Dissertations / Theses: 'Laser holography'

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Li, Song, and 李松. "Multi-pulse laser holography of vibrating objects." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31213376.

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Li, Song. "Multi-pulse laser holography of vibrating objects /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B17489350.

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Amer, Mohamed Eynas. "Pulsed laser ablation studied using digital holography /." Luleå : Department of Applied Physics and Mechanical Engineering, Luleå University of Technology, 2009. http://pure.ltu.se/ws/fbspretrieve/3315450.

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Amer, Eynas. "Pulsed laser ablation studied using digital holography." Doctoral thesis, Luleå tekniska universitet, Strömningslära och experimentell mekanik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18194.

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Pulsed digital holographic interferometry has been used to study the plume and the shock wave generated in the laser ablation process on different targets under atmospheric air pressure. A pulsed Nd-YAG laser system (pulse duration 12 ns) has been used both for ablating the material (wavelength 1064 nm) and for measurement (wavelength 532 nm). Digital holograms were recorded for different time delays using collimated laser light passed through the volume along the target. Numerical data of the integrated refractive index field were calculated and presented as phase maps. The Radon inversion has been used to estimate the 3D refractive index fields measured from the projections assuming rotational symmetry. Intensity maps have been calculated from the recorded digital holograms and used to calculate the attenuation of the probing laser beam by the ablated plume. Qualitative and quantitative information have been extracted from both the phase map and the intensity map to help describing the laser ablation process. Also 3D information about the induced plume has been obtained by numerical reconstruction of the digital holograms at different planes along the plume. The amount of released energy due to laser impact on a PCBM target has been estimated using the point explosion model. The released energy is normalized by the incident laser pulse energy and the energy conversion efficiency between the laser pulse and the target has been calculated and it seems to be constant around 80 %. The 3D refractive index fields have been used to calculate the shock wave front density and the electron number density distribution within the induced plasma. The electron number densities are found to be in the order of 1018 cm-3 and decay at a rate of 3x1015 electrons/cm3ns. The effect of the laser spot diameter on the shock wave generated in the ablation process of a Zn target has been studied. The induced shock wave has an ellipsoidal shape that approaches a sphere for decreasing spot diameter. A model was developed that approaches the density distribution that facilitates the derivation of the particle velocity field. The method provides quantitative results that are discussed; in particular a comparison with the point explosion theory. The effect of the physical properties of the target on the laser ablation process has been studied. The comparison of the laser ablation of Zn and Ti shows that different laser ablation mechanisms are observed for the same laser settings and surrounding gas. At a laser fluence of 5 J/cm2, phase explosion appears to be the ablation mechanism in case of Zn, while for Ti normal vaporisation seems to be the dominant mechanism. The results show that pulsed digital holographic interferometry is a promising technique to give a physical picture and increase the understanding of the laser ablation process in a time resolved manner.
Godkänd; 2009; 20091018 (eyname); DISPUTATION Ämnesområde: Experimentell mekanik/Experimental Mechanics Opponent: Reader in Laser Engineering Bill O’Neill, University of Cambridge, UK Ordförande: Professor Mikael Sjödahl, Luleå tekniska universitet Tid: Fredag den 20 november 2009, kl 10.00 Plats: E 231, Luleå tekniska universitet

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Oliveira, Glaura Caroena Azevedo de. "Estudo de esforços mastigatórios utilizando técnica de interferometria holográfica\"." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-06032008-132023/.

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A interferometria holográfica é um poderoso método óptico para observação de fenômenos perturbativos e na análise de superfícies, sendo extremamente útil em aplicações em pesquisa básica, biomédicas e tecnológicas. Os cristais fotorefrativos se apresentam como um meio atrativo para registro de hologramas. O fenômeno que caracteriza esses cristais é o efeito fotorrefrativo. Tal efeito consiste na modulação do índice de refração através de fotoindução e efeito eletro-óptico linear (Efeito Pockels), o que permite o registro de hologramas de fase em volume. Entre as características que recomendam os cristais fotorrefrativos para interferometria holográfica podemos citar: o processo de registro e leitura ocorre de maneira dinâmica através da técnica de mistura de duas ondas; o fato de serem meios revers´?veis dispensando processamento químico e a boa resolução implicando imagens holográficas de boa qualidade. Analisamos as diversas tensões que ocorrem no processo mastigatório, estudando principalmente a concentração de cargas e as dissipações nesse processo, utilizando a técnica holográfica de dupla exposição e o cristal fotorrefrativo Bi12SiO20 (BSO), da família das Silenitas, como meio de registro. O estudo em crânio seco e a simulação dos principais feixes dos músculos da mastigação permitem realizar a contração dos mesmos, com aproximação melhor que os métodos de elementos finitos e resinas fotoelásticas, em estruturas anisotrópicas como o crânio.
The holographic interferometry is a powerful optical method for observation of the disturbance phenomena and in the analysis of surface, being extremely useful in application in basic research, biomedical and technological. The photorefractive crystals present as an attractive holographic recording medium. The phenomenon that characterize these crystals is the photorefractive effect. Such effect consistis of the index of refraction modulation grating via the linear eletro-optic effect (the Pockels effect) and photoindution, that it allow phase holographic recording in volume. Among the characteristics that admit the photorefractive crystals for holographic interferometry we can cite: recording and reading tecniques to occur in dynamics way through the tecnique of two-wave mixing, it is reversible medium resulting holographic images of good quality. We analyze the varied strains that occur in the masticatory process, mainly studying the load concentration and the dissipation in this process, using the double-exposure holographic technique and the photorefractive crystals Bi12SiO20 (BSO), of the sillenite family, as holographic recording medium. The study in dry skull and the simulation of main beams of the mastication muscles allow to realize the concentration of the same ones, with better approach than the methods of finite elements and photoelastics resins, in anisotropic structures as the skull.

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Yeo, Terence E. "Novel high precision microlithographic techniques applicable to distributed feedback laser grating manufacture." Thesis, Loughborough University, 1993. https://dspace.lboro.ac.uk/2134/13625.

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Distributed feedback, DFB, lasers are a major source for long haul optical fibre based telecommunication systems. They rely on ultrahigh precision gratings to reduce mode competition within the laser cavity, thereby making single frequency operation possible. Techniques applied to DFB grating manufacture tend to be either holographic, or a direct serial write process using slow and expensive electron beam lithographic machines. An entirely new approach is proposed which compliments the accuracy of the electron beam systems with the high throughput and relatively low cost of a conventional contact mask regime. The new process relies on a group of materials which are able to retain an embossed relief upon curing with ultraviolet radiation. The main manufacturing stages of this new technique are presented including details of the embossing tool fabrication using reactive ion etching, and characterisation of material properties. It is proposed that the technique, whilst intended for DFB manufacture, could find applications in many other areas, for instance as a route to low cost replication of photomasks. In addition a new grating assessment technique, based on normal reflectance measurements, has been developed. The technique has been used to investigate hitherto unmeasured effects in electron beam lithography on a variety of substrate materials before and after semiconductor overgrowth. Details of a theoretical exercise which agrees closely with experimental results are included. The technique is non-destructive and should be of interest to all areas of microlithography and holographic imaging where it is important to have control over a wide range of process stages or where the feature size rules out the use of conventional optical microscopes.

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Khmaladze, Alexander. "Three-dimensional microscopy by laser scanning and multi-wavelength digital holography." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002638.

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Puyo, Léo. "Application clinique de l'holographie laser Doppler en ophtalmologie." Thesis, Paris Sciences et Lettres (ComUE), 2019. http://www.theses.fr/2019PSLET022.

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Cette thèse porte sur l'introduction de l'holographie laser doppler (LDH) au domaine de l'ophtalmologie afin d'imager le flux sanguin dans le pôle postérieur de l'œil. Les anomalies de perfusion jouent un rôle central dans le développement des pathologies oculaires, ce qui nécessite le développement d'instruments appropriés pour mieux le comprendre. Le LDH avait déjà démontré sa capacité à effectuer une imagerie non invasive et quantitative du flux sanguin, mais uniquement chez les rongeurs. Dans cette thèse, il est montré qu'avec une caméra rapide et une analyse à transformée de Fourier à temps court sur l'élargissement Doppler, le LDH peut imager les changements de flux sanguin dans la rétine humaine au cours du cycle cardiaque avec une résolution de quelques millisecondes. Le LDH permet de mesurer les variations systolodiastoliques propres aux artères et veines rétiniennes et peut être utilisée pour cartographier en plein champ l’indice de résistivité local permettant l’identification sans ambiguïté des artères et des veines de la rétine. Le LDH peut également être utilisé pour révéler la choroïde avec une qualité de contraste similaire à celle d'instruments de pointe basés sur l'angiographie au vert d'indocyanine et la tomographie par cohérence optique, mais contrairement à ces méthodes, le LDH fournit en outre un contraste quantitatif du flux sanguin. Cette capacité a été utilisée pour mettre en évidence de grandes différences de débit sanguin entre les artères et les veines choroïdiennes, une caractéristique qui peut être exploitée pour effectuer une autre différenciation artérioveineuse adaptée aux vaisseaux choroïdiens. Les décalages de fréquence Doppler plus élevés de la lumière diffusée dans les artères choroïdiennes permettent au LDH d'être particulièrement efficace pour les révéler, dans certains cas dès leur formation au niveau des artères ciliaires postérieures jusqu'aux ramifications artériolaires. Globalement, la résolution temporelle incomparable avec laquelle le LDH est capable de mesurer le flux sanguin et les nouveaux contrastes avec lequel il permet d'imager la choroïde en font un instrument prometteur pour la suite des applications cliniques
This PhD aimed at introducing laser Doppler holography (LDH) into the field of ophthalmology in order to image blood flow in the eye posterior pole. Perfusion abnormalities play a central role in the development of ocular pathologies, which calls for the development of suitable instruments to elucidate it. LDH had previously demonstrated its ability to perform non-invasive and quantitative blood flow imaging with a high temporal resolution, but only in rodents. In this thesis, it is demonstrated that with a fast camera and a short-time Fourier transform analysis of the Doppler broadening, LDH can image blood flow changes in the human retina during cardiac cycles with a resolution of a few milliseconds. LDH is able to measure distinct systolodiastolic variations in retinal arteries and veins, and can be used for a full field mapping of the local resistivity index that allows unambiguous identification of retinal arteries and veins. LDH can also be used to reveal the choroid with a contrast quality similar to that of state of art instruments based on indocyanin-green angiography and optical coherence tomography, but unlike these methods LDH additionally provides a quantitative blood flow contrast. This ability was used to bring to light large differences of blood flow between choroidal arteries and veins, which is a feature that can be exploited to perform another arteriovenous differentiation appropriate for choroidal vessels. The higher Doppler frequency shifts of light scattered in choroidal arteries allows LDH to be especially efficient to reveal them, in some cases from their formation at short posterior ciliary arteries all the way to the arterioles branching. Overall, the unmatched temporal resolution with which LDH is able to measure blood flow and the new insight it provides into the choroid are especially full of promise for further clinical applications

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Whyte, Graeme B. "Analogies between light and matter waves : from laser modes to phase holography." Thesis, University of Glasgow, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438921.

