This project investigates a laser radar system. The system is based on the principles of time-correlated single photon counting, and by measuring the times-of-flight of reflected photons it can find range profiles and perform three-dimensional imaging of scenes. Because of the photon counting technique the resolution and precision that the system can achieve is very high compared to analog systems. These properties make the system interesting for many military applications. For example, the system can be used to interrogate non-cooperative targets at a safe distance in order to gather intelligence. However, signal processing is needed in order to extract the information from the data acquired by the system. This project focuses on the analysis of different signal processing methods. The Wiener filter and the Richardson-Lucy algorithm are used to deconvolve the data acquired by the photon counting system. In order to find the positions of potential targets different approaches of non-linear least squares methods are tested, as well as a more unconventional method called ESPRIT. The methods are evaluated based on their ability to resolve two targets separated by some known distance and the accuracy with which they calculate the position of a single target, as well as their robustness to noise and their computational burden. Results show that fitting a curve made of a linear combination of asymmetric super-Gaussians to the data by a method of non-linear least squares manages to accurately resolve targets separated by 1.75 cm, which is the best result of all the methods tested. The accuracy for finding the position of a single target is similar between the methods but ESPRIT has a much faster computation time.

Les propulseurs électriques sont de plus en plus utilisés pour des missions de correction de trajectoire des satellites et pourront dans un avenir proche être utilisés pour le transfert d’orbite. Ces propulseurs constituent une excellente alternative aux propulseurs chimiques grâce à leur rendement élevé et une substantielle économie de carburant réalisée par rapport aux propulseurs chimiques. Les propulseurs à effet Hall créent la poussée par l’accélération d’ions positifs de xénon ou de krypton dans un plasma confiné par un champ magnétique. L’objet de ce manuscrit concerne principalement les caractéristiques de l’accélération des ions et des atomes dans un propulseur à effet Hall. Les influences de la largeur du canal de décharge, de la topologie magnétique et de la cathode sur l’efficacité d’accélération des ions sont étudiées. Des pistes d’optimisation de l’architecture du propulseur sont alors proposées qui pourraient être particulièrement avantageuses sur les propulseurs de petite taille, comme l’élargissement du canal et l’augmentation du champ magnétique près des parois du canal. L’influence de la position et du potentiel de la cathode sur la déviation du faisceau ionique est révélée. L’évolution temporelle basse fréquence du champ électrique est mesurée par comptage synchrone de photons et suggère que la température atomique joue un rôle important dans les oscillations basse fréquence de la décharge. Par ailleurs, l’influence du champ magnétique sur les performances d’un propulseur proche des modèles de vol a été mesurée grâce à l’utilisation d’un moteur doté d’une topologie magnétique flexible. Ceci a montré la difficulté de définir un paramètre numérique capable de synthétiser l’information complexe de la répartition spatiale du champ magnétique dans le canal de décharge. Les très faibles modifications des performances par le champ magnétique soulignent l’importance de la précision dans la mesure. / Electric propulsion systems are more and more often used for trajectory correction of satellites and may soon be used for orbit transfer. These devices represent a great alternative to classic chemical propulsion devices thanks to their high efficiency and propellant mass savings. Hall effect thruster provide thrust by the acceleration of xenon or krypton ions in a magnetized confined plasma. The study presented in this manuscript mainly addresses characteristics of ion and atom acceleration in a Hall effect thruster. Influence of channel width, magnetic topology and cathode parameters on ion acceleration efficiency is investigated. Ways to optimize thruster architecture are suggested that may be particularly relevant for low power thrusters, such as widening thruster channel and increasing magnetic field amplitude near channel walls. Influence of cathode position with respect to the thruster channel exit plane and its potential with respect to ground on ion beam deviation has been revealed with two thrusters. Low frequency time evolution of the accelerating electric field was measured using lock-in photon counting system. Results strongly suggest that the atom temperature plays a crucial role in low frequency time evolution of the whole plasma discharge. Measurement of performances as a function of the magnetic field demonstrated that numeric parameters are compulsory to carry on a relevant parametric study. These parameters would summarize the 2D information of magnetic topology. Weak influence of magnetic topology revealed that thrust measurement precision needs to be increased by at least one order of magnitude if one wants to reach a better understanding of plasma confinement in a Hall effect thruster.

