The optical design of a LED illuminator and camera imaging system were studied for potential use in a small medical "robotic type" probe to be used for minimally invasive abdominal surgery. Beam shaping optical reflectors were studied to increase the intensity distribution of the LED beam directed toward a close-by target surface. A CMOS/CCD camera and lens was used to image the targeted area. In addition, extensive optical ray tracing simulations were made to predict the intensity patterns. The experimental measurements and ray tracing simulations were in good agreement, and indicated that 20 degree cone reflectors for the LED sources and appropriate micro-lens/CCD chip imaging optics should provide a useful image at a working distance of about 5 cm.

La mise en forme de lumière blanche incohérente à l’aide d’un nouveau composant est proposée dans cette thèse. L'objectif était de réaliser une carte d'irradiance arbitraire sur un écran à l’aide d’une structure originale contenant seulement des facettes, légèrement inclinées par rapport à la direction d'origine selon leurs axes propres. Une approche basée sur l’optique géométrique a été utilisée pour concevoir et analyser la structure proposée. Celle-ci est constituée d’une matrice de facettes jouant le rôle de déflecteur. Nous avons étudié le cas en transmission et en réflexion. L’obtention des angles d’inclinaison s’est faite avec deux approches différentes : l'optimisation sous Zemax et le calcul analytique. Plusieurs critères de qualité ont été proposés pour comparer la carte d'irradiance. Le tolérancement a démontré qu’il est plus intéressant de travailler en transmission qu’en réflexion. Une réalisation a été faite avec succès en utilisant une technologie additive innovante. / Beam shaping of incoherent white light with a large spectrum is proposed in this PhD thesis. The objective was to realize an arbitrary irradiance map on a target plane using a faceted structure. To maintain the design result within the geometrical optics domain, large facet element dimensions are required to obtain usable results. Each facet element can slightly tilt along its own axes to deflect the incident light, either by reflection, either by transmission. The calculation of the tilt angles is made by an analytical approach, and also by automatic optimization with Zemax. Several quality factors are proposed in order to qualify the illumination/irradiance chart on the screen. Because of the required tolerances on the fabrication technique, we show that it is more interesting to design a transmissive structure than a reflective one. With a new additive technology, a structure is realized successfully, showing the interest of the concept.

The demand for high optical resolution has brought researchers to explore the use of beam shaping diffractive optical elements (DOEs) for improving performance of high numerical aperture (NA) optical systems. DOEs can be designed to modulate the amplitude, phase and/or polarization of a laser beam such that it focuses into a targeted irradiance distribution, or point spread function (PSF). The focused PSF can be reshaped in both the transverse focal plane and along the optical axis. Optical lithography, microscopy and direct laser writing are but a few of the many applications in which a properly designed DOE can significantly improve optical performance of the system. Designing DOEs for use in high-NA applications is complicated by electric field depolarization that occurs with tight focusing. The linear polarization of off-axis rays is tilted upon refraction towards the focal point, generating additional transverse and longitudinal polarization components. These additional field components contribute significantly to the shape of the PSF under tight focusing and cannot be neglected as in scalar diffraction theory. The PSF can be modeled more rigorously using the electromagnetic diffraction integrals derived by Wolf, which account for the full vector character of the field. In this work, optimization algorithms based on vector diffraction theory were developed for designing DOEs that reshape the PSF of a 1.4-NA objective lens. The optimization techniques include simple exhaustive search, iterative optimization (Method of Generalized Projections), and evolutionary computation (Particle Swarm Optimization). DOE designs were obtained that can reshape either the transverse PSF or the irradiance distribution along the optical axis. In one example of transverse beam shaping, all polarization components were simultaneously reshaped so their vector addition generates a focused flat-top square irradiance pattern. Other designs were obtained that can be used to narrow the axial irradiance distribution, giving a focused beam that is superresolved relative to the diffraction limit. In addition to theory, experimental studies were undertaken that include (1) fabricating an axially superresolving DOE, (2) incorporating the DOE into the optical setup, (3) imaging the focused PSF, and (4) measuring aberrations in the objective lens to study how these affect performance of the DOE.

No description available.

