Global ETD Search

1	Semiconductor surface plasmons : a route to terahertz waveguides and sensors Stone, Edmund K. January 2012 (has links) The terahertz regime has until recently been some what neglected due to the difficulty of generating and measuring terahertz radiation. Terahertz time domain spectroscopy has allowed for affordable and broadband probing of this frequency regime with phase sensitive measurements (chapter 3). This thesis aims to use this tool to add to the knowledge of the interactions between electromagnetic radiation and matter specifically in regard to plasmonics. This thesis covers several distinct phenomena related to plasmonics at terahertz frequencies. The generation of terahertz radiation from metal nanoparticles is first described in chapter 4. It is shown that the field strength of the plasmon appears to relate to the strength of the generated field. It is also shown that the power dependence of the generated terahertz radiation is not consistent with the optical rectification description of this phenomenon. An alternative explanation is developed which appears more consistent with the observations. A simple model for the power dependence is derived and compared to the experimental results. In chapter 5 the parameters that make good plasmonic materials are discussed. These parameters are used to assess the suitability of semiconductors for terahertz surface plasmon experiments. The Drude permittivity of InSb is measured here, leading to a discussion of terahertz particle plasmons in chapter 6. Finite element method modelling is used to show some merits of these over optical particle plasmons. This also includes a discussion of fabrication methods for arrays of these particles. Finally, chapter 7 is a discussion of so called spoof surface plasmons. This includes some experimental work at microwave frequencies and an in depth analysis of open ended square hole arrays supported by model matching method modelling. Perfect endoscope effects are discussed and compared to superlensing. The thesis ends with a brief conclusions chapter where some of the ideas presented are brought together. 530.44
2	On Plasmonic Superradiance, the Scaling Laws of Spontaneous Parametric Downconversion, and the Principles and Recent Advances in Nonlinear Optics Choudhary, Saumya January 2016 (has links) This thesis covers three different topics. The first part is a pedagogical review of the basic principles and recent advances in nonlinear optics. It was originally written as a chapter for the proceedings of the “International School of Physics (Enrico Fermi)” summer school on Photonics held in June, 2014. It is included to provide some background information about nonlinear optical processes in general, and is particularly relevant for the third part of this thesis which is based on the second-order nonlinear optical process of spontaneous parametric downconversion. The second part is based on original research, and deals with superradiance in plasmonic nanostructures. The process of superradiance, as introduced by Dicke in 1954, entails the shortening of the spontaneous emission lifetime of a collection of N quantum emitters as a consequence of the development of a macroscopic dipole moment. Specifically, the lifetime is shortened by a factor of 1/N, and the linewidth is broadened by a factor of N. Such a linewidth dependence has been previously observed in systems of several plasmonic ‘emitters’. However, a clear physical insight into this phenomenon and how it relates to Dicke superradiance has not been shown yet. In this part, we demonstrate by experiment, simulation, and a simple analytical model that Dicke’s superradiance can indeed be observed in a planar array of plasmonic nanoantennas, with a linewidth that scales linearly with the number of nanoantennas within a square wavelength. The third part is also based on original research, and is based on the scal- ing laws of spontaneous parametric downconversion (SPDC) for a type-I phase- matching configuration. The variation of bi-photon generation rate, heralding efficiency and radiance with parameters such as crystal length, pump focussing and collection waist sizes are examined for collinear and non-collinear emission. The results can be used to maximize the brightness of the SPDC source or increase the heralding efficiency depending on the application. Superradiance Nanoantenna arrays Particle plasmon resonances Spontaneous parametric downconversion Type-I phase-matching Bi-photon rate
3	Exploration of how light interacts with arrays of plasmonic, metallic nanoparticles Humphrey, Alastair Dalziell January 2015 (has links) The content of this thesis is based upon the interaction of light with metallic nanoparticles arranged in different array geometries. An incident electric field (light) can force the conduction electrons of a metallic nanoparticle to oscillate. At particular frequencies, in the optical regime for gold and silver particles, absorption and scattering of the light by the particle is enhanced, corresponding to the particle plasmon resonance. The spectral position and width of the particle plasmon resonance of an isolated single particle may be tuned by adjusting its size and shape, thus changing the surface charge distribution. Periodic arrays of particles offer additional control over the frequency and width of the resonance attributed to the re-radiating (scattering) property of plasmonic particles. By fabricating arrays with a pitch comparable to the wavelength of an isolated single particle plasmon resonance, a coherent interaction between particles may be produced, known as surface lattice resonances (SLRs). The electromagnetic coupling between in-plane particle plasmon modes