No description available.

[pt] Dois dispositivos de contagem de fótons únicos, sensíveis a comprimentos de onda no infravermelho próximo e médio, são propostos e experimentalmente investigados. Ambos utilizam uma técnica de dois estágios, composta de uma etapa inicial de conversão de freqüências em um cristal não-linear seguida de detecção por um fotodiodo avalanche de silício. Enquanto o primeiro projeto é voltado à detecção de fótons únicos a 1.55 μm para comunicações quânticas via fibra óptica, usando um processo intra-cavidade, o segundo projeto prevê o desenvolvimento de um contador de fótons operando a 4.65 μm para sistemas de espaço livre. Neste caso, um estudo de viabilidade para um sistema prático de criptografia quântica operando em um comprimento de onda no infravermelho médio é realizado. Os resultados mostram que, usando a tecnologia disponível na atualidade, tal sistema pode ser construído, embora sua utilidade se mostre restrita a enlaces possuindo certas condições meteorológicas específicas. / [en] Two single photon counting devices, operating at near- and mid-infrared wavelengths, are introduced and experimentally investigated. Both use a twostage technique, comprised of an initial frequency up-conversion procedure inside a nonlinear crystal followed by a silicon avalanche photodiode. Whereas the first project consists on detection of single photons at 1.55 ìm for fiber-optic-based quantum communications, using a cavity-enhanced procedure, the second project envisions the development of a single-photon counter operating at 4.65 ìm for free-space systems. In this case, a feasibility study for a practical quantum key distribution system operating in a mid-infrared wavelength is performed. The results show that, using present-day technology, such a system can be constructed, albeit its usefulness would be restricted to operation under very specific weather conditions.

No description available.

During the past years photon-counting detectors (PCDs) have emerged as an alternative to conventional energy-integrating detectors and may significantly improve the standard of care for computed tomography (CT). There are two main alternatives for the material of the detector: cadmium telluride (CdTe) and silicon (Si). The settings of the X-ray tube and the applied filters need to be evaluated and optimized for the new detector technology. In this report, Monte Carlo simulations are used to determine how image quality is affected by different X-ray tube voltages and filter thicknesses. The image quality indicators that were chosen to evaluate are detective quantum efficiency (DQE) for material quantification and both DQE and dose-normalized signal-difference-to-noise ratio (SDNR) for detection tasks. Overall, silicon-based detectors performed better than cadmium-based detectors for quantification imaging tasks for all object thicknesses, while cadmium-based detectors were superior for detection imaging tasks in larger patients. For both silicon- and cadmium-based detectors, the dose-normalized image quality was largely independent of filter thickness, while the X-ray tube voltage had a more distinct impact on the result, where low voltages were optimal. / Under de senaste åren har fotonräknande detektorer blivit aktuellt som ett alternativ till konventionella energiintegrerande detektorer och kommer troligen förbättra datortomografibilder avsevärt. För de nya detektorerna finns det två huvudsakliga materialalternativ: kadmiumtellurid (CdTe) och kisel (Si). Inställningarna för röntgenröret och det pålagda filtret behöver utvärderas och optimeras för den nya detektorteknologin. I denna rapport användes Monte Carlo-simuleringar för att bestämma hur bildkvaliteten påverkades av rörspänningen och filtertjockleken. Bildkvaliteten bestämdes sedan utifrån tre indikatorer, detective quantum efficiency (DQE) för materialbestämning samt både DQE och dosnormaliserad signal-difference-to-noise ratio (SDNR) för detektionsuppgifter.    Den kiselbaserade detektorn presterade bättre än den kadmiumbaserade för materialbestämning för alla patientstorlekar medan den kadmiumbaserade presterade bättre på detektionsuppgifterna för större patienter. Vidare var den dosnormaliserade bildkvaliteten för både kisel- och kadmiumdetektorer svagt beroende av filtertjocklek medan båda påverkades starkt av rörspänningen, där låga spänningar var att föredra.

No description available.