Les télécommunications laser en espace libre sont limitées en portée par la turbulence atmosphérique. L'optique adaptative, par la correction de la phase turbulente à l'émission du faisceau, a permis d'étendre leur domaine d'exploitation.Toutefois, sur de longues distances de propagation, cette correction n'est plus suffisante et il faut également précompenser l'amplitude du faisceau émis. De premières études numériques ont montré que le principe de retournement temporel, ou plus exactement de conjugaison de phase bidirectionnelle itérative, conduirait à des conditions satisfaisantes de focalisation du faisceau laser en fort régime de turbulence.Le principe de conjugaison de phase n'ayant été étudié que théoriquement jusque-là, mon travail de thèse s'est attaché à mettre en oeuvre un démonstrateur expérimental pour quantifier les performances de cette technique dans des conditions maîtrisées. En parallèle, une simulation de bout en bout de l'expérience a permis d'évaluer l'influence d'erreurs d'étalonnage sur les performances finales de la correction et de valider les résultats expérimentaux obtenus. Les points durs de la mise en oeuvre d'un système de télécommunications laser en espace libre ont ainsi été identifiés.L'ensemble de ces travaux constitue la toute première démonstration expérimentale du principe de retournement temporel optique. D'autres domaines d'application comme les lasers de puissance ou la propagation à travers des milieux biologiques très diffusants, nécessitant également de corriger le faisceau à l'émission, sont concernés. / Free Space Optical communications (FSO) are range limited due to atmospheric turbulence. Adaptive optics can mitigate turbulence effects by adding a phase modulation on the emitted laser beam. However, both phase and amplitude modulation are needed to perform long range FSO. Previous numerical studies have shown that iterative phase conjugation is an efficient modulation technique for lasercom systems.This PhD thesis is dedicated to the development and the realization of the first experimental demonstration of the iterative phase conjugation principle in a controlled turbulence environment. An optical bench, representative of a long range propagation through strong turbulence, has been scaled down to few-meters propagation in visible.Several methods for complex field measurement and modulation are numerically studied. Selected methods are implemented and tested, such as a novel focal plane technique for complex field measurement. Finally, iterative phase conjugation is performed and results cross-correlated with an end-to-end model representative of the optical bench.This work is the first experimental demonstration of the optical phase conjugation principle. Applications can be found in other fields than lasercoms, such as high power lasers or propagation through highly diffusing biological tissues, both in need of laser emission modulation.

La technique d’usinage par impulsions laser femtosecondes possède de nombreux avantages du fait des spécificités physique de l’interaction laser/matière en mode ultra-bref et est donc susceptible d’intéresser le monde industriel. Néanmoins elle présente aussi certaines limitations, principalement en terme de flexibilité et de productivité, limitant l’accès à ce marché. Pour repousser ces limites, nous proposons d’adjoindre des techniques de contrôle du faisceau, à la fois en taille, et plus généralement en forme, exploités par ailleurs dans d’autres domaines scientifiques (pincettes optiques notamment). Ces techniques reposent sur l’utilisation de modulateurs spatiaux de lumière (SLM). Deux solutions sont proposées : la modulation d’amplitude en configuration d’imagerie, et la modulation de phase pure en configuration de Fourier. Le formalisme, les différentes problématiques et la mise en oeuvre de ces deux techniques au sein d’une station de travail prototype que nous avons développée sont présentés. Enfin, nous mettons en évidence le gain apporté par ces techniques sur des problématiques concrètes, tels que l’usinage de réseaux résonant à l’échelle nanométrique, la réduction du temps d’usinage de ces réseaux (ou d’autres motifs), et l’amélioration de la qualité d’usinage de rainures / Femtosecond laser machining processes present many interesting properties owing to the specificities of the light/matter interaction in ultrafast regime. Thus the process may be of prime interest in industrial applications. However some aspects are not compatible with industrialization: namely a lack of flexibility and productivity. To overcome this limitations we propose to add beam shaping techniques in the process that allow control of the beam both in size and shape. These techniques are based on Spatial Light Modulators (SLM). Two different solutions are proposed: amplitude modulation in a geometrical conjugation scheme, and pure phase modulation in a Fourier scheme. Both are integrated in a prototype workstation. We justify the different choices made during the development by the analysis of the formalisms and specific problematics. Finally, enhancements of the femtosecond laser machining process are practically demonstrated in three different fields: reducing the resolution to nanometric scale, reducing the processing time of different texturations and enhancing the quality of simple grooves by modifying only the beam shape