for different particle array geometries is explored through experiment and theory. Firstly, SLRs in square, hexagonal and honeycomb arrays are investigated by normal-incidence extinction measurements and compared to a simple-coupled dipole model. Secondly, to verify the nature of the coupling between the scattered electric field associated with particle resonances, the incident electric field polarization-dependence of the extinction of rectangular arrays and chains is studied. Thirdly, the optical response of square arrays with a symmetric two-particle basis is investigated, particularly the retardation of the scattered electric field between particles in a pair. Fourthly, square arrays with an asymmetric two-particle basis are fabricated to explore the symmetric (dipole moments of both particles are parallel) and anti-symmetric (dipole moment of both particles anti-parallel) SLRs, excited by normal-incidence light. 530
4	Plasmonic effects upon optical trapping of metal nanoparticles Dienerowitz, Maria January 2010 (has links) Optical trapping of metal nanoparticles investigates phenomena at the interface of plasmonics and optical micromanipulation. This thesis combines ideas of optical properties of metals originating from solid state physics with force mechanism resulting from optical trapping. We explore the influence of the particle plasmon resonance of gold and silver nanospheres on their trapping properties. We aspire to predict the force mechanisms of resonant metal particles with sizes in the Mie regime, beyond the Rayleigh limit. Optical trapping of metal nanoparticles is still considered difficult, yet it provides an excellent tool to investigate their plasmonic properties away from any interface and offers opportunities to investigate interaction processes between light and nanoparticles. Due to their intrinsic plasmon resonance, metal nanoparticles show intriguing optical responses upon interaction with laser light. These differ greatly from the well-known bulk properties of the same material. A given metal nanoparticle may either be attracted or repelled by laser light, only depending on the wavelength of the latter. The optical forces acting on the particle depend directly on its polarisability and scattering cross section. These parameters vary drastically around the plasmon resonance and thus not only change the magnitude but also the direction and entire nature of the acting forces. We distinguish between red-detuned and blue-detuned trapping, that is using a trapping wavelength shorter or longer than the plasmon resonance of the particle. So far optical trapping of metal nanoparticles has focussed on a wavelength regime far from the particle’s resonance in the infrared. We experiment with laser wavelengths close to the plasmon resonance and expand the knowledge of metal nanoparticle trapping available to date. Existing theoretical models are put to the test when we compare these with our real experimental situations. 535
5	In situ Raman-Spektroskopie an Metallphthalocyaninen: Von ultradünnen Schichten zum organischen Feldeffekttransistor Ludemann, Michael 06 July 2016 (has links) (PDF) Im ersten Teil der Arbeit werden Signalverstärkungsmechanismen für Raman-Spektroskopie erschlossen und evaluiert. Die als geeignet bewerteten Methoden finden im zweiten Teil ihre Anwendung zur Untersuchung der vibronischen Eigenschaften von dünnen Manganphthalocyaninschichten, die anschließend mit Kalium interkaliert werden. Hierbei sind verschiedene Phasen identifizierbar, die ein ganzzahliges Verhältnis von Kaliumatomen zu Manganphthalocyaninmolekülen besitzen. Im dritten Teil werden die elektrischen Eigenschaften durch die Verwendung dieses Materialsystems als aktives Medium eines Feldeffekttransistors untersucht. Raman-Spektroskopie Resonanz-Raman (RR) Nanosphärenlithografie (NSL) Partikelplasmonen organische Halbleiter Pthtalocyanine Dotierung organischer Feldeffekttransistor Raman spectroscopy surface enhanced Raman scattering interference enhanced Raman scattering resonance Raman nanosphere lithography particle plasmon organic semiconductor phthalocyanine doping organic field effect transistor ddc:535 Halbleiterphysik Feldeffekttransistor Spektroskopie Lithografie Phthalocyanin Interkalation Dotierung Interferenz
6	In situ Raman-Spektroskopie an Metallphthalocyaninen: Von ultradünnen Schichten zum organischen Feldeffekttransistor Ludemann, Michael 01 July 2016 (has links) Im ersten Teil der Arbeit werden Signalverstärkungsmechanismen für Raman-Spektroskopie erschlossen und evaluiert. Die als geeignet bewerteten Methoden finden im zweiten Teil ihre Anwendung zur Untersuchung der vibronischen Eigenschaften von dünnen Manganphthalocyaninschichten, die anschließend mit Kalium interkaliert werden. Hierbei sind verschiedene Phasen identifizierbar, die ein ganzzahliges Verhältnis von Kaliumatomen zu Manganphthalocyaninmolekülen besitzen. Im dritten Teil werden die elektrischen Eigenschaften durch die Verwendung dieses Materialsystems als aktives Medium eines Feldeffekttransistors untersucht.:1. Einleitung 2. Theoretische Grundlagen der angewendeten Effekte 3. Experimentelle Details 4. Herstellung, Charakterisierung und Optimierung von Substraten für Raman-Oberflächenverstärkungseffekte 5. Untersuchung zu Verstärkungsmechanismen des Raman-Effekts an dünnen organischen Schichten 6. Interkalation mit Kalium in dünne Schichten aus Manganphthalocyanin 7. MnPc unter Spannungs- und Stromeinfluss - Der Feldeffekttransistor 8. Zusammenfassung Anhang Literatur Abbildungsverzeichnis Eidesstattliche Versicherung Lebenslauf Liste wissenschaftlicher Leistungen Danksagung info:eu-repo/classification/ddc/535 ddc:535

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