Photorefractive effect in polymer doped with PNP

Photorefractive materials are of considerable interest for the development of optical devices. Recently, attention has been drawn to the photorefractive polymer owing to its excellent properties. In this paper, photorefractive polymer composite based on photoconductor poly(N-vinylcarbazole)(PVK) is described. As a electro-optic chromopher (S)-(-)-N-(5-nitro-2-pyridyl)prolinol(PNP) is used in the composite. In order to decrease the grass transition temperature N-ethylcarbazole (ECZ) is added. A small amount of 2-4-7 trinitro-9 fluorenon(TNF) is also added to increase the photosensitivity in visible region. The composition is PNP: PVK:ECZ:TNF 50:33:16:1 wt%. The mixture of these materials is dissolved in THF and is stirred sufficiently. The PR samples are prepared by casting the mixture onto the glass plate and pressed another glass at about 140 C. The glass plates are coated with transparent electrode for application of the external electric field. The films thus obtained is light yellow and the optical absorption coefficient of this film is 25 cm(-1) at 633 nm. Two coherent writing beams from He-Ne laser are overlapped in the sample to create a fringe patten. From the measured increase and decrease in the writing beam powers, the two beam coupling gain coefficient is calculated. In our experiment gain coefficient is 101 cm(-1) and 68 cm(-1) for p-polarized and s-polarized light respectively at 100 V/10(-6) m.