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Pejchang, Darawan. "Measurement of nanoparticles by digital in-line holography." Rouen, 2015. http://www.theses.fr/2015ROUES052.

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Dans cette thèse, nous proposons une nouvelle méthode pour mesurer la taille et la forme de nanoparticules en utilisant l'holographie numérique dans l’axe en association un processus photo-thermique d’échauffement induit par laser. Une suspension de nanoparticules en très faible concentration et en milieu dilué dans une goutte d’eau, est chauffée par un laser impulsionnel. Une bulle de vapeur d’eau, stable, entourant la nanoparticule secondaire à l’échauffement est créée. La transposition de taille de l’échelle nanométrique à l’échelle micrométrique est alors obtenue. Ce processus photo-thermique est utilisé pour relier la taille de la bulle à la taille de la nanoparticule. On obtient les relations fonctionnelles entre le rapport d'aspect et le volume de la bulle et ceux de la nanoparticule. Ces fonctions dépendent des caractéristiques de l'impulsion laser, de la température initiale de la nanoparticule et l’indice optique de l'eau et sont également spécifiques à la matière et à la forme de la nanoparticule. Une nanoparticule sphérique de TiO2 est utilisée dans cette démonstration. Le diamètre mesuré expérimentalement est en bon accord avec le diamètre moyen de l'échantillon. Cela signifie que la mesure indirecte utilisant la bulle de vapeur d’eau obtenue par cavitation autour de la nanoparticule peut être considéré comme efficace pour obtenir la taille d'une nanoparticule
In this thesis we study and develop a new methodology to measure the size and shape of individual nanoparticles by using digital in-line holography (DIH) microscopy in association with a photothermal process. Due to the limited resolution of the direct DIH technique at the nanoscale, an indirect measurement is treated. Instead of recording the hologram of a nanoparticle directly, the nanoparticle suspension is suddenly heated by a powerful pulse laser. Then a vapor bubble cavitation surrounding the nanoparticle is formed in order to increase the object size from the DIH point of view. The photothermal process is used to link the size of the bubble to the size of the nanoparticle. We obtain the functional relations between the aspect ratio and volume of the bubble and those of the nanoparticle from this process. These functions are dependent on the characteristics of the laser pulse, the initial temperature of the nanoparticle and the water medium, and are also specific to the material and shape of the nanoparticle. A spherical nanoparticle of TiO2 is used in this demonstration. The measured diameter is in good agreement with the average diameter of the sample. This means that the indirect measurement employing the cavitation vapor bubble around the nanoparticle can be considered as efficient to obtain the size of a nanoparticle. This technique has the ability to take into account the shape (ellipticity) of the bubble

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Han, Jiho. "Phase modulated fibre amplifier array for high power real-time arbitrary beam shaping." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267906.

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BENKHEROUROU, SAHNOUNE SOURAYA. "Contribution a l'uniformisation du faisceau laser gaussien collimate par holographie numerique." Université Louis Pasteur (Strasbourg) (1971-2008), 1988. http://www.theses.fr/1988STR13084.

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Presentation de deux techniques pour uniformiser le faisceau. La premiere est fondee sur le filtrage lineaire dans le domaine des frequences ou le faisceau est considere comme etant l'objet pouvant etre modifie par un filtre (hologramme) pour produire l'image filtree (faisceau uniforme). La seconde est constituee par deux filtres de phase. Le premier filtre sert a devier les rayons lumineux de facon a obtenir une repartition uniforme. Le second permet de collimater le faisceau deja uniformise par le premier

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Shin, Dong-Ik. "Laser Scanning Imaging for Increased Depth-Of-Focus." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/44190.

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Throughout the decades, different techniques have been proposed to improve the depth-of-focus in optical microscopy. Common techniques like optical sectioning microscopy and scanning confocal microscopy have innate problems. By simply modifying the pupil function in microscope imaging system, we can also extend the depth-of-focus. The scanning system with a thin annular pupil has a high depth-of-focus and can scan the whole object, but the output light is too dim to be detected well by a photodetector. In this thesis, we propose a scanning technique employing an optical heterodyne scanning system using a difference-of-Gaussians (DoG) pupil. The object is illuminated by the combined beam which consists of two Gaussian beams with different waists, frequencies, and amplitudes. This system does not block most light like the annular pupil system and can obtain high depth-of-focus. The main objective of the thesis is to extend the depth-of-focus using the proposed system. The depth-of-focus characteristics of the DoG pupil function are examined and compared with those of well-known functions such as the circular, annular, and Gaussian pupils.
Master of Science

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Grewell, David A. "Modeling of molecular healing for micro-laser welding of plastics with diffractive optical elements as spatial modulators." Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1123082743.

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Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xxiv, 223 p.; also includes graphics. Includes bibliographical references (p. 210-214). Available online via OhioLINK's ETD Center

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Parisot-Dupuis, Hélène. "Application de l'holographie acoustique en soufflerie par mesures LDV." Thesis, Toulouse, ISAE, 2012. http://www.theses.fr/2012ESAE0035/document.

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L’ Holographie acoustique de champ proche (NAH) est une méthode d’imagerie acoustique robuste, mais son application en écoulement peut être limitée par l’utilisation de mesures intrusives de pression ou de vitesse acoustique. Dans cette étude, une procédure holographique applicable en écoulement utilisant des mesures de vitesse non-intrusives est proposée. Cette méthode est basée sur le théorème intégral de Kirchhoff-Helmholtz convecté. La fonction de Green convectée est alors utilisée pour déterminer des propagateurs spatiaux convectés définis dans l’espace réel et incluant l’effet d’un écoulement subsonique uniforme. Les transformées de Fourier discrètes de ces propagateurs permettent alors d’évaluer les champs acoustiques à partir de la mesure du champ de pression ou de vitesse acoustique normale. Le but étant de développer une méthode de caractérisation de sources aéroacoustiques à partir de mesures de vitesse non-intrusives, cette étude se concentre essentiellement sur les propagateurs réels convectés basés sur la mesure de vitesse acoustique. Afin de valider cette procédure,des simulations ont été menées dans le cas de combinaisons de sources monopolaires et dipolaires convectées corrélées ou non. La procédure holographique développée donne de bons résultats par comparaison aux champs acoustiques théoriques. Une comparaison des résultats obtenus par les propagateurs convectés réels, développés dans cette thèse, avec ceux obtenus par leurs formes spectrales, développés par Kwon et al. fin 2010 pour des mesures de pression acoustique, montre l’intérêt d’utiliser la forme réelle pour la reconstruction de la pression acoustique à partir de la mesure de vitesse acoustique normale. L’efficacité de la procédure développée est confirmée par une campagne de mesure en soufflerie avec un haut-parleur affleurant rayonnant au sein d’un écoulement à Mach 0.22, et des mesures non-intrusives effectuées par Vélocimétrie Laser Doppler (LDV). Les champs de vitesse acoustique utilisés pour la procédure holographique sont dans ce cas extraits des mesures LDV par corrélation avec un microphone de référence. La faisabilité de prendre en compte des variations de l’écoulement dans la direction de reconstruction holographique est également vérifiée
Nearfield Acoustic Holography (NAH) is a powerful acoustic imaging method but its application in flow can be limited by intrusive measurements of acoustic pressure or velocity. In this work, a moving fluid medium NAH procedure using non-intrusive velocity measurements is proposed. This method is based on the convective Kirchhoff-Helmholtz integral formula. The convective Green’s function is then used to derive convective realspace propagators including uniform subsonic airflow effects. Discrete Fourier transforms of these propagators allow then the assessment of acoustic fields from acoustic pressure or normal acoustic velocity measurements. As the aim is to derive an aeroacoustic sources characterisation method from non-inrusive velocity measurements, this study is especially focused on real convective velocity-based propagators. In order to validate this procedure, simulations in the case of combinations of monopolar and dipolar sources correlated or not, radiating invarious uniform subsonic flows, have been performed. NAH provides very favorable results when compared to the theoretical fields. A comparison of results obtained by real convective propagators, developed in this work, and those obtained by the spectral ones, developed by Kwon et al. at the end of 2010 for acoustic pressure measurements, shows the interest of using the real-form for NAH acoustic pressure reconstruction from normal acoustic velocity measurements. The efficiency of the developed procedure is confirmed by a wind tunnel campaign with a flush-mounted loudspeaker radiating in a flow at Mach 0.22 and non-intrusive Laser Doppler Velocimetry (LDV) measurements. Acoustic velocity fields used for the NAH procedure are in this case extracted from LDV measurements by correlation with a reference microphone. The feasibility of taking into account mean flow variations in the direction of NAH reconstruction is also checked

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Han, Wei. "Computational and experimental investigations of laser drilling and welding for microelectronic packaging." Link to electronic thesis, 2004. http://www.wpi.edu/Pubs/ETD/Available/etd-0513104-155241/.

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Thesis (Ph. D.)--Worcester Polytechnic Institute.
Keywords: Optoelectronic holography; Microwelding; Microelectronic packaging; Microdrilling; Laser micromachining; Computational modeling. Includes bibliographical references (p. 204-212).

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Barszczak, Sardinha Anna Luiza. "Coherent imaging of nano-objects with ultra-short X-ray pulses." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX006/document.

