Phenomenological modeling of image irradiance for non-Lambertian surfaces under natural illumination.

Various vision tasks are usually confronted by appearance variations due to changes of illumination. For instance, in a recognition system, it has been shown that the variability in human face appearance is owed to changes to lighting conditions rather than person\u27s identity. Theoretically, due to the arbitrariness of the lighting function, the space of all possible images of a fixed-pose object under all possible illumination conditions is infinite dimensional. Nonetheless, it has been proven that the set of images of a convex Lambertian surface under distant illumination lies near a low dimensional linear subspace. This result was also extended to include non-Lambertian objects with non-convex geometry. As such, vision applications, concerned with the recovery of illumination, reflectance or surface geometry from images, would benefit from a low-dimensional generative model which captures appearance variations w.r.t. illumination conditions and surface reflectance properties. This enables the formulation of such inverse problems as parameter estimation. Typically, subspace construction boils to performing a dimensionality reduction scheme, e.g. Principal Component Analysis (PCA), on a large set of (real/synthesized) images of object(s) of interest with fixed pose but different illumination conditions. However, this approach has two major problems. First, the acquired/rendered image ensemble should be statistically significant vis-a-vis capturing the full behavior of the sources of variations that is of interest, in particular illumination and reflectance. Second, the curse of dimensionality hinders numerical methods such as Singular Value Decomposition (SVD) which becomes intractable especially with large number of large-sized realizations in the image ensemble. One way to bypass the need of large image ensemble is to construct appearance subspaces using phenomenological models which capture appearance variations through mathematical abstraction of the reflection process. In particular, the harmonic expansion of the image irradiance equation can be used to derive an analytic subspace to represent images under fixed pose but different illumination conditions where the image irradiance equation has been formulated in a convolution framework. Due to their low-frequency nature, irradiance signals can be represented using low-order basis functions, where Spherical Harmonics (SH) has been extensively adopted. Typically, an ideal solution to the image irradiance (appearance) modeling problem should be able to incorporate complex illumination, cast shadows as well as realistic surface reflectance properties, while moving away from the simplifying assumptions of Lambertian reflectance and single-source distant illumination. By handling arbitrary complex illumination and non-Lambertian reflectance, the appearance model proposed in this dissertation moves the state of the art closer to the ideal solution. This work primarily addresses the geometrical compliance of the hemispherical basis for representing surface reflectance while presenting a compact, yet accurate representation for arbitrary materials. To maintain the plausibility of the resulting appearance, the proposed basis is constructed in a manner that satisfies the Helmholtz reciprocity property while avoiding high computational complexity. It is believed that having the illumination and surface reflectance represented in the spherical and hemispherical domains respectively, while complying with the physical properties of the surface reflectance would provide better approximation accuracy of image irradiance when compared to the representation in the spherical domain. Discounting subsurface scattering and surface emittance, this work proposes a surface reflectance basis, based on hemispherical harmonics (HSH), defined on the Cartesian product of the incoming and outgoing local hemispheres (i.e. w.r.t. surface points). This basis obeys physical properties of surface reflectance involving reciprocity and energy conservation. The basis functions are validated using analytical reflectance models as well as scattered reflectance measurements which might violate the Helmholtz reciprocity property (this can be filtered out through the process of projecting them on the subspace spanned by the proposed basis, where the reciprocity property is preserved in the least-squares sense). The image formation process of isotropic surfaces under arbitrary distant illumination is also formulated in the frequency space where the orthogonality relation between illumination and reflectance bases is encoded in what is termed as irradiance harmonics. Such harmonics decouple the effect of illumination and reflectance from the underlying pose and geometry. Further, a bilinear approach to analytically construct irradiance subspace is proposed in order to tackle the inherent problem of small-sample-size and curse of dimensionality. The process of finding the analytic subspace is posed as establishing a relation between its principal components and that of the irradiance harmonics basis functions. It is also shown how to incorporate prior information about natural illumination and real-world surface reflectance characteristics in order to capture the full behavior of complex illumination and non-Lambertian reflectance. The use of the presented theoretical framework to develop practical algorithms for shape recovery is further presented where the hitherto assumed Lambertian assumption is relaxed. With a single image of unknown general illumination, the underlying geometrical structure can be recovered while accounting explicitly for object reflectance characteristics (e.g. human skin types for facial images and teeth reflectance for human jaw reconstruction) as well as complex illumination conditions. Experiments on synthetic and real images illustrate the robustness of the proposed appearance model vis-a-vis illumination variation. Keywords: computer vision, computer graphics, shading, illumination modeling, reflectance representation, image irradiance, frequency space representations, {hemi)spherical harmonics, analytic bilinear PCA, model-based bilinear PCA, 3D shape reconstruction, statistical shape from shading

