A photopolymer system doped with gold nanoparticles (Au NPs) was studied using Surface Enhanced Raman Scattering (SERS) technique in this work. In the system, polyvinyl alcohol is a binder, acrylamide and methylene-bisacrylamide are two monomers, methylene blue (MB) is a photosensitizer and triethanolamine is an initiator. Two types of Au NPs--- bare Au NPs with 13nm and 25nm diameter, and their corresponding SiO<sub>2</sub> shell-isolated Au (Au@SiO<sub>2</sub>) NPs with ~2nm shell thickness, were prepared and doped into the photopolymer for reducing the shrinkage of holograms. The shield of SiO<sub>2</sub> shell avoids the dark reaction originating from electron transfer between Au NPs and MB molecules. More importantly, under 633nm laser excitation, the resonance Raman scattering of MB can be triggered, and the Raman signal of MB can be enhanced greatly due to the local enhanced electromagnetic field by Au@SiO<sub>2</sub> NPs. Both of them made the in-situ Raman detection of the photopolymer more feasible. The experimental results not only show the excitation process of MB but also display the polymerization process of the photopolymer. In addition, the excitation rate of MB and the polymerization rate of monomers can also be obtained using their time Raman spectra. This provides an experimental tool for detecting the photochemical kinetics process of the photopolymer.
A novel photopolymer based on polyvinyl-alcohol for holographic storage was fabricated. The
material with riboflavin (RF), methylene bule (MB), erythrosin B (ErB) as the photosensitizers for
holographic storage has a broad absorption spectrum range (more than 500nm). The photopolymer
can be sensitized by the whole visible light, and that will improve storage capacity and density of the
holographic storage greatly, especially under the short wavelength recording. Photo-induced
reaction processes in the photopolymer and phase grating of index modulation for holographic
storage were studied. The surface structure of the grating and the images of reaction processes were
scanned by SEM (Scanning Electron Microscope). The experimental results are compared with the
kinetics theory of the polymerization and they are fitted well. Furthermore, the grating constant can
be estimated from grating images which were scanned by SEM. Some holographic characteristics of
the photopolymer were analyzed. Using a standard holographic setup, we recorded unslanted
diffraction gratings.The material has high maximum diffraction efficiency (≥68%), good sensitivity
(≥3.03×10<sup>-3</sup> cm<sup>2</sup>/mJ), and high index modulation (≥4.58 ×10<sup>-4</sup>) when its tickness is about 300μm.
Two dimentional simulate images generated by SLM (Spatial Light Modulator) were stored in the
film, and the reconstructed data pages had good fidelity. The results show that the material has a
better potential in holographic storage.
We prepared a photopolymer material sensitized by acridine orange for high-density holographic storage. The absorption
peak of this sample is near 490nm, which is especially appropriate for using 488nm exposure wavelength of Ar<sup>+</sup> laser for
holographic recording. We illuminated it with three exposure wavelengths (476nm, 488nm and 496nm) and the
experimental results show that the maximum diffraction efficiency is 52%. Some holograms stored in this medium can
be reconstructed clearly. It is found that this photopolymer is appropriate for high-density volume holographic storage.