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L'utilisation des rayons X est indispensable pour obtenir la résolution spatiale de la dizaine de nanomètres. La durée de ces flashs va de la dizaine de femtosecondes (1 fs =10-15 s) à la centaine d'attosecondes (1as=10-18 s). Durant ce laps de temps, les nano-objets n'ont pas le temps d'évoluer, assurant l'obtention d'une image précise. En excitant les nano-objets entre deux flashs de rayons X, il est alors possible de suivre sont évolution temporelle et ainsi de réaliser un « film » de son évolution suite à une excitation. Cette information est extrêmement importante car elle permettra d'identifier les états structuraux intermédiaires des nano-objets qui sont connus comme étant les plus importants pour comprendre leur pouvoir réactionnel.Ce genre d'études vient uniquement de débuter dans le monde en raison de l'apparition très récente des sources de rayons X suffisamment brèves et intenses pour réaliser ce genre d'images. La source de référence est un laser dit à « électrons libres » (LEL) dont il existe trois exemplaires au monde, en Allemagne, aux USA et au Japon. Le faible nombre d'exemplaires provient du coût extrêmement élevé de cette machine. Depuis plusieurs années, nous avons montré au LOA que les lasers pouvaient produire un rayonnement X femtoseconde et suffisamment intense pour réaliser des images de nano-objets avec des résolutions spatiales et temporelles équivalentes à celles obtenues sur LEL.La présente thèse a etait construite autour de trois phases : réalisation d'une source de rayons X polarisés circulairement, réalisation d'un nouveau système plus performant d'imagerie, et test sur des échantillons possédants des nano-structures dont la vitesse d'évolution après excitation est prévue aux environs de 100 fs. Ces études ont eu lieu ao LOA, LCLS, Laboratoire de Chimie-Physique, Matière et Rayonnement (LCPMR) et le CEA de Saclay et BESSY-II en Alemagne. Ils ont permis de acquérir une forte expertise en imagerie nanométrique basée sur la nouvelle technique que nous avons développé
The use of X-rays is fundamental to obtain a spatial resolution in the order of the dozen of nanometers. The duration of the flashes of radiation is placed between the dozen of femtoseconds (1 fs =10-15 s) to the hundreds of attoseconds (1as=10-18 s). During this time frame nano-objects are static in time, image wise it translates as a precise image. Exciting these nano-objects with flashes of X-ray beams it is possible to follow its temporal evolution and record a "movie" of the evolution due to excitation. This type of information is extremely important since it can allow the identification of intermediary structural states and therefore attaining a better understanding of their reactional power.This type of studies it is making its debut in the scientific community due to the recent development of ultra-fast and intense X-ray sources needed to perform this type of imaging. The referenced source is a free electron laser (FEL) and there are only tree of them in the world nowadays. One in Germany, one in the USA and one in Japan. The small amount of FELs is mainly due to its elevated costs. From some years the LOA has shown that lasers can also provide an X-ray beam in the femtosecond region and intense enough to produce images of nano-objects with equivalent temporal and spatial resolutions.This present thesis was built in tree phases: realization of an X-ray laser source, circularly polarized; realization of a new improved imaging system and testing of the nano-samples possessing nano-structures. These nano-structures have a velocity of evolution after excitation in the range of 100 fs. These studies have had place at LOA, LCLS, Laboratoire de Chimie-Physique, Matière et Rayonnement (LCPMR), the CEA de Saclay, BESSY-II in Germany. These cooperations have insured a specific training and expertise in the world of nanometric imaging based on the new technique developed during this work

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Gabolde, Pablo. "Measurements of the spatio-temporal profiles of femtosecond laser pulses." Diss., Available online, Georgia Institute of Technology, 2007, 2007. http://etd.gatech.edu/theses/available/etd-06272007-101312/.

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Thesis (Ph. D.)--Physics, Georgia Institute of Technology, 2008.
Trebino, Rick, Committee Chair ; Kennedy, Brian, Committee Member ; Kuzmich, Alex, Committee Member ; Curtis, Jennifer, Committee Member ; Buck, John, Committee Member.

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Dawson, Paula Heatley Art College of Fine Arts UNSW. "The Concrete Holographic Image: an Examination of Spatial and Temporal Properties and their Application in a Religious Art Work." Awarded by:University of New South Wales. School of Art, 2000. http://handle.unsw.edu.au/1959.4/18201.

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The premise of this thesis is that the ???concrete holographic image???, a laser transmission hologram which has an object or a hologram of an object as its subject, has unique spatial and temporal properties which can suggest a plurality of tenses to a viewer. There is a lack of comprehensive analysis of the holographic representational system within art related theoretical and critical writing and a tendency to analyse individual works only in terms of generalities which apply to the concepts surrounding the holographic medium. While these form an important background for art image production, in some cases corresponding to artists works, the existing written material on the subject is inadequate as a model from which to draw the all important temporal conclusions. To date the critical reception of holograms has made no mention of acuity, the size of the viewing frustum, the depth of the image and scant mention of interference phenomena which are the intrinsic factors which I believe precipitate temporal illusions. Therefore this thesis examines the concrete holographic image in great detail on its own terms, firstly through theories of the basic image forming phenomena of interference and diffraction and secondly through the techniques of production as they have been adapted for the making of my art works. The extent of the metaphorical and allegorical potential of the spatial and temporal properties of the concrete holographic image are put to the ultimate test in a commission for St Brigid???s Church, Coogee. The Shrine of the Sacred Heart commission for St Brigid???s requires a concrete holographic image to facilitate devotion to the Sacred Heart. The Sacred Heart is not a physical thing but a complex, evolving spiritual entity with a realist pictorial history.

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Döring, Sebastian. "Oberflächengitter in azobenzenhaltigen Schichten für organische DFB-Laser." Phd thesis, Universität Potsdam, 2011. http://opus.kobv.de/ubp/volltexte/2012/5921/.

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Ein neuentwickeltes azobenzenhaltiges Material, das auf einem supramolekularen Konzept basiert, wird bezüglich seiner Strukturbildung während einer holografischen Belichtung bei 488 nm untersucht. Im Mittelpunkt stehen dabei eindimensionale, sinusförmige Reliefs mit Periodizitäten kleiner 500 nm. Es wird gezeigt, wie der Grad der Vernetzung der photosensitiven Schicht die Strukturbildung in diesem Größenbereich beeinflusst. Zur Maximierung der Strukturtiefe werden gezielt Prozessparameter der Belichtung sowie Materialparameter variiert. Unter Standardbedingungen und moderaten Belichtungsintensitäten von ca. 200 mW/cm² bilden sich innerhalb weniger Minuten bei einer Periode von 400 nm Strukturtiefen von bis zu 80nm aus. Durch die Beeinflussung von Materialparametern, wie Oberflächenspannung und Viskosität, wird die maximale Strukturtiefe auf 160nm verdoppelt. Durch Mehrfachbelichtungen wird auch die Bildung von zweidimensionalen Gittern untersucht. Die Originalstrukturen werden in einem Abformverfahren kopiert und in Schichten von unter UV-Licht aushärtenden Polymeren übertragen. Durch das Abformen kommt es zu einer geringfügigen Verschlechterung der Oberflächenqualität sowie Abnahme der Strukturtiefe. Dieser Verlust wird durch eine Verringerung der Prozesstemperatur verringert. Mithilfe kopierter Oberflächengitter werden organische Distributed Feedback-(DFB)-Laser zweiter Ordnung hergestellt, um den Einfluss von Gitterparametern auf die Emissionseigenschaften dieser Laser zu untersuchen. Dazu erfolgt zunächst die Charakterisierung der optischen Verstärkungseigenschaften ausgewählter organischer Emittermaterialien mittels der Variablen Strichlängenmethode. Das mit dem Laserfarbstoff Pyrromthen567 (PM567) dotierte Polystyrol (PS) zeigt dabei trotz konzentrationsbedingter geringer Absorption eine vergleichsweise geringe Gewinnschwelle von 50µJ/cm² bei ca. 575 nm. Das aktive Gast-Wirt-System der konjugierten Polymere MEH-PPV und F8BT* weist eine hohe Absorption und eine kleine Gewinnschwelle von 2,5 µJ/cm² bei 630 nm auf. Dieses Verhalten spiegelt sich auch in den Emissionseigenschaften der damit hergestellten DFB-Laser wieder. Die Dicke der aktiven Schichten liegen im Bereich hunderter Nanometer und wird so eingestellt, dass sich nur die transversalen Grundmoden im Wellenleiter ausbreiten können. Die Gitterperiode sind so gewählt, dass ein Lichtmode im Verstärkungsbereich des Emittermaterials liegt. Die Emissionslinien der Laser sind mit FWHM-Werten von bis zu 0,3 nm spektral sehr schmalbandig und weisen auf eine sehr gute Gitterqualität hin. Die Untersuchungen liefern minimale Laserschwellen und maximale differentielle Effizienzen von 4,0µJ/cm² und 8,4% für MEH-PPV in F8BT* (bei ca. 640nm) sowie 80 µJ/cm² und 0,9% für PM567 in PS (bei ca. 575 nm). Die Vergrößerung der Strukturtiefe von 40nm auf 80nm in mit MEH-PPV dotierten F8BT*-Lasern zu einem deutlichen Anstieg der ausgekoppelten Energie sowie der differentiellen Effizienz und einem geringen Absinken der Laserschwelle. Dies ist ein Resultat der erhöhten Kopplung von Lasermode und Gitter. Die Emission von DFB-Lasern mit zweidimensionalen Oberflächengittern zeigen eine Verringerung der Divergenz aber kein Einfluss auf die Laserschwelle. Abschließend erfolgt eine Vermessung der Photostabilität von DFB-Lasern unter verschiedenen Bedingungen. Das Einbringen eines konjugierten Polymers in eine aktive Matrix sowie der Betrieb in einer Stickstoffatmosphäre führen dabei zu einer Erhöhung der Lebensdauer auf über eine Million Pulse. Durch die Kombination von Oberflächengittern in PDMS-Filmen mit elektroaktiven Substraten wird eine elektrisch steuerbare Deformation des Beugungsgitters erreicht und auf einen DFB-Laser übertragen. Die spannungsinduzierte Verformung wird zunächst in Beugungsexperimenten charakterisiert und ein optimaler Arbeitspunkt bestimmt. Mit den beiden Elastomeren SEBS12 und VHB4910 werden in den Gittern maximale Periodenänderungen von 1,3% bzw. 3,4% bei einer Steuerspannung von 2 kV erreicht. Der Unterschied resultiert aus den verschiedenen Elastizitätsmoduln der Materialien. Übertragen auf DFB-Laser resultiert eine Variation der Gitterperiode senkrecht zu den Gitterlinien in einer kontinuierlichen Verschiebung der Emissionswellenlänge. Mit einem Spannungssignal von 3,25 kV wird die schmalbandige Emission eines elastischen DFB-Lasers kontinuierlich um fast 50nm von 604 nm zu 557 nm hin verschoben. Aus dem Deformationsverhalten sowohl der reinen Beugungsgitter als auch der Laser werden Rückschlüsse auf die Elastizität der verwendeten Materialien gezogen und erlauben Verbesserungen der Bauteile.
The photoinduced surface relief formation in a newly developed azobenzene containing material is investigated. A photosensitive film based on a supramolecular material concept is illuminated in a holographic setup with light at 488 nm leading to sinusoidal surface structures. It can be shown how the degree of network formation within the material influences structure formation at periods below 500nm. Different material and process parameters are varied to determine maximum possible structure amplitude. At moderate recording conditions and illumination intensities of 200 mW/cm² maximum structure amplitudes of 80 nm are formed within several minutes at periods of approximately 400 nm. Changing material parameters like surface tension and viscosity leads to an increase of maximum amplitude to 160 nm. Additionally, twodimensional structures are fabricated by multiple recording steps. Original surface structures are copied by soft lithography methods into films of UV cured polymers. This replication leads to a decrease of structure contrast and increase of surface roughness. It is shown that structure contrast is preserved by reduction of process temperature. Organic second order distributed feedback (DFB) lasers are prepared with the help of replicated surface gratings covered with organic active layers with thicknesses of several hundred nanometers. The lasers are investigated regarding the influence of grating amplitude on laser threshold and slope efficiency. For this, the optical gain of two green/red emitter materials, polystyrene (PS) doped with laser dye pyrromethene567 (PM567) and active guest host system of conjugated polymers MEH-PPV and F8BT*, is measured. PS doped with PM567 shows relatively low gain threshold of 50 µJ/cm² at 575 nm caused by the low dye concentration while F8BT* doped with MEH-PPV shows threshold gain of 2.5 µJ/cm² at 630 nm. Similar behavior is observed during laser action. Following Bragg-condition grating periods at approximately 400nm lead to laser emission within the gain spectra of the materials. DFB lasers show single mode narrow line emission with FWHMs of down to 0.3nm. This is a result of high grating quality. Lasers based on MEH-PPV-F8BT* exhibit laser thresholds and slope efficiencies of 4.0µJ/cm² and 8.4%, respectively. PM567-PS lasers exhibit 80 µJ/cm² and 0.9%. An increase of grating amplitude of a MEH-PPV-F8BT*-DFB laser from 40nm to 80nm leads to a considerable increase of energy output and a slight decrease of laser threshold. This is a result of an increase of coupling between light mode and grating which relates to an increase of reflectivity. The use of a two dimensional grating leads to a decrease of divergence angle of laser emission but shows no influence on laser threshold. Finally, laser lifetime is observed under different conditions. Doping the conjugated polymer MEH-PPV in an active matrix in combination with the allocation of nitrogen atmosphere leads to an prolongation of half life time to several million pulses. The combination of elastic surface relief gratings with electro active substrates enables electrical controlled deformation of the surface structure. This deformation is characterized by diffraction measurements. At optimal working conditions electro active substrates based on elastomers SEBS12 and VHB4910 show maximum grating deformation of 1.3% und 3.4% at actuation voltages of 2kV, respectively. The different results are caused by the different elastic modulus of the elastomer materials. The transfer of deformation principle to elastic DFB lasers leads to a continuously shift of emission wavelength. At an actuation voltage of 3.25kV an elastic DFB laser based on polyvinylacetate doped with PM567 shows a shift of nearly 50 nm, from 604 nm to 557 nm. Deformation behavior of grating and laser allow to draw conclusions on elasticity of the material and with this is tool for the improvement of the device.