Classical and quantum aspects of the optical response at the nanoscale

Nanophotonics is one of today’s basic sciences and technologies: an in-depth understanding of the interaction between light and matter on the nano-scale, besides its intrinsic associated scientific interest, enables the precise control of light, that is relevant for technology in diverse applications such as telecommunications, energy and medicine. Plasmonics –the study of the collective oscillations of conduction electrons in materials with a metallic behaviour– has become one of its most essential sub-branches in recent years: the strong confinement of the electromagnetic energy density and its high sensitivity to the environment render plasmons as a key tool for the control of light at the nanoscale. In this thesis, we explore several new paths that open up to Nanophotonics in general, and Plasmonics in particular, with the appearance on stage of materials such as graphene, which host optical excitations of increasingly smaller wavelengths, therefore requiring increasingly more compact structures. This new scenario demands new theoretical models that capture the structure of matter on an atomic scale. After introducing the necessary fundamental concepts in Chapter 1, the thesis proceeds by exploring processes that can still be treated in terms of classical models for the optical response, such as geometrical plasmon focusing. Specifically, we apply this idea in Chapter 2 to graphene nanostructures, proposing a lens design capable of focusing plasmons and enhancing the third-order nonlinear response of this material. We then move to more microscopic models of light-matter interaction: the description of the optical response of a nanoparticle from the individual response of its electrons allows us to explore in Chapter 3 the plasmon decay into hot-electron distributions, as well as the subsequent relaxation of these electrons back to their equilibrium state, thus presenting a complete picture of ultrafast plasmon and hot electron dynamics in nanoparticles. From here on, we explore collective oscillations in molecular-sized structures, which demand the use of microscopic models incorporating many-body electronic response by massively demanding the numerical solution of Schrödinger’s equations including the interaction with incident light. In particular, in Chapter 4 we have applied timedependent density-functional theory (TD-DFT) to model the optical response of DNA that, besides being ubiquitous in biological organisms, we claim it to have some potential uses in nanotechnology. Finally, we study light-matter interactions associated with ionic displacements of structures, quantised as phonons. In Chapter 5, we study the coupling between these excitations and plasmons supported in 2D materials: the distortions introduced into the electronic structure by ionic vibrations allow us to explain recent experiments in which the presence of vibrational modes modifies the plasmonic dispersion. We also studied, in Chapter 6, the possibility of directly exciting and analysing these vibrational modes, not by optical methods, but rather with electron beams, in clear analogy with plasmonic modes in nanostructures. To summarise, this thesis explores the use of different theoretical models in Plasmonics, covering a wide gap between entirely classical macroscopic descriptions and quantum-mechanical atomic modelling, which we hope will contribute to a deeper understanding of optical phenomena at the nanoscale.La nanofotónica es una de las ciencias y tecnologías básicas en la actualidad: una profunda comprensión de la interacción entre la luz y la materia en la nanoescala, además de su innegable interés científico asociado, permite el control preciso de la luz, lo que resulta relevante en aplicaciones tecnológicas diversas como las telecomunicaciones, la energía y la medicina. La plasmónica –el estudio de las oscilaciones colectivas de los electrones de conducción en materiales– se ha convertido durante los últimos años en una de sus subramas más importantes: el gran confinamiento de la densidad de energía electromagnética y su alta sensibilidad al entorno hacen de los plasmones una herramienta clave para el control de la luz en la nanoescala. En esta tesis exploramos varios nuevos caminos que se abren a la nanofotónica en general, y a la plasmónica en particular, con la aparición en escena de materiales como el grafeno, que soportan excitaciones ópticas de longitudes de onda de menor tamaño, requiriendo por tanto estructuras cada vez más compactas. Este nuevo escenario reclama nuevos modelos teóricos que capturen la estructura de la materia a escala atómica. Una vez introducidos los conceptos fundamentales necesarios en el Capítulo 1, la tesis procede a explorar los procesos que siguen teniendo cabida en los modelos clásicos de respuesta óptica, como la focalización geométrica de plasmones. Concretamente, en el Capítulo 2 aplicamos esta idea a nanoestructuras de grafeno, planteando un diseño de lente capaz de enfocar plasmones y realzar la respuesta no lineal de tercer orden de este material. A continuación, nos adentramos en modelos más microscópicos de interacción luzmateria: la descripción de la respuesta óptica de una nanopartícula a partir de la respuesta individual de sus electrones nos permite explorar en el Capítulo 3 el decaimiento de los plasmones en distribuciones de electrones fuera del equilibrio, así como su posterior relajación, presentando así una