Temperature dependence of photorefractive properties of PVK-based composites

We studied the temperature dependencies of electric field-induced birefringence, conductivity, and photorefractive properties of two poly (n-vinylcarbazole) (PVK)-based composites with different nonlinear optical chromophores: 2,5-dimethyl-4-(4'-nitrophenylazo)anisole (DMNPAA) and its derivative, 4-butoxy-3-propyl-1-(4-nitrophenyazo) benzene (m3p4). Both composites showed similar temperature dependencies; the photorefractive responses were faster at higher temperatures and the diffraction efficiencies increased with temperature and then began to decrease. Such behavior is consistent with the measured temperature dependencies of the field-induced birefringence and the conductivity. We found that the m3p4 composite exhibited a faster photorefractive response rate than the DMNPAA composite when compared at the same reduced temperature T - T-g, where T is the temperature of the measurement and T-g is the glass transition temperature. The results indicate that one can enhance the total photorefractive response rate by changing the nonlinear optical chromophore.