Tesi sul tema "Optical Properties"
Segui questo link per vedere altri tipi di pubblicazioni sul tema: Optical Properties.
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Optical Properties".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Park, Seung-Han. "Excitonic optical nonlinearities in semiconductors and semiconductor microstructures". Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184551.
Testo completoAbstract (sommario):
This dissertation describes the study of excitonic optical nonlinearities in semiconductors and semiconductor microstructures. The main emphasis is placed on the evolution of optical nonlinearities as one goes from bulk to quantum-confined structures. Included are experimental studies of molecular-beam-epitaxially-grown bulk GaAs and ZnSe, GaAs/AlGaAs multiple-Quantum-Wells (MQW's), and finally, quantum-confined CdSe-doped glasses. The microscopic origins and magnitudes of the optical nonlinearities of bulk GaAs and ZnSe were investigated and the exciton recovery time in ZnSe was measured. A comparison with a plasma theory indicates that in GaAs, band filling and screening of the continuum-state Coulomb enhancement are the most efficient mechanisms, while in ZnSe, exciton screening and broadening are the dominating mechanism for the nonlinearity. The maximum nonlinear index per excited electron-hole pair of ZnSe at room temperature is comparable to that of bulk GaAs and the exciton recovery times are of the order of 100 ps or less. A systematic study of the dependence of the optical nonlinearities on quantum well thickness for GaAs/AlGaAs MQWs and the results of nonlinear optical switching and gain in a 58 A GaAs/AlGaAs MQW are reported and discussed. The maximum change in the refractive index is greatest for the MQWs with the smallest well size and decreases with increasing well size, reaching a minimum for bulk GaAs. The maximum index change per photoexcited carrier increases by a factor of 3 as the well size decreases from bulk to 76 A MQW. A differential energy gain of 0.2 and the contrast of 4 are measured for a 58 MQW using 3 ns laser pulses. The linear and nonlinear optical properties of CdSe semiconductor microcrystallites grown under different heat treatments in borosilicate glasses are investigated. Pump-probe spectroscopic techniques and interferometric techniques were employed to study size quantization effects in these microcrystallites (quantum dots). Nonlinear optical properties due to the transitions between quantum confined electron and hole states are reported for low temperature and room temperature. A relatively large homogeneous linewidth is observed. Single beam saturation experiments for quantum confined samples were performed to study the optical nonlinearities as a function of microcrystallite size. Results indicate that the saturation intensity is larger for smaller size quantum dots.
2
Urban, Joanna. "Optical and vibrational properties". Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30092.
Testo completoAbstract (sommario):
Les matériaux bidimensionnels avec une faible symétrie, conduisant à une anisotropie dans le plan des propriétés électroniques et optiques sont particulièrement intéressants du point de vue de l'application. Dans cette thèse, les propriétés optoélectroniques de trois matériaux stratifiés à anisotropie dans le plan, phosphore noir, disulfure de rhénium et franckéite, sont étudiées par spectroscopie optique. Le phosphore noir (BP), avec une structure orthorhombique plissée, présente une anisotropie significative dans le plan et une bande interdite directe qui varie fortement selon le nombre de couches. Un obstacle important du point de vue de la réalisation de dispositifs basés sur BP est sa dégradation dans les conditions ambiantes, qui peut être évitée par encapsulation, par exemple en utilisant du nitrure de bore hexagonal (h-BN). Nous avons étudié les propriétés vibratoires du phosphore noir encapsulé dans le h-BN à l'aide de la spectroscopie Raman et nous présentons ici la première observation expérimentale d'un nouveau pic théoriquement prévu légèrement au-dessus du mode A1g. Nous expliquons son apparition par une différence des fréquences de modes vibratoires dans les couches internes et les couches de surface, et nous discutons de cet effet dans le contexte du fort couplage entre couches dans BP et de l'influence de l'encapsulation sur les propriétés du réseau cristallin. La deuxième partie de cette thèse présente les résultats d'études de photoluminescence du disulfure de rhénium avec une épaisseur de quelques couches atomiques. La réponse optique de ReS2 est dominée par deux excitons anisotropes énergétiquement non dégénérés X1 autour de 1,55eV et X2 autour de 1,57 eV qui peuvent être observés en absorption et émission de la lumière polarisée linéairement. Une controverse existe sur le caractère de bande interdite de ReS2, en particulier sur la présence d'un passage de gap direct à gap indirect avec la variation de l'épaisseur. Nous avons étudié l'émission polarisée liée aux états excitoniques à basse température en fonction du nombre de couches et comparé les résultats expérimentaux avec les prédictions d'un modèle cinétique décrivant la recombinaison radiative et la diffusion entre états excitoniques. Nous concluons d'une part que les caractéristiques observées en photoluminescence sont liées à l'émission des états excitoniques associés à une bande interdite directe, et d'autre part que la bande interdite fondamentale est indirecte. Nous proposons un modèle ou un état excitonique associé à une bande interdite indirecte de plus basse énergie assiste au dépeuplement des états excitoniques directs. Sa présence explique l'intensité d'émission relativement faible et le rapport d'émission X1et X2observé.La franckéite, un minéral sulfuré complexe, a attiré l'attention en tant qu'hétérostructure na-turelle de type II composée de couches alternées pseudohexagonales et pseudotétragonales. Le caractère incommensurable des deux réseaux mène à une ondulation unidimensionnelle. La dernière partie de cette thèse décrit notre observation de la dépendance de polarisation anormale des modes Raman dans les couches de franckéite exfoliées, ce qui suggère la présence d'une anisotropie optique. L'observation de cette dépendance de polarisation pourrait être utilisée comme une méthode rapide et non invasive pour identifier la direction des ondulationsAtomically thin layered materials with low symmetry which leads to in-plane anisotropy of electronic and optical properties are particularly interesting from the point of view of applications. In this thesis, the optoelectronic properties of three layered materials within-plane anisotropy, black phosphorus, rhenium disulfide and franckeite are investigated using optical spectroscopy. Black phosphorus (BP), with a puckered orthorhombic structure, has significant in-plane anisotropy and a direct bandgap which varies strongly with the number of layers. A significant hindrance from the point of view of the realization of BP-based devices is its degradation in ambient conditions, which can be prevented by encapsulation, for example using hexagonal boron nitride (h-BN). We have investigated the vibrational properties of h-BN encapsulated black phosphorus using Raman spectroscopy and report the first experimental observation of a theoretically predicted new peak slightly above the A1g mode. We explain its appearance by a difference of the mode frequencies in the inner and surface layers and discuss this effect in the context of the strong interlayer coupling in BP and the influence of the encapsulation on the lattice properties. The second part of this thesis presents the results of photoluminescence studies of few-layer rhenium disulfide. The optical response of ReS2is dominated by two energetically nondegenerate anisotropic excitons X1around 1.55 eV and X2 around 1.57 eV which can be observed in polarized absorption and emission. A controversy exists regarding the nature of the fundamental bandgap of ReS2, in particular the presence of a crossover from indirect to direct bandgap with changing thickness. We have studied the polarized emission related to the excitonic states at low temperature as a function of the number of layers and compared the experimental results with the predictions of a kinetic model describing the radiative recombination and scattering between excitonic states. We conclude that the features observed in photoluminescence arise due to hot emission from direct excitonic states and that a smaller, indirect bandgap and a related excitonic state are responsible for the depopulation of the direct states, the relatively weak emission intensity and the observed X1and X2 emission ratio. Franckeite, a complex sulfide mineral, has attracted attention as a natural type-II heterostructure composed of alternating pseudo-hexagonal and pseudo-tetragonal layers. The incommensurate character of the two lattices leads to one-dimensional rippling. The last part of this thesis describes our observation of anomalous polarization dependence of the Raman modes in exfoliated franckeite flakes, which suggested the presence of optical anisotropy and could be used as a rapid and non-invasive method to identify the rippling direction
3
Rochford, Kent Blair. "Linear and nonlinear optical properties of polydiacetylene waveguides". Diss., The University of Arizona, 1990. http://hdl.handle.net/10150/185340.
