Zinc oxide (ZnO) is a wide band-gap semiconductor that is of interest for application in dye sensitized solar cells (DSSCs) because of similarity of its properties to TiO2. Unlike TiO2, ZnO can readily be grown in a wide variety of morphologies, using inexpensive, simple, and low temperature methods. Recent research on ZnO-based DSSCs focuses on modifying the ZnO layer morphology in order to maximize surface area, and enhance the electron collection by providing fast electron transport. It is expected that the improvement in cell performance by morphology modification is due to higher dye loading, increased electron lifetime and fast electron transport. However, ZnO properties may be affected by various synthesis methods. It is difficult to make a conclusion whether the change of performance are attributed to change of morphology or a change in the defect types and/ or defect concentrations. In this study, the influence of ZnO nanoparticle properties on cell performance has been investigated. Commercial ZnO nanoparticles with different sizes and optical properties were utilized. It was found that there is a complex relationship between native defects, dye loading, charge transport and photovoltaic performance. In particular, the presence of non-radiative defects was found to be detrimental to photovoltaic performance. In addition, with the similar defect emission intensities, sample exhibiting orange-red defect emission showed better performance than the samples emitting green defect emission. Nanoparticle properties and their relationship between dye adsorption, electron injection, electron lifetime and electron transport, and photovoltaic performance will be discussed. / published_or_final_version / Physics / Master / Master of Philosophy

Modern communications technology has encouraged an intimate connection between Semiconductor Physics and Optics, and this connection shows best in the combination of electron-confining structures with light-confining structures. Semiconductor quantum dots are systems engineered to trap electrons in a mesoscopic scale (the are composed of [approximately] 10000 atoms), resulting in a behavior resembling that of atoms, but much richer. Optical microrseonators are engineered to confine light, increasing its intensity and enabling a much stronger interaction with matter. Their combination opens a myriad of new directions, both in fundamental Physics and in possible applications. This dissertation explores both semiconductor quantum dots and microresonators, through experimental work done with semiconductor quantum dots and microsphere resonators spanning the fields of Quantum Optics, Quantum Information and Photonics; from quantum algorithms to polarization converters. Quantum Optics leads the way, allowing us to understand how to manipulate and measure quantum dots with light and to elucidate the interactions between them and microresonators. In the Quantum Information area, we present a detailed study of the feasibility of excitons in quantum dots to perform quantum computations, including an experimental demonstration of the single-qubit Deutsch-Jozsa algorithm performed in a single semiconductor quantum dot. Our studies in Photonics involve applications of microsphere resonators, which we have learned to fabricate and characterize. We present an elaborate description of the experimental techniques needed to study microspheres, including studies and proof of concept experiments on both ultra-sensitive microsphere sensors and whispering gallery mode polarization converters. / text

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The mirrors used in high energy laser systems have at least two requirements that are uncommon in optical engineering: the reflectance of such mirrors must be very high (> 0.999), and the level of aberrations introduced by the mirrors is desired to be very low, typically λ/50 peak at 3.8 μ. The first requirement can be met by using multilayer thin film coatings, but such coatings can themselves produce aberrations in an optical system. One possible effect in multilayers is that such coatings produce an optical phase change on reflection that varies with angle of incidence and polarization of the illuminating beam. On a strongly curved mirror, such as an f/1.5 parabola used as a collimator, these effects may be appreciable for some coatings (e.g., λ/13 for a broadband all-dielectric reflector), but for an enhanced silver coating the effects are small, typically λ/400 of error that is almost entirely in the form of a small focus shift. If this same parabola is tested at its center of curvature, the coating-caused aberration due to angle of incidence effects are nearly zero (e.g., λ/50,000 for the broadband reflector that gave λ/13 when the parabola was used as a collimator). The wavefront errors due to coating nonuniformities are usually more important than angle of incidence effects. The simplest type of coating nonuniformity to analyze is a proportional error, i.e., an error where the ratios of the thicknesses of the layers are fixed but the thin film stack varies in total thickness across a surface. For a six-layer enhanced reflector for use at 3.8 μ, a 1% thickness error produces an approximate λ/100 wavefront error. At visible wavelengths, however, the aberration produced by such a coating error can be very different because of the optical interference nature of the coating. Means may be developed to estimate the performance of such an infrared reflector from measurements at visible wavelengths. If the errors produced by the coating are to be distinguished from those existing in the test due to misalignment or gravitational flexure of a large mirror, two or more wavelengths must be chosen. There are ambiguities in such a test that may be resolved by choice of an appropriate coating design or by using enough wavelengths in the visible, and both means have been studied. A technique was found where the infrared wavefront can be determined for a coating with proportional thickness errors if the coating prescription is known: interferograms of the mirror are made at three visible wavelengths, and the IR wavefront error due to the coating error is determined in a way that is insensitive to any errors caused by distortion of the substrate or even fairly large misalignments in the optical test of a mirror's figure.

Tirta ErMnO3 optinės savybės: apskaičiuotos dielektrinių skvarbų spektrinės priklausomybės, optinių šuolių energijos, lūžio ir sugerties rodikliai. Tyrimai atlikti elipsometru, dielektrinė funkcija apskaičiuojama pagal vienašio kristalo modelį. / Manganites have attracted a lot of attention due to their magnetical properties: colossal magnetoresistance, variety of phase, but the optical properties of ErMnO3 were not widely investigated. Investigation of optical properties of ErMnO3 single crystal were studie by means of ellipsometry method. Ellipsometric studies have been carried out in the spectral range of 1- 5 eV. The photimetric ellipsometer with rotating analyzer was used. Experimental ellipsometer data were analysed in the isotropical and uniaxial crystal models. The optical properties of ErMnO3 were investigated: ellipsometric parameters Ψ and Δ were determinated, the components of dielectric function and energy of optical transition were found, calculated refractive and absorption indexs.

Theoretical predictions of the AC conductivity of both monolayer and Bernal-stacked bilayer graphene have largely been in agreement with experimental observations. Due to the recent realization of AA-stacked samples, we provide theoretical predictions for this system. We begin this thesis with a review of the optical properties of graphene and provide a brief discussion of the previously studied Bernal-stacked bilayer. We then calculate the optical conductivity of AA-stacked bilayer graphene as a function of frequency for several interesting cases. We are primarily interested in the case of finite doping due to charging. Unlike the monolayer, we see a Drude absorption at charge neutrality as well as an interband absorption with strength twice that of the monolayer background conductivity which onsets at twice the interlayer hopping energy. We examine the behaviour as we vary the chemical potential relative to the interlayer hopping energy scale and compute the partial optical sum. We also consider the effect of adding a bias across the layers and find it serves merely to renormalize the interlayer hopping parameter. While interested in the in-plane conductivity we also provide the perpendicular conductivity of the AA-stacked bilayer. We then extend the ideas to the AAA-stacked trilayer. Based on proposed models for topological insulators discussed in the literature, we consider the effect of spin orbit coupling in both one and two layers on the optical properties of the AA-stacked bilayer which illustrates the effect of opening an energy gap in the band structure.