Time-Resolved diffuse optics is a powerful and safe technique to quantify the optical properties (OP) for highly scattering media such as biological tissues. The OP values are correlated with the compositions of the measured objects, especially for the tissue chromophores such as hemoglobin. The OP are mainly the absorption and the reduced scattering coefficients that can be quantified for highly scattering media using Time-Resolved Diffuse Optical Spectroscopy (TR-DOS) systems. The OP can be retrieved using Time-Resolved Diffuse Optical Imaging (TR-DOI) systems to reconstruct the distribution of the OP in measured media. Therefore, TR-DOS and TR-DOI can be used for functional monitoring of brain and muscles, and to diagnose some diseases such as detection and localization for breast cancer and blood clot. In general, TR-DOI systems are non-invasive, reliable, and have a high temporal resolution. TR-DOI systems have been known for their complexity, bulkiness, and costly equipment such as light sources (picosecond pulsed laser) and detectors (single photon counters). Also, TR-DOI systems acquire a large amount of data and suffer from the computational cost of the image reconstruction process. These limitations hinder the usage of TR-DOI for widespread potential applications such as clinical measurements. The goals of this research project are to investigate approaches to eliminate two main limitations of TR-DOI systems. First, building TR-DOS systems using custom-designed free-running (FR) and time-gated (TG) SPAD detectors that are fabricated in low-cost standard CMOS technology instead of the costly photon counting and timing detectors. The FR-TR-DOS prototype has demonstrated comparable performance (for homogeneous objects measurements) with the reported TR-DOS prototypes that use commercial and expensive detectors. The TG-TR-DOS prototype has acquired raw data with a low level of noise and high dynamic range that enable this prototype to measure multilayered objects such as human heads. Second, building and evaluating TR-DOI prototype that uses a computationally efficient algorithm to reconstruct high quality 3D tomographic images by analyzing a small part of the acquired data. This work indicates the possibility to exploit the recent advances in the technologies of silicon detectors, and computation to build low-cost, compact, portable TR-DOI systems. These systems can expand the applications of TR-DOI and TR-DOS into several fields such as oncology, and neurology. / Thesis / Doctor of Philosophy (PhD)

Un nouveau contrôleur de EMCCD (Electron multiplying Charge Coupled Device) est présenté. Il permet de diminuer significativement le bruit qui domine lorsque la puce EMCCD est utilisé pour du comptage de photons: le bruit d'injection de charge. À l'aide de ce contrôleur, une caméra EMCCD scientifique a été construite, caractérisée en laboratoire et testée à l'observatoire du mont Mégantic. Cette nouvelle caméra permet, entre autres, de réaliser des observations de la cinématique des galaxies par spectroscopie de champ intégral par interférométrie de Fabry-Perot en lumière Ha beaucoup plus rapidement, ou de galaxies de plus faible luminosité, que les caméras à comptage de photon basées sur des tubes amplificateurs. Le temps d'intégration nécessaire à l'obtention d'un rapport signal sur bruit donné est environ 4 fois moindre qu'avec les anciennes caméras. Les applications d'un tel appareil d'imagerie sont nombreuses: photométrie rapide et faible flux, spectroscopie à haute résolution spectrale et temporelle, imagerie limitée par la diffraction à partir de télescopes terrestres (lucky imaging), etc. D'un point de vue technique, la caméra est dominée par le bruit de Poisson pour les flux lumineux supérieurs à 0.002 photon/pixel/image. D'un autre côté, la raie d'hydrogène neutre (HI) à 21 cm a souvent été utilisée pour étudier la cinématique des galaxies. L'hydrogène neutre a l'avantage de se retrouver en quantité détectable au-delà du disque optique des galaxies. Cependant, la résolution spatiale de ces observations est moindre que leurs équivalents réalisés en lumière visible. Lors de la comparaison des données HI, avec des données à plus haute résolution, certaines différences étaient simplement attribuées à la faible résolution des observations HI. Le projet THINGS (The HI Nearby Galaxy Survey a observé plusieurs galaxies de l'échantillon SINGS (Spitzer Infrared Nearby Galaxies Survey). Les données cinématiques du projet THIGNS seront comparées aux données cinématiques obtenues en lumière Ha, afin de déterminer si la seule différence de résolution spatiale peut expliquer les différences observées. Les résultats montrent que des différences intrinsèques aux traceurs utilisées (hydrogène neutre ou ionisé), sont responsables de dissemblances importantes. La compréhension de ces particularités est importante: la distribution de la matière sombre, dérivée de la rotation des galaxies, est un test de certains modèles cosmologiques. / A new EMCCD (Electron multiplying Charge Coupled Device) controller is presented. It allows the EMCCD to be used for photon counting by drastically taking down its dominating source of noise : the clock induced charges. A new EMCCD camera was built using this controller. It has been characterized in laboratory and tested at the observatoire du mont Mégantic. When compared to the previous generation of photon counting cameras based on intensifier tubes, this new camera renders the observation of the galaxies kinematics with an integral field spectrometer with a Fabry-Perot interferometer in Ha light much faster, and allows fainter galaxies to be observed. The integration time required to reach a given signal-to-noise ratio is about 4 times less than with the intensifier tubes. Many applications could benefit of such a camera: fast, faint flux photometry, high spectral and temporal resolution spectroscopy, earth-based diffraction limited imagery (lucky imaging), etc. Technically, the camera is dominated by the shot noise for flux higher than 0.002 photon/pixel/image. The 21 cm emission line of the neutral hydrogen (HI) is often used to map the galaxies kinematics. The extent of the distribution of the neutral hydrogen in galaxies, which goes well beyond the optical disk, is one of the reasons this line is used so often. However, the spatial resolution of such observations is limited when compared to their optical equivalents. When comparing the HI data to higher resolution ones, some differences were simply attributed to the beam smearing of the HI caused by its lower resolution. The THINGS (The HI Nearby Galaxy Survey) project observed many galaxies of the SINGS (Spitzer Infrared Nearby Galaxies Survey) project. The kinematics of THINGS will be compared to the kinematic data of the galaxies obtained in Ha light. The comparison will try to determine whether the sole beam smearing is responsible of the differences observed. The results shows that intrinsic dissimilarities between the kinematical tracers used are responsible of some of the observed disagreements. The understanding of theses differences is of a high importance as the dark matter distribution, inferred from the rotation of the galaxies, is a test to some cosmological models.

