| It is well known that subwavelength-and nanometer-sized metal structures can generate surface plasmon polaritons (SPPs), causing a strong collective conduction electron shock and at which the huge electric field enhancement established on metal surface. Due to the material nonlinearity, these plasmonic structures can produce obvious third harmonic generation (THG). In this thesis, we studied the third harmonic generation from a variety of metal microstructures prepared by the self-organizing colloidal crystal template replication technology.The work presented is divided into the main two sections. Initially, We obtained optical THG from two-dimensional periodically arrayed gold-island films. The gold-island films were fabricated using nanosphere lithography (NSL). By a reflection-type optical system, these arrays produce significant THG with the help of a spectrum-resolved femto-second laser. At the localized surface plasmon (LSP) excitation wavelength of fundamental wave, THG is greatly enhanced due to the strong light localization effect. The radiation direction of THG verified the momentum matching condition.In the second section we studied the THG from several kind of two-dimensional periodically arrayed gold nano-hemispherical shell films developed by NSL. Enhanced THG was achieved from the "opening-up" structures whose cavity opening direction parallel to the incident light. During this process, we observed some amusing results of the THG:depolarization and decoherence. To find the answer of these phenomena, we designed a series of test. By a comparative experiment from gold "opening-down" structures whose cavity opening direction antiparallel to the incident light, we found that neither depolarization nor decoherence was observed, which was similar to the perfect gold film. And by studying different sizes of "opening-up" structures, we ultimately found that depolarization and decoherence might relate to surface induced plasmonic excitations. |
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