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Davies, Emlyn John. "Scattering properties of suspended particles." Thesis, University of Plymouth, 2013. http://hdl.handle.net/10026.1/1577.

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Effective monitoring and modelling of the marine environment is of importance to both the general public and the scientific community, but relies on the ability to obtain accurate measurements of suspended particle characteristics. Many instruments for measuring particles rely on optical and acoustic scattering from the particles and use this information to infer a particle size and concentration. However, assumptions such as spherical particles of a known composition are widely used, both in measurement technology and in numerical modelling. Various imaging techniques have shown great variability in the shape, size and composition of marine particles when measured within their natural environment. Subsequently, there is substantial uncertainty in the response of light scattering instruments to this diverse range of particles. In this study, a holographic camera was modified to simultaneously record in-focus images of marine particles with their forward angle scattering characteristics. This was achieved by combining both laser scattering and transmissometry with digital holography. The results from this system were compared with theoretical models of scattering from spherical particles within the intended size range of both instruments (15-500microns), with particle size information from both techniques agreeing well during these idealised conditions. The combined holographic and light scattering system was then used to investigate the response of the LISST-100 (Sequoia Scientific Inc.) to spherical particles with diameters extending beyond that intended by the instrument 250microns for type-B and 500microns for type-C derivatives), but that have been observed in-situ with imaging methods. This revealed an aliasing of single large particles into multiple smaller particles during the inversion of LISST-100 scattering into a particle size distribution. For spheres greater than the type-C instrument range, the inversion of scattering produces particle volume distributions that peak at varying sizes between 250-400microns. This key finding highlights the need for care to be taken when interpreting particle size distributions from the LISST-100 when there is potential for particles outside of its range limit. Natural particles, extracted from coastal waters, were then recorded by the combined laboratory system. These complex particles produced highly variable scattering properties which were contaminated by asymmetrical features within the azimuthal plane. This observation of strong azimuthal asymmetry is of concern for both measurements and models of optical properties that assume a symmetrical scattering function for natural particle populations. The azimuthal asymmetry in scattering contributed to additional variability in the response of the instrument in comparison to the holographic camera, which was also subjected to apparent particle break-up via segmentation during image processing. A discussion of holographic imaging and laser diffraction for characterising particles in-situ forms the final part of this thesis, which utilises data from a magnified holographic system that covers the same size range of the LISST-100. This final analysis demonstrated the need for future technology to accurately measure size distributions over a much larger range of sizes than is currently possible (e.g. <2microns to 1000microns). In summary, three key factors were identified to cause an increase in the apparent number of small particles reported by the LISST-100: 1) contamination from scattering of particles larger than the intended size range of the instrument; 2) a decrease in refractive index (particle composition); 3) additional scattering from small sub-components of particle geometry. The standard holographic camera systems are capable of accurately obtaining particle size and concentration measurements that are comparable to other techniques such as the LISST-100. However, in situations where background illumination is poor, errors in the image processing routines can cause an apparent particle break-up due to incorrect binarisation. Despite this, the holographic method provides a unique and powerful mechanism that enables images of particles to be analysed within the context of their in-situ environment.

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22

Ibrahim, Ahmad. "Development of photoinitiating systems for free radical Photopolymerization usable for laser Imaging." Thesis, Mulhouse, 2011. http://www.theses.fr/2011MULH4082.

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Le sujet de thèse sur lequel je travaille depuis trois ans est l’étude et le développement des systèmes photoamorceurs pour des applications holographiques. Ce travail a lieu en collaboration avec l’équipe BMS (Bayer Material Science) de Bayer-Leverkusen (Allemagne). Mes études se sont limitées aux systèmes utilisables avec une source d’irradiation appartenant à la partie visible du spectre électromagnétique de la lumière (400 nm – 700 nm).Parmi les différents types des réactions de polymérisation, nous avons choisi la polymérisation radicalaire. L’étape cruciale dans cette réaction réside dans la génération des radicaux qui amorcent la réaction. Ces derniers sont formés par transformation, via absorption de lumière, d’un composé photosensible. La formation de ces espèces est en général en compétition avec plusieurs processus de désactivation. Les polymérisations radicalaires sont en particulier fortement inhibées par l’oxygène de l’air. Pour réduire l’effet de l’oxygène et pour avoir des conditions comparables à ceux appliqués dans l’industrie, nos échantillons ont été préparés en utilisant la technique laminée (l’échantillon est mis entre deux films de polypropylène). [...]
The subject of the thesis I have been working on for three years is the study and development of photoinitiating systems for holographic applications. This work takes place in collaboration with the BMS (Bayer Material Science) team from Bayer Leverkusen (Germany). My studies have been limited to systems used with a radiation source belonging to the visible part of the electromagnetic spectrum of light (400 nm - 700 nm). Among the different types of polymerization reactions, we chose the radical polymerization. The critical step in this reaction is the generation of radicals which initiate the reaction. These are formed by transformation via absorption of light of a photosensitive compound. The formation of these species is generally in competition with several deactivation process. [...]

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Laforest, Timothé. "Nouveaux dispositifs intégrés pour l'analyse et le contrôle de lumière cohérente : conception conjointe de circuits opto-électroniques et systèmes optiques." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENT113/document.

