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Gergely, Mathias [Verfasser], und Kurt [Akademischer Betreuer] Roth. „Snow Characterization by Optical Properties / Mathias Gergely ; Akademischer Betreuer: Kurt Roth“. Heidelberg : Universitätsbibliothek Heidelberg, 2011. http://d-nb.info/1180067789/34.
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Reay, Holly J. „Optical properties of snow and sea-ice : a field and modelling study“. Thesis, Royal Holloway, University of London, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.594224.
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The work contained within this thesis is a field and laboratory study of snowpack and sea-ice optical and physical properties, and a computation modelling study of photochemical reaction rates within snowpack. The contribution of snow photochemistry to snow and atmospheric oxidative capacity is controlled in part by snow albedo and e-folding depths in snow. Albedo and e-folding depths (and thus snow photochemistry) are a function of black carbon mass ratio in snow. The work contained within this thesis demonstrates the complicated response of albedo, e-folding depth (wavelengths 300-600 run) and depth-integrated production rates of N02 and OH radicals to increasing black carbon mass ratio in well-characterised snowpacks of the Barrow OASIS campaign, Alaska. All snowpacks were reworked layered windpacks and were found to have similar responses to changes in black carbon mass ratio. The radiative-transfer calculations demonstrate two light absorption regimes: ice-dominated and black carbon dominated. The ice-dominated and black carbon dominated behaviour of albedo, e-folding depth and depth-integrated production rates with increasing black carbon mass ratios are presented. For black carbon mass ratios greater than 20 ng g-I (wavelength range of 300---600 nm), e-folding depth and depth integrated production rate have an inverse power law relationship with black carbon mass ratio. Doubling the black carbon mass ratio decreases the e-folding depth to -70% of the initial value and for solar zenith angles greater than 60°, doubling the black carbon mass ratio decreases depth-integrated production rates of N02 and OH to - 70% and - 65% of their original values respectively.
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Chukir, Patrik. „Realistické zobrazování sněhu“. Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2021. http://www.nusl.cz/ntk/nusl-445479.
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This diploma thesis follows visualization of snow formations, which are called penitentes. This work includes also collecting the data needed to derive the optical properties of the penitentes material. Which are different phases between snow and ice. For visualization method is used Progressive Transient Photon Beams, that this work implements with the help of SmallUbpb.
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Canestraro, Carla Daniele. „Electrical and optical properties of thin film SnO₂ and SnO₂:F : transparent electrodes in organic photovoltiaics /“. Stockholm : Materials Science and Engineering (Materialvetenskap), Kungliga Tekniskan högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4832.
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Carmagnola, Carlo Maria. „Mesure, analyse et modélisation des processus physiques du manteau neigeux sec Implementation and evaluation of prognostic representations of the optical diameter of snow in the SURFEX/ISBA-Crocus detailed snowpack model Snow spectral albedo at Summit, Greenland: measurements and numerical simulations based on physical and chemical properties of the snowpack“. Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENU014.
