Photorefractive trapping and the correlation between recording and erasure dynamics in a polymer composite

The fast time constants of holographic contrast growth and erasure for various photorefractive polymer composites were measured under a wide range of experimental conditions. Either of two sensitizers, 2,4,7-trinitro-9-fluorenone (TNF) or (2,4,7-trinitro-9-fluorenylidene)malonodinitrile (TNFDM), were used in a degenerate four-wave mixing experiment under varying conditions of field, wavelength and intensity. Collected together, the fast growth and erasure time constants were found to be correlated with a coefficient of 0.96. From this correlation we conclude that the charge generation process during holographic recording and the optical de-trapping process during hologram erasure are indistinguishable. Hence in accordance with the photorefractive crystal model, hole recombination with the sensitizer anions forms the primary charge trapping mechanism in the majority of photorefractive polymer composites.