Quasipermanent photochemical gratings in a dual use photorefractive polymer composite

The dual nature of ~3-~2-~4-~N,N-diethylamino!phenyl!ethenyl!-5,5-dimethyl-1,2-cyclohexenylidene!propanedinitrile ~Lemke-e! allows us to write both quasipermanent and erasable holographic gratings in the same storage volume. In the presence of a triplet excited sensitizer, Lemke-e undergoes a photochemical reaction allowing the creation of quasipermanent photochemical holographic gratings. In addition, applying an electric field to the composite allows the storage of erasable photorefractive holograms in the same location as previously stored permanent photochemical holograms. Photochemical gratings (h.10%) can be written in less than 1 min while photorefractive gratings (h.50%) can be written in less than 1 s. The photochemical gratings have a dark lifetime of several days. © 1999 American Institute of Physics. @S0003-6951~99!00619-1#