 w/w% PSF showed no observable change regarding the d-coefficient and its temporal stability.