Browsing by Subject "Surface Plasmons"

Now showing 1 - 4 of 4

Open Access
Beaming and localization of electromagnetic waves in periodic structures
(2010) Çağlayan, Hümeyra
We want to manipulate light for several applications: microscopy, data storage, leds, lasers, modulators, sensor and solarcells to make our life healthier, easier or more comfortable. However, especially in small scales manipulating light have many difficulties. We could not focus or localize light into subwavelength dimensions easily, which is the key solution to beat today’s devices both in performance and cost. Achievements in three key research fields may provide the answer to these problems. These emerging research fields are metamaterials, photonic crystals and surface plasmons. In this thesis, we investigated beaming and localization of electromagnetic waves in periodic structures such as: subwavelength metallic gratings, photonic crystals and metamaterials. We studied off-axis beaming from both a metallic subwavelength aperture and photonic crystal waveguide at microwave regime. The output surfaces are designed asymmetrically to change the beaming angle. Furthermore, we studied frequency dependent beam steering with a photonic crystal with a surface defect layer made of dimmers. The dispersion diagram reveals that the dimer-layer supports a surface mode with negative slope. Thus, a photonic crystal based surface wave structure that acts as a frequency dependent leaky wave antenna was presented. Additionally, we investigated metamaterial based cavity systems. Since the unit cells of metamaterials are much smaller than the operation wavelength, we observed subwavelength localization within these metamaterial cavity structures. Moreover, we introduced coupled-cavity structures and presented the transmission spectrum of metamaterial based coupled-cavity structures. Finally, we demonstrated an ultrafast bioassay preparation method that overcomes the today’s bioassay limitations using a combination of low power microwave heating and split ring resonator structures.
Open Access
Coupled surface plasmon structures and applications
(2009) Gürel, Kemal
Surface plasmons have attracted great interest during past decades due to their unique physical properties. In this thesis, we study grating-coupled surface plasmons for sensing and filtering applications. We first present simple physical and chemical procedures that allow tuning and modification of the topography of gratings present in optical storage discs into geometries optimal for grating coupled plasmon resonance excitation. After proper metal coating, the tuned surfaces exhibit sharp plasmon resonances that can be excited at wavelengths ranging from 260 nm to over 2.7 µm with relatively high quality factors. As an immediate exemplary application, use of such optimized gratings in aqueous medium for refractive index measurement is demonstrated. We also report another plasmonic component based on a pair of surfaces displaying grating coupled plasmon enhanced transmission. We observe high quality factor transmission peaks as high as 100 through our plasmonic filter based on gratings obtained directly from optical storage disks. Wavelength and polarization dependent transmission is also demonstrated in the visible and infrared portions of the spectrum. The resonance wavelength of this filter can be tuned by simply changing the angle of incidence. Numerical calculations agree well with measurements. Our work can open up directions toward disposable optical components such as filters and polarizers. Morever, we investigate plasmonic force between two coupled metallic layers. We observe the mode splitting due to coupling between plasmonic surfaces by using finite difference time domain simulations.
Open Access
Microfluidics for plasmonic sensors
(2009) Ertaş, Yavuz Nuri
In this thesis, we integrate microfluidics with grating-coupled surface plasmon configurations for sensing applications. First, in order to observe optimal excitations, we introduce procedures for modification of the surface profiles of gratings acquired from commercially available optical storage disks. A must requirement in plasmonic systems, thin film metal deposition is performed. Soft lithographic techniques are applied to coated disks to transfer the surface topography of the disks to an elastomeric material, PDMS. Optical lithography is used to fabricate microfluidic channels to where fluid will be injected. After fabricating the final structure, ellipsometric measurement is used to investigate the device performance. Experimental results were in consistence with the theoretical simulations providing similar behaviours of reflection spectra. The resonance wavelengths are found to be occuring very near to the expected values along with high quality factors. However, to the device structure, an intensity loss is observed which can be further improved. We achieved the tuning of the resonance wavelength by changing the refractive index of the medium inside the microchannel. Integration of the microfluidic channel to surface plasmon studies may open up many applications such as biomolecular sensing.
Open Access
Plasmonic nanoantennas for enhanced light-matter interactions and graphene based tunable nanophotonic devices
(2015) Çakmakyapan, Semih
Focusing, manipulating and beaming of electromagnetic waves are important for many applications such as antennas, optical isolators, biological sensor, chemical sensors, and solar cells. There is an extensive research about the manipulation of light, and its interaction with di erent types of materials including subwavelength structures. However, manipulating light at the nanoscale has many di culties due to the di raction limit. In this thesis, we mainly focus on the characterization and experiments of subwavelength plasmonic structures. We investigated the spatial distribution of the electric eld through subwavelength slits by using symmetric and non-symmetric periodic metallic grating structures in order to obtain one-way transmission, o -axis beaming, collimation and diode-like beaming. We also studied various plasmonic structures such as circular rings and fractal bowtie antennas. After combining them with Raman active molecules, we showed that these plasmonic structures can be used as e cient surface enhanced Raman spectroscopy substrates. Finally, we designed, fabricated and measured nanoantennas and split ring resonators on graphene in order to tune their optical response using the electrically controllable doping property of the graphene.