<title>Photopolymeric holographic recording media: in-situ and real-time characterization</title>

Abstract

Photoactive polymer matrices are investigated by and for holographic recording at 514 nm. The photopolymers are based on acrylamide monomers, which are dissolved together with xanthine dyes and other additives in polyvinylalcohol. Dry plastic coatings are obtained by casting the aqueous polymer solutions on glass substrates. Photorecording occurs in real-time and in-situ, without any post-exposure processing. This paper describes the influences of chemical additives on the photorecording process. Specifically, the addition of diphenyl iodonium chloride (DPI-Cl), in conjunction with triethanolamine (TEA), significantly increases the exposure sensitivities, by a factor of over three (to about 15 mJ/cm<SUP>2</SUP>). This sensitizing effect is shown to originate from a superadditive effect between TEA and DPI-Cl. The mechanism of the superadditive effect is discussed by a proposed reaction model. The exposure sensitivities are also significantly influenced by the PVA binder parameters, such as average molecular weights and degree of hydrolization. The present formulations produce large enough refractive index modulations, so that very high diffraction efficiencies (DEs &gt; 90%) are obtained. The dynamic range of refractive index modulations was increased from 0.014 to 0.018 by the addition of glutaraldehyde crosslinking, which also improves the dimensional stability of the holograms.