Le problème de l'interaction de N atomes avec un faisceau laser et les modes du vide peut donner lieu à de nombreux phénomènes intéressants concernant l’émission spontanée de la lumière et sa propagation dans l’échantillon. Les effets coopératifs, par exemple, tels que la super- et la sous-radiance, sont des effets liés à la cohérence créée entre les atomes lorsqu'un photon est émis spontanément par un seul atome excité. La super-radiance peut être définie comme le renforcement de l'émission spontanée due à une interférence constructive de la lumière diffusée. Son homologue, la sous-radiance, est le piégeage d'une partie de la lumière restante en raison d'interférences destructives. Dans les atomes froids, certains travaux théoriques antérieurs prédisent et caractérisent ces deux effets coopératifs dans un nuage atomique large et diluée, dans le régime des faibles intensités et à grands désaccords du laser incident. Le modèle théorique est un modèle de dipôles couplés pour atomes à deux niveaux pilotés par un champ de faible intensité et dans l'approche scalaire. L'expérience consiste à mesurer les taux de d’décroissance super- et sous-radiants à partir de l’intensité temporelle émise après la coupure du laser incident en régime stationnaire. Notre schéma expérimental consiste en un piège magneto-optique d’atomes de rubidium 87 à grandes épaisseurs optiques à résonance. Un faisceau sonde excite les atomes proches de la raie D2. L’intensité émise est détectée par un détecteur de photons uniques dépourvu d’afterpulsing et une procédure d’étalonnage nous permet de déterminer l’épaisseur optique résonante du nuage et sa température. Dans ce travail, nous rapportons l’observation expérimentale de la super- et sous-radiance dans un grand nuage d’atomes froids. Pour la sous-radiance, le résultat principal est l’évolution linéaire du temps caractéristique avec l’épaisseur optique résonante du nuage et son indépendance du désaccord. Pour la super-radiance, on observe la super-radiance en dehors de la direction vers l’avant. Nous vérifions la validité de nos interprétations avec les prédictions du modèle de dipôles couplés. Finalement, nous discutons l’interaction entre la sous-radiance et le piégeage de radiation, ainsi que des prévisions théoriques concernant : la configuration d’un nuage phasé, pour contrôler l’émission de l’amplitude sousradiante ; et les effets de température, où la sous-radiance s’avère robuste dans une large gamme de températures. / The problem of the interaction of N atoms with a laser beam and vacuum modes can give rise to many interesting phenomena concerning the spontaneous emission of light and its propagation in the medium. The cooperative effects, for example, such as superadiance and subradiance, are effects related to the coherence created between the atoms when a photon is emitted spontaneously by a single excited atom. Superradiance can be defined as the enhancement of the spontaneous emission due to constructive interference of the scattered light. Its counterpart, subradiance, is the trapping of some remaining light due to destructive interference. In cold atoms, some previous theoretical works predict and characterize these two cooperative effects in a large and diluted atomic cloud, in the regime of low intensities and large detunings of the incident laser. The theoretical model is a coupled-dipole model for two-level atoms driven by a low-intensity field and in the scalar approach. The experiment consists in measuring the super- and subradiant decay rates from the temporal emitted intensity after the switch off of the incident laser in the steady state. Our experimental setup consists in a magneto-optical trap of rubidium 87 atoms at large resonant optical thicknesses. A probe beam excites the atoms close to the D2 line. The intensity emitted is detected by a single photon detector with no afterpulsing and a calibration procedure allows us to determine the resonant optical thickness of the cloud and its temperature. In this work, we report the experimental observation of super- and subradiance in a large cloud of cold atoms. For subradiance, the main result is the linear evolution of the characteristic time with the resonant optical thickness of the cloud and its independence of the detuning. For superradiance, we observe superradiance out of the forward direction. We verify the validity of our interpretations with the predictions of the coupled-dipole model. Finally, we discuss the interplay of subradiance and radiation trapping, as well as theoretical predictions for: a setup of a phased cloud, to control the subradiant amplitude emission; and temperature effects, where subradiance is shown to be robust in a large range of temperatures.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

The object of this work is to create software implementing two algorithms for global ilumination computing. Iradiance and radiance caching should be implemented in CUDA framework on graphics card (GPU). Parallel implementation on GPU should dramatically improve algoritm speed compared to CPU implementation. The software will be written using already done framework for global illumunation computation. That allow to focus to algorithm implementation only. This work should speed up testing of new or existing methods for global illumination computing, because saving and reusing of intermediate results can be used for other algorithms too. Powered by TCPDF (www.tcpdf.org)