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La neige est un matériau poreux dont la microstructure change en permanence. L'ensemble de ces transformations, qui prend le nom de ``métamorphisme", est susceptible d'affecter les propriétés thermiques, mécaniques et électromagnétiques de la neige au niveau macroscopique. En particulier, les échanges d'énergie et de matière à l'intérieur du manteau neigeux et entre la neige et l'atmosphère sont fortement influencés par l'évolution au cours du temps de la microstructure de la neige. Une représentation adéquate du métamorphisme dans les modèles de manteau neigeux s'avère donc cruciale. La microstructure d'un matériau poreux peut être raisonnablement décrite en se servant d'un nombre réduit de variables. En effet, la masse volumique, la surface spécifique (SSA) et la distribution de courbure permettent de caractériser la microstructure d'un matériau. Cependant, dans le cas de la neige cette approche n'en est qu'à ses débuts et n'a pas encore été appliquée de façon systématique. Des variables semi-empiriques, difficiles à mesurer et dépourvues de lien direct avec d'autres propriétés physiques, sont encore largement utilisées dans les modèles détaillés de manteau neigeux. Ce travail de thèse s'inscrit dans cette tentative de représenter la microstructure de la neige au cours du temps à l'aide de variables bien définies et mesurables sur le terrain. Parmi ces variables, nous nous sommes attachés notamment à la SSA, qui constitue une grandeur essentielle pour l'étude du manteau neigeux et de son évolution temporelle. Différentes lois d'évolution de la SSA ont été étudiées, à partir de relations empiriques basées sur des ajustements de données expérimentales jusqu'aux modèles physiques qui représentent le flux de la vapeur d'eau entre les grains de neige. Ces lois ont été dans un premier temps testées à l'aide d'un modèle simplifié de manteau neigeux et puis introduites directement dans le modèle SURFEX/ISBA-Crocus. Pour ce faire, la SSA dans Crocus a été transformée en variable prognostique, en remplaçant d'autres variables semi-empiriques préexistantes. Les différentes formulations de l'évolution temporelle de la SSA ont été comparées à des mesures de terrain, acquises lors de deux campagnes à Summit (Groenland) et au Col de Porte (France). Ces mesures ont été effectuées en utilisant de nouvelles techniques optiques et ont permis d'obtenir un riche jeu de données avec une grande résolution verticale. Les résultats montrent que les différentes formulations sont comparables et reproduisent bien les mesures, avec un écart quadratique moyen entre les valeurs de SSA simulées et observées inférieur à 10 m^2/kg. Enfin, nous avons contribué à faire le pont entre la microstructure de la neige et ses propriétés macroscopiques. En particulier, nous nous sommes intéressés au lien entre, d'une part, la SSA et, d'autre part, les propriétés mécaniques et optiques. Dans le premier cas, nous avons investigué la corrélation entre la SSA et la résistance à l'enfoncement mesurée avec un Snow Micro Pen (SMP). Les résultats encore préliminaires semblent indiquer que la SSA peut être dérivée de la masse volumique et de grandeurs micro-mécaniques estimées à partir du signal du SMP avec un modèle statistique. Dans le deuxième cas, nous avons simulé l'albédo de surface à Summit à partir des profils mesurés de masse volumique et de SSA et du contenu en impuretés. Les résultats de cette étude ont démontré que l'albédo spectral peut être correctement simulé à l'aide d'un modèle de transfert radiatif et l'énergie absorbée par le manteau neigeux peut être estimée avec une précision d'environ 1%Snow is a porous medium whose microstructure is constantly subjected to morphological transformations. These transformations, which take the name of ``metamorphism", are likely to affect the thermal, mechanical and electromagnetic properties of snow at the macroscopic level. Specifically, the exchange of energy and matter within the snowpack and between the snow and the atmosphere above are strongly impacted by the evolution over time of the snow microstructure. Therefore, an adequate representation of metamorphism in snowpack models is crucial. The microstructure of a porous medium can be reasonably described using a reduced number of variables. Indeed, the density, the specific surface area (SSA) and the curvature distribution are able to characterize the microstructure of such a material. However, in the case of snow this approach is still in its infancy and has not yet been systematically applied. Semi-empirical variables, difficult to measure and not directly linked to other relevant physical properties, are still widely used in so-called detailed snowpack models. This work contributes to the attempt to represent the state of the snow using well-defined and easily measurable microstructural variables. Among these variables, we focused particularly on the SSA, which is a key quantity for the study of snow and its temporal evolution. Different evolution laws of SSA were studied, starting from empirical relationships based on experimental data adjustments to physical models that represent the flow of water vapor between snow grains. These laws were initially tested using a simplified snowpack model and then introduced directly into the SURFEX/ISBA-Crocus snowpack model. To this end, the SSA in Crocus was turned into a prognostic variable, replacing other preexisting semi-empirical variables. The different formulations of the temporal evolution of the SSA were compared with field measurements, acquired during two campaigns at Summit (Greenland) and the Col de Porte (France). These measurements were carried out using new optical techniques and yielded a rich dataset with high vertical resolution. The results show that the different formulations are comparable and reproduce well the observations, with an average root-mean-square deviation value between simulated and measured SSA lower than 10 m^/kg. Finally, we contributed to bridge the gap between snow microstructure and macroscopic properties. In particular, we investigated the link between the SSA on the one hand and the mechanical and optical properties on the other hand. In the first case, we investigated the correlation between the SSA and the penetration resistance measured with a Snow Micro Pen (SMP). The preliminary results suggest that the SSA can be retrieved from the snow density and the micro-mechanical parameters estimated from the SMP signal using a statistical model. In the second case, we simulated the surface albedo at Summit from the measured profiles of density, SSA and impurities within the snowpack. The results of this study showed that the spectral albedo can be simulated successfully using a radiative transfer model and the energy absorbed by the snowpack can be estimated with a good accuracy (about 1%)
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Lintzén, Nina. „Mechanical properties of artificial snow“. Licentiate thesis, Luleå tekniska universitet, Geoteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16798.
