Transformation of Optical Properties between Plasmonic and Non-plasmonic Nano-structures

  • 蘇 于倫

Student thesis: Doctoral Thesis

Abstract

Transmission through nano apertures have attracted much attention since Ebbsen’s first report on the extraordinary transmission through nano hole arrays in metal films The role of surface plasmons in the enhanced transmission has been a debate over the past decade In the hole-array structure the surface plasmons indeed play a crucial role to overcome the cutoff limitation set by the sub-wavelength apertures And the surface plasmon dispersion relation must be taken into account for the correct interpretation of measured transmission spectra However in slit structures there have been many reports on the negative contributions by surface plasmons Despite numerous successes in applying slit structure for bio-sensors waveguide filters nano plasmonic lasers etc there still lack detailed analysis and intuitive interpretation on the transmission behavior of a simple structure such as the single nano slit In contrast to conventional emphases on plasmonic effects similar transmission properties between a plasmonic and non-plasmonic 2D single slit are demonstrated in this thesis A special case of resonant transmissions and the underlying physics of the similarities are explored Extension to non-resonant transmission and the general transformation are proposed At resonant transmission plasmonic and non-plasmonic single slits exhibit similar near-field mode at their corresponding resonant wavelengths Their resonant transmission wavelengths can be transformed via a simple mapping with surface plasmon dispersion relation Revisit of the Babinet’s principle implies that localized surface plasmon resonances play no role in the enhanced transmission of a 2D single slit Fabry-Perot resonance funneling at slit end faces and waveguide dispersion dominate the resonant transmission properties To further extend the mapping for non-resonant condition complex reflection and transmission coefficients at the end faces of a semi-infinite slit are analyzed to reconstruct the whole transmission spectra The complex reflection coefficients are found similar at the same effective wavelength for both plasmonic and non-plasmonic cases The reconstructed spectrum by a Fabry-Perot model matches the transmission spectrum of a non-plasmonic slit and can be transformed into that of a plasmonic case by wavelength stretching with plasmonic waveguide dispersion Same mapping method applies for a single slit with substrate and periodic case Furthermore the optical property of a plasmonic slit can be achieved by a non-plasmonic slit via dimension scaling The focusing lens effect of a plasmonic slit array can be mimicked by a non-plasmonic slit array with dimension scaling The unified transmission properties of plasmonic and non-plasmonic 2D single slits can simplify the design of slit structures for plasmonic applications Other plasmonic nanostructure such as Mach-Zehnder Interferometers and sea-urchin like 3D multi-branch nanoparticles were discussed in the thesis The influence of branch shapes size and angle in-between for the extinction spectrum of the multi-branch nanoparticles were explained by a simple Coulomb potential model
Date of Award2015 Jan 22
Original languageEnglish
SupervisorShih-hui Chang (Supervisor)

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