Improvement And Third-Order Optical Nonlinearity Of PMMA /Titania Composite Material

With the development of nanoscience and nanotechnology, the requirement of organic-inorganic composite material is increasingly high, especially of poly-mer/semiconductor nanocomposites. This kind of nanocomposite possesses some new optical, electric,dynamic and mechanical characteristics which are not in the single organic or inorganic and macroscopic bulk organic-inorganic material. The composite can combine the processibility, high mechanism and anti-ruption merit of polymer with the small size effect, surface effect, quantum effect and cotrollable morpology of inorganic TiO₂ nanoparticles, bringing the composite more excellent properties. Titania has higher refractive index and more carriers. So it is the first choise in optical nonlinearity materials. In this article, we mainly research on im-provement of polymer PMMA and TiO₂, demonstrate the third-order optical nonlinearity enhancement of nanocomposite films by effective medium theory and surface enhancement electric-magnetic field theory. The research work and results have been summarized as follows:The core-shell structure is prepared using the surfactant improvement. We synthesize polymer composites with high concentration and dispersive TiO₂ nanoparticles by"ex-situ"sol-gel/polymerization method. We confirm the optimum reaction ratio for preparing titania nanoparticles. From the FT-IR spectra, we can get the surface ligands of acetylacetone (Acac) have successfully acted between the surface of titania and PMMA, and obtain the core-shell structure composites.Linear and nonlinear optical properties are studied by effective medium theory in core-shell structure. This kind of core-shell structure can concentrate the optical filed to the titania core and the surrounding shell, making the optical enhanced, and thus increase the polarization of the nanoparticles, the nonlinearity is enhanced fi-nally. We demonstrate the nonlinearity by Z-scan technique at 800nm femtosecond laser. The Z-scan results show the nanocomposites with core-shell structure have large nonlinearity enhancement compared with inorganic TiO₂ films, which indicate the linear and third-order optical nonlinear properties can be effectively tuned by TiO₂ nanoparticles, showing the potential application in photonic devices.The ellipsoid-shaped nanoparticles are synthesized by using the mixed surfac- tant. Because of the polar character, TiO₂ nanoparticles can absorb the stronger po-lar surfactant TEOA. We study the effects of different ellipsidal particles'size, shape and surrounding medium on the third-order nonlinearity of PMMA/TiO₂ nanocomposite materials. We report on the effective third-order optical nonlinearity en-hancement of nanocomposite films by effective medium theory under different TiO₂ nanoparticle concentration, especially the high TiO₂ nanoparticle concentraion. We propose the optimum nonlinearity enhancement by the surface enhancement elec-tric-magnetic filed theory, which indicates the important application in tunable nonlinear optical devices.