Testo completoAbstract (sommario):
The linear and nonlinear optical properties of a spin-coated polydiacetylene, [5,7-dodecadiyn-1,12-diol-bis(n-butoxy-carbonyl-methyl-urethane)], or poly(4BCMU), were measured to predict its performance in all-optical devices at 1.319 μm. Material requirements for all-optical devices were identified and figures-of-merit noted. A two-photon absorption figure of merit was verified by numerical simulation of a waveguide device. The refractive index and waveguide loss in spin-coated poly(4BCMU) films were measured. A photo-induced bleaching was observed, and its effect on linear and nonlinear optical properties was quantified. Fabrication of integrated-optical structures using this photobleaching process was demonstrated. The nonlinear refractive index and absorption were measured at 1.319 μm with 60 picosecond laser pulses, using poly(4BCMU) strip-loaded channel waveguides. A novel pulse-modulated interferometer was developed for measuring the intensity-dependent refractive index. The fast electronic contribution was found to be n₂ = (4.8 ± 2.7) x 10⁻⁸ cm²/MW, an a slower thermal contribution of n₂(T) = -(7.9 ± 4.5) x 10⁻¹¹ cm²/MW was measured. The thermal index change was shown to limit the duty cycle of operation for a poly(4BCMU) device. The two-photon absorption coefficient was also measured, yielding γ < 0.25 cm/GW. These values were used to estimate performance of a poly(4BCMU) all-optical device using standard figures-of-merit. For this specific waveguide, the figures-of-merit indicated poor performance. If waveguide losses were neglected, (by assuming improved fabrication for example), and assuming the nonlinearity does not saturate at intensities below the damage threshold, the figures-of-merit improve to useful levels. The limit on duty cycle imposed by thermal effects appears to restrict operation to GHz frequencies of slower.
4
Li, Qing. "Optical properties of III-nitride semiconductors". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B30162488.
Testo completo
5
Gleeson, H. F. "Optical and electro-optical properties of chiral mesophases". Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383374.
Testo completo
6
Alshammary, Marzook. "Optical and magneto-optical properties of doped oxides". Thesis, University of Sheffield, 2011. http://etheses.whiterose.ac.uk/2066/.
Testo completoAbstract (sommario):
This study aimed to understand the optical and magneto-optical properties of pure, transition metals doped, and tin and transition metals co-doped In2O3 thin films grown in various growth conditions, and aimed to investigate the role of the oxygen defect states in every situation. Indium oxide doped with magnetic transition metals is a promising material for spintronics. This study presents results on the magnetic, transport, optical and magneto-optical properties of thin films of pure and transition metal (Fe,Co) doped In2O3 investigated at different transition metal concentrations and at different growth conditions. The optical and magneto-optical measurements at low temperature confirmed the formation of the defect states associated with oxygen vacancies within the forbidden range of the optical band gap energy of In2O3 and located below the conduction band. The density of the donor states is tuned using the oxygen partial pressureto give oxygen vacancies or by doping with tin; this gives control over the carrier concentration in the system as well as affecting the magnetic properties. This study developed optical and magneto-optical systems and undertook the world's first optical and magneto-optical measurements of In2O3. A new lab-based alternative technique to the Extended X-ray Absorption Fine Structurewas developed to identify the existence of magnetic nanoparticles in addition to provide the fraction and the contribution of these nanoparticles to the magnetisation and magneto-optical properties. The Maxwell-Garnett analysis of magnetic circular dichroism was used to obtain quantitative measures of the amount of defect phases present for Co metal. Similar to Maxwell-Garnett analysis, a new equation for Fe3O4 nanoparticles was developed in this study. This magneto-optical method was found to be more precise than EXAFS in determining the fraction and the contribution of nanoparticles to the total response of the system. However, these nanoparticles disappeared when thin films were co-doped with tin, indicating that doping with Sn not only introduced more carriers but also inhibited the growth of defect phases in semi magnetic semiconductor thin films. Finally, this study identified the origin of the magnetism in the class of magnetic oxides whereferromagnetism originated from the polarized electrons in localized donor states associated with the oxygen vacancy defect.
7
Papapanayotou, I. "Chemical properties and optical properties of carbonaceous particles". Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383288.
Testo completo
8
Auguié, Baptiste. "Optical properties of gold nanostructures". Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/73955.
