RELAXATION OF HOLOGRAPHIC GRATINGS IN LIQUID-CRYSTALLINE SIDE-CHAIN POLYMERS WITH AZO CHROMOPHORES

The relaxation of holographic phase gratings was examined to obtain some information about the involved photochemically induced changes. The studies were performed with statistical liquid-crystalline side group copolymers having different concentrations of the azobenzene dye. The formation of mesophases, which normally exist in the thermodynamic equilibrium, was prevented during the sample preparation by quenching the polymer films. Two relaxation processes were found in this glassy state of the polymers. The faster one could be described by a dispersive stretched exponential function and was attributed to relaxation processes which are related to the amorphous phase of the sample, while the slower one, corresponding to a single exponential process, correlates with the formation of light-induced liquid-crystalline microstructures. The latter are believed to be the main cause for the modulation of the refractive index.