Three-dimensional confocal Raman imaging of volume holograms formed in ZrO2 nanoparticle-photopolymer composite materials

We describe physicochemical microanalyses of plane-wave volume holograms recorded in ZrO2 nanoparticle-photopolymer composite films with approximately 50 mu m thickness. Transversal and longitudinal density distributions of compositions embedded in holograms are analyzed by a confocal scanning Raman microscope. Other microscopic measurements using an electron-probe microanalyzer and an atomic force microscope are also performed to examine hologram's compositional and structural morphology near the surface. It is found that the induced density distributions of ZrO2 nanoparticles and the formed polymer are 180 degrees out of phase with each other in holograms. This result shows a decisive evidence of the counterdiffusion of monomer molecules and ZrO2 nanoparticles in a film under two-beam holographic exposure. It is also found that when grating spacing is 5 mu m or longer, a relief structure of a few 10 nm appears on a film's surface and its height increases with the grating spacing. This result indicates a significance of the surface tension effect at shorter grating spacing and the imperfect compensation of local volume changes in the counterdiffusion process. (C) 2008 American Institute of Physics.