Testo completoAbstract (sommario):
The optical properties of gold in the visible are dominated by the response of the free conduction electrons to light. In gold nanostructures, the surface charge density adopts a configuration that is constrained by the shape of the nanoparticles. As a result, the scattering of light by gold nanoparticles exhibits a resonant response characterised by a strong scattering and absorption in a narrow range of frequencies. The spectral range of this \emph{localised surface plasmon resonance} (LSPR) can be tuned by varying the size and shape of the gold nanoparticle --- the nanoparticles act as nanoscale antennas for the visible light. Confirmation of this scaling rule is obtained by conducting experiments with nanoparticles of varying size and aspect ratio. Such particles are fabricated by electron-beam lithography, and characterised by dark-field spectroscopy. Not only does the LSPR shift in frequency with a change of particle size, but its spectral lineshape is also modified. The intensity and width of the LSPR are dictated by a variety of factors that are related to the intrinsic material properties (the complex dielectric function of gold), and to the particle geometry and environment. The optical response of small gold nanorods is well described by a simple oscillating dipole model --- the incident electromagnetic field induces a current in the particle that re-radiates light (scattering). A series of refinements can be made to model more accurately the optical response of realistic particles. If the dipole moment characterising the particle is allowed to vary in phase across the particle, retardation effects provide a correction for the effective dipole moment of the particle. As the particle size approaches the wave length in the surrounding medium, the dipolar approximation breaks down and higher order multipoles need to be considered. The Mie theory provides a very accurate description of the response of spheres of arbitrary size. Further, the T-matrix and other numerical techniques can be employed to accurately reproduce the scattering properties of particles of arbitrary shapes. When the scattering sample consists of a collection of gold nanoparticles, the collective optical response is affected by two key factors. First, the measured LSPR is a convolution of the distribution of particle sizes with the individual response of a single particle. This leads to an inhomogeneous broadening of the LSPR lineshape. Second, the light that is scattered by one such particle near resonance can strongly affect its neighbours which scatter light in proportion to the net field they experience, that is the sum of the incident field plus the perturbation arising from the neighbouring particles. The onset of such multiple scattering events is observed even for particle separations that are several times larger than the particle size. Several regimes of interaction can be distinguished according to the ratio separation / wavelength. First, when the particles are in close proximity (separation $\ll$ wavelength), near-field interactions dominate and result in a spectral shift of the LSPR accompanied with a spectral broadening. Second, when the separation is commensurate with the wavelength, a coherent interaction can develop that couples a large number of particles. In ordered arrays, such coupling gives rise to a geometrical resonance that can strongly affect the LSPR of the particles. In particular a sharp spectral feature is observed that depends on both the single particle response and the geometrical arrangement of the particles in the array. The coherence of such multiple scattering in diffractive arrays of gold nanoparticles can be broken by introducing disorder in the distribution of particle sizes, or in the particle positions. The optical properties of an irregular array reflect the departure from a periodic system and the spectral lineshape evolves as the level of disorder is increased. In the limit of uncorrelated positions, the diffractive coupling is suppressed and the response of the collection of the particles rejoins the response of isolated particles.
9
Crook, Robert J. "Optical properties of organic waveguides". Thesis, University of Exeter, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359604.
Testo completo
10
Zhou, Yuming. "Optical properties of living organisms". Thesis, Open University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301878.
Testo completo
11
Wan, Wai Man Vivian. "Optical properties of conjugated polymers". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621328.
Testo completo
12
Rosenow, Judith. "Optical Properties of Condensation Trails". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-205659.
Testo completoAbstract (sommario):
Persistent condensation trails are clouds, induced by the exhaust of an aircraft engine in a cold and ice-supersaturated environment. These artificial ice clouds can both cool and heat the atmosphere by scattering solar radiation and absorbing terrestrial radiation, respectively. The influence of condensation trails on the Earth-atmosphere energy balance and therewith the answer to the question of the dominating process had been mostly approximated on a global scale by treating the condensation trail as plane parallel layer with constant optical properties. Individual condensation trails and the influence of the solar angle had been analyzed, always using a course spatial grid and never under consideration of the aircraft performance, generating the condensation trail. For a trajectory optimization, highly precise results of the impact of condensation trails on the radiation budget and the influence of the aircraft performance on this impact is needed, so that future air traffic may consider the main factors of flight performance on the environmental impact of condensation trails. That’s why, a model is developed in this thesis to continuously estimate the scattering and absorption properties and their dependence on the aircraft performanceLanglebige Kondensstreifen sind Eiswolken, welche durch Kondensation von Wasserdampf an Rußpartikeln in einer eisübersättigten Atmosphäre entstehen. Der Wasserdampf entstammt einerseits aus dem Triebwerkabgas und andererseits aus der Atmosphäre. Kondensstreifen können die Atmosphäre durch Rückstreuung solarer Strahlung kühlen und durch Rückstreuung und Absorption terrestrischer Strahlung erwärmen. Der Einfluss von Kondensstreifen auf den Wärmehaushalt der Atmosphäre und damit die Antwort auf die Frage nach dem dominierenden Effekt wurde bisher zumeist auf globaler Ebene ermittelt, wobei der Kondensstreifen als planparallele Schicht mit konstanten optischen Eigenschaften angenähert wurde. Individuelle Kondensstreifen und der Einfluss des Sonnenstandes wurden bisher nur mithilfe eines groben Rasters betrachtet und niemals unter Berücksichtigung der Flugleistung des Luftfahrzeuges, welches den Kondensstreifen generiert hat. Für eine Trajektorienoptimierung sind jedoch präzise Berechnungen des Strahlungseinflusses und eine gewissenhafte Berücksichtigung der Flugleistung notwendig. Nur so kann der zukünftige Luftverkehr die Haupteinflussfaktoren der Flugeigenschaften auf den Strahlungseinfluss der Kondensstreifen berücksichtigen. Aus diesem Grund wurde in dieser Arbeit ein Modell entwickelt, welches die Eigenschaften des Strahlungstransfers durch den Kondensstreifen kontinuierlich bestimmt und die aus der Flugleistung resultierenden Parameter berücksichtigt
13
Khan, Saima Ishfaque. "The optical properties of metamaterials". Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7781/.