imagen completa de la dinámica ultrarrápida de los plasmones y de los electrones dentro de estas nanopartículas De aquí en adelante, exploramos las oscilaciones colectivas en estructuras de dimensiones moleculares, las cuales exigen el uso de modelos microscópicos que incorporan la respuesta electrónica de múltiples cuerpos mediante la solución (numéricamente exigente) de las ecuaciones de Schrödinger, incluyendo la interacción con la luz incidente. En particular, en el Capítulo 4 aplicamos la teoría del funcional de la densidad dependiente del tiempo (TD-DFT por sus siglas en inglés) para modelar la respuesta óptica del ADN: una estructura que, además de ser ubicua en los organismos biológicos, se le atribuyen usos potenciales en nanotecnología. Finalmente, estudiamos las interacciones luz-materia asociadas con desplazamientos iónicos de estructuras, cuantizadas en forma de fonones. En el Capítulo 5 se estudia el acoplamiento entre estas excitaciones y los plasmones soportados por materiales 2D: las distorsiones introducidas en la estructura electrónica por las vibraciones iónicas permiten explicar experimentos recientes en los que el comportamiento de los plasmones se ve alterado por la presencia de modos vibracionales. También estudiamos, en el Capítulo 6, la posibilidad de excitar y analizar directamente estos modos vibracionales, no empleando métodos ópticos, sino mediante haces de electrones, en clara analogía con los modos plasmónicos en nanoestructuras. En resumen, esta tesis explora el uso de diferentes modelos teóricos en plasmónica, cubriendo el espacio entre las descripciones macroscópicas, totalmente clásicas, y el modelado atómico mecánico-cuántico, con el fin de contribuir a una comprensión más profunda de los fenómenos ópticos en la nanoescala.La nanofotònica és una de les ciències i tecnologies fonamentals avui en dia: el coneixement profund de la interacció entre la llum i la matèria en l’escala nanomètrica, a més del propi interès científic que té associat, permet el control precís de la llum, el qual la converteix en una tecnologia rellevant en aplicacions aparentment tan diferents com les telecomunicacions, l’energia i la medicina. Una de les seves subbranques més importants en els últims anys és la plasmònica, o l’estudi de les oscil·lacions col·lectives dels electrons de conducció en materials: el gran confinament de la densitat d’energia electromagnètica i la seva alta sensitivitat a l’entorn converteixen els plasmons en peces clau pel control de la llum en la nanoescala. En aquesta tesi, explorem les noves vies que se li obren a la nanofotònica en general, i a la plasmònica en particular, amb l’entrada en escena de materials com el grafè, que suporten excitacions òptiques de longituds d’ona menors, requerint per tant estructures cada vegada més compactes. Aquest nou escenari requereix de nous models teòrics que capturin l’estructura de la matèria a escala atòmica. Després d’introduir els conceptes fonamentals necessaris en el Capítol 1, la tesi comença explorant processos que encara accepten un tractament en termes de models clàssics de resposta òptica, com per exemple processos de focalització de plasmons. En concret, en el Capítol 2 apliquem aquests estudis a nanoestructures de grafè, i proposem un disseny de lent capaç de focalitzar plasmons i potenciar la resposta no lineal de tercer ordre en aquest material. A continuació, avancem cap a models més microscòpics d’interacció llum-matèria: la descripció de la resposta òptica d’una nanopartícula a partir de la resposta individual dels seus electrons ens permet explorar, en el Capítol 3, el decaïment dels plasmons en distribucions d’electrons fora de l’equilibri, així com la relaxació de tornada al seu estat d’equilibri, presentant així una imatge completa de la dinàmica ultraràpida dels plasmons i dels electrons en l’interior d’aquestes nanopartícules. D’ara en endavant, explorem les oscil·lacions col·lectives en estructures de mida molecular, que exigeixen l’ús de models microscòpics que incorporen la resposta electrònica de múltiples electrons mitjançant la solució (numèricament farragosa) de les equacions de Schrödinger, incloent la interacció amb la llum incident . En particular, en el Capítol 4 apliquem la teoria del funcional de la densitat depenent del temps (TDDFT per les seves sigles en anglès) per a modelar la resposta òptica de l’ADN: una estructura que, a més de ser ubiqua en els organismes biològics, se li atribueixen usos potencials en nanotecnologia. Finalment, aquesta tesi també estudia els efectes dels desplaçaments iònics de les estructures, quantitzats en forma de fonons. En el Capítol 5 s’estudia l’acoblament entre aquestes excitacions i els plasmons suportats per materials 2D: les distorsions introduïdes en l’estructura electrònica per les vibracions iòniques permeten explicar resultats experimentals recents en què el comportament dels plasmons es veu alterat per la presència de modes vibracionals. També vam estudiar, en el Capítol 6, la possibilitat d’excitar i analitzar directament aquests modes vibracionals, no mitjançant mètodes òptics, sinó emprant feixos d’electrons, en clara analogia amb els modes plasmònics en nanoestructures. En resum, aquesta tesi explora l’ús de diferents models teòrics en plasmònica, cobrint l’espai entre les descripcions macroscòpiques, totalment clàssiques, i el modelatge atòmic mecànic-quàntic, en l’objectiu de contribuir a una comprensió més profunda dels fenòmens òptics en la nanoescala

