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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Light scattering in fibrous sheets

Arnold, Edwin W. 01 January 1962 (has links)
No description available.
2

Ultrasound-modulated optical tomography in soft biological tissues

Sakadzic, Sava 17 September 2007 (has links)
Optical imaging of soft biological tissues is highly desirable since it is nonionizing and provides sensitive contrast information which enables detection of physiological functions and abnormalities, including potentially early cancer detection. However, due to the diffusion of light, it is dificult to achieve simultaneously both good spatial resolution and good imaging depth with the pure optical imaging modalities. This work focuses on the ultrasound-modulated optical tomography - a hybrid technique which combines advantages of ultrasonic resolution and optical contrast. In this technique, focused ultrasound and optical radiation of high temporal co-herence are simultaneously applied to soft biological tissue, and the intensity of the ultrasound-modulated light is measured. This provides information about the optical properties of the tissue, spatially localized at the interaction region of the ultrasonic and electromagnetic waves. In experimental part of this work we present a novel implementation of high-resolution ultrasound-modulated optical tomography that, based on optical contrast, can image several millimeters deep into soft biological tissues. A long-cavity confocal Fabry-Perot interferometer was used to detect the ultrasound-modulated coherent light that traversed the scattering biological tissue. Using 15-MHz ultrasound, we imaged with high contrast light absorbing structures placed 3 mm below the surface of chicken breast tissue. The resolution along the axial and the lateral directions with respect to the ultrasound propagation direction was better than 70 and 120¹m, respectively. This technology is complementary to other imaging technologies, such as confocal microscopy and optical-coherence tomography, and has potential for broad biomedical applications. In the theoretical part we present various methods to model interaction be-tween the ultrasonic and electromagnetic waves in optically scattering media. We first extend the existing theoretical model based on the diffusing-wave spectroscopy approach to account for anisotropic optical scattering, Brownian motion, pulsed ul-trasound, and strong correlations between the ultrasound-induced optical phase in-crements. Based on the Bethe-Salpeter equation, we further develop a more general correlation transfer equation, and subsequently a correlation diffusion equation, for ultrasound-modulated multiply scattered light. We expect these equations to be applicable to a wide spectrum of conditions in the ultrasound-modulated optical tomography of soft biological tissues.
3

Up-conversion In Rare-earth Doped Micro-particles Applied To New Emissive 2d Dislays

Milliez, Anne 01 January 2006 (has links)
Up-conversion (UC) in rare-earth co-doped fluorides to convert diode laser light in the near infrared to red, green and blue visible light is applied to make possible high performance emissive displays. The infrared-to-visible UC in the materials we study is a sequential form of non-linear two photon absorption in which a strong absorbing constituent absorbs two low energy photons and transfers this energy to another constituent which emits visible light. Some of the UC emitters' most appealing characteristics for displays are: a wide color gamut with very saturated colors, very high brightness operation without damage to the emitters, long lifetimes and efficiencies comparable to those of existing technologies. Other advantages include simplicity of fabrication, versatility of operating modes, and the potential for greatly reduced display weight and depth. Thanks to recent advances in material science and diode laser technology at the excitation wavelength, UC selected materials can be very efficient visible emitters. However, optimal UC efficiencies strongly depend on chosing proper operating conditions. In this thesis, we studied the conditions required for optimization. We demonstrated that high efficiency UC depends on high pump irradiance, low temperature and low scattering. With this understanding we can predict how to optimally use UC emitters in a wide range of applications. In particular, we showed how our very efficient UC emitters can be applied to make full color displays and very efficient white light sources.
4

Influence de l’histoire thermique sur la diffusion optique dans les préformes et les fibres optiques GeO2-SiO2 : F / Influence of thermal history on optical scattering in preforms and optical fibers GeO2-SiO2 : F