Testo completoAbstract (sommario):
This thesis studies the parametric investigation, polarisation dependence and characterization of fishnet structure at near infrared wavelengths. Detailed simulations are performed to understand the behaviour of the structure at near infrared and optical wavelengths. Simulations are performed to obtain negative refractive index of the fishnet structure formed from nanoimprint lithography (NIL) by taking into account the effect of substrate and polymethyl methacrylate (PMMA) beneath it. Two different structures have been designed and fabricated of varying dimensions using NIL and their resonant wavelength measured in the near infrared at 1.45 µm and 1.88 µm. Simulations suggest that a negative refractive index real part with the magnitude -0.24 is found at 1.53 µm and this decrease to a maximum magnitude of -0.57 at 1.9 µm. The PMMA and suppressed pillars are here responsible for the increasing material losses and limiting the value of negative refractive index. An analytical approach has been suggested to characterise fishnet structures at oblique incidence. The expressions for an absorbing medium are rewritten for an alternative definition of refractive index. The expressions are initially validated for a dielectric slab and a metal film. These results provide the possibility that this proposal may yield a general algorithm for obtaining the complex reflection and transmission coefficients for artificial structures. FDTD simulations have been extensively used in this thesis to understand the optical metamaterials and their characterization.
14
González, Ganzábal A. (Alejandro). "Optical properties of leaf replicas". Master's thesis, University of Oulu, 2018. http://urn.fi/URN:NBN:fi:oulu-201808232657.
Testo completoAbstract (sommario):
In order to fulfill the increasing energy demand, several improvements can be done in already existing means of producing energy. Based on the idea of light harvesting, several main ideas of optimizing natural leaves (or even creating from a master), such as morphology, super-hydrophobity and waterproofing, among others, have been analyzed.
Experimentally, it has been shown that by means of applying natural coatings of wax (from bilberry and lingonberry) onto the surface of silicon and PDMS the reflectance varies in the visible spectrum. In the case of silicon the reflectance decreased on average 17.5% in the case of the bilberry wax and 18.4% for lingonberry wax. For PDMS, the curves were more complex and implied an increase of reflectance of 1.3% for bilberry and 2.4% for lingonberry.
Finally, a Scanning Electron Microscope imaging experiment was carried out, revealing that for a film coating of wax bigger specks formed (circa 0.1 mm), thus leading to the conclusion that a spin coating is the best option to achieve optimal properties, since the smaller specks would not override other applied coating and natural properties.
15
Lee, Timothy. "Nonlinear properties of optical microfibres". Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355529/.
Testo completoAbstract (sommario):
Glass microfibre waveguides offer an intriguing platform for the investigation of nonlinear effects, due to their high effective nonlinearity which arises from the tight modal confinement down to dimensions comparable to the wavelength of guided light. This thesis presents theoretical and experimental work towards achieving efficient third and second harmonic generation in silica microfibres, as well as in microfibre loop resonators for enhancing the conversion. Since microfibre resonators themselves exhibit interesting nonlinear behaviour, the polarisation dependent properties of microcoil resonators were also studied. Efficient third harmonic generation is possible through intermodal phase matching, and experiments using short tapers have demonstrated significant efficiencies up to 10
16
Molloy, Peter J. "Optical properties of concentrated dispersions". Thesis, London Metropolitan University, 1986. http://repository.londonmet.ac.uk/2939/.
Testo completoAbstract (sommario):
Apparatus and methods have been developed to measure the diffuse transmittance T and reflectance R of multiple scattering, concentrated, colloidal dispersions. The variation of R and T with pathlength, wavelength, and concentration has been investigated for non-spherical particles in concentrated dispersions, over a range of pH and surfactant concentrations. Measurements of diffuse transmittance and reflectance required large corrections to be made for the presence of any specular interfaces i.e. windows. These corrections were minimised by developing a bifurcated fibre optic bundle reflectance method, which allowed R and T to be measured at volume fractions up to at least 0.3. Using magnetic, acoustic and shear fields to align the non-spherical kaolinite particles changes In R and T were measured at volume fractions upto 0.3. The amplitude of the changes and the relaxation of the changes Induced by the applied fields were measured. The amplitude of the change was found to vary strongly with pH and surfactant concentration. For any particular face diameter platelet, the amplitude of the change followed closely the flocculation process, and was sensitive to the mode of particle-particle aggregation, e.g. face-face, or face-edge. The amount of surfactant per unit mass of kaolinite required to stabilise dispersions Is found to vary with particle size and concentration. This showed that information about particle orientation can be obtained through multiple scattering systems when subjected to an aligning field. Kubelka-Munk two flux theory was used to relate R and T to the diffuse flux scattering parameter S. A simple theory was developed relating S to the size shape and orientation of the non-spherical particles, hence allowing the particle orientation to be determined for any aligning field The insight Into particle behaviour given by the optical method Is superior to that given by rheology alone, which does not provide an unambiguous measure of the mode of particle alignment.
17
Wang, Jun, e 王俊. "Optical properties of graphene/GaN hybrid structure". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2014. http://hdl.handle.net/10722/206660.
Testo completoAbstract (sommario):
Optical properties of graphene/GaN hybrid structure were investigated by using a variety of optical spectroscopy techniques including low-temperature photoluminescence (PL) spectroscopy, time-resolved PL (TRPL) spectroscopy, confocal scanning micro-Raman spectroscopy.
Single-layer graphene grown by chemical vapor deposition was transferred to GaN epilayer surface, which is verified by the Raman spectrum with a sharp characteristic peak at ~2690 cm-1and a homogeneous Raman image. Three main band-edge emissions including the free exciton A transition (denoted as FXA), the donor bound exciton transition (denoted as DX) and the third peak (denoted as Ix) were well resolved in the PL spectra of the hybrid structure as well as the as-grown GaN epilayer at low temperatures. Interestingly, the FXA transition and Ix line of the GaN epilayer were found to be dramatically altered by the top graphene layer while the DX is almost unaffected. The intensity of Ix line substantially drops after the transfer of graphene layer on GaN, indicating surface defect nature of the Ix line. More interestingly, an unpredictable dip structure develops in the FXA peak when the temperature is beyond 50 K. Similar spectral structure change also occurred in the emission of free exciton B (referred as FXB)with higher transition energy .A free exciton dissociation and electron transfer model was proposed to explain the “dip effect”. More supporting evidence to the model was found in the time-resolved PL spectra of the hybrid structure and the control sample. The results showed the significant influence of graphene monolayer on the fundamental optical properties of GaN.published_or_final_version
Physics
Master
Master of Philosophy
18
LEE, YONG HEE. "ROOM-TEMPERATURE OPTICAL NONLINEARITIES IN GALLIUM-ARSENIDE AND FAST OPTICAL LOGIC GATES". Diss., The University of Arizona, 1986. http://hdl.handle.net/10150/183920.