Classical and quantum aspects of the optical response at the nanoscale

Nanophotonics is one of today’s basic sciences and technologies: an in-depth understanding of the interaction between light and matter on the nano-scale, besides its intrinsic associated scientific interest, enables the precise control of light, that is relevant for technology in diverse applications such as telecommunications, energy and medicine. Plasmonics –the study of the collective oscillations of conduction electrons in materials with a metallic behaviour– has become one of its most essential sub-branches in recent years: the strong confinement of the electromagnetic energy density and its high sensitivity to the environment render plasmons as a key tool for the control of light at the nanoscale. In this thesis, we explore several new paths that open up to Nanophotonics in general, and Plasmonics in particular, with the appearance on stage of materials such as graphene, which host optical excitations of increasingly smaller wavelengths, therefore requiring increasingly more compact structures. This new scenario demands new theoretical models that capture the structure of matter on an atomic scale. After introducing the necessary fundamental concepts in Chapter 1, the thesis proceeds by exploring processes that can still be treated in terms of classical models for the optical response, such as geometrical plasmon focusing. Specifically, we apply this idea in Chapter 2 to graphene nanostructures, proposing a lens design capable of focusing plasmons and enhancing the third-order nonlinear response of this material. We then move to more microscopic models of light-matter interaction: the description of the optical response of a nanoparticle from the individual response of its electrons allows us to explore in Chapter 3 the plasmon decay into hot-electron distributions, as well as the subsequent relaxation of these electrons back to their equilibrium state, thus presenting a complete picture of ultrafast plasmon and hot electron dynamics in nanoparticles. From here on, we explore collective oscillations in molecular-sized structures, which demand the use of microscopic models incorporating many-body electronic response by massively demanding the numerical solution of Schrödinger’s equations including the interaction with incident light. In particular, in Chapter 4 we have applied timedependent density-functional theory (TD-DFT) to model the optical response of DNA that, besides being ubiquitous in biological organisms, we claim it to have some potential uses in nanotechnology. Finally, we study light-matter interactions associated with ionic displacements of structures, quantised as phonons. In Chapter 5, we study the coupling between these excitations and plasmons supported in 2D materials: the distortions introduced into the electronic structure by ionic vibrations allow us to explain recent experiments in which the presence of vibrational modes modifies the plasmonic dispersion. We also studied, in Chapter 6, the possibility of directly exciting and analysing these vibrational modes, not by optical methods, but rather with electron beams, in clear analogy with plasmonic modes in nanostructures. To summarise, this thesis explores the use of different theoretical models in Plasmonics, covering a wide gap between entirely classical macroscopic descriptions and quantum-mechanical atomic modelling, which we hope will contribute to a deeper understanding of optical phenomena at the nanoscale.La nanofotónica es una de las ciencias y tecnologías básicas en la actualidad: una profunda comprensión de la interacción entre la luz y la materia en la nanoescala, además