Mechanisms of Photorefractivity in Polymeric Materials

Abstract

Abstract : This grant has featured a multi-faceted effort to develop new photorefractive polymers, demonstrate previously unobserved physical effects, and most importantly, to understand the mechanisms controlling the performance. Significant progress has occurred in all areas. In the synthetic area, a modular approach to the synthesis of photorefractive polymers has been developed based on grafting of various functional components onto siloxane polymers and post-graft chemical modifications. We have thoroughly explored the class of host-guest photorefractive polymers based on poly(n-vinyl carbazole) and dicyanostyrene-containing nonlinear optical chromophores. These materials have shown gain coefficients up to 200/cm, and single-pass gain factors of 500 times, and grating growth times as small as 4 ms at 1 W/sq cm. These extremely high performance levels have led to the first observations of beam fanning, self-pumped phase conjugation, and the detection of laser-based ultrasound under this grant. In the mechanistic area, for the first time the active trapping species has been identified to be the fullerene anion, and the compensator species as the nonlinear optical chromophore. This should allow future optimization of space charge field, the phase shift, resolution, and the index modulation.