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Mechanical properties of snow have been a subject of research since the mid-20th century. Theresearch done is based on natural snow. During the last decades the winter business industryhas been growing and also the interest for constructing buildings and artwork of snow. Suchconstructions are generally built using artificial snow, i.e. snow produced by snow guns. Up tothe present constructions of snow are designed based on knowledge by experience. Only minorscientific studies on artificial snow and its properties has been published. Hence it is ofimportance to investigate material properties for artificial snow.A survey of current state of the art knowledge of properties for natural snow was done andbasic material properties for different qualities of artificial snow were investigated. Strengthand deformation properties for artificial snow were evaluated through uniaxial compressivetests where cylindrical test specimens were subjected to different constant deformation rates.The results show that artificial snow at low deformation rates will have a plastic deformationbehavior where the initial deformation will cause a hardening of the snow structure. At higherdeformation rates brittle failure may occur. For artificial snow with a homogeneous and finegrained structure the deformation behavior was found to change from plasticity to brittleness ata certain critical deformation rate. Artificial snow with coarse grained structure was found to bebrittle giving unstructured results independent of the load level.Four point loading was applied on beams of artificial snow to study creep deformation, bendingstrength and to determine the ultimate load for the different snow qualities. The results showedcoarse grained artificial snow underwent relatively small creep deformations. Both the creepbehavior and the ultimate strength varied randomly at the same applied load. Large plasticdeformations were observed with the fine grained artificial without any failure of the beams.The ultimate load was relatively high and repeatable results were achieved for all test.Previous presumptions that coarse grained artificial snow with high density would have highstrength and were not confirmed by the experiments performed on different qualities ofartificial snow. The performed tests indicate that fine grained artificial snow of lower densityhave more predictable strength properties of equally high or higher magnitude as for coarsegrained artificial snow. The plastic deformations were however higher for the fine grainedartificial snow. High deformations are not favorable for structures which should maintain theshape during the winter season. When designing constructions of snow both strength anddeformation properties should be taken into account.Godkänd; 2013; 20131002 (ninlin); Tillkännagivande licentiatseminarium 2013-10-23 Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Nina Lintzén Ämne: Geoteknik/Soil Mechanics and Foundation Engineering Uppsats: Mechanical Properties of Artificial Snow Examinator: Professor Sven Knutsson, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Tekn. lic. Lars Vikström, LKAB, Luleå Tid: Fredag den 15 november 2013 kl 10.00 Plats: F1031, Luleå tekniska universitet
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Bourgeois, C. Saskia. „The radiative properties of snow at Summit, Greenland /“. Zürich : ETH, 2006. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16758.
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Wooldridge, Robyn Elaine. „The effects of explosives on the physical properties of snow“. Thesis, Montana State University, 2013. http://etd.lib.montana.edu/etd/2013/wooldridge/WooldridgeR0513.pdf.
