Les structures planes supportent la propagation de modes de Lamb, dont certains présentent une vitesse de groupe nulle et une vitesse de phase finie. Ces modes ZGV, favorablement engendrés et détectés par ultrasons laser, donnent lieu à des résonances locales étroites qui sont sensibles à l'épaisseur, aux propriétés élastiques et aux conditions de surface. Dans le premier volet de cette thèse, l'optimisation spatiale de la source laser (Faisceau rectangle ou Gaussien, anneau à profil rectangle ou Gaussien obtenu à l'aide d'un axicon) est étudiée afin d'améliorer la génération d'un mode de Lamb de longueur d'onde λ. Il est démontré que le rayon optimal d'un faisceau Gaussien est égal à λ/π. Les résultats théoriques sont en bon accord avec les simulations semi-analytiques et les mesures réalisées à la fréquence du mode ZGV S1S2 dans une plaque de Duralumin. Le second volet est dédié au contrôle de plaques collées par résonance ZGV. Ces structures sont décrites par un modèle rhéologique adhésif faisant intervenir des raideurs d'interface. La sensibilité des fréquences ZGV aux paramètres de la couche d'adhésif et aux raideurs d'interface est étudiée. La mesure des résonances ZGV a conduit à l'obtention des cartes de raideurs et d'épaisseur de colle. Elle a également permis de différencier des assemblages à tenue mécanique contrôlée / For some Lamb modes propagating in plane structures, the group velocity vanishes while the phase velocity remains finite. These modes are associated with local and narrow resonances and are sensitive to thickness, elastic properties and boundary conditions. Laser ultrasound techniques are well suited to generate and detect these resonances. In the first part of this thesis, spatial optimization of laser sources (Top-Hat and Gaussian beam, rectangular and Gaussian ring produced by an axicon-lens system) are studied in order to enhance the generation of a Lamb mode at wavelength λ. Optimal radius of a Gaussian beam is demonstrated to be λ/π. Theoretical results are shown to be in a good agreement with semi-analytical simulation and experimental results performed in a Duralumin plate at the S1S2-ZGV mode frequency. The second part of this work is dedicated to the use of ZGV resonances for the inspection of bonded plates. Trilayers are described by rheological model where interfaces are modelized by stiffnesses. The sensitivity of ZGV frequencies to the interfacial stiffnesses as well as adhesive layer parameters has been studied. Stiffnesses and adhesive thickness maps have been extracted from ZGV resonance measurements. In addition, ZGV mode measurements have been shown to allow the differenciation of controled bond strengh samples

When an intense femtosecond laser pulse propagates in a gas, it undergoes filamentation, a spectacular process where the pulse spatial, spectral and temporal characteristics change considerably. A thin short-lived plasma column is formed in the wake of the propagating pulse. My PhD work has been dedicated to the further understanding of the filamentation process. In a first part, I compare the properties of a usual filament with those of a filament formed by a femtosecond laser pulse with a Bessel beam profile. Using a laser pulse of same intensity and duration, I show that a Bessel beam can form a longer and more uniform plasma column in air, but that the plasma density is significantly lower. In a second part, I show that it is possible to increase considerably the lifetime of the plasma column, using a dual femtosecond/nanosecond laser pulse technique. To obtain an increased lifetime over a significant segment of a plasma column, I rely on the properties of Bessel beams in the nonlinear regime developed in the first chapter. In a third part, I study the dynamics of free electrons that are produced in the filamentation process. To do this, I have developed a specially designed current probe. Experiments reveal a very rich behaviour. The longitudinal displacements of electrons in the plasma column depend sensitively on the nature of the gas and its pressure as well as on the laser polarization of the laser. I propose a model to explain this behaviour. The direction of electron flow results from the competition between pure laser forces and a Coulomb wake field force. In the last chapter, I study filamentation in a Helium gas. This required improving the laser characteristics in order to reach the necessary power for filamentation. Improved characteristics have been achieved by implementing a planar compression stage which shortened the laser pulse from 50 fs to 10 fs without appreciable energy loss. The first experimental evidence for filamentation in He is presented at the end of the thesis. Agreement is found with a numerical simulation.

