Electric-field stabilization and competition of gratings in a photorefractive polymer

We report observations of electric-field stabilization of gratings and grating competition in a new photorefractive polymer mixture composed of 40 wt. % diethylamino-benzaldehyde-diphenyl hydrazone dissolved in Bisphenol A 4,4'-nitroaminotolane. Gratings formed with a 650-nm optical wavelength in 145-microm-thick films at 138-kV/cm bias field have a diffraction efficiency as high as 0.11%, require an energy density of ~1 J/cm(2) for formation, and show cancellation, revelation, and electric-field-stabilized persistence. We propose a model in which fast recording is associated with one set of photosensitive traps, whereas a slower cancellation and subsequent revelation are associated with a competing grating formed in a set of insensitive shallow traps. The model also accounts for observed fatigue of the photoconductivity.