de su innegable interés científico asociado, permite el control preciso de la luz, lo que resulta relevante en aplicaciones tecnológicas diversas como las telecomunicaciones, la energía y la medicina. La plasmónica –el estudio de las oscilaciones colectivas de los electrones de conducción en materiales– se ha convertido durante los últimos años en una de sus subramas más importantes: el gran confinamiento de la densidad de energía electromagnética y su alta sensibilidad al entorno hacen de los plasmones una herramienta clave para el control de la luz en la nanoescala. En esta tesis exploramos varios nuevos caminos que se abren a la nanofotónica en general, y a la plasmónica en particular, con la aparición en escena de materiales como el grafeno, que soportan excitaciones ópticas de longitudes de onda de menor tamaño, requiriendo por tanto estructuras cada vez más compactas. Este nuevo escenario reclama nuevos modelos teóricos que capturen la estructura de la materia a escala atómica. Una vez introducidos los conceptos fundamentales necesarios en el Capítulo 1, la tesis procede a explorar los procesos que siguen teniendo cabida en los modelos clásicos de respuesta óptica, como la focalización geométrica de plasmones. Concretamente, en el Capítulo 2 aplicamos esta idea a nanoestructuras de grafeno, planteando un diseño de lente capaz de enfocar plasmones y realzar la respuesta no lineal de tercer orden de este material. A continuación, nos adentramos en modelos más microscópicos de interacción luzmateria: la descripción de la respuesta óptica de una nanopartícula a partir de la respuesta individual de sus electrones nos permite explorar en el Capítulo 3 el decaimiento de los plasmones en distribuciones de electrones fuera del equilibrio, así como su posterior relajación, presentando así una imagen completa de la dinámica ultrarrápida de los plasmones y de los electrones dentro de estas nanopartículas De aquí en adelante, exploramos las oscilaciones colectivas en estructuras de dimensiones moleculares, las cuales exigen el uso de modelos microscópicos que incorporan la respuesta electrónica de múltiples cuerpos mediante la solución (numéricamente exigente) de las ecuaciones de Schrödinger, incluyendo la interacción con la luz incidente. En particular, en el Capítulo 4 aplicamos la teoría del funcional de la densidad dependiente del tiempo (TD-DFT por sus siglas en inglés) para modelar la respuesta óptica del ADN: una estructura que, además de ser ubicua en los organismos biológicos, se le atribuyen usos potenciales en nanotecnología. Finalmente, estudiamos las interacciones luz-materia asociadas con desplazamientos iónicos de estructuras, cuantizadas en forma de fonones. En el Capítulo 5 se estudia el acoplamiento entre estas excitaciones y los plasmones soportados por materiales 2D: las distorsiones introducidas en la estructura electrónica por las vibraciones iónicas permiten explicar experimentos recientes en los que el comportamiento de los plasmones se ve alterado por la presencia de modos vibracionales. También estudiamos, en el Capítulo 6, la posibilidad de excitar y analizar directamente estos modos vibracionales, no empleando métodos ópticos, sino mediante haces de electrones, en clara analogía con los modos plasmónicos en nanoestructuras. En resumen, esta tesis explora el uso de diferentes modelos teóricos en plasmónica, cubriendo el espacio entre las descripciones macroscópicas, totalmente clásicas, y el modelado atómico mecánico-cuántico, con el fin de contribuir a una comprensión más profunda de los fenómenos ópticos en la nanoescala.La nanofotònica és una de les ciències i tecnologies fonamentals avui