Heili, Manon 19 November 2013 (has links)
Les fibres optiques sont présentes de manière incontournable dans les télécommunications et les réseaux d’accès à internet. Longs fils de verre fabriqués en silice vitreuse ultra pure, elles permettent de transmettre des informations sur de longues distances sous forme de signaux lumineux. Malgré leurs capacités de transmission déjà excellentes, la réduction des pertes optiques demeure un enjeu économique. En effet, en dessous d’une certaine atténuation, il est possible de supprimer des amplificateurs localisés dans des zones peu accessibles où leur installation est très couteuse. L’objectif de ce travail de thèse est donc d’explorer de nouvelles voies permettant de réduire significativement l’atténuation du signal optique.La silice est un élément de choix pour les applications optiques du fait de ses propriétés physico-chimiques (haute transparence de l’IR à l’UV, forte résistance mécanique,…). L’incorporation de composés dans le verre de silice modifie ses caractéristiques (viscosité, densité,…) sans détérioration des propriétés optiques ; en particulier l’ajout de fluor F diminue son indice de réfraction tandis que l’oxyde de germanium GeO2 l’augmente. En revanche, le désordre structural du verre augmente avec ces ajouts et, par conséquent, l’atténuation de même. Ce désordre dépend de l’histoire thermique et est décrit au moyen de la température fictive Tf qui correspond à la température pour laquelle la structure du verre a été gelée. La Tf du verre détermine de nombreuses propriétés du matériau telles que les fluctuations d’indice de réfraction et de densité.La diffusion Rayleigh est la principale source de pertes dans les fibres optiques, représentant une part de ~90% à la longueur d’onde de 1550 nm. Cette diffusion trouve son origine dans les fluctuations de constante diélectrique dont deux types de contributions sont déjà connues : les fluctuations de densité et les fluctuations de concentration. En appliquant une approche thermodynamique, un autre terme est proposé pour compléter cette description : les fluctuations de température fictive, résultant d’une distribution des temps de relaxation du verre. Cette approche a mis en évidence l’importance d’étudier la relation existante entre la densité ρ et la Tf d’une part, et entre l’indice n et la Tf d’autre part, afin de réduire les pertes par diffusion Rayleigh.Dans une fibre optique, ce sont les conditions de fibrage essentiellement, c’est-à-dire la température, la tension et la vitesse, qui déterminent le passé thermique du matériau. Une étude expérimentale a permis de distinguer l’impact de ces conditions sur les pertes par diffusion dans des fibres monomodes conventionnelles. Les connaissances sur l’origine des objets diffusants (tailles et formes) dans les fibres d’histoires thermiques différentes ont pu être approfondies. Idéalement, il faudrait pouvoir s’affranchir des conditions de fibrage. Contrairement aux autres verres d’oxydes, le verre de silice admet un comportement dit ‘anormal’ pour sa densité : celle-ci augmente avec la température fictive. Cette anomalie disparait en incorporant une certaine quantité d’éléments chimiques (F, Cl, GeO2 mais pas TiO2) dans le matériau. Nous avons montré que certaines compositions, en supprimant la sensibilité de la diffusion Rayleigh à la Tf, permettent de minimiser les pertes optiques de la famille de fibres que nous avons étudiées.La spectroscopie Raman a ensuite été utilisée afin de comprendre l’origine structurale de cette anomalie. Les mesures réalisées ont montrées que les bandes D1 et D2 reliées à la vibration des petits cycles de tétraèdres dans le verre ne sont pas corrélées à la densité macroscopique. En conséquence, elles ne constituent pas une signature fiable du phénomène de densification dans les verres binaires. Des études complémentaires sur la coordinence du silicium dans la matrice sont nécessaires pour pouvoir conclure sur l’origine structurale de l’anomalie de la silice. / Optical fibers are inevitably present in telecommunications and Internet access networks. Long glass threads made of ultra-pure vitreous silica, they allow to relay information on long distances in the form of light signal. Despite their good transmission capacities, the reduction of optical losses remains an economical stake. Indeed, under a certain attenuation, it is possible to avoid amplifiers located in hardly accessible area where their setting is very expensive. The objective of this work is thus to explore new ways allowing to reduce significantly optical signal attenuation.The silica is a specific element for optical applications because of its physical chemistry properties (high transparency from IR to UV, strong mechanical resistance,…). Adding components in silica glass changes its characteristics (viscosity, density,…) without strong deterioration of optical properties. Especially, the addition of fluorine decreases the refractive index whereas germanium oxide GeO2 increases it. However, the glass structural disorder increases, and, therefore the optical attenuation as well. The disorder depends on thermal history. It is described by means of fictive temperature Tf that corresponds to the temperature at which the glass structure is frozen. The Tf of glass determines many material properties such as the fluctuations of refractive index and density. Rayleigh scattering is the main reason of optical losses in optical fibers, representing ~90% at 1550 nm wavelength. This scattering originates from the dielectric constant fluctuations, which contain two kinds of contributions: the density and the concentration fluctuations. By applying a thermodynamics approach, another term is suggested to complete this description: the fictive temperature fluctuations, resulting from a distribution of glass relaxation times. This approach highlighted importance of studying the relationship between density ρ and Tf on one hand, and between index n and Tf on the other hand, in order to reduce the Rayleigh scattering losses.In optical fiber process, Tf is essentially defined by the drawing conditions, i.e. furnace temperature, fiber drawing tension and speed. An experimental study allowed distinguishing the impact of these conditions on scattering losses in single mode conventional fibers. The knowledge about the origin of scattered objects (sizes and shapes) in fibers with different thermal histories has been made deeper. Ideally, it should be better to be disconnected from the drawing conditions.Contrary to the other oxide glasses, silica glass presents an anomalous behavior for its density: this one increases with fictive temperature. This anomaly disappears by adding a certain amount of chemical elements (F, Cl, GeO2, but not TiO2) in the material. We showed that some compositions, by deleting sensitivity of Rayleigh scattering to Tf, allows minimizing optical losses in the fibers family we studied. Raman spectroscopy has been then used in order to understand structural origin of this anomaly. Measurements revealed that D1 and D2 bands, which are related to small tetrahedral membered rings vibrations in glass, are not correlated to the macroscopic density. Consequently, they are not a reliable signature of densification phenomenon in binary glasses. Supplementary studies about the silicon coordination in the network are needed to conclude on structural origin of the silica anomaly.
5