Testo completoAbstract (sommario):
This dissertation studies the physics of room-temperature optical nonlinearities in GaAs and their application to the optical logic gates. The microscopic origins of the room-temperature optical nonlinearities in GaAs are investigated experimentally and theoretically. The data of nonlinear absorption measurement are analyzed in the framework of a semiconductor plasma theory in combination with excitation-dependent line broadening. The importance of the plasma screening of the continuum-state Coulomb enhancement and band filling are emphasized for GaAs at room temperature. Optical bistability and optical logic gating are direct consequences of the nonlinear refractive index changes in etalons. The nonlinear index changes are directly measured by a new technique of observing the Fabry-Perot transmission peak shift using the self-photoluminescence as a broad-band source. The validity of a Kramers-Kronig technique under quasi-steady state conditions is crosschecked by an independent measurement of Δn under identical pumping conditions. Thermal index changes are also directly measured to establish the criteria on the temperature stability condition that is needed for reliable operation of devices based on dispersive nonlinearities. Optical logic gates based on dispersive optical nonlinearities may be the critical components of an all-optical computer in the future. Five optical logic functions are demonstrated in a nonlinear GaAs/AlGaAs MQW etalon. Specially designed dielectric mirrors are used to observe low-energy (3-pJ) operation of optical logic gates. Parallel operation using as many as eight optical logic devices is achieved with Wollaston prisms. Toward practical devices, optical logic gating using diode lasers is demonstrated in a setup much smaller than the usual argon-laser pumped dye laser setup. The cycle time of optical logic devices is limited, not by the switch-on time, but by the switch-off time which depends on the carrier relaxation rather than the switch-on time. To reduce the carrier relaxation time windowless GaAs is employed to take advantage of the faster surface recombination of carriers at the GaAs/dielectric mirror interface compared to that at the GaAs/GaAlAs interface. The speed and effectiveness of the windowless GaAs are compared with those of the proton-bombarded GaAs as optical logic gates.
19
Mohamed, Mona Bakr. "Metallic and semiconductor nanoparticles : synthesis, characterization and femtosecond laser spectroscopic studies". Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/31057.
Testo completo
20
Hill, Isiah Jasper Jr. "Synthesis of azodyes and polyurethanes for use as nonlinear optical materials". Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/28930.
Testo completo
21
Lowry, Curtis Wayne. "Optical nonlinearities in passive and active gallium arsenide with applications to optical switching and laser instabilities". Diss., The University of Arizona, 1993. http://hdl.handle.net/10150/186295.
Testo completoAbstract (sommario):
Nonlinear optical properties of passive and active semiconductors are investigated experimentally and theoretically. Improvement of switching cycle time in optical nonlinear etalons to 40 ps is demonstrated, and strained-layer InGaAs/GaAs quantum well material is used in an asymmetric etalon to greatly improve switching power and contrast. Coherent energy transfer (CET) induced by injection of an external light field is demonstrated in a GaAs quantum well vertical-cavity surface-emitting laser (VCSEL). The evolution of CET induced asymmetric gain with increasing injected power is investigated experimentally and theoretically, and it is found that the CET induced effective gain peak and dip are detuned proportionally with injected power as in homogeneously broadened media and in contrast to other multi-wave effects in GaAs which are detuned proportionally with the light field. Transfer of gain modification between orthogonally polarized modes of the VCSEL and cascading of gain modification within a mode is observed and investigated. The approach of a laser to an injection locked state through increased injected power is investigated experimentally and theoretically, showing new emission frequencies produced which evolve to chaos-like behavior before reaching the phase locked state. CET induced gain modification is used to demonstrate low-power high-contrast switching between polarization modes of the VCSEL with differential gain of 3,510. Switching speed and switching bistability is observed and investigated. Injection induced modification of VCSEL transverse modes is studied experimentally and theoretically. Field defects in the resulting field are observed, and their locations are dependent on the frequency of the injected field, in contrast to the temporally evolving defects normally observed. The rich behavior of nonlinear properties, especially in gain media provide interesting results and valuable applications.
22
Balasubramanian, Kunjithapatham. "Structural inhomogeneity and anisotropy in optical filters and thin films; applications to optical storage media". Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184564.
Testo completoAbstract (sommario):
Optical filters and thin film optical devices play an important role in Science and Industry. Several significant applications have emerged in optics, microelectronics and computer technology. In this work, we study some aspects of their design and applications. One class of optical fibers, known as Christiansen filters, are based on scattering phenomena in suspensions of solid particles in a liquid medium. Some new scattering filters in the visible and the near UV regions and their performance characteristics are reported here. Feasibility to fabricate such optical filters in solid matrix form is established. Some applications of these scattering filters are discussed. After an introduction to the optics of homogeneous and isotropic thin films, I discuss the general design of anisotropic thin film media and a scheme implemented to calculate their performance. Optical anisotropy, produced by the growth-induced columnar microstructure in thin films and its effects on the performance of optical filters are studied. Large shifts in the peak wavelength of a typical narrow band filter are predicted. Magneto-optical (MO) thin film media of great importance to erasable optical data storage technology are studied. An approximate technique based on a 2 x 2 matrix formalism is developed to calculate the normal incidence performance of these media. To investigate anisotropic effects, to incorporate more than one magnetic film with arbitrary orientations of magnetization, and to study oblique incidence performance, a completely general 4 x 4 matrix technique is implemented in a computer program. Effects of substrate/superstrate birefringence in the read-out signal of MO media are investigated. Several optimizing design criteria, particularly, the effectiveness in employing appropriate metal or dielectric reflector layers are studied. The influence of the plasma edge of metals in enhancing the polar Kerr rotation of MO media is discussed with illustrations. A contour plot of the Kerr rotation and reflectance is developed to help in the design of these media. An explanation is given for the observation of Kerr rotation enhancement near the plasma reflection edge of the reflector layer adjacent to the active MO layer and in general, where the reflectance spectrum shows a steep gradient.