en dia: el coneixement profund de la interacció entre la llum i la matèria en l’escala nanomètrica, a més del propi interès científic que té associat, permet el control precís de la llum, el qual la converteix en una tecnologia rellevant en aplicacions aparentment tan diferents com les telecomunicacions, l’energia i la medicina. Una de les seves subbranques més importants en els últims anys és la plasmònica, o l’estudi de les oscil·lacions col·lectives dels electrons de conducció en materials: el gran confinament de la densitat d’energia electromagnètica i la seva alta sensitivitat a l’entorn converteixen els plasmons en peces clau pel control de la llum en la nanoescala. En aquesta tesi, explorem les noves vies que se li obren a la nanofotònica en general, i a la plasmònica en particular, amb l’entrada en escena de materials com el grafè, que suporten excitacions òptiques de longituds d’ona menors, requerint per tant estructures cada vegada més compactes. Aquest nou escenari requereix de nous models teòrics que capturin l’estructura de la matèria a escala atòmica. Després d’introduir els conceptes fonamentals necessaris en el Capítol 1, la tesi comença explorant processos que encara accepten un tractament en termes de models clàssics de resposta òptica, com per exemple processos de focalització de plasmons. En concret, en el Capítol 2 apliquem aquests estudis a nanoestructures de grafè, i proposem un disseny de lent capaç de focalitzar plasmons i potenciar la resposta no lineal de tercer ordre en aquest material. A continuació, avancem cap a models més microscòpics d’interacció llum-matèria: la descripció de la resposta òptica d’una nanopartícula a partir de la resposta individual dels seus electrons ens permet explorar, en el Capítol 3, el decaïment dels plasmons en distribucions d’electrons fora de l’equilibri, així com la relaxació de tornada al seu estat d’equilibri, presentant així una imatge completa de la dinàmica ultraràpida dels plasmons i dels electrons en l’interior d’aquestes nanopartícules. D’ara en endavant, explorem les oscil·lacions col·lectives en estructures de mida molecular, que exigeixen l’ús de models microscòpics que incorporen la resposta electrònica de múltiples electrons mitjançant la solució (numèricament farragosa) de les equacions de Schrödinger, incloent la interacció amb la llum incident . En particular, en el Capítol 4 apliquem la teoria del funcional de la densitat depenent del temps (TDDFT per les seves sigles en anglès) per a modelar la resposta òptica de l’ADN: una estructura que, a més de ser ubiqua en els organismes biològics, se li atribueixen usos potencials en nanotecnologia. Finalment, aquesta tesi també estudia els efectes dels desplaçaments iònics de les estructures, quantitzats en forma de fonons. En el Capítol 5 s’estudia l’acoblament entre aquestes excitacions i els plasmons suportats per materials 2D: les distorsions introduïdes en l’estructura electrònica per les vibracions iòniques permeten explicar resultats experimentals recents en què el comportament dels plasmons es veu alterat per la presència de modes vibracionals. També vam estudiar, en el Capítol 6, la possibilitat d’excitar i analitzar directament aquests modes vibracionals, no mitjançant mètodes òptics, sinó emprant feixos d’electrons, en clara analogia amb els modes plasmònics en nanoestructures. En resum, aquesta tesi explora l’ús de diferents models teòrics en plasmònica, cobrint l’espai entre les descripcions macroscòpiques, totalment clàssiques, i el modelatge atòmic mecànic-quàntic, en l’objectiu de contribuir a una comprensió més profunda dels fenòmens òptics en la nanoescala.Postprint (published version

