| Summary: | 碩士 === 國立交通大學 === 光電工程研究所 === 104 === We propose a metal plasmonic lens, Ag-Au hybrid circular nanoslits. By different widths of circular nanoslits to achieve the phase modulation of incident wave so that it can focus behind the plasmonic lens. Through the two metal combined nanostructure can reduce the FWHM of focus and improve the transmittance.
In this thesis, we focus on reducing and optimizing the FWHM of focus by geometry tuning of circular nanoslits including metal thickness, ratio of metal and circular nanoslits width to generate ideal narrow subwavelength focusing. The results of simulation and experiment show that the focusing properties including subwavelength focusing, transmittance are dependent on the structural geometry. In order to rendered the sub-wavelength focusing characteristics, we conducted a near-field measurement analysis. In the scanning near-field microscope experiments, we measure optical near field at different height position to get consistent results with simulation. At incident wavelength 633 nm, the focus is at height 110 nm above Ag-Au hybrid circular nanoslits and reaching the subwavelength focusing with FWHM = 285 nm. Through this study, we investigate the mechanism and geometrical influence of sub-wavelength focusing. It provides the design rules of plasmonic lens for excellent resolution in the future.
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