Investigation Of The Third-Order Optical Nonlinearity And Photoluminescent Properties Of Metallic Nanorod Arrays

The establishment of theoretical model for surface plasmon (SP) hybridization and the application of numerical simulation methods such like discrete dipole approximation (DDA) as well as finite-difference time domain (FDTD) methods in recent years make it easier to investigate the SP related properties of nanostructures. Through comparing the simulation results with experimental data, micro-mechanisms behind various macro-characters of nanostructures have been uncovered. In addition, the understanding of people for physical processes taking place in SP nanostructures has also been deepened thanks to the application of experimental techniques such as optical Kerr and ultrafast time-resolved transient absorption measurements.In order to further explore the undefined inner mechanisms of some physical processes in SP nanostructures, and to pave the way for the design and fabrication of future photoelectronic devices with these kinds of structures, we carried out investigations on the third-order nonlinearity and photoluminescent (PL) properties of metallic nanorod/nanowire arrays with the help of FDTD electromagnetic simulations. The main works are listed as following:1. The SP resonant absorption and electromagnetic field distribution of gold nanoparticle/nanorod monomers, as well as the interactions between adjacent monomers were simulated with FDTD solutions. We found that large localized field enhancement factor can be obtained by effectively exciting the surface plasmon hot-spots within the sub-10 nm gaps of surface plasmonic nanostructures, which could be used to enhance the optical nonlinear response and PL of kinds of materials.2. Two types of photoluminescent behaviors of Au nanorod arrays deposited in porous anode aluminum oxide (AAO) membranes were investigated. During the study of the avalanche-like PL in Au nanorod array without Al metal substrate, we observed for the first time a "loop" structure of PL intensity around the threshold excitation power density (EPD), as well as the ultraslow variation of PL intensity at sub-second time scale under different EPDs and illumination durations. Taking the reported study and the experimental results into consideration, we put forward a SP assisted black-body radiation model to explain the actual origin of this avalanche-like PL behavior. The correctness of this model was well demonstrated by blue-shift of PL spectrum and variation character of the radiation intensity calculated according to Planck's formula of black-body radiation. Then we performed preliminary research on the supercontinuum generation (SCG) from Au nanorod array sample without removing the Al substrate, and found that the SCG was greatly enhanced at the present of Au nanorods. This enhanced SCG shows ultrashort lifetime that is far below the system response time, suggesting distinct nature of the two broadband PL behaviors referred to as SCG and avalanche-like PL, respectively. Therefore, one can obtain either ultrafast broad band SCG light source or ultraslow broadband black-body radiation light source just by deciding whether the Al substrate is removed.3. Near-ultraviolet (UV)-enhanced broadband third-order optical nonlinear susceptibility of metallic (Au, Ag, Al) nanorod array films (NRAFs) with 7 nm inter-rod gaps was researched by Z-scan technique. This nanostructure exhibits extremely large third-order optical nonlinear susceptibility and figure of merit which show similar tendency for each sample to their extinction spectrum in the broad range of 360-900 nm. The third-order optical nonlinear susceptibility, figure of merit and optical transmittance of Al-NRAF are found apparently better than the identically structured Au and Ag ones respectively below 500 nm,750 nm and in the whole wavelength range. The PL enhancement of CdSe/ZnS quantum dots placed on top of these films demonstrate that Al-NRAF is more suitable for use as photoluminescent enhancement substrate in the near-UV regieme. We concluded from all these results that this Al-NRAF plasmonic nanostructure with sub-10 nm gaps is a promising candidate for the development of new photonic devices in the visible and UV range.4. A brief introduction to the researches on SP resonance enhanced magneto-optical rotation nanostructures, as well as description about the design of nanostructures and measurement equipements was made. We clarified in this part the basic designing principles from aspects including material selection and structure design. Magneto-optical rotation measurement system was built up and optimized for use under pulsed high magnetic fields, by which we hope to pave the way forthe developmentof new magneto-plasmonic nanostructures showing large magneto-optical rotation property in the future.