The goal of this project is to study novel nanoscale excitation volumes, sensitive enoughto study individual chromophores and go on to study new and exciting self assemblyapproaches to this problem. Small excitation volumes may be engineered using light con-finement inside apertures in metal films. These apertures enhance fluorescence emissionrates, quantum yields, decrease fluorescence quenching, enable higher signal-to-noiseratios and allow higher concentration single chromophore fluorescence, to be studied byrestricting this excitation volume. Excitation volumes are reported on using the chro-mophore's fluorescence by utilising fluorescence correlation spectroscopy, which monitorsfluctuations in fluorescence intensity. From the correlation in time, we can find the res-idence time, the number of chromophores, the volume in which they are diffusing andtherefore the fluorescence emission efficiency. Fluorescence properties are a probe ofthe local environment, a particularly powerful tool due to the high brightness (quantumyield) fluorescent dyes and sensitive photo-detection equipment both of which are readilyavailable, (such as avalanche photodiodes and photomultiplier tubes). Novel materialscombining the properties of conducting and non-conducting materials at scales muchsmaller than the incident wavelength are known as meta-materials. These allow combi-nations of properties not usually possible in natural materials at optical frequencies. Theproperties reported so far include; negative refraction, negative phase velocity, fluorescenceemission enhancement, lensing and therefore light confinement has also been proposed tobe possible. Instead of expensive and slow lithography methods many of these materialsmay be fabricated with self assembly techniques, which are truly nanoscopic and otherwiseinaccessible with even the most sophisticated equipment. It was found that nanoscaled volumes from ZMW and HMMs based on NW arrays wereall inefficient at enhancing fluorescence. The primary cause was the reduced fluorescencelifetime reducing the fluorescence efficiency, which runs contrary to some commentatorsin the literature. NW based lensing was found to possible in the blue region of the opticalspectrum in a HMM, without the background fluorescence normally associated with a PAAtemplate. This was achieved using a pseudo-ordered array of relatively large nanowireswith a period just smaller than lambda / 2 which minimised losses. Nanowires in the traditionalregime lambda / 10 produced significant scattering and lead to diffraction, such that they werewholly unsuitable for an optical lensing application.