A new highly photorefractive polymer composite for optical data storage application

A novel photorefractive effect based on a photochemical process has been developed. The system is composed of methyl red (MR) doped poly(methylmethacrylate) (PMMA) polymer with benzyldimethylketal (BDK) as a photoinitiator. Large changes in optical constants were obtained in the MR/BDK film upon exposure to extremely low power UV light (265 µW cm −2 ) at wavelength 254 nm. These changes reach about 90% of their maximum value in 5 s. Changes in the refractive index Δ n = −0.47 at 570 nm and in the absorption coefficient Δα = −1.4 × 10 5 cm −1 at 470 nm in the MR/BDK film and Δ n = 0.03 and Δα = −8 × 10 4 cm −1 in MR/BDK/PMMA film were measured. The origin of such high changes in optical constants may be attributed to the photodeprotonation of MR by the radicals formed by the photodecomposition of BDK by UV light. The optical constants and film thickness change were measured using a variable angle spectroscopic ellipsometer.