Epoxy resin-photopolymer composites for volume holography

Efficient materials for recording volume holograms are described that could potentially find application in archival data storage. These materials are prepared by mixing photopolymerizable vinyl monomers with a liquid epoxy resin and an amine hardener. A solid matrix is formed in situ as the epoxy cures at room temperature. The unreacted vinyl monomers are subsequently photopolymerized during hologram recording. A key feature of these materials is the separation of the epoxy and vinyl polymerizations. This separation allows for a large index contrast to be developed in holograms when components are optimized. The standard material described in this work consists of a low index matrix (n congruent to 1.46), comprised of diethylenetriamine and 1,4-butanediol diglycidyl ether, and a high index photopolymer mixture (n congruent to 1.60) of N-vinylcarbazole and N-vinyl-2-pyrrolidinone. This material is functional in thick formats (several millimeters), which enables narrow angular bandwidth and high diffraction efficiency. A dynamic range (M/#) up to 13 has been measured in these materials. Holographic performance is highly dependent on the amount of amine hardener used, as well as on photopolymer shrinkage.