Dans cette thèse, nous présentons le développement d'une méthode de nanoscopie optique superrésolue en trois dimensions pour résoudre des émetteurs quantiques uniques à température cryogénique. Cette méthode, appelée microscopie à saturation d'état excité (ESSat), est une technique d'imagerie confocale à balayage basée sur la saturation optique de la raie sans phonon de l'émetteur. Elle utilise un faisceau d’illumination structurée comprenant une zone d'intensité nulle au foyer de l'objectif de microscope, avec un gradient d'intensité important autour. En imageant des molécules fluorescentes aromatiques individuelles à 2 K, nous avons atteint une résolution de 28 nm dans la direction latérale et 22 nm dans la direction axiale, avec de faibles intensités laser d'environ dix kWcm-2, soit cinq ordres de grandeur inférieures à celles utilisées à température ambiante dans les méthodes de nanoscopie basées sur la déplétion par émission stimulée. Notre technique offre une opportunité unique de super-résoudre des molécules uniques séparées par des distances nanométriques et avec des résonances optiques qui se recouvrent. De plus, la méthode fournit une détermination directe de l'orientation des dipôles moléculaires à partir des images ESSat de fluorescence. La microscopie ESSat ouvre ainsi la voie à des études approfondies des interactions cohérentes dipôle-dipôle optiques entre émetteurs quantiques individuels, qui nécessitent des distances relatives nanométriques. En particulier, cette méthode permettra d'étudier les riches signatures spatiales et fréquentielles du système couplé et de manipuler leur degré d'intrication. / In this thesis, we present the development of a cryogenic super-resolution optical nanoscopy thatcan resolve molecules at nanometric distances, called the Excited State Saturation (ESSat)Microscopy.ESSat microscopy is a scanning confocal imaging technique based on the optical saturation of thezero phonon line of a single fluorescent molecule. It uses a patterned illumination beam thatcontains a ‘zero-intensity’ region at the focus of the microscope objective with a large intensitygradient around. We achieved a sub-10 nm resolution in the lateral direction and 22 nm resolutionin the axial direction with extremely low excitation intensities of few tens of kWcm-2. Comparedto other super-resolution imaging techniques, like STED, RESOLFT, etc., our technique offers aunique opportunity to super-resolve single molecules with overlapping optical resonances and thatare much closer than the diffraction limit. In addition, it is possible to determine the orientation ofmolecular dipoles from the fluorescent ESSat images. Since coherent dipole-dipole couplinginteractions between single quantum emitters have a very high coupling efficiency at short distancemuch smaller than the diffraction limit, it is important to resolve them well below it. ESSatmicroscopy thus paves a way to disclose the rich spatial and frequential signatures of the coupledsystem and to manipulate their degree of entanglement.

Optical microscopy is a cornerstone of biomedical research. Advances in optical techniques enable specific, high resolution, sterile, and biologically compatible imaging. In particular, beam shaping has been used to tailor microscopy techniques to enhance microscope performance. The aim of this Thesis is to investigate the use of novel beam shaping techniques in emerging optical microscopy methods, and to apply these methods in biomedicine. To overcome the challenges associated with high resolution imaging of large specimens, the use of Airy beams and related techniques are applied to light-sheet microscopy. This approach increases the field-of-view that can be imaged at high resolution by over an order of magnitude compared to standard Gaussian beam based light-sheet microscopy, has reduced phototoxicity, and can be implemented with a low-cost optical system. Advanced implementations show promise for imaging at depth within turbid tissue, in particular for neuroscience. Super-resolution microscopy techniques enhance the spatial resolution of optical methods. Structured illumination microscopy is investigated as an alternative for electron microscopy in disease diagnosis, capable of visualising pathologically relevant features of kidney disease. Separately, compact optical manipulation methods are developed with the aim of adding functionality to super-resolution techniques.

Diploma thesis deal with design of laser beam shaping system. The theoretical part presents basic information about the light spread lika the optical beams. There are also properties of optical and optoelectronic components that are used for shaping the laser beam. The next section provides basic molding methods, their principles and qualities. In the last, experimental, part is first introduced designed computer algorithm, which is then used to calculate the quality parameters shaped laser beams. Following, there are presented the results of measurements and calculations for some of these methods.

This master´s thesis provides basic properties and measurement of optical beams. In the first chapter is shown division of light on ray, wave and beam optics. Atmospheric optics and properties associated with propagation of light through the earth's atmosphere is presented in the second chapter. In the third part are shown basic techniques for Gaussian beam shaping. The last chapter deals with measurement of optical beam after propagating through a turbulent medium. In this section is shown distribution of relative variance of optical intensity in Gaussian and Top-Hat beam. There is also measured spatial coherence of laser beam in the turbulent atmospheric transmission media. Finally effect of the beam wander is investigated.