The objective of this work is to create software implementing two algorithms for global ilumination computation. Iradiance and radiance caching should be implemented in CUDA framework on a graphics card (GPU). Parallel implementation on the GPU should improve algoritm speed compared to CPU implementation. The software will be written using an already done framework for global illumunation computation. That allows to focus on algorithm implementation only. This work should speed up testing of new or existing methods for global illumination computing, because saving and reusing of intermediate results can be used for other algorithms too. Powered by TCPDF (www.tcpdf.org)

<p>Denna rapport presenterar ett alternativt sätt att ljussätta terräng i datorgrafik. Tidigare modeller har vanligtvis byggt på lokal ljussättning, som inte tar hänsyn till kringliggande geometri, och har med en extra process approximerat effekten av ljusinteraktionen. Genom att använda sig av en teknik som kallas precomputed radiance transfer (PRT) kan man förberäkna hur en punkt interagerar med ljus för olika inkommande riktningar och undviker därmed att göra detta under programkörningen. Det är viktigt att denna teknik även fungerar tillsammans med level-of-detail (LOD) terrängrenderingsalgoritmer eftersom rendering av alla trianglar i terrängen för varje skärmuppdatering inte är optimalt för dagens grafikkort. Man vill därför representera den underliggande terrängen med fler trianglar närmare betraktaren och färre längre bort. Motiveringen till detta är att trianglar längre ifrån betraktaren kommer resultera i färre pixlar på skärmen, så att rendera större trianglar gör en liten visuell skillnad. Arbetet visar på att tekniken fungerar med LOD-terrängrenderingsalgoritmer med bra prestanda och visuell kvalitet.</p>

In 2009, NASA's LCROSS mission impacted Cabeus Crater near the Lunar South Pole with the spent Centaur upper stage rocket. The impact was observed by the trailing sheperding spacecraft (S-S/C) that impacted the moon 250 seconds after the Centaur impact. The main objective of the LCROSS mission was to verify the existence of water ice in the lunar regolith---the subsequent analysis of the data confirmed water ice present in the crater. The analysis of the S-S/C instrument data suggested that the plume consisted of two components: a central "spike" component and a thin, outward "cone" component. A model has been developed at The University of Texas at Austin improve the analysis of the data obtained by the S-S/C. This model is created with a free-molecular ballistic grain code that involves simulating individual regolith grains in the debris plume through grain-heating and grain-movement models and then modeling the spectral radiance properties of the grains as observed by the S-S/C. Mie scattering theory is used to model scattering and absorption of incoming solar radiation by the particles in the plume assuming they are perfect spheres. The UT LCROSS code was utilized in a parametric study that evaluated the effect of variations in assumed model plume parameters on the modeling of S-S/C UV-VIS instrument observations. The plume parameters were chosen based on the assumption that the dust plume was split into two components: a central spike and a surrounding high angle cone. The following parameters were varied: the spike and cone angles, the spike and cone grain radius distributions, and the spike mass fraction. The following parameters could be varied but were given fixed values: ice fraction between plume components, ice grain purity, albedo, and ice fraction in plume. The impact of these plume parameters upon plume brightness and blue/red color ratio was determined. Two grain models were used. In the initial grain species model all grains have a soil core surrounded by a thin ice shell. In the second, two species model two grain types were utilized: a pure ice grain component and a pure soil grain component. / text

Šiame darbe nagrinėjami radiaciniai defektai bei jų tarpusavio reakcijos silicyje. Atlikti eksperimentai, kurių metu pasitelkus minkštąją Rentgeno spinduliuotę buvo generuojami defektai. Vėliau bandiniai buvo tiriami FT-IR spektroskopijos metodais. Darbo apimtis 52 puslapiai. Darbas susideda iš 5 dalių. Pirmoje dalyje apžvelgiami Rentgeno spinduliuotės šaltiniai ir spinduliuotės savybės. Antroje - dalyje radiaciniai defektai silicyje. Trečioje - defektų tyrimo metodai. Ketvirtoje - dalyje defektų reakcijos. Penktoje - eksperimento metodika ir eksperimento rezultatai. / In this work, we are researching radiation defects and their reactions in silicon. During experiments defects were generated using soft Rentgen radiance. Later samples were researched using FT-IR methods of spectroscopy. Work amount is 52 pages. Work consists from 5 parts. First part - overview of sources and features of Rentgen radiance. Second part – radiation defects in silicon. Third part – methods of defect researching. Fourth part – reactions of defects. Fifth part – Methods and results of experiment.

