Dark polymerization of radicals and its contribution for grating formation in SiO2 nanoparticles dispersed glass like photopolymer

Dark polymerization of active radicals at post-exposure is investigated in SiO2 nanoparticles and phenathrenequinone dispersed poly(methyl methacrylate) photopolymer experimentally and theoretically. In experiments, the grating formation and improvement of photosensitivity due to SiO2 nanoparticles at short exposure and post-exposure are presented. For analyzing the contribution of dark reaction and dark diffusion to the modulation depth enhancement, the dark reaction time is quantitatively extracted using diffusion model. The longer dark reaction time appeared at high recording intensity and low diffusion rate of components that is evidently dependent on the holographic characteristic parameter, i.e. the ratio of diffusion rate divided by the polymerization rate. The incorporations of SiO2 nanoparticles obviously accelerate the dark reaction and enhance the contribution of dark reaction for the dark grating enhancement. The modulation increment by dark reaction is closed to 35.7% relative to the dark enhancement of grating at 96.2 mW/cm and 0.1 wt% SiO2. The analyzing results indicate that the dark reaction dominates the grating enhancement at short periods after exposure, and the later dark diffusion of components still play a significant role for dark enhancement of grating at long time periods. The investigation can accelerate the understanding photochemical dynamics in the photopolymer, and bring about a significant foundation in determining the appropriate time interval in multiplexing technology. & 2013 Elsevier B.V. All rights reserved.