Solar Seismology from Space. a Conference at Snowmass, Colorado

The quality of the ground based observing environment suffers from several degrading factors: diurnal interruptions and thermal variations, atmospheric seeing and transparency fluctuations and adverse weather interruptions are among the chief difficulties. The limited fraction of the solar surface observable from only one vantage point is also a potential limitation to the quality of the data available without going to space. Primary conference goals were to discuss in depth the scientific return from current observations and analyses of solar oscillations, to discuss the instrumental and site requirements for realizing the full potential of the seismic analysis method, and to help bring new workers into the field by collecting and summarizing the key background theory. At the conclusion of the conference there was a clear consensus that ground based observation would not be able to provide data of the quality required to permit a substantial analysis of the solar convection zone dynamics or to permit a full deduction of the solar interior structure

Investigation and Optimization of Extraordinary Electroconductance (EEC) Sensors & The Role of Magnetic Disorder in the Formation of Spin Glasses

PART I: Investigation and Optimization of Extraordinary Electroconductance (EEC) Sensors This thesis presents an investigation and geometric optimization of Extraordinary Electroconductance (EEC) sensors, a member of an established class of sensors that exhibit `extraordinary\u27 phenomenon driven by interfaces that maximize current redistribution under an applied perturbation. EEC sensors are responsive to both applied electrical fields and optical illumination and show promising application in the detection of complex biological signals that can aid in conclusive diagnoses. The EEC device response to nonuniform illumination establishes greater versatility for EEC devices by allowing for position-dependent light sensing while under local illumination. Additionally, an enhanced light responsivity of EEC sensors via modification of shunt geometry, as well as a bifurcation in sensor response to direct reverse bias and light irradiance based on measurement lead location was observed. Significantly increased light responsivity was achieved by simultaneously biasing the EEC device while exposing to light, resulting in an over 614% increase in resistance from 11mW/cm2 irradiance of HeNe laser light and maximum a specific detectivity of D* = 3.67x1011 cmHz1/2/W. PART II: The Role of Magnetic Disorder in the Formation of Spin Glasses This thesis presents data on the magnetic properties of two classes of layered spin S=1/2 antiferromagnetic quasi-triangular lattice materials: Cu2(1-x)Zn2x(OH)3NO3 (0≤x≤0.65) and its long organic chain intercalated derivatives Cu2(1-x)Zn2x(OH)3C7H15COO.mH2O (0≤x≤0.29), where non-magnetic Zn substitutes for Cu isostructurally. It is found that the intercalated compounds, even in a clean system in the absence of dilution, x=0, show spin-glass behavior, as evidenced by DC and AC susceptibility measurements, and by time dependent magnetization measurements. A striking feature is the observation of a sharp crossover between two successive power law regimes in the DC susceptibility above the freezing temperature. In contrast to standard theoretical expectations, these power laws are insensitive to doping. Specific heat data are consistent with a conventional phase transition in the unintercalated compounds, and glassy behavior in the intercalated compounds. The emergence of a cluster spin glass under no imposed magnetic disorder suggests that the historical assumption that magnetic disorder is required to form a spin glass may be wrong. Research into additional examples of non-diluted spin glasses should lend phenomenological insight into the factors driving the frustrated magnetic system into a spin glass phase

