Browsing by Subject "Polaritons (Physics)"

Now showing 1 - 3 of 3

Open Access
Fabrication, characterization and simulation of plasmonic cavities
(2010) Karabıyık, Mustafa
Surface plasmon polaritons (SPPs) originate from the collective oscillations of conduction electrons coupled with photons propagating at metal-dielectric interfaces. A uniform metallic gratings change the dispersion (energy-momentum relation) of a flat metal surfaces due to the interaction of SPPs with the periodic structure. By breaking the symmetry of the periodic plasmonic structure, SPP cavities can be achieved and SPPs can be localized inside the cavity regions. The aim of this thesis is to understand the physics of phase shifted grating based plasmonic cavities. To this end, we fabricated uniform gratings and phase shifted gratings using electron beam lithography, and optically characterized these SPP structures with polarization dependent reflection spectroscopy. We verified experimental results with numerical simulations SPP propagation and localization on the grating structures. Dispersion curves of SPPs have been calculated by solving Maxwell’s wave equations using finite difference time domain method (FDTD) with appropriate boundary conditions in agreement with experimentally obtained data. We studied the dispersion curve as a function of grating profile modulation where we vary the ridge height and width of the ridges. We find that the plasmonic band gap width increases as the ridge height of the ridges in the grating increases. Optimum duty cycle of grating to observe plasmonic band gap is determined to be half of the grating period. Amount of the phase shift added to the periodicity of the uniform grating defines the energy of the cavity state, which is periodically related to the phase shift. A plasmonic cavity with a quality factor 80 has been achieved. The propagation mechanism of SPPs on coupled cavities is plasmon hopping from a given cavity to the next one.
Open Access
Grating based plasmonic cavities
(2009) Şenlik, Servet Seçkin
Surface plasmon polaritons are dipole carrying electromagnetic excitations occur- ing at metal-dielectric interfaces. Metallic periodic structures exhibit modi¯ed transmission and re°ection spectra owing to the interaction of propagating SPPs with the periodicity. These periodic surfaces are used to demonstrate localiza- tion of propagating SPPs. Thin metallic ¯lms surrounded by Bragg re°ectors, selective loading of biharmonic metallic surfaces and Moire patterns are used to demonstrate plasmonic cavity formation. The quality factor, Q, a characteristic value that indicates rate of energy loss relative to the stored energy in the cavity is a crucial parameter for classifying these cavities. It was proposed that the Q factor should strongly depend on the surface geometry. However, there was not a sytematic study on the Q factor of these cavity structures. In this work, we report on a comparative study of grating based plasmonic band gap cavities. Numerically, we calculate the quality factors of the cavities based on three types of grating surfaces; uniform, biharmonic and Moirµe surfaces. Experimentally, we demonstrate the existence of plasmonic cavities based on uniform gratings. E®ective index perturbation and cavity geometries are obtained by additional dielectric loading. Furthermore, we fabricate 2D plasmonic structures, observe plasmonic band gaps in the symetry axis and propose cavity geometries for this structure.
Open Access
Plasmonic band gap cavities
(2008) Kocabaş, Aşkın
Surface plasmon polaritons (SPP’s) are trapped electromagnetic waves coupled to free electrons in metals that propagate at the metal-dielectric interfaces. Due to their surface confinement and potential in sub-wavelength optics, SPP’s have been extensively studied for sensing and nanophotonic applications. Dielectric structures and metallic surfaces, both periodically modulated, can form photonic band gaps. Creating a defect cavity region in the periodicity of dielectrics allows specific optical modes to localize inside a cavity region. However, despite the demonstration of numerous plasmonic surfaces and unlike its dielectric counterparts, low index modulation in metallic surfaces limits the formation of plasmonic defect cavity structures. This thesis describes new approaches for plasmonic confinement in a cavity through the use of selective loading of grating structures as well as through the use of Moiré surfaces. In our first approach, we demonstrate that a high dielectric superstructure can perturb the optical properties of propagating SPPs dramatically and enable the formation of a plasmonic band gap cavity. Formation of the cavity is confirmed by the observation of a cavity mode in the band gap both in the infrared and the visible wavelengths. In addition to the confinement of SPP’s in the vertical direction, such a cavity localizes the SPP’s in their propagation direction. Additionally, we have demonstrated that such biharmonic grating structures can be used to enhance Raman scattering and photoluminescence (PL). Using biharmonic grating structure 105 times enhancement in Raman signal and 30 times enhancement in PL were measured. Furthermore, we show that metallic Moiré surfaces can also serve as a basis for plasmonic cavities with relatively high quality factors. We have demonstrated localization and slow propagation of surface plasmons on metallic Moiré surfaces. Phase shift at the node of the Moiré surface localizes the propagating surface plasmons in a cavity and adjacent nodes form weakly coupled plasmonic cavities. We demonstrate group velocities around v = 0.44c at the center of the coupled cavity band and almost zero group velocity at the band edges can be achieved. Furthermore, sinusoidally modified amplitude about the node suppresses the radiation losses and reveals a relatively high quality factor for plasmonic cavities.