Optical scattering from nanoparticle aggregates

Travis, Kort Alan 09 February 2011 (has links)
Nanometer-scale particles of the noble metals have been used for decades as contrast enhancement agents in electron microscopy. Over the past several years it has been demonstrated that these particles also function as excellent contrast agents for optical imaging techniques. The resonant optical scattering they exhibit enables scattering cross sections that may be many orders of magnitude greater than the analogous efficiency factor for fluorescent dye molecules. Biologically relevant labeling with nanoparticles generally results in aggregates containing a few to several tens of particles. The electrodynamic coupling between particles in these aggregates produces observable shifts in the resonance-scattering spectrum. This dissertation provides a theoretical analysis of the scattering from nanoparticle aggregates. The key objectives are to describe this scattering behavior qualitatively and to provide numerical codes usable for modeling its application to biomedical engineering. Considerations of the lowest-order dipole-dipole coupling lead to simple qualitative predictions of the behavior of the spectral properties of the optical cross sections as they depend on number of particles, inter-particle spacing, and aggregate aspect ratio. More comprehensive analysis using the multiple-particle T-matrix formalism allows the elaboration of more subtle cross-section spectral features depending on the interactions of the electrodynamic collective-modes of the aggregate, of individual-particle modes, and of modes associated with groups of particles within the aggregate sub-structure. In combination these analyses and the supporting numerical code-base provide a unified electrodynamic approach which facilitates interpretation of experimental cross section spectra, guides the design of new biophysical experiments using nanoparticle aggregates, and enables optimal fabrication of nanoparticle structures for biophysical applications. / text
6

Experimental Validation of the Generalized Harvey-Shack Surface Scatter Theory

Nattinger, Kevin T. 10 September 2018 (has links)
No description available.
7

Understanding of infrared heating for thermoforming of semi-crystalline thermoplastics / Compréhension de chauffage infrarouge de thermoplastiques semi-cristallins