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Parmi les techniques d'imagerie optiques utilisées en milieu clinique, la principale limitation est la faible résolution lorsque la profondeur d'examen dépasse quelques mm. Cette limite de résolution ne permet pas à l'heure actuelle de concurrencer les techniques d'imagerie médicales permettant de réaliser un examen du corps dans son intégralité (Rayons X, IRM, Scanner). Dans ce cadre, l'imagerie acousto-optique présente plusieurs avantages: elle permet de mesurer des propriétés optiques utiles pour la détection de tumeur, à la résolution spatiale des ultrasons. Cependant, les dispositifs de détection utilisés présentent un manque de sensibilité et de rapidité qui freinent le transfert de cette technique en milieu clinique.Ce constat nous a conduit à étudier les caractéristiques intrinsèques du signal acousto-optique afin de proposer deux architectures de pixels basées sur des technologies CMOS. La première architecture, totalement analogique, présente des caractéristiques de vitesse d'acquisition compatibles avec le temps de corrélation des milieux biologiques (<1 ms)et un pré-traitement du signal utile. La seconde architecture intègre une fonction de conversion analogique-numérique de manière à simplifier le montage optique, et traiter le signal plus efficacement.Par ailleurs, le contrôle de la phase en plusieurs points du front est essentiel pour refocaliser les signaux lumineux. Pour contourner les limitations de vitesse des dispositifs de contrôle adaptatif de phase de l'état de l'art, nous avons développé un dispositif monolithique constitué de l'empilement physique d'un modulateur de lumière en phase, à cristaux liquides, sur un circuit CMOS constitué d'une matrice de photo-détecteurs et de circuits de traitement afin de permettre le contrôle de front d'onde dès son acquisition. Le dispositif opto-électronique a été proposé et couplé à la première architecture électronique. Il permet de réaliser une opération sur la phase de l'onde lumineuse en chaque pixel (conjugaison de phase par ex.) en parallèle sur les pixels d'une matrice, dans un intervalle de temps inférieur au temps de corrélation des milieux biologiques
Among the optical medical imaging techniques used in medicine, the main limitation is the low resolution at a penetration depth greater than a few mm. This limitation does not allows competing with the standard imaging techniques such as X rays or RMI based imaging. In that scope, the acousto-optical imaging features several advantages: it allows measuring an optical contrast useful to detect tumors, in conjunction with the spatial resolution of ultrasound. However, the state of the art detecting devices feature a lack of sensitivity, which prevent its transfer to medical practitioners.This leads us to study the intrinsic features of the acousto-optical signal in order to propose two CMOS pixel architectures. The first one, fully analog, is compliant with the correlation time of biological tissue (1 ms typ.) and features an analog processing of the relevant signal. The second one is based on a digital pixel which contains an analog to digital converter, allowing simplifying the optical setup and increasing the robustness of the processing.In addition, related to the recent progress in wavefront control, an opto-electronic device, coupled with the first pixel architecture, has been proposed. It allows performing an optical phase operation (e.g. phase conjugation) in parallel on a pixels array, within the correlation time of biological media. Thus, this monolithic device circumvents the speed limitations of state of the art setup by a physical stacking of a liquid crystals spatial light modulator over a CMOS image sensor

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Jayet, Baptiste. "Acousto-optic and photoacoustic imaging of scattering media using wavefront adaptive holography techniques in NdYO4." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066039/document.

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L'imagerie optique des tissus biologiques est un défi du fait de la diffusion de la lumière. Pour sonder les propriétés optiques à quelques cm de profondeur, on peut coupler l'information optique des ultrasons. De cette idée sont nées les imageries acousto-optique et photoacoustique. La première repose sur la modulation de la lumière par des ultrasons balistiques. La seconde se base sur la génération d'ultrasons lors de l'absorption de lumière par un objet. Que ce soit pour l'une ou pour l'autre, l'enregistrement du signal nécessite la mesure de très faibles modulations de phase dans une figure de speckle. L'holographie dynamique est une bonne solution. En effet, les techniques interférométriques sont suffisamment sensibles pour mesurer de telles modulations et l'holographie permet de corriger la nature speckle de la lumière. Dans cette thèse nous démontrons la faisabilité de fabriquer un système d'holographie adaptative basé sur un milieu laser (Nd :YVO4). Un des grands avantages de ce type de milieu est le temps de réponse. On montrera que le rafraîchissement d'un hologramme dans notre cristal peut se faire en moins de 100 ?s, bien inférieur au temps de décorrélation du speckle (? 1ms) qui pourrait grandement perturber les techniques de détection plus lentes lors d'expériences in vivo. Trois montages sont présentés ici, le premier pour la détection acousto-optique par conjugaison de phase, le deuxième pour la détection acousto-optique par adaptation de front d'onde et enfin le troisième pour détection photoacoustique. Dans les trois cas on mesure un temps de réponse entre 15 ?s et 50 ?s, et on utilise le montage imager un échantillon
Strong scattering properties of biological media make their optical imaging in depth a challenge. A solution to probe the local optical properties is to couple the optical information with ultrasound. Two imaging techniques were born from this idea, acousto-optic imaging and photoacoustic imaging. The first technique is based on the local modulation of light by ballistic ultrasound. The latter relies on the emission of ultrasound following the absorption of light by an object. Whether it is acousto-optic imaging or photoacoustic imaging, the recording of the the signal requires a detection system sensitive to weak phase modulation. In addition, the detection system must be compatible with a speckle pattern. Dynamic holography is a good solution. Indeed, as it is based on interferometry, it is very sensitive to small phase variations and holography can be used to correct the speckle nature of light. In this manuscript, we show the use of an holographic detection system based on a laser medium (Nd:YVO4). One of the main advantage of this type of material is the very fast response time. It will be highlighted that the recording of a hologram inside our crystal can be done in less than 100 μs, much faster than the speckle decorrelation time (≈ 1ms), which is one of the major obstacle towards in vivo imaging. Three optical setups will be presented in this manuscript. The first one is a phase conjugation setup for acousto-optic detection. The second one is a wavefront adaption setup, also for acousto-optic detection. Finally, the third setup is an adaptive vibrometry setup for photoacoustic detection. In each setups the measured response time is between 15 μs and 50 μs

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Millichope, Allen John. "Application of a charge coupled device Raman microscope imaging system for quantitative analysis of aqueous surfactant phases." Thesis, Liverpool John Moores University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327678.

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Blanche, Pierre-Alexandre, Brittany Lynn, Robert A. Norwood, and Nasser Peyghambarian. "Mechanisms for the reciprocity failure in photorefractive polymers." SPIE-INT SOC OPTICAL ENGINEERING, 2016. http://hdl.handle.net/10150/622716.

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We measured the diffraction efficiency response of two photorefractive polymer devices according to the duration of the single laser pulse used to record the hologram. The pulse duration was varied from 6 nanoseconds to 1 second, while the pulse energy density was maintained constant at 30 mJ/cm(2). This changed the peak power from 5 x 10(9) mW to 30 mW. We observed a strong reciprocity failure of the efficiency according to the pulse duration, with a reduction as large as a factor 35 between 1 second and 30 mu s pulse duration. At even lower pulse duration (< 30 mu s), the efficiency leveled out and remained constant down to the nanosecond exposure time. The same behavior was observed for samples composed of the same material but with and without buffer layers deposited on the electrodes, and different voltages applied during the holographic recording. We explained these experimental results based on the charge transport mechanism involved in the photorefractive process. The plateau is attributed to the single excitation of the charge carriers by short pulses (T-p < 30 mu s). The increase of efficiency for longer pulse duration (T-p > 30 mu s) is explained by multiple excitations of the charge carriers that allows longer distance to be traveled from the excitation sites. This longer separation distance between the carriers increases the amplitude of the space-charge field, and improves the index modulation. The understanding of the response of the diffraction efficiency according to the pulse duration is particularly important for the optimization of photorefractive materials to be used at high refresh rate such as in videorate 3D display.

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Bobb, Ross Lee. "Doppler Shift Analysis for a Holographic Aperture Ladar System." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1334950140.

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Dann, Stephen John David. "Progress towards a demonstration of multi-pulse laser Wakefield acceleration and implementation of a single-shot Wakefield diagnostic." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:6a7fe676-a9f4-4b50-a04e-9052e08cdd1b.

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An ongoing experiment is described to demonstrate the principle of multi-pulse laser wakefield acceleration, in which a plasma wakefield is resonantly excited by a train of laser pulses, spaced by the plasma wavelength. Particle-in-cell simulations of the initial single-pulse experimental setup are presented, in order to calculate the expected signal. Preliminary results are presented and future plans, based on work done so far, are discussed. Part of this work involves the implementation of a single-shot wakefield diagnostic - frequency-domain holography, which records the phase shift caused by passage of a probe pulse through the plasma. This implementation is described in detail, along with the associated analysis procedure. Practical difficulties encountered while implementing the diagnostic are discussed, along with possible ways of mitigating them in the future. A method is presented by which the noise level in the resulting phase measurements can be predicted, much more accurately than any previously published method for this technique. Methods of generating pulse trains for use in future multi-pulse laser wakefield acceleration experiments are presented. These include techniques proposed for use in this demonstration experiment, as well as one intended for use in a dedicated high-efficiency, high repetition-rate, multi-pulse driver laser. This last method, based on programmable pulse shaping using a spatial light modulator, requires a suitable mask to be computed based on the parameters of the required pulse train; an algorithm is described to perform this computation.

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Hansel, Thomas. "Anwendung ultrakurzer Lichtimpulse in der digital-holographischen Interferometrie." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2010. http://dx.doi.org/10.18452/16194.

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In dieser Arbeit wird die digital-holographisch-interferometrische Zwei-Wellenlängen-Formerfassung sehr schnell bewegter Objekte behandelt und dafür unter Nutzung einer Ultrakurzpuls-Laserquelle mit der digitalen Einzelimpuls-Mehr-Wellenlängen-Holographie ein neuartigen Ansatz der digital-holographischen Aufnahme und Auswertung entwickelt. Mit der Entwicklung spezieller Methoden zur Formung der spektralen Signatur einer Ultrakurzpuls-Laserquelle hoher Leistungsdichte wurde zum ersten Mal die Voraussetzung für eine Zwei-Wellenlängen-Formerfassung hochdynamischer Objekte geschaffen. Die intrinsisch kurze Belichtungszeit unter einer Pikosekunde macht das Verfahren absolut stabil gegenüber Umwelteinflüssen. Für die simultane Aufnahme werden die spektral verschiedenen Hologramme mit einem eigens entwickelten Prinzip der Polarisationskodierung räumlich getrennt und zum ersten Mal mit zwei synchron laufenden Kameras gespeichert. Mit den in der digital-holographischen Einzelimpuls-Mehr-Wellenlängen-Interferometrie zusammengefassten numerischen Routinen zur Rekonstruktion und Phasenauswertung wird eine Zwei-Wellenlängen-Formerfassung mit mehreren Kameras möglich. In Anwendung des neuartigen Verfahrens an verschiedenen dynamischen Mikrosystemen konnte eine Genauigkeit von einem Zwanzigstel der erzeugten synthetischen Wellenlänge, bei der Auswertung der spektralen Differenzphase an Objekten in Reflexion erreicht werden. In einer digital-holographischen Hochgeschwindigkeitsformerfassung in Transmission wurden erstmals Bildfolgefrequenz von mehr als 0,4 kHz erreicht und der interferometrische Eindeutigkeitsbereich auf mehr als das 60-fache der optischen Wellenlänge ausgedehnt. Es wurden die Voraussetzungen für eine digitale Vier-Wellenlängen-Holographie geschaffen. Zukünftig wird eine Formerfassung mit einer Genauigkeit von 10nm über einen eindeutigen interferometrischen Bereich einiger 10 μm und die Untersuchungen von Prozessen auf einer Pikosekunden-Zeitskala möglich sein.
This work deals with the digital holographic interferometric two-wavelength contouring of very fast moving objects and develops with the digital single pulse multiwavelength holography a novel approach of digital holographic recording and analysis, using an ultrashort pulse laser source. The development of several methods to shape the spektral signature of an high power ultrashort pulse laser source provides the precondition for a two-wavelength contouring of highly dynamic objects for the first time. The intrinsically short exposure time shorter than a picosecond makes the system stable regarding external impacts. For the simultaneous recording the spektral different holograms are spatially separated in novel interferometric setups by the especially developed principle of polarization encoding and stored with two synchronized cameras for the first time. The digital holographic single pulse multi-wavelength interferometry combines the numeric routines of reconstruction and phase evaluation that make a two-wavelength contouring possible using more than one camera. The novel approach is successfully demonstrated on several dynamic microsystems. Evaluating the spectral phase difference for objects in reflection an accuracy of 2 μm, which corresponds to the twentieth of the realized synthetic wavelength, could be achieved. In a digital holographic high speed contouring in transmission a frame rate higher than 0,4 kHz was achieved for the first time and the interferometric range of unambiguity was extended larger than sixty times the optical wavelength. Furthermore, the developed digital holographic single pulse multi-wavelength interferometry is not limited to the evaluation of two wavelength. The principles of the method allow to perform digital four-wavelength holography. Future a contouring with an accuracy of 10nm over the unambiguous interferometric range of several 10 μm and the investigation of processes on a picosecond time scale will be possible.