Experimental Investigations of Carbon and Titanium Molecular Species in Laser Ablation Plumes

A new multi-parameter apparatus has been developed for this dissertation in order to study laser ablation. The purpose of this apparatus is to better understand the evolution and energy partitioning of an ablation plume from the warm dense plasma stage to the cool neutral gas stage. The Laser Ablation Plume Experiment (LAPeX) apparatus was designed and built to include a large number of optical and spectroscopic diagnostics, various background environment configurations, and adjustable laser intensity. This new experimental platform required the design, assembly, alignment, calibration, and testing of the various components involved. Extensive metrology and characterization of the diagnostic elements of the apparatus were undertaken to ensure the quality of the data. Diatomic carbon was investigated using absorption spectroscopy. Graphite was ablated into a 100 Torr nitrogen atmosphere with a 1,024 nm pulsed Nd:YAG laser. A quasi-CW supercontinuum laser was used to generate the absorption probe beam. High resolution spectroscopic data of the Swan bands for Δv = 0 and Δv = 1 was collected and compared to simulations. A data reduction method was developed to extract an absorption spectrum from the data. Simulations indicated that the plume was not in thermodynamic equilibrium. TiO was produced by ablating titanium into a 100 Torr oxygen atmosphere. TiO absorption is observed in material ejected from the yellow hypergiant ρ Cassiopeiae. Fast imaging of the plume, with a band-pass filter to allow only TiO γ band emission, showed emission at t ≥ 5 μs after target irradiation. Spectroscopic analysis of emission from neutral titanium at 5 μs indicated a temperature of ∼1,000 K. The strongest TiO emission was observed 1-3 mm behind the shock wave with fast imaging and spectroscopy

Project Tech Top study of lunar, planetary and solar topography Final report

Data acquisition techniques for information on lunar, planetary, and solar topograph

Photon-induced near-field electron microscopy (PINEM): theoretical and experimental

Electron imaging in space and time is achieved in microscopy with timed (near relativistic) electron packets of picometer wavelength coincident with light pulses of femtosecond duration. The photons (with an energy of a few electronvolts) are used to impulsively heat or excite the specimen so that the evolution of structures from their nonequilibrium state can be followed in real time. As such, and at relatively low fluences, there is no interaction between the electrons and the photons; certainly that is the case in vacuum because energy–momentum conservation is not possible. In the presence of nanostructures and at higher fluences, energy–momentum conservation is possible and the electron packet can either gain or lose light quanta. Recently, it was reported that, when only electrons with gained energy are filtered, near-field imaging enables the visualization of nanoscale particles and interfaces with enhanced contrast (Barwick et al 2009 Nature 462 902). To explore a variety of applications, it is important to express, through analytical formulation, the key parameters involved in this photon-induced near-field electron microscopy (PINEM) and to predict the associated phenomena of, e.g., forty-photon absorption by the electron packet. In this paper, we give an account of the theoretical and experimental results of PINEM. In particular, the time-dependent quantum solution for ultrafast electron packets in the nanostructure scattered electromagnetic (near) field is solved in the high kinetic energy limit to obtain the evolution of the incident electron packet into a superposition of discrete momentum wavelets. The characteristic length and time scales of the halo of electron–photon coupling are discussed in the framework of Rayleigh and Mie scatterings, providing the dependence of the PINEM effect on size, polarization, material and spatiotemporal localization. We also provide a simple classical description that is based on features of plasmonics. A major part of this paper is devoted to the comparisons between the theoretical results and the recently obtained experimental findings about the imaging of materials and biological systems