New photorefractive polymers for real-time holography

We investigated polymeric materials based on polysiloxane (PSX), polymethylmethacrylate (PMMA), polyurethane (PU), as well as a triphenylamin-based glass (DRDCTA) with respect to their photorefractive properties. Electric-field dependencies of the two-beam coupling gain, diffraction efficiencies, refractive index amplitudes and holographic rise-times could be obtained by means of two-wave mixing and degenerate four-wave mixing measurements. The examined PSX polymer systems were composed of a photoconducting polysiloxane host doped with trinitrofluorenone (TNF) as a sensitizing moiety and various chromophores, namely, an azo derivative, a stilben derivative and a tolan derivative. Due to their comparatively low glass-transition temperatures T-g, an orientational enhancement of the photorefractive properties was observed. Furthermore, the influence of photoisomerisation (based on trans-cis-trans cycles) on the holographical properties could be determined for the different chromophores. In addition, a class of fully functionalized polymers with azo chromophores and carbazole-units covalently attached to PMMA-and PU-backbones was synthesized. These systems show comparatively high glass transition temperatures of more than 80 degrees C. The third type of materials investigated is a glass of triphenylamin with attached carbazole and NLO-chromophore moieties. It has a glass transition temperature of 120 degrees C. For the high-T-g materials, poling procedures - essential for the photorefractive properties - could be monitored in-situ by second-harmonic generation. Absolute values for the nonlinear Pockels coefficients chi((2)) (-omega;omega,0) have been obtained by electro-optical measurements.