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Rosová, Kateřina. "Justážní kolimátor pro Fluorescenční holografický mikroskop." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-392837.

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For the proper function of the Fluorescence olographic microscope, it is necessary to adjust all the optical components of the microscope. Furthermore, the precise adjustment is the very critical condition for proper imaging of the Coherence-controlled holographic microscope. Therefore, it is necessary to create a sight collimator for these microscopes for their adjustment. The fluorescence holographic microscope is based on an interference and holographic principles, whose history is mentioned in the theoretical part of the thesis. The existing state of the art of laser sight collimators and their use in practice is also mentioned. The optical and mechanical design of the laser sight collimator and its realization are described in the next part of the thesis. The software for detecting the black sight cross was created for the use of the laser sight collimator in practice. The software is necessary to evaluate the correctness of the alignment of the adjusted microscope. The descriptions of the adjustment procedures for the laser sight collimator and for the Fluorescence holographic microscope are mentioned in the last part of the thesis. These procedures are necessary for proper manipulation and use with the proposed laser sight collimator.

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Kraczek, Jeffrey Read. "Piston Phase Measurements to Accelerate Image Reconstruction in Multi-Aperture Systems." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1323284036.

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Samaan, Julien. "Étude et applications de l'imagerie sans lentille par diffraction cohérente." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS557/document.

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Ce mémoire est dédié à l’imagerie par diffraction cohérente. Dans un premier temps, nous présentons la conception et à la mise en oeuvre expérimentale d’un système d’imagerie compact fonctionnant sur ce principe. Il est composé d’unediode UV (λ = 400 nm), d’une caméra CCD, et d’une plate-forme pour placer l’échantillon à observer. Le faisceau cohérent issu de la diode éclaire l’échantillon, et la figure de diffraction est enregistrée par la caméra. La rétro-propagation du champ détecté permet, en principe, de déterminer le profil de l’échantillon. Néanmoins, la phase du champ, perdue lors de la détection, nous contraint à employer desméthodes de « reconstruction de la phase », cette quantité étant nécessaire à l’opération d’inversion. Plusieurs techniques ont été utilisées. L’holographie par Transformée de Fourier, par exemple, est une méthode déterministe qui consiste à utiliser une référence circulaire (ou rectangulaire) gravée à côté de l’échantillon. La phase est encodée dans la figure de diffraction, sous la forme de franges d’interférences issues de l’objet et de la référence. Une simple Transformée de Fourier du signal permet alors de retrouver le profil de l’échantillon. Uneméthode itérative a également été mise en oeuvre, basée sur un jeu de contraintes dans les espaces réel et réciproque. En particulier, l’objet éclairé doit être « isolé », i.e. plus petit que le faisceau incident. Bien que cette méthode soit non-déterministe, nous verrons toutefois qu’elle est plus robuste et permet d’obtenir de meilleures résolutions spatiales qu’en holographie. Cette étude est un point de départ à l’observation d’objets tridimensionnels. Nous présentons une première méthode déterministe, basée sur l’holographie par Transformée de Fourier. Pour ce faire, une « pupille holographique » est utilisée et sert de support à une première reconstruction 2D du champ. Celui-ci est ensuite rétro-propagé vers l’échantillon placé à proximité, afin de réaliser une mise au point entièrement numérique de ce dernier. La contrainte « d’isolation » de l’objet est alors levée par l’utilisation de cette pupille. Avec cette méthode, le champ latéral est toutefoislimité par le diamètre de la pupille. Pour l’observation d’échantillons plus larges, la technique d’holographie « en ligne » a également été exploitée. Elle consiste à éclairer l’objet avec une onde sphérique et à enregistrer les franges d’interférences (ou « hologramme »). Une rétro-propagation est ensuite effectuée pour faire la mise au point sur l’échantillon. Le caractère divergent du faisceau permet de disposer d’un champ latéral de plusieurs millimètres. Le problème de « l’image jumelle », inhérent à cette configuration, est résolu via unalgorithme itératif couplé à la rétro-propagation. Des reconstructions tridimensionnelles ont été effectuées sur divers échantillons, avec cesdeux méthodes — reconstruction pupillaire et holographie en ligne. Pour chacune d’entre elles, des interfaces de reconstruction ont été mises au point et fonctionnent pendant la détection, afin d’observer l’objet en temps réel. Nous disposons alors d’un prototype d’imagerie sans lentille compact et complet. Enfin, nous présentons l’application d’une technique de reconstruction de la phase, appelée LIFT (pour LInearized Focal plane Technique), appliquée à un analyseur de front d’onde Shack-Hartmann. Usuellement, de tels capteurs ont une résolution spatiale limitée par le pas des micro-lentilles : seules les pentes locales (tip/tilt) sont déterminées. Le LIFT consiste à déterminer la phase à l’échelle de chaque micro-lentille, en exploitant le profil du spot correspondant. Des matrices d’interaction sont calculées afin de linéariser la relation entre l’espace réel (micro-lentilles) et l’espace réciproque (matrice CCD), et une boucle itérative permet d’étendre cedomaine de linéarité. Un gain de résolution spatiale de l’ordre de 3, au niveau de chaque micro-lentille, est attendu avec cette technique
This dissertation is dedicated to coherent diffractive imaging. Firstly, we present the conception and experimental implementation of a compact imaging system, working on this principle. It is made of an UV laser diode (λ = 400 nm), a CCD camera,and a platform to place the sample. The coherent beam coming from the diode illuminates the sample, and the diffraction pattern is recorded by the camera. Back-propagating the detected field should allow, in principle, to derive the sample’s profile. Nevertheless, the field’s phase, lost during the detection, forces us to use “phase retrieval” methods, this quantity being necessary to the inversion process. Several techniques have been used for that purpose. Fourier Transform Holography (FTH), for example, is a deterministic method thatconsists in using a circular reference, closely drilled nearby the sample. The phase is encoded in the diffraction pattern, in the form of interference fringes coming from the object and the reference. Then, a simple inverse Fourier Transform of the signal leads the profile of the sample. An iterative method has also been implemented, based on a set of constraints in the real and reciprocal spaces. In particular, the illuminated object must be “isolated”, i.e. smaller than the incident beam. Although this method is non-deterministic, we will see thatit is more robust and gives better resolutions than the holographic cases. This study is the starting point of three-dimensional imaging. We present a first deterministic method, based on FTH. For this purpose, a “holographic pupil” is used and serves as a support for a first 2D reconstruction of the field. The latter is then back-propagated towards the sample closely placed, in order to realize an entirely numerical focusing on it. The “isolation constraint” is then removed by the use of this pupil. However, with this method, the field of view is limitedby the pupil’s diameter. In order to observe larger samples, the “in-line holography” technique has been exploited as well. It consists in illuminating the object with a spherical wave and recording the interference fringes (or “hologram”). A back-propagation is made after the fact in order to do the focusing on the sample. The divergent nature of the beam allows for reaching several millimeters for the lateral field of view. The “twin image problem”, inherent to this configuration, is solved via an iterative algorithm coupled to the back-propagation process. Three-dimensional reconstructions have been made on varied samples, with these two methods — pupil reconstruction and in-line holography. In both cases, reconstruction interfaces have been implemented and work during the detection, in order to observe the object in real time. We then have a compact and complete lens-less imaging prototype. Finally, we present the application of a phase retrievaltechnique, named LIFT (LInearized Focal plane Technique), applied to a Shack-Hartmann wavefront sensor. Usually, such sensors have a spatial resolution that is limited by the micro-lenses size : only the local slopes, i.e. tip and tilt, are retrieved. The LIFT consists in determining the phase at the scale of each micro-lens, by exploiting the corresponding spot profile. Interaction matrices are calculated in order to linearize the relation between the real space (micro-lenses) and the reciprocal space (CCD chip), and an iterative loop allows for increasing this linearity domain. With this technique, a gain in spatial resolution by a factor 3 is expected

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Antier-Murgey, Marie. "Mesure interférométrique de phase et application à la combinaison cohérente d’un grand nombre de fibres amplificatrices." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112334/document.