23
Zongo, Sidiki. "Nonlinear optical properties of natural dyes based on optical resonance". Thesis, University of the Western Cape, 2012. http://hdl.handle.net/11394/4635.
Testo completoAbstract (sommario):
>Magister Scientiae - MScRecent research shows that the study of optical properties of organic material natural dyes has gained much consideration. The specific functional groups in several natural dyes remain essential for the large nonlinear absorption expressed in terms of nonlinear optical susceptibilities or other mechanism of absorption such as two photon absorption (TPA), reverse saturable absorption (RSA) or intensitydependent refractive index characteristic. In this thesis we highlight the optical limiting responses of selected natural dyes as nonlinear response in the femtosecond regime. This technique refers to the decrease of the transmittance of the material with the increased incident light intensity.Three dyes derived from beetroot, flame flower and mimosa flower dyes were investigated. The results showed a limiting behaviour around 795 mW for the beetroot and the flame dye while there is total transmission in the flame dye sample. The performance of the nonlinearity i.e. the optical limiting is related to the existence of alternating single and double bonds (i.e. C-C and C=C bonds) in the molecules that provides the material with the electron delocalization, but also it is related to the light intensity.Beside nonlinearity study, crystallographic investigation was carried out for more possible applicability of the selected dyes and this concerned only the mimosa and flame flower dye thin film samples since the beetroot thin film was very sensitive to strong irradiation (i.e. immediately destroyed when exposed to light with high intensity). For more stability,dye solutions were encapsulated in gels for further measurements.
24
Faber, Dirk Johannes. "Functional optical coherence tomography spatially resolved measurements of optical properties /". [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2005. http://dare.uva.nl/document/88794.
Testo completo
25
Neethling, Pieter. "Determining non-linear optical properties using the Z-scan technique". Thesis, Link to the online version, 2005. http://hdl.handle.net/10019/1135.
Testo completo
26
Zheng, Changcheng, e 郑昌成. "Nonlinear optical properties of zinc oxide". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47147751.
Testo completo
27
Cha, Cheol Yong. "Structure-property study of kapton PMDA-ODA polyimide films". Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/9332.
Testo completo
28
Craig, Duncan Wilson. "Optical nonlinearities in CdHgTe". Thesis, Heriot-Watt University, 1987. http://hdl.handle.net/10399/1015.
Testo completo
29
Anderson, Richard M. "Magneto-optical properties of superparamagnetic spinel ferrite nanoparticles". Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/30027.
Testo completo
30
Park, Wounjhang. "Optical properties of thin film phosphors". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/30078.
Testo completo
31
Hartschuh, Ryan D. "Optical Spectroscopy of Nanostructured Materials". University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195016254.
Testo completo
32
Thielen, Peter. "Nonlinear optical properties of chalcogenide glasses /". For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.
Testo completo
33
Rybka, Marcin. "Optical properties of MAX-phase materials". Thesis, Linköping University, Applied Optics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-60008.
Testo completoAbstract (sommario):
MAX-phase materials are a new type of material class. These materials are potentiallyt echnologically important as they show unique physical properties due to the combination of metals and ceramics. In this project, spectroscopic ellipsometry in the spectral range of 0.06 eV –6.0 eV was used to probe the linear optical response of MAX-phases in terms of the complexd dielectric function ε(ω) = ε1(ω) + iε2(ω). Measured data were fit to theoretical models using the Lorentz and generalized oscillator models. Data from seven different samples of MAX-phase materials were obtained using two ellipsometers. Each sample dielectric function was determined, including their infrared spectrum.
34
Neff, Curtis Wayne. "Optical Properties of Superlattice Photonic Crystals". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/14108.
Testo completoAbstract (sommario):
Photonic band gap materials, commonly referred to as photonic crystals (PCs), have been a topic of great interest for almost two decades due to their promise of unprecedented control over the propagation and generation of light. We report investigations of the optical properties of a new PC structure based upon a triangular lattice in which adjacent [i, j] rows of holes possess different properties, creating a superlattice (SL) periodicity. Symmetry arguments predicted and quot;band folding and quot; and band splitting behaviors, both of which are direct consequences of the new basis that converts the Brillouin zone from hexagonal (six-fold) to rectangular (two-fold). Plane wave expansion and finite-difference time-domain (FDTD) numerical calculations were used to explore the effects of the new structure on the photonic dispersion relationship of the SL PC. Electron beam lithography and inductively coupled plasma dry etching were used to fabricate 1 mm2 PC areas (lattice constant, a =358 nm and 480 nm) with hole radius ratios ranging from 1.0 (triangular) to 0.585 (r2/r1 = 73.26 nm/125.26 nm) on Silicon-on-insulator wafers. The effects of modifying structural parameters (such as hole size, lattice constant, and SL strength) were measured using the coupled resonant band technique, confirming the SL symmetry arguments and corroborating the band structure calculations. Analysis of the dispersion contours of the static SL (SSL) PC predicted both giant refraction (change in beam propagation angle of 110 for an 8 change in incident angle) and superprism behavior (change in beam propagation angle of 108 for a 12% change in normalized frequency) in these structures. Dynamic control of these refraction effects was also investigated by incorporating electro-optic and nonlinear materials into the SSL PC structure. Wave vector analyses on these structures predicted a change in beam propagation angle and gt;96 when the refractive index inside of the holes of the structure changed from n=1.5 to 1.7. Through this investigation, the first successful measurement of the band folding effect in multidimensional PCs as well as the first explicit measurement of the dielectric band of a 2D PC were reported. In addition, the SL PCs impact on new opto-electronic devices was explored.
35
Yildirim, Hasan. "Nonlinear Optical Properties Of Semiconductor Heterostructures". Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607438/index.pdf.