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Explosives are a critically important component of avalanche control programs. They are used to both initiate avalanches and to test snowpack instability by ski areas, highway departments and other avalanche programs around the world. Current understanding of the effects of explosives on snow is mainly limited to shock wave behavior demonstrated through stress wave velocities, pressures and attenuation. This study seeks to enhance current knowledge of how explosives physically alter snow by providing data from field-based observations and analyses that quantify the effect of explosives on snow density, snow hardness and snow stability test results. Density, hardness and stability test results were evaluated both before and after the application of 0.9 kg cast pentolite boosters as surface and air blasts. Changes in these properties were evaluated at specified distances up to 5.5 meters (m) from the blast center for surface blasts and up to 4 m from the blast center for air blasts. A density gauge, hand hardness, a ram penetrometer, Compression Tests (CTs), and Extended Column Tests (ECTs) were used. In addition to the field based observations, the measurement error of the density gauge was established in laboratory tests. Results from surface blasts did not provide conclusive data. Air blasts yielded statistically significant density increases out to a distance of 1.5 m from the blast center and down to a depth of 50 centimeters (cm). Statistically significant density increases were also observed at the surface (down to 20 cm) out to a distance of 4 m. Hardness data showed little to no measurable change. Results from CTs showed a statistically significant decrease in the number of taps needed for column failure 4 m from the blast center in the post-explosive tests. A smaller data set of ECT results showed no overall change in ECT score. The findings of this study provide a better understanding of the physical changes in snow following explosives, which may lead to more effective and efficient avalanche risk mitigation.
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Lampkin, Derrick Julius. „Optical Remote Sensing for Monitoring Evolution of Ablation Season Mountain Snow Cover“. Diss., Tucson, Arizona : University of Arizona, 2005. http://etd.library.arizona.edu/etd/GetFileServlet?file=file:///data1/pdf/etd/azu%5Fetd%5F1120%5F1%5Fm.pdf&type=application/pdf.
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Cuthill, Fergus. „The influence of snow microstructure and properties on the grip of winter tyres“. Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/29534.
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The friction of tyres on roads has been of practical importance for many years with nearly 80% of terrestrial traffic making use of rubber tyres. Tyres provide the grip required for vehicle acceleration, braking and cornering. In order for a tyre to grip on a snow covered surface friction mechanisms such as “ploughing”, (where sharp tread block edges dig into and break bonds between the snow grains) and fluid film lubrication must be considered. These are not present when a tyre interacts with tarmac. In addition metamorphism of the snow over time can result in variations of the structure and mechanical properties, this can occur rapidly especially when dealing with temperatures close to snows melting point. When full car-scale outdoor testing is carried out the snow conditions cannot be controlled and vary daily. This means the snow properties must be measured every day so that any observed variations in friction can be attributed to the tyres rather than the snow. At present the simple measurements being carried out on the snow tracks have not proved sufficient to pick up on the variations in the snow. This leads to inconsistent results: one tyre behaves differently on two different days, even though the snow was measured to be the same. This has resulted in the need for further study of the way snow variations influence the grip of winter tyres. The primary aim of this study is to identify which snow properties contribute to the friction of tyres on snow and be able to estimate the friction from measurements of snow properties. This work is the first comprehensive study to combine: multiple snow properties, microstructure characterisation, measurement of friction behaviour and different snow (both artificial and natural). In order to study the way snow affects the grip of winter tyres, methods of manufacturing artificial snow with consistent mechanical properties and microstructure are used. A method of blending ice chips (a solid state fracturing process) and compressing the resulting snow to form a test track was developed during a previous PhD carried out in our group. An alternate snow microstructure was created by using an established process of creating snow by vapour deposition. The process was simplified and downscaled, the resulting snow consisted of large dendritic grains, very different to the blended ice chips. Both snows were pressed in identical manners to create snow testing tracks. In addition, natural snow collected from the field was tested to compare with the artificial snow. In order to investigate how the variations in the snow affected the friction of tyres extensive testing was carried out in a cold room using a linear tribometer, using procedures established in previous studies. Two analytical rubber samples were used to investigate the friction, a rounded edge sample and a siped sample. Testing was carried out at -10°C at speeds of 0.01m/s, 0.1m/s and 1m/s. A significant part of this PhD involved the development of new methods and equipment which have not been used to study snow in this way before. In order to characterise mechanical properties, shear testing, compression testing and cohesion testing were carried out. To investigate snow microstructure, surface profilometry, microscopy and X-ray microtomography were used. Correlating the changes observed in snow characteristics with the changes recorded in the coefficient of friction has allowed the development of an empirical equation. This can be used to predict the coefficient of friction of a given snow based on three relatively simple snow measurements: a compression test to calculate the effective modulus, a roughness measurement to calculate the peak count density and a snow penetration test. For the first time this study allows us to use the empirical equation to estimate the relative contributions of the ploughing and surface friction mechanisms to the total friction. This allows the comparison of full car-scale test data as it is now possible to account for variations in the snow test tracks.