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Les propriétés intrinsèques des fibres amplificatrices telles que leur robustesse, leur efficacité, leur qualité de faisceau ou encore leur compacité ou leur bonne gestion thermique, en font un candidat idéal pour le développement de sources lasers de haute puissance, capables de rivaliser aujourd’hui avec les lasers solides. Les applications de ces sources avec de fortes puissances sont nombreuses : l’industrie (usinage, marquage), la défense (télémétrie, imagerie), la physique des particules. Dans ce dernier cas, des sources ultra-brèves et ultra-intenses permettent d’envisager de nouvelles applications telles que la proton-thérapie ou bien le remplacement des synchrotrons actuels par des architectures moins encombrantes et ayant un rendement plus important. Ce travail de thèse s’est déroulé dans le contexte du projet ICAN qui vise à étudier l’architecture de ces nouvelles sources.La combinaison cohérente de plusieurs amplificateurs fibrés en parallèle permet d’augmenter la puissance de ces sources. Pour atteindre les énergies visées dans le projet ICAN, la combinaison cohérente de 10 000 fibres doit être envisagée. L’objectif de cette thèse est de développer des techniques de contrôle de la phase compatibles avec un très grand nombre de fibres, pour leur application aux lasers ultra-intenses nécessaires à la physique des particules.Deux architectures de combinaison cohérente basées sur une mesure de phase interférométrique ont été réalisées dans cette thèse. La première, basé sur l’holographie numérique, permet un contrôle de la phase sans aucun calcul, collectif tant au niveau de la mesure que de la correction. La seconde architecture possède un contrôle actif de phase basé sur un algorithme de traitement d’images et elle a une bande passante compatible avec le spectre de bruit des amplificateurs. La combinaison cohérente de 16 fibres à 1kHz avec une erreur résiduelle de phase de λ/60mrs a été démontrée. La compatibilité de ces deux architectures avec 10 000 fibres a été étudiée et nous avons apporté quelques éléments pour la combinaison cohérente d’un très grand nombre de fibres
The intrinsic properties of optical fibers like robustness, efficiency, beam quality, compactness and good thermal management can now compete with solid state lasers to develop high power laser sources. The applications of such sources include industry (machining, marking), defense (telemetry, lidar), and fundamental research. In this case, high intensity lasers are compulsory to produce the next generation of particles accelerators more efficient and more compact, both for fundamental research and its direct applications such as proton therapy. This work was done in the context of the ICAN project, which studies the feasibility of such sources.To overcome the limitations in terms of power of a single amplified fiber, an idea is to use several fiber lasers and to combine them coherently. To reach the ultra-high peak power and high average power requirements for these applications, the coherent beam combining of 10,000 fiber amplifiers has to be envisaged. The goal of the work is to develop a scheme of phase control scalable to a high number of combined fibers.Two schemes based on an interferometric phase measurement are realized in this work. The fist scheme, based on digital holography, permits a collective phase measurement and correction without calculation. The second scheme is based on an active phase control with individual phase modulators. This control requires an image processing algorithm and has a bandwidth compatible with the phase spectral noise of the amplifiers. The coherent combining of 16 fibers at 1kHz with a residual phase shift error of λ/60rms is achieved in this case. We use this second scheme to evaluate its scalability. We show that the coherent combining of 10,000 fibers using off-the-shelf components is already possible

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Hendricks, Jason Mark. "Holographic laser resonators." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/15485/.

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The work presented within this thesis details the development and characterisation of a CW solid-state adaptive resonator that uses phase-conjugation to actively correct for phase distortions present within the resonator loop. It is shown that the phase-conjugate of a given beam can be produced by the process of degenerate four-wave mixing inside a gain medium. In this scheme two mutually coherent beams overlap within a population inverted region of a laser amplifier and the subsequent interference pattern between them spatially hole burns a grating into the gain. The diffraction efficiency of such gain-gratings is studied both theoretically and experimentally and it is shown that, due to the stored inversion, CW phase-conjugate reflectivities of greater than 100 can be achieved in Nd:YVO4. Using this gain four-wave mixing scheme an adaptive resonator is built that is capable of oscillating with a phase-conjugate mode. The ability of the volume gain-grating to encode and react dynamically to phase distortions present within the resonator loop ensures that the phaseconjugate output beam from the resonator always remains a faithful reproduction of the beam used to seed the resonator. The interactions occurring within the resonator are modelled and a resonator capable of producing an 11.6 W near-diffraction limited output is demonstrated. The powerscaling capabilities of such lasers is then considered and it is shown that the output power can be increased whilst maintaining phase-conjugate oscillation. It is shown that a phase-conjugate output of 6 W can be scaled to 11.7 W with the addition of a power amplifier placed into the existing setup.

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Preto, André de Oliveira. "Caracterização de materiais por interferometria holografica em cristais fotorrefrativos utilizando lasers de diodo multimodo." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3140/tde-20072009-094804/.

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Este trabalho apresenta o estudo e o desenvolvimento de dois arranjos de interferometria holográfica utilizando como meio de registro holográfico cristais fotorrefrativos de Bi12TiO20 (BTO). O primeiro arranjo utiliza dois lasers de diodo sintonizáveis, emitindo em comprimentos de onda diferentes, em torno de 660 nm. Neste caso, a imagem holográfica do objeto estudado surge coberta de franjas de interferência que descrevem o relevo de sua superfície. O comprimento de onda sintético, que define a resolução do sistema na análise de superfícies, foi ajustado de modo a adequá-lo ao relevo da superfície estudada. A superfície de dois circuitos integrados e o relevo de uma moeda foram analisados, através de métodos de deslocamento de fase. O segundo arranjo gerou imagens holográficas e interferogramas, também com cristais BTO, através da montagem de Denisiuk para holografia de reflexão. Através da incorporação de um divisor de feixes polarizante, conseguiu-se melhorar a qualidade das imagens holográficas e reduzir o ruído. Medidas de deformação e vibração em pequenos objetos foram realizadas, assim como o estudo da dependência da intensidade do sinal holográfico sobre a orientação do cristal BTO.
This work presents the study and the development of two optical setups using Bi12TiO20 (BTO) photorefractive crystals for holographic interferometry. The first one employs two tunable diode lasers emitting at slightly different wavelengths around 660 nm. In this case, the holographic image of the studied object appears modulated by interference contour fringes. The resulting synthetic wavelength which determines the system resolution was selected in order to make it suitable for measuring the surface relief. The surfaces of two integrated circuits and a coin were analyzed with the help of phase shifting methods. The second BTO-based setup generated holographic images and interferograms through the Denisiuk scheme for reflection holography. The interferogram visibility and the optical noise were significantly reduced by using a polarizing beam splitter. Deformation and vibration measurements were performed, and the dependence of the reconstructed wave intensity on the BTO crystal orientation was studied as well.

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Hillier, David Ianto. "Holographic lasers." Thesis, University of Southampton, 2004. https://eprints.soton.ac.uk/65502/.

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This thesis presents the development of CW adaptive solid state lasers which dynamically correct for phase distortions within their cavity by phase conjugation. A fibre based four-wave mixing scheme is investigated but no experimental evidence of any phase conjugation is observed.

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Gonzalez, Angarita Aura Inés. "Single shot lensless imaging with coherence and wavefront characterization of harmonic and FEL sources." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112055/document.

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L’imagerie sans lentille a élargi le champ d’applications de l’imagerie aux sources cohérentes de courte longueur d’onde dans le domaine XUV, pour lequel les systèmes optiques pour l’imagerie ne sont pas facilement disponibles. En outre, les sources pulsées ultra brèves XUV et X basées sur la génération d’harmoniques laser d’ordre élevé (HHG) et les lasers à électrons libres (FEL) offrent une très bonne résolution temporelle (femto 10-15s - atto 10-18s). Ce sont donc les outils indispensables pour suivre les dynamiques ultrarapides à l’échelle nanométrique. Il est donc nécessaire de disposer de techniques d’imagerie en un tir unique pour profiter pleinement des capacités de ces sources XUV. Les techniques d’imagerie sans lentille sont basées sur la mesure directe du champ électromagnétique diffracté lors de l’interaction de la source avec l’échantillon. La diffraction est liée à la transmittance de l’objet mais aussi à la cohérence spatiale de la source et à son front d’onde. La caractérisation en un tir unique de ces propriétés permet l’amélioration de la résolution de la reconstruction de l’objet.Les résultats de cette thèse sont présentés en deux parties dans ce manuscrit. La première partie est consacrée à la caractérisation des sources XUV et la deuxième au développement de nouvelles techniques d’imagerie multidimensionnelle. Nous présentons différentes applications de la mesure du front d’onde en un tir unique des sources XUV. Les résultats sont le produit de différentes campagnes expérimentales, sur des sources HHG et les FEL LCLS (Stanford) et FERMI (Trieste). Nous présentons également une nouvelle méthode pour la caractérisation en simple tir de la cohérence spatiale qui ne nécessite pas la connaissance de la distribution d’intensité du faisceau incident. De plus, nous présentons une nouvelle technique d’imagerie basée sur l’holographie par transformée de Fourier pour améliorer la résolution dans la reconstruction de l’objet dans le cas de l’utilisation d’une source partialement cohérente.La deuxième partie est consacrée à deux techniques d’imagerie multidimensionnelle développées pendant cette thèse. Une nouvelle technique d’imagerie 3D en simple tir, facile à implémenter et réduisant fortement la dose de rayonnement reçu par l’échantillon, est présentée. Différents schémas expérimentaux pour la génération de deux sources XUV synchronisées pour cette technique d’imagerie stéréographique 3D sont proposés. D’autre part, nous présentons une technique holographique compatible avec une source de large bande spectrale. Deux applications sont envisagées. La première est l’imagerie ultrarapide résolue spectralement, la deuxième est l’imagerie attoseconde. A la fin du manuscrit des conclusions générales du travail accompli pendant la thèse, ainsi que des perspectives sont présentées
Lensless imaging techniques have broadened imaging applications to coherent sources in the short wavelength XUV domain, where optical systems to create an image are still not readily available. Furthermore, high harmonic generation sources (HHG) and free electron lasers (FEL) have the advantage of providing short temporal resolutions (atto 10-18s - femto 10-15s), opening the way towards ultrafast time resolved nanoscale imaging. Single shot imaging techniques are then highly important to exploit the shortest temporal resolution that can be reached with XUV sources. Lensless imaging is based on the direct measurement of the electric field diffracted by the sample. The diffraction pattern depends on the object transmittance but also on the source spatial coherence and wavefront. Single shot characterization of those properties thus leads to an improvement of the resolution of the object reconstruction.The results presented in this thesis are divided in two parts; the first one is focused on the characterization of the sources and the second on the development of new multidimensional imaging techniques. We will present different applications of single shot wavefront sensing of XUV sources. The results presented are the product of different experimental campaigns performed during this thesis using HH sources and FEL facilities at LCLS (Stanford) and FERMI (Trieste). Furthermore, a new method for single shot characterization of the spatial coherence that does not require the simultaneous measurement of the intensity distribution is presented. Additionally, we present a new holographic technique to improve the resolution of the object reconstruction when a partially coherent source is used.The second part is dedicated to two new multidimensional imaging techniques developed during the thesis. A new tri-dimensional imaging technique that is single shot, easy to implement and that lowers drastically the X-ray dose received by the sample, is presented. Different experimental setups for the generation of two synchronized XUV sources suitable for this ultrafast single shot 3D stereo imaging technique are presented. In addition, we present a holographic technique to extend imaging using a broadband source towards spectrally resolved single shot imaging and attosecond applications. Finally, we present the general conclusions from the work done during the thesis, together with the perspectives drawn from this work

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Bourderionnet, Jérôme. "Correction des aberrations et mise en forme spatiale d'un faisceau laser par contrôle de phase intracavité." Versailles-St Quentin en Yvelines, 2001. http://www.theses.fr/2001VERS0026.