Testo completoAbstract (sommario):
The nonlinear optical properties of semiconductor heterostructures, such as GaAsAl/GaAs alloys, are studied with analytic and numerical methods on the basis of quantum mechanics. Particularly, second and third-order nonlinear optical properties of quantum wells described by the various types of confining potentials are considered within the density matrix formalism. We consider a Pöschl-Teller type potential which has been rarely considered in this area. It has a tunable asymmetry parameter, making it a good candidate to investigate the effect of the asymmetry on the nonlinear optical properties. The calculated nonlinear quantities include nonlinear absorption coefficient, second-harmonic generation, optical rectification, third-harmonic generation and the intensity-dependent refractive index. The effects of the DC electric field on the corresponding nonlinearities are also studied. The results are in good agreement with the results obtained in other types of quantum wells, such as square and parabolic quantum wells. The effects of the Coulomb interaction among the electrons on the nonlinear intersubband absorption are considered within the rotating wave approximation. The result is applied to a Si-delta-doped, square quantum well in which the Coulomb interaction among the electrons are relatively important, since there has been no work on the nonlinear absorption spectrum of the Si-delta-doped quantum well. The results are found to be new and interesting, especially when a DC electric field is included in the calculations.
36
Fischer, Peer. "Nonlinear optical properties of chiral media". Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/265442.
Testo completoAbstract (sommario):
This thesis concerns nonlinear optical phenomena in liquids and at interfaces. Optical processes are considered in chiral liquids and at chiral surfaces to second order in the applied electric fields, and to third-order in fluids. Time-dependent perturbation theory is used to describe the response of molecules to electromagnetic fields in terms of molecular electric-dipole polarizabilities. The inclusion of phenomenological damping in the sum-overstates expressions for the nonlinear polarizabilities is discussed, both at optical frequencies and in the limit that one or more applied electromagnetic fields are static. The reality condition for the polarization and the applied field is shown to define the sign of the damping terms. Electro-optical effects, linear in the electrostatic field, are considered in chiral liquids. Symmetry arguments are presented to show that the Pockels effect is forbidden in any non-conducting isotropic medium, and it is shown that this also follows from the statistical average of its sum-over-states expression when damping is correctly incorporated. A linear effect of an electrostatic field on the intensity of sum- and difference-frequency generation in a chiral liquid is predicted. The effect changes sign with the enantiomer and on reversing the direction of the electrostatic field. The sum-frequency polarizability and the electric field-induced sum-frequency polarizability interfere and their contributions to the scattering power can be distinguished. Experiments are described where, symmetry permitting, the third-harmonic is generated simultaneously in a second and in a third-order nonlinear optical mixing process. The third-order nonlinear optical properties of some simple liquids are characterized by all-electric phase-matched four-wave mixing. However, no three-wave mixing was observed in chiral liquids. Finally, a theory of surface nonlinear optical activity, applicable to various surface symmetries, is developed for sum-frequency generation. The potential of the three-wave mixing processes as probes of molecular chirality is examined. An optically active conformation for water in a static electric field parallel to the surface is proposed.
37
Al, Shakhs Mohammed Hashim. "Engineering optical properties using layered metamaterials". Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62525.
Testo completoAbstract (sommario):
This thesis explores the concept of metamaterials; a fairly recent concept in the literature which has attracted the attention of researchers due to their abnormal electromagnetic properties. We will particularly consider one dimensional version of a metamaterial made of layers. At the first glance, layered metamaterials are simply multi-layer thin films. The distinguishing feature of layered metamaterials is that they usually incorporate metals whereas most thin film structures in the past have only incorporated dielectrics. The immense interest in certain layered configurations of metals
and dielectrics, particularly when the thicknesses are really thin compared to the wavelength, is due to their exhibition of seemingly counter-intuitive or impossible properties such as refraction to the same side of normal (negative refraction), evanescent wave amplification, or light focusing with a flat interface (flat lensing). The simple configuration of layered metamaterials and their interesting properties are the prime motivations of this work. In this thesis, we first start with a very generic electromagnetic description of the optical properties of layered structures. This general description appears to be novel due to presenting theory in new form. We use this understanding to explain how and why certain layered structures can exhibit negative refraction or flat lensing. This investigation has also led to several new predictions of new optical properties of layered metamaterial structures. We conclude this work by various experimental studies which validate the predictions of the work and also explore fabrication challenges in the making of layered metamaterials.Applied Science, Faculty of
Engineering, School of (Okanagan)
Graduate
38
Shi, Shenlei. "Exciton related optical properties of ZnO". Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B38284881.
Testo completo
39
Quraishi, Qudsia. "Optical frequency combs: Properties and applications". Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3284408.
Testo completo
40
Bentley, Caroline. "Optical and microwave properties of ferrofluids". Thesis, Bangor University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290411.
Testo completo
41
Shi, Shenlei, e 施申蕾. "Exciton related optical properties of ZnO". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B38284881.
Testo completo
42
Apostol, Adela. "COHERENCE PROPERTIES OF OPTICAL NEAR-FIELDS". Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2715.
Testo completoAbstract (sommario):
Next generation photonics-based technologies will ultimately rely on novel materials and devices. For this purpose, phenomena at subwavelength scales are being studied to advance both fundamental knowledge and experimental capabilities. In this dissertation, concepts specific to near-field optics and experimental capabilities specific to near-field microscopy are used to investigate various aspects of the statistical properties of random electromagnetic fields in the vicinity of optically inhomogeneous media which emit or scatter radiation. The properties of such fields are being characterized within the frame of the coherence theory. While successful in describing the far-field properties of optical fields, the fundamental results of the conventional coherence theory disregard the contribution of short-range evanescent waves. Nonetheless, the specific features of random fields at subwavelength distances from interfaces of real media are influenced by the presence of evanescent waves because, in this case, both propagating and nonpropagating components contribute to the detectable properties of the radiation. In our studies, we have fully accounted for both contributions and, as a result, different surface and subsurface characteristics of inhomogeneous media could be explored. We investigated different properties of random optical near-fields which exhibit either Gaussian or non-Gaussian statistics. We have demonstrated that characteristics of optical radiation such as first- and second-order statistics of intensity and the spectral density in the vicinity of random media are all determined by both evanescent waves contribution and the statistical properties of the physical interface. For instance, we quantified the subtle differences which exist between the near- and far-field spectra of radiation and we brought the first experimental evidence that, contrary to the predictions of the conventional coherence theory, the values of coherence length in the near field depend on the distance from the interface and, moreover, they can be smaller than the wavelength of light. The results included in this dissertation demonstrate that the statistical properties of the electromagnetic fields which exist in the close proximity of inhomogeneous media can be used to extract structural information. They also suggest the possibility to adjust the coherence properties of the emitted radiation by modifying the statistical properties of the interfaces. Understanding the random interference phenomena in the near-field could also lead to new possibilities for surface and subsurface diagnostics of inhomogeneous media. In addition, controlling the statistical properties of radiation at subwavelength scales should be of paramount importance in the design of miniaturized optical sources, detectors and sensors.Ph.D.