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Lintzén, Nina. „Properties of snow with applications related to climate change and skiing“. Doctoral thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-59846.
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Snow has been a subject of research since the mid-20th century. Research on mechanical properties of snow started as an off-shoot of soil mechanics, where methods, tools and instruments used often are the same. However, during the last decades the winter business industry has been growing requiring a number of new fields of research. The aim with this PhD thesis is to investigate and contribute to solutions of some of the new research problems appearing in this area. Machine-made snow is commonly used for buildings and artwork of snow. Only minor scientific studies of machine-made snow and its properties have been published. Therefore, mechanical properties of machine-made snow were investigated. Strength and deformation properties were evaluated through uniaxial compressive tests where cylindrical test specimens were subjected to different constant deformation rates. Creep deformation, bending strength and ultimate load were also evaluated through beam tests. The results showed that the deformation rate is crucial if the snow will deform plastically or if brittle failure will occur. The grain size and structure of the snow had a strong influence on the strength properties. Snow is a constantly changing material with a large variety of grain sizes and shapes. Therefore it is of importance to classify snow. Classication of snow can be done using different methods depending on the property that is to be investigated. Several non-contact detection methods to evaluate snow properties exist. In this thesis, spectral reflectance measurements were performed to investigate liquid water content in snow using two different systems, a spectrometer and an optical sensor called Road Eye. The Road Eye sensor was also used to classify snow in cross-country ski tracks. This method enables a fast classication of a complete track where different types of snow can be distinguished. The properties of a ski track and the characteristics of the snow determine the type of skis that should be selected for optimum sliding properties. Cross-country skis have different mechanical properties, which to a large extent can be evaluated from the span curve of the ski. Depending on the skiing style, the skier's skills, terrain and track conditions different ski properties are required, which is particularly important for competitive skiing. Span curves of cross-country skis were measured using a digital instrument called Skiselector. Results from the investigations showed that skis within the same pair may have signicantly different properties. Moreover, temperature influences the span curve and thus the mechanical properties of the skis. Therefore, skis should be measured at a temperature close to where they are aimed to be used. Field tests of skis with similar span curves but different ski base topography were tested during wet and cold snow conditions. The results indicate that different topographies are preferable during different snow conditions. Due to the climate change, winters have become shorter and warmer with less natural snow. To compensate for the lack of natural snow, ski resorts and other stakeholders produce machinemade snow in order to run their business. Storing snow in insulated piles is an alternative and sometimes a complement to snow production. Studies on stored snow show that the surface area of the pile should be minimized in order to reduce the melt rate. Furthermore, the pileshould be covered with a suciently thick insulating layer, preferably with good evaporation properties. Theoretical calculations can be used to estimate the amount of snow that melts and to predict the efficiency of different materials as thermal insulation on snow. These calculations coincide well with experiments performed in northern Sweden where snow melt was measured. This PhD thesis consists of five publications and an introduction to this area which in particular puts these publications into a more general frame.
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Urban, Joanna. „Optical and vibrational properties“. Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30092.
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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
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Voigt, Stefan. „Advanced methods for operational mapping snow cover using medium resolution optical satellite data /“. Bern : Geographisches Institut der Universität Bern, 2000. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.
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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.
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Alshammary, Marzook. „Optical and magneto-optical properties of doped oxides“. Thesis, University of Sheffield, 2011. http://etheses.whiterose.ac.uk/2066/.
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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.
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Shertzer, Richard Hayden. „Fabric tensors and effective properties of granular materials with application to snow“. Diss., Montana State University, 2011. http://etd.lib.montana.edu/etd/2011/shertzer/ShertzerR0811.pdf.
