Based On Local Area Surface From The Molecular Orientation Of Excimer Resonance And Heterogeneous Molecular Performance To Control Efficiency

Nanophotonics is a new branch of science which studies the interaction between matter and nanomaterials. Among kinds of nanomaterials, metal nanomaterials are research concern. Surface plasmon resonance (SPR) of metal materials can break the diffraction limit of conventional optics, leading to the integration of light and electron on the same chip. Meantime, SPR is able to enhance the radiation efficiency of fluorescence molecules and control the rotation and orientation of nanoparticles, making metal nanomaterials a good choice to change the physical-optical properties of matter. This Ph.D thesis focuses on the research topic "Controlling photoisomerization quantum efficiency (PQE) of azobenzene dye and enhancing optical-induced reorientation of liquid crystals (LC) by localized surface plasmon resonance (LSPR) of gold nanoparticle film". The influence of LSPR to PQE of azobenzene dye and optical nonlinear property of LC has been investigated. The main achievements are as follow:1. for first time we obtain the second order hyperpolarizability of cis isomer. Contribution of cis isomer to third-order nonlinear susceptibility of azobenzene film is brought in and the theory of optically induced anisotropy of third-order nonlinear susceptibility in azobenzene dye polymers is supplemented. Experimentally optical third harmonic generation (THG) of azobenzene dye polymer under various intensity of linearly polarized optical beam was recorded. Then experimental data was fitted by theory and finally the second order hyperpolarizability of cis isomer is deduced to be5.6×10-33esu.2. trans-to-cis photoisomerization quantum efficiency (PQE) of azobenzene dye is artificially modified by surface plasmon resonance (SPR) induced local field enhancement and energy transfer of Au nanoparticles film. PQE can either increase one time larger or decrease dramatically. Using surface enhanced raman scattering and fluorescence quenching experiments, it is found that SPR of Au nanoparticles film enhances PQE and energy transfer lows it. PQE is further accurately modified by controlling the distance between azobenzene dye and Au nanoparticles film.3. surface anchoring energy of Au nanoparticles coated liquid crystal cell can be effectively decreased when pumped by resonant optical beam. As a result, the threshold of optical Freedericksz phase transition is lowed by one to two orders of magnitude. Meanwhile, the response time of LC to optical pump is also shortened.