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Les exigences industrielles actuelles impliquent le développement de sources monomodes transversalement (TEM00) délivrant une puissance moyenne allant de la centaine de Watts à plusieurs kWatts. Dans de telles conditions, le pompage optique implique sur les milieux amplificateurs une charge thermique très importante, qui génére par effets thermo-optique et thermo-mécanique une quantité non-négligeable d'aberrations thermiques dans le milieu amplificateur. Dans un premier temps, nous avons étudié théoriquement les incidences de ces aberrations thermiques sur les performances d'un oscillateur fonctionnant sur le mode fondamental. Nous avons ainsi déterminé les pertes induites, la dégradation de la qualité spatiale du faisceau, ainsi que les perturbations de la stabilité du laser, en fonction de l'amplitude de l'aberration thermique. Ces considérations nous amènent à envisager une correction des aberrations thermiques lorsque les puissances visées atteignent plusieurs centaines de Watts, et si l'on veut optimiser l'efficacité de la source. Nous proposons alors deux techniques originales de contrôle de la phase du faisceau laser. La première consiste à utiliser une lame de phase holographique fixe dans la cavité laser. Enfin, on utilise une valve à cristaux liquides adressée optiquement comme lame de phase programmable intracavité qui permet de contrôler dynamiquement le faisceau délivré par l'oscillateur. Nous démontrons que cette technique permet également de mettre en forme spatialement le faisceau délivré par l'oscillateur. Nous avons ainsi réalisé expérimentalement un résonateur pouvant produire des faisceaux de profils spatiaux variés.

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Amara, Mohamed Kamel Eddine. "Applications de l'effet photoréfractif en métrologie optique : velocimetrie holographique par imagerie de particules & vélocimétrie Doppler laser." Rouen, 1998. http://www.theses.fr/1998ROUES019.

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La PIV permet de cartographier des distributions de vitesses dans les écoulements divers, flammes, jets, elle n'est cependant pas adaptée à l'étude de distributions de vitesses à trois composantes dans un volume d'étude. Des systèmes associant l'holographie à la PIV ont permis d'étendre l'étude aux volumes en utilisant des plaques photosensibles. Ils sont donc lents à cause du développement chimique et souffrent d'un RSB moyen. Dans la première partie de ce travail, un système de HPIV utilisant un cristal photoréfractif, support dynamique totalement recyclable, a été réalisé. Il se base sur l'enregistrement holographique instantané de plusieurs nappes dans le volume d'un cristal BSO. L'exploitation des puissances spectrales, via un calcul d'auto-corrélation, permet de déterminer les composantes de vitesses transversales. Une méthode de calcul de phase a été élaborée pour déterminer la composante axiale des vecteurs vitesses. Les tests de faisabilité se sont avérés encourageants. Dans la seconde partie de ce travail, on a procédé à une étude théorique de faisceaux non-diffractants produits par diffraction d'une onde convergente sur une ouverture annulaire. Pour compenser la faible efficacité de conversion, on a eu recours à une amplification optique des faisceaux par mélange à deux ondes dans un cristal photoréfractif Batio#3. On a montré aussi que, dans la LDV avec des faisceaux gaussiens, des erreurs d'estimations de vitesses de particules peuvent être induites à cause de la variation de l'interfrange dans le volume d'étude. Celles-ci peuvent être réduites par l'utilisation de faisceaux non-diffractants.

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Mokhov, Sergiy V. "Theoretical study of beam transformations by volume diffraction." Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4986.

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Laser beams can be manipulated by volume diffractive elements in addition to conventional optical elements like mirrors, lenses, and beam splitters. Conventional optical elements can be described by applying the basic laws of reflection and refraction at the surfaces of the elements. Even diffraction by surface gratings utilizes relatively simple mathematics. This is to be contrasted with the volume diffraction, which requires coupled wave theory in the slowly varying envelope approximation (SVEA) to obtain accurate results. Efficient spatially distributed diffraction of laser beams is possible due to the high coherence of laser light, and it occurs at specific resonant Bragg conditions. This research work is inspired and driven by the successful development of recording technology for robust, high-efficiency volume Bragg gratings (VBGs) in photo-thermo-refractive (PTR) glass. Mostly VBGs of the reflective type are discussed in this dissertation. Starting with an analysis of electro-magnetic wave propagation in layered media, we have reformulated Fresnel and volume reflection phenomena in terms of a convenient parameter--strength of reflection. The influence that the different non-uniformities inside a VBG have on its spectral properties has been examined. One important result of this work is the proposal of moire VBG and the derivation of an analytical expression for its bandwidth. A multiplexed VBG used as a coherent combiner is discussed as well. Beam distortion via transmission through and/or reflection by a heated VBG due to residual absorption is analyzed.
ID: 030423243; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 114-127).
Ph.D.
Doctorate
Optics and Photonics

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Rozas, David. "Generation and Propagation of Optical Vortices." Digital WPI, 1999. https://digitalcommons.wpi.edu/etd-dissertations/348.

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"Optical vortices are singularities in phase fronts of laser beams. They are characterized by a dark core whose size may dramatically affect their behavior upon propagation. Previously, only large-core vortices have been extensively studied. The object of the research presented in this dissertation was to explore ways of generating small-core optical vortices (also called optical vortex filaments), and to examine their propagation using analytical, numerical and experimental methods. Computer-generated holography enabled us to create arbitrary distributions of optical vortex filaments for experimental exploration. We used hydrodynamic paradigms to develop an heuristic model which described the dependence of vortex motion on other vortices and the background beam, both qualitatively and quantitatively. We predicted that pair of optical vortex filaments will rotate with angular rates inversely proportional to their separation distance (just like vortices in a fluid). We also reported the first experimental observation of this novel fluid-like effect. It was found, however, that upon propagation in linear media, the fluid-like rotation was not sustained owing to the overlap of diffracting vortex cores. Further numerical studies and experiments showed that rotation angle may be enhanced in nonlinear self-defocusing media. The results presented in this thesis offer us a better understanding of dynamics of propagating vortices which may result in applications in optical switching, manipulation of micro-particles and optical limiting."

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Minassian, Ara. "Conventional and holographic Ti:sapphire laser oscillators." Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248802.

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Chateau, Nicolas. "Modélisation et caractérisation de réseaux holographiques ; étude de composants optiques holographiques en gélatine bichromatée." Phd thesis, Université Paris Sud - Paris XI, 1993. http://pastel.archives-ouvertes.fr/pastel-00715993.

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Dans les systèmes optiques modernes, l'importance des composants holographiques ne cesse d'augmenter. Parmi les matériaux holographiques disponibles, la gélatine bichromatée se distingue par la très bonne qualité des hologrammes obtenus. Cette thèse décrit la mise au point de techniques de fabrication et de caractérisation de composants holographiques en gélatine bichromatée. L'interprétation des mesures de caractérisation s'appuie sur une modélisation approfondie de la diffraction par des structures périodiques: une nouvelle méthode de résolution de la théorie d'ondes couplées, plus stable numériquement que les précédentes, est proposée. De plus, la théorie de la diffraction par des réseaux est étendue a des cas importants de restitution en lumière quasi-monochromatique. Les dispositifs expérimentaux développés ont permis l'étude et la réalisation de quatre nouveaux types d'hologrammes: réseaux pour la compression temporelle d'impulsions ultra brèves, hologramme synthétique séparateur et uniformiseur de faisceau laser, lentille holographique pour diode laser infrarouge et hologramme en ligne pour la réplication globale de disques compacts.

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Udaiyan, Darren. "Novel self-adaptive Nd:YAG laser resonators." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300857.

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Amer, Eynas. "Pulsed laser ablation studied using digital holographic interferometry." Licentiate thesis, Luleå : Luleå University of Technology, 2008. http://epubl.ltu.se/1402-1757/2008/55/.

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Yau, Suet Man. "Slanted layer photonic structures in silver-halide gelatin emulsions /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202006%20YAU.

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Raouf, Abdul. "Three dimensional image structure in in-line Fraunhofer holography." Thesis, Brunel University, 1991. http://bura.brunel.ac.uk/handle/2438/7278.

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Abstract:

In this thesis a new theoretical model for the three dimensional images from a finite aperture in-line Fraunhofer hologram is presented. Existing work only deals with the case of single object, in this thesis this work has been extended to the case of two identical coplanar discs. The resulting image equation is solved numerically for several different limiting apertures and their results are compared with the image intensity data from the holograms recorded on Agfa BE 75HD film. Excellent quantitative agreement is found, verifying the theoretical predictions. Three different criteria for determining the disc diameter and disc separation describing their errors are discussed for both numerical and experimental data. A data acquisition system based upon a digital interfaced with a PC, and high resolution video camera is described.

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Jones, Richard. "Application of ultrafast lasers to photorefractive holography through turbid media." Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298783.

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Olsson, Erik. "Digital holographic reconstructions of ultrasound from laser vibrometry recordings /." Luleå, 2004. http://epubl.luth.se/1402-1757/2004/024.

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Chen, Jhen-Si. "Holographic 3D image display : layer-based method and coarse integrated holograms." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708806.

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Dissertations / Theses on the topic 'Laser holography'

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