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Granular materials e.g., gravel, sand, snow, and metallic powders are important to many engineering analysis and design problems. Such materials are not always randomly arranged, even in a natural environment. For example, applied strain can transform a randomly distributed assembly into a more regular arrangement. Deviations from random arrangements are described via material symmetry. A random collection exhibits textural isotropy whereas regular patterns are anisotropic. Among natural materials, snow is perhaps unique because thermal factors commonly induce microstructural changes, including material symmetry. This process temperature gradient metamorphism produces snow layers that can exhibit anisotropy. To adequately describe the behavior of such layers, mathematical models must account for potential anisotropy. This feature is absent from models specifically developed for snow, and, in most granular models in general. Material symmetry is quantified with fabric tensors in the constitutive models proposed here. Fabric tensors statistically characterize directional features in the microstructure. For example, the collective orientation of intergranular bonds impacts processes like conduction and loading. Anisotropic, microstructural models are analytically developed here for the conductivity, diffusivity, permeability, and stiffness of granular materials. The methodology utilizes homogenization an algorithm linking microscopic and macroscopic scales. Idealized geometries and constitutive assumptions are also applied at the microscopic scale. Fabric tensors tying the granular arrangement to affected material properties are a natural analysis outcome. The proposed conductivity model is compared to measured data. Dry dense snow underwent temperature gradient metamorphism in a lab. Both the measured heat transfer coefficient and a developing ice structure favored the direction of the applied gradient. Periodic tomography was used to calculate microstructural variables required by the conductivity model. Through the fabric tensor, model evolution coincides with measured changes in the heat transfer coefficient. The model also predicts a different conductivity in directions orthogonal to the gradient due to developing anisotropy. Models that do not consider directional microstructural features cannot predict such behavior because they are strictly valid for isotropic materials. The conclusions are that anisotropy in snow can be significant, fabric tensors can characterize such symmetry, and constitutive models incorporating fabric tensors offer a more complete description of material behavior.
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Christensen, Eric. „Measurement and modelling of snow properties in urban and suburban Montreal neighbourhoods“. Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86748.
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Although snow's behaviour is well known in rural contexts through a long standing and widespread network of measurement and recording, the specificity of existing urban datasets to where they were measured limits their applicability to other cities. In this study, snow measurements were performed in urban and suburban Montreal, Québec, Canada over the course of the winter of 2007-2008. Observations of density, depth and albedo showed general trends similar to those expected from rural snow but with density values closer to those measured in other urban studies. Snow properties were scaled up to the convective footprint of an eddy covariance flux tower. Convective fluxes showed little to no relationship with observed snow conditions. Snow evolution data was used in the validation of an offline version of the snow subroutine that is part of the ISBA land surface model. Best results were found for locations subjected to little or no disturbance. Worst results were found for highly disturbed locations.Malgré que le comportement de la neige soit bien documenté en milieu rural grâce à des réseaux de mesure en place depuis longtemps, la complexité des milieux urbains fait en sorte que le transfert de données acquises dans une ville à une autre n'est pas justifiable. Dans le but de la recherche présentée dans cette thèse, des mesures de la couverture neigeuse ont été effectuées dans un quartier résidentiel de la ville de Montréal, Québec, Canada et dans une de ses banlieues au cours de la saison hivernale 2007-2008. Les tendances générales se comportent similairement à celles observées en milieu rural à l'exception que les valeurs de densité se rapprochaient plus de valeurs observées au cours d'autres études urbaines. Les propriétés de la neige ont alors été mises à l'échelle de la zone source convective d'équipements de mesure de flux énergétiques. Les flux convectifs n'ont pas montrés de signe d'une dépendance aux conditions de neige. La base de données de l'évolution des propriétés de la neige a également servi dans la validation d'une version autonome du modéle de neige faisant partie du modéle d'échange de surface ISBA. Les meilleurs résultats ont étés obtenus pour des endroits subissant le minimum de perturbations humaines. Les pires résultats découlent de la simulation d'endroits très dérangés.
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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.
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Auguié, Baptiste. „Optical properties of gold nanostructures“. Thesis, University of Exeter, 2009. http://hdl.handle.net/10036/73955.
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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.
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Crook, Robert J. „Optical properties of organic waveguides“. Thesis, University of Exeter, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359604.
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Zhou, Yuming. „Optical properties of living organisms“. Thesis, Open University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301878.
