ORGANIC MATERIALS FOR REAL-TIME HOLOGRAPHIC RECORDING

Photoactive organic layers, such as photochromic polymers and photopol ymers, are investigated for real-time and in-situ holographic recordin g. The results with photochromic polymers containing spiropyran and sp irooxazine dyes revealed that variations in the UV beam excitation and visible recording beam procedures significantly changed the exposure sensitivity and diffraction efficiency. These effects were exploited f or all-optical modulation of the holographic gratings and explained by the photochemical and thermal transformations between photochromic st ereoisomers. Copolymers of the photochromic spiropyrans were investiga ted for optical recording with infrared laser radiation at 10.5 and 10 .6 mu m. Although the recording primarily occurs by thermal bleaching, some nonthermal IR processes are also involved. Holographic recording in photopolymer layers, based on acrylamide monomers dissolved in pol yvinylalcohol, is influenced by chemical additives. Specifically, a su peradditive sensitization effect of diphenyl iodonium chloride togethe r with triethanolamine significantly increased the exposure sensitivit ies at 514 nm, by a factor of more than 3 (to about 15 mJ/cm(2)). Seve ral formulations produce large enough refractive index modulations so that very high diffraction efficiencies (DE > 90%) are obtained. For c ertain conditions, under highly asymmetric recording angles, the diffr action efficiency is significantly reduced, and was found to originate from fringe bending due to nonlinear shrinkage. The introduction of c rosslinking and gelling agents stabilize the formed grating structures against dimensional distortions.