Boztepe, Sinan 14 December 2018 (has links)
Les thermoplastiques et les composites thermoplastiques sont généralement mis en œuvre par thermoformage et sont alors le plus souvent préchauffés en utilisant un chauffage IR. L’avantage du chauffage radiatif est qu'il permet de chauffer les polymères à cœur grâce au caractère semi-transparent des polymères. Néanmoins, dans le cas des polymères semi-cristallins, le chauffage radiatif est affecté par la structure cristalline et cette thèse a donc eu pour objectif d’améliorer la compréhension de l'interaction entre la structure cristalline et les propriétés optiques dans le but de proposer un modèle prédictif de chauffage de thermoplastiques semi-cristallins.Cette étude répond à une problématique industrielle relative au contrôle de la température des thermoplastiques semi-cristallins dans les procédés recourant au chauffage radiatif. L’optimisation de ces procédés requiert un code de calcul suffisamment robuste pour permettre une bonne prédiction du champ de température tout en conservant des temps de calcul acceptables. Une approche combinée expérimentale et numérique a ainsi été proposée dans le but de modéliser la capacité d’absorption du rayonnement thermique de milieux polymères semi-cristallins et le transfert de chaleur par rayonnement avec changement des phases de cristaux/amorphe. Ces travaux se concentrent sur le PEHD, qui présente un intérêt particulier pour l’entreprise Procter&Gamble.Dans cette thèse, après avoir établi une revue bibliographique mettant en avant les couplages existants entre les phénomènes de diffusion optique, la microstructure des polymères semi-cristallins et la température, une caractérisation et une analyse poussées des propriétés radiatives de deux polyéthylènes sont proposées. Les analyses morphologiques et optiques ont été réalisées à température ambiante et dans des conditions de chauffage afin d’identifier les formations cristallines à l’origine de la diffusion optique dans des polymères semi-cristallins et l’évolution de ce couplage au cours du chauffage. A travers ce travail de recherche, un coefficient d’extinction spectral thermo-dépendant a été proposé afin de décrire le caractère optiquement hétérogène du milieu semi-cristallin par un milieu homogène équivalent. Sur la base de la caractérisation de la capacité d'absorption du rayonnement thermique, un modèle thermique conducto-radiatif thermo-dépendant a été développé. Afin d’évaluer la précision de la modélisation, une méthodologie expérimentale spécifique a été proposée pour mesurer la température de surface par thermographie IR dans le cas du PEHD semi-transparent. L’étape finale a consisté à confronter les résultats issus des simulations numériques basées sur cette modélisation à plusieurs campagnes de mesures expérimentales. Les résultats de ces travaux démontrent la forte influence de la structure morphologique des polymères semi-cristallins sur les transferts de chaleur radiatifs. / Thermoplastics and thermoplastic composites are promising candidates for manufacturing highly cost- effective and environmental-friendly components in terms of rapid forming and recyclability. Thermoforming is extensively used for the processing of thermoplastics where IR heating is widely applied. The major advantage of radiative heating is that the significant portion of radiation penetrates into the semi-transparent polymer media.This thesis focuses on understanding of IR heating of semi-crystalline thermoplastics which aims to analyze the driven mechanisms for radiation transport in optically heterogeneous unfilled semi-crystalline polymer media. Considering the relatively narrow thermoforming window of semi-crystalline thermoplastics, accurate temperature control and close monitoring of temperature field is crucially important for successful forming process. It is thus required to build a numerical model robust enough to allow a good prediction of the temperature field while maintaining acceptable calculation times. In this research work, a combined experimental-numerical approach has been proposed which enables both to characterize the radiation absorption capacity of semi-crystalline polymer media and, to model the radiation heat transfer considering the crystalline/amorphous phases change under heating. This research focuses on a particular polymer - highly crystalline HDPE- which is supported by Procter & Gamble.In this thesis, the literature was reviewed at first for highlighting the existing coupled relation between the optical properties and the crystalline structure of semi-crystalline polymers. The role of crystalline morphology on the optical properties and optical scattering of two type of polyethylene, namely HDPE and LLDPE, were addressed. More specifically, the morphological and optical analyses were performed at room temperature and under heating to determine: which crystalline formations are responsible for optical scattering in semi-crystalline polymer media and, how does their coupled relationship evolve under heating conditions? Hence, one of the key contributions of this research is on establishing a temperature-dependent spectral extinction coefficient of HDPE allowing to describe temperature- dependent radiation absorption capacity of its semi-crystalline medium and, to model radiative transfer considering an equivalent homogeneous medium. Based on the characterization of radiation absorption capacity of semi-crystalline media, a temperature-dependent conduction-radiation model was developed. In order to assess the modeling accuracy, an experimental methodology was proposed for non-invasive surface temperature measurements via IR thermography on semi-transparent polymer media. The final step was to compare the results of numerical simulations with the several IR heating experiments to prove the strong influence of the crystalline morphology on heat transfer.
8

Optical spectroscopic microscopies study of nano-to-submicron scale structural alterations in human brain cells/tissues and skin fibroblasts due to brain diseases using mesoscopic physics

Alharthi, Fatemah 08 December 2023 (has links) (PDF)
Optical scattering techniques are suitable probes for studying weak disordered refractive index media such as biological cells and tissues. Several brain diseases accompany the nano-to-submicron scales’ structural alterations of the basic building blocks of cells/tissues in the brain and skin fibroblasts. For example, several molecular modifications such as DNA methylation, and histone degradation occur in cells earlier than morphological changes detectable at a microscopic level. These alterations also change the refractive index structures of the cells/tissues at the nano-to-submicron scales. Unfortunately, traditional methods do not allow the detection of these alterations in the early stages of diseases. Recent developments in mesoscopic optical physics-based techniques can probe these alterations. Particularly, mesoscopic light transport and localization approaches enable the measurements and quantifications of the degree of structural alterations in the cells/tissues and unprecedented information on progressive brain diseases. This dissertation provides a detailed study of the structural changes at nano-to-submicron levels in human brain cells/tissues and human skin fibroblasts in two major neurodegenerative diseases, Alzheimer’s disease (AD) and Parkinson's disease (PD), using dual spectroscopic imaging techniques, namely partial wave spectroscopy (PWS) for light transport and inverse participation ratio (IPR) for weak light localization. In particular, a nanoscale-sensitive advanced PWS technique is used to quantify the structural alterations in cells/tissues. Further, the IPR technique is used to quantify molecular-specific mass density alterations within cells using their light localization properties via confocal imaging. These dual optical scattering techniques were utilized to measure the degree of structural disorders, termed ‘disorder strength’, by distinguishing the diseased cells/tissues from normal ones in the human brain and human skin fibroblasts due to neurodegenerative diseases. Our results show that the degree of structural disorder (����) increases in the affected cells and tissues relative to the normal, both at the cellular/tissue level and in the DNA molecular mass density structural levels. The results of the studies strongly reveal that the degree of structural disorder strength (����) is an effective biomarker/numerical indicator for brain disease diagnostics.

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