Novel polymer systems with pseudo-photorefraction

Abstract

While the word "photorefraction" may literally describe all kinds of photoinduced changes of the refractive index of a material, photoinduced phase grating which shows two beam coupling via phhotoconduction and electro-optic effect is generally considered as only "photorefraction". When a photorefractive material is exposed to light, free charge carriers are generated by excitation from impurity energy levels to an energy band, at a rate proportional to the optical power. This process is much like that in a extrinsic photoconductor. These carriers then diffuse and drift away from the positions of high intensity where they were generated, leaving behind fixed charges of the opposite sign when the external electric field was applied. The free carriers can be trapped by ionized impurities at other locations, depositing their charge there as they recombine. The result is the creation of an inhomogeneous space-charge distribution that can remain in place for a period of time after the light is removed. This charge distribution creates an internal electric field pattern that modulates the local refractive index of the electrically poled material by virtue of the electro-optic effect. Thus the poling and applied external electric field is essential to generate the photorefraction. In the other hand, photoisomerization and photobleaching is believed not to be able to create the phase shifted grating, which implies that two beam coupling gain cannot be obtained via these photochemical reaction. In the initial stage of this study, we prepared photorefractive polymer blend containing photoconducting polymer(PVK) and non-linear optical(NLO) polymer in order to achieve phase stability and optimized photorefraction. DR1 attached PMMA polymer was synthesized as NLO polymer. Polymer blend shows phase stability u pto 15wt% based on the...