Optical recording of refractive-index patterns in doped poly-(methyl methacrylate) films

Abstract

Thin films (3–6 μm) of poly-(methyl methacrylate) and benzildimethylketal were deposited from solutions in methyl methacrylate or styrene. The formation of refractive-index changes (Δn) by illumination with 366-nm light was studied over a large concentration range of ketal. For low concentrations benzildimethylketal acts mainly as a photoinitiator inducing Δn patterns via polymerization of the residual monomer. In the region of higher ketal contents the Δn formation is caused presumably by a photochemical reaction of benzildimethylketal. After thermal development and fixing, refractive-index changes up to 5 × 10−2 could be obtained.