Rewritable holograms based on azobenzene-containing liquid-crystalline polymers

The design and preparation of azobenzene-containing polymers showing a large photoinduced change in refractive index, and their applications to rewritable Raman-Nath and Bragg holograms are reviewed. Optically transparent films with a thickness of > 200 mu m have been prepared with random copolymers, which contain photoresponsive and amplifying components in the side chain. Various azobenzene chromophores are used as the photoresponsive component. Cyanobiphenyl and tolane moieties are incorporated as the amplifying component, which enhances the change in refractive index triggered by the azobenzene. When two writing beams are made to overlap in the film, a periodic change in refractive index is induced, and an incident probe beam is diffracted at similar to 100% diffraction efficiency. The recorded holograms can be erased by thermal treatment or by photoirradiation with a single writing beam. Angular multiplicity is discussed from the viewpoint of high-density information storage. Polymer Journal (2010) 42, 525-533; doi:10.1038/pj.2010.45; published online 26 May 2010