The radiance distribution provides complete information regarding the geometrical structure of the ambient light field within the ocean. A quantitative study of the radiance field in the dynamic ocean water is presented in this thesis work. The study starts with the development of a novel radiance camera for the measurement of the full spherical radiance distribution at the ocean surface and depth. Nonlinear response functions are designed and advanced radiometric calibrations are developed. The resulting camera measures the radiance distribution in absolute units over an extremely high dynamic range at fast rates. With the newly obtained radiance data, I have examined the fine structure of both the downwelling and upwelling radiance distribution and its variation with depth in optically diverse water types. The fully specified radiance distribution data are used to derive all apparent optical properties and some inherent optical properties including the absorption coefficient. With the camera fixed at shallow depths, I have observed and determined the sea surface wave disturbance of the radiance distribution. It is found that the radiance fluctuates anisotropically with regard to its amplitude and periodicity. Typical spatial structures of the dynamic radiance field are identified and shown relevant to the surface waves and the solar zenith angles. The variability in the radiance field also propagates to the irradiance field; the variability is pronounced in measured irradiance depth profiles in the upper layers of the ocean. The statistics of the irradiance fluctuations along the water depth, including the dominant frequency and coefficient of variation, are derived using wavelet techniques and fitted to novel analytic models. The results from the irradiance depth-profile decomposition are in agreement with theoretical models and other independent measurements. This thesis work represents the first attempt to quantify the full light field and its variability in dynamic ocean waters and is of significant relevance to many other optics-related applications.

Des nouvelles courbes de polarisation et de radiances en fonction de l'angle de diffusion sont étudiées à _ = 632,8 nm et 543,5 nm en utilisant des instruments PROGRA2 (Propriétés Optiques des GRains Astronomiques et Atmosphériques) pour différents types d'échantillons de suie et de noir de carbone en lévitation dans l'air et déposés sur une surface. Les échantillons de suie sont produits dans des conditions de combustion différentes, affectant ainsi leurs propriétés morphologiques. Un générateur de suie a été également utilisé pour étudier des suies 'jeunes' émises par la combustion du propane. Une comparaison des propriétés optiques entre les suies en lévitation et déposées sur une surface a été discutée. Enfin, ces courbes sont comparées à celles produites par différents types de sable. Les amplitudes de polarisation produites par la suie diffèrent en fonction du diamètre des particules primaires et de la distribution en taille. Ces courbes seules sont donc insuffisantes pour estimer la nature des agglomérats solides qui pourraient être détectés par des mesures à distance dans la stratosphère. D'autre part les courbes de radiance produites par ces échantillons montrent un comportement différent de celles produites par les échantillons de sable et par la poussière interplanétaire. Il est donc important lors de l'interprétation des mesures stratosphériques de combiner les courbes de radiances avec les courbes de polarisation pour déterminer la nature des agglomérats et de fournir des informations sur la nature de suie détectée telle que la taille des particules primaires ainsi que la distribution en taille.

This PhD thesis evaluated the applicability of Climate-Based Daylight Modelling (CBDM) as it is presently done. The objectives stated in this thesis aimed at broadly assessing applicability by looking at multiple aspects: (i) the way CBDM is used by expert researchers and practitioners; (ii) how state-of-the-art simulation techniques compare to each other and how they are affected by uncertainty in input factors; (iii) how the simulated results compare with data measured in real occupied spaces. The answers obtained from a web-based questionnaire portrayed a variety of workflows used by different people to perform similar, if not the same, evaluations. At the same time, the inter-model comparison performed to compare the existing simulation techniques revealed significant differences in the way the sky and the sun are recreated by each technique. The results also demonstrated that some of the annual daylight metrics commonly required in building guidelines are sensitive to the choice of simulation tool, as well as other input parameters, such as climate data, orientation and material optical properties. All the analyses were carried out on four case study spaces, remodelled from existing classrooms that were the subject of a concurrent research study that monitored their interior luminous conditions. A large database of High Dynamic Range images was collected for that study, and the luminance data derived from these images could be used in this work to explore a new methodology to calibrate climate-based daylight models. The results collected and presented in this dissertation illustrate how, at the time of writing, there is not a single established common framework to follow when performing CBDM evaluations. Several different techniques coexist but each of them is characterised by a specific domain of applicability.