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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.
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Khan, Saima Ishfaque. „The optical properties of metamaterials“. Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7781/.
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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.
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Lee, Timothy. „Nonlinear properties of optical microfibres“. Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355529/.
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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
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González, Ganzábal A. (Alejandro). „Optical properties of leaf replicas“. Master's thesis, University of Oulu, 2018. http://urn.fi/URN:NBN:fi:oulu-201808232657.
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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.
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Molloy, Peter J. „Optical properties of concentrated dispersions“. Thesis, London Metropolitan University, 1986. http://repository.londonmet.ac.uk/2939/.
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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.
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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.
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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
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Kenyon, Suzanne Laura Physics Faculty of Science UNSW. „A universe of sky and snow: site-testing for optical astronomy at Dome C, Antarctica“. Awarded by:University of New South Wales. Physics, 2007. http://handle.unsw.edu.au/1959.4/40822.
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The unique advantages for astronomy on the Antarctic plateau are now well established. In particular, Dome C, Antarctica is potentially one of the best new sites for optical, infrared and sub-millimeter astronomy, presenting the opportunity to build unique astronomical instruments. Located high on the Antarctic plateau, Dome C offers low wind, clear skies, and negligible precipitation. This thesis addresses three additional properties of the site relevant to optical astronomy-sky brightness, atmospheric extinction and optical turbulence. The sky at an optical astronomy site must be dark, and the atmosphere very clean with minimal light extinction. At present little is known from an astronomer's perspective about the optical sky brightness and atmospheric extinction at most Antarctic sites. The high latitude of Dome C means that the Sun spends a relatively small amount of time far below the horizon, implying longer periods of astronomical twilight and less optical dark time than other sites, especially those close to the equator. We review the contributions to sky brightness at high-latitude sites, and calculate the amount of usable dark time at Dome C. We also explore the implications of the limited sky coverage of high-latitude sites, and review optical extinction data from the South Pole. A proposal to extend the amount of usable dark time through the use of polarising filters is examined, and we present the design and calibration of an instrument (called Nigel) to measure the brightness, spectrum and temporal characteristics of the twilight and night sky. The atmospheric turbulence profile above an astronomical site limits the achievable resolution and sensitivity of a telescope. The atmospheric conditions above high plateau Antarctic sites are different to temperate sites; the boundary layer of turbulence is confined very close to the surface, and the upper atmosphere turbulence very weak. We present the first winter-time turbulence profiles of the atmosphere above Dome C, and characterise the site in terms of the achievable precision for photometry and astrometry, and the isoplanatic angle and coherence time for the adaptive optics.
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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.
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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.
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>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.
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Neff, Curtis Wayne. „Optical Properties of Superlattice Photonic Crystals“. Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/14108.
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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.
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Yildirim, Hasan. „Nonlinear Optical Properties Of Semiconductor Heterostructures“. Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607438/index.pdf.
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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.
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Park, Wounjhang. „Optical properties of thin film phosphors“. Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/30078.
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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.
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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.
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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.
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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.
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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.
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Bentley, Caroline. „Optical and microwave properties of ferrofluids“. Thesis, Bangor University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.290411.
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Li, Qing. „Optical properties of III-nitride semiconductors“. Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B30162488.
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Shi, Shenlei, und 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.
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Zheng, Changcheng, und 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.
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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.
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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
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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.
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Westland, S. „The optical properties of printing inks“. Thesis, University of Leeds, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383339.
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Zeng, Yong. „Optical properties of active photonic materials“. Doctoral thesis, Stockholm : Bioteknologi, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4497.
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Zijp, Jacob Rudolf. „Optical properties of dental hard tissues“. [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2001. http://irs.ub.rug.nl/ppn/315857544.
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Evans, H. I. „The optical properties of oxide bronzes“. Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47054.
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Błaszczak, Zuzanna. „Optical properties of the vertebrate retina“. Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708798.
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Black, Marcie R. (Marcie Rochelle). „The optical properties of bismuth nanowires“. Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/17594.
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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.
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Jian-Ming, Lin. „Optical Properties of Nanoheterostructures of ZnO/Pt and ZnO/SnO“. 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-0307200615383800.
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