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.
© 1984 Optical Society of America
Hilmar Franke, "Optical recording of refractive-index patterns in doped poly-(methyl methacrylate) films," Appl. Opt. 23, 2729-2733 (1984)