Other
Optics and Photonics
Optics
43
Adderley, B. M. "Nonlinear optical properties of semiconductor superlattices". Thesis, University of Newcastle Upon Tyne, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239137.
Testo completo
44
Westland, S. "The optical properties of printing inks". Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383339.
Testo completo
45
Evans, H. I. "The optical properties of oxide bronzes". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47054.
Testo completo
46
Błaszczak, Zuzanna. "Optical properties of the vertebrate retina". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708798.
Testo completo
47
Black, Marcie R. (Marcie Rochelle). "The optical properties of bismuth nanowires". Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17594.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 170-177).
The optical absorption of bismuth nanowires in the energy (wavenumber) range of 600 - 4000cm-1 is studied. Optical reflection and transmission spectra reveal that bismuth nanowires have a large and intense absorption peak as well as several smaller absorption peaks which are not measured in bulk bismuth. The smaller absorption peaks fit reasonably well to theoretical models for intersubband absorption in bismuth nanowires. The wire diameter, polarization, and doping dependencies as well as the spectral shape of the dominant peak agree with simulations of the optical absorption resulting from an L-point valence to T-point valence band electronic transition. The large absorption peak is present even for nanowires too large to exhibit quantum confinement, thus showing that the absorption results from a surface-induced effect and not from quantum confinement. The enhanced optical absorption in nanowires over bulk bismuth is attributed to a surface term in the matrix element which results from the spacial gradient of the dielectric function and the large dielectric mismatch between bismuth and the surrounding alumina or air. A comparison of the measured spectra with simulations of optical absorption resulting from direct L-point electronic transitions demonstrated that this absorption mechanism is not dominant in our materials. In order to explore the optical properties of bismuth nanowires, two methods were developed. First, effective medium theory applied in reverse was used to deduce the dielectric function of materials smaller than the wavelength of light. Second, a technique to fabricate nanowires with diameters above 200nm was transfered into our laboratory.
(cont.) The enhanced coupling between the L-T point valence bands in nanowires may lead to a very accurate measurement of the band gap and band overlap in bismuth as a function of doping and temperature. In addition, the discovery of the enhanced interband coupling resulting from the surface contribution to the matrix element has many implications, especially if this result is applicable to other systems.
by Marcie R. Black.
Ph.D.
48
Zuehlsdorff, Tim Joachim. "Computing optical properties of large systems". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/29208.
Testo completoAbstract (sommario):
In recent years, time-dependent density-functional theory (TDDFT) has been the method of choice for calculating optical excitations in medium sized to large systems, due to its good balance between computational cost and achievable accuracy. In this thesis, TDDFT is reformulated to fit the framework of the linear-scaling density-functional theory (DFT) code ONETEP. The implementation relies on representing the optical response of the system using two sets of localised, atom centered, in situ optimised orbitals in order to ideally describe both the electron and the hole wavefunctions of the excitation. This dual representation approach requires only a minimal number of localised functions, leading to a very efficient algorithm. It is demonstrated that the method has the capability of computing low energy excitations of systems containing thousands of atoms in a computational effort that scales linearly with system size. The localised representation of the response to a perturbation allows for the selective convergence of excitations localised in certain regions of a larger system. The excitations of the whole system can then be obtained by treating the coupling between different subsystems perturbatively. It is shown that in the limit of weakly coupled excitons, the results obtained with the coupled subsystem approach agree with a full treatment of the entire system, with a large reduction in computational cost. The strengths of the methodology developed in this work are demonstrated on a number of realistic test systems, such as doped p-terphenyl molecular crystals and the exciton coupling in the Fenna-Matthews-Olson complex of bacteriochlorophyll. It is shown that the coupled subsystem TDDFT approach allows for the treatment of system sizes inaccessible by previous methods.
49
Djalalian, Assl Amir. "Tailoring Properties of Magneto-Optical Crystals". Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-199258.
Testo completoAbstract (sommario):
Magneto-Optic Photonic Crystals (MOPC) used in low dimension lasers whereby acting as Faraday rotators capable of 45o rotation where insertion loos is compensated by photoluminescence effect are of significant interest. In low dimension sensors MOPCs act as optical filters to selectively detect only lights at certain wavelengths. Combined with the photoluminescence effect, sensors may be designed capable of detecting signals with extremely low intensity, thus high quantum efficiency. In this work, MOPC with various Erbium dopant concentration, acting as photoluminescence centre, were modelled under high pumping power regime associated to 0.985 inversion population to identify the minimum Erbium concentration and number of layers for the target 45o FR, 0.9 transmittance and minimal ellipticity at resonance wavelength 1531nm. Further optimization of Magneto-optical (MO) properties versus the microcavity position within the MOPC was investigated. An optimum multilayered configuration and composition was identified with a reduction in both erbium concentration and total thickness compared to what was reported previously without compromising the target MO properties.
50
Kuhta, Nicholas Anthony. "The optical properties of multi-scale plasmonic structures and their applications in optical characterization and imaging". Thesis, 2012. http://hdl.handle.net/1957/31106.
Testo completoAbstract (sommario):
The optical response of metallic structures is dominated by the dynamics of their free electron plasma. Plasmonics, the area of optics specializing in the electromagnetic behavior of heterogeneous structures with metallic inclusions, is undergoing rapid development, fueled in part by recent progress in experimental fabrication techniques and novel
theoretical approaches. In this thesis I outline the behavior of four plasmonic material systems, and discuss the underlying physics that governs their optical response. First, the anomalous optical properties of solution-derived percolation films are explained using scaling theory. Second, a novel technique is developed to characterize the optics of amorphous nanolaminates, leading to the creation of a meta-material with anisotropic (hyperbolic) dispersion. The properties of such materials can be tuned by adjusting their composition. Third, the electrodynamics of vertically aligned multi-walled carbon nanotubes is derived through the development of a spectroscopic terahertz transmission ellipsometry algorithm. Lastly, a new diffraction based imaging structure based on metallic gratings is presented to have resolution capabilities which far outperform the diffraction limit.Graduation date: 2013