Axicons have been proposed for imaging applications since they offer the advantage of extended depth of field (DOF). This enhanced DOF comes at the cost of degraded image quality. Image processing has been proposed to improve the image quality. Initial efforts were focused on the use of an axicon in a borescope thereby extending depth of focus and eliminating the need for a focusing mechanism. Though promising, it is clear that image processing would lead to improved image quality. This would also eliminate the need, in certain applications, for a fiber optic imaging bundle as many modern day video borescopes use an imaging sensor coupled directly to the front end optics. In the present work, three types of refractive axicons are examined: a linear axicon, a logarithmic axicon and a Fresnel axicon. The linear axicon offers the advantage of simplicity and a significant amount of scientific literature including the application of image restoration techniques. The Fresnel axicon has the advantage of compactness and potential low cost of production. As no physical prior examples of the Fresnel axicons were available for experimentation until recently, very little literature exists. The logarithmic axicon has the advantage of nearly constant longitudinal intensity distribution and an aspheric design producing superior pre-processed images over the aforementioned elements. Point Spread Functions (PSFs) for each of these axicons have been measured. These PSFs form the basis for the design of digital image restoration filters. The performance of these three optical elements and a number of restoration techniques are demonstrated and compared.

La miniaturisation des systèmes d'imagerie présente aujourd'hui un fort potentiel dans plusieurs domaines, dont le développement de nouveaux dispositifs biomédicaux. Les exigences associées concernant l'imagerie demandent un effort substantiel dans le développement de composants optiques de haute qualité. Un meilleur contrôle de la propagation de la lumière ou de ses caractéristiques dans de tels systèmes est également important. Les composants doivent donc, par exemple, contenir les aberrations optiques pouvant affecter la résolution, la mise en œuvre de composants optiques dont le profil de phase continu est bien contrôlé est une voie intéressante. Ces composants devraient, de plus, être réalisés à partir de matériaux robustes en vue de leur assemblage au sein de dispositifs miniatures. Ce manuscrit de thèse de doctorat porte donc sur la conception et la fabrication parallèle de tels micro-composants optiques réfractifs réalisés en verre. Dans ce but, deux technologies ont été étudiées et optimisées, la lithographie à niveaux de gris et un procédé de soufflage de verre. En exemple, des microaxicons en verre ont été fabriqués et la génération de faisceaux de Bessel démontrée. Ce type de faisceau est caractérisé par une longue distance de propagation non-diffractive le long de l'axe optique, suivie d'une forme de faisceaux creux, qui les rend très utiles dans de nombreux domaines. Ces travaux de thèse ont été soutenus par le projet SMYLE (Small Systems for a Better Life) et le conseil Régional de Franche-Comté. / Miniaturization of imaging systems shows nowadays a strong potential for many applications, in particular, e. g., for novel biomedical devices. Related imaging specifications require a substantial effort onto the development of high quality microoptical components. better control of light propagation and features in such system sis also of particular interest. Components should then e.g. contain optical aberrations in order to reach high resolutions. In purpose of searching higher diffraction efficiencies or resolutions, optical components with well-controlled continuous phase profiles are sought. In addition, they also should be made of robust materials to handle their further assembly into miniaturized devices. Consequently, the manuscript focuses on the design and the parallel fabrication of such microoptical components made of glass. To that end, two technologies have been studied and optimized, namely gray-scale lithography and glass-blowing processes. As an example, glass-based microaxicons have been fabricated and Bessel beams generation has been demonstrated. This type of beam exhibits a long non-diffractive propagation distance along the optical axis followed by a dark hollow shape which makes them useful in many different applications. This work has been supported by the SMYLE (Smart Systems for a Better Life) European project and the Ranche-Comté Regional Council.

Cette thèse se concentre sur la contrôlabilité de l'indice de réfraction au niveau sub-micronique par changements d'indice induits par laser sur de longues dimensions i.e., avec des hauts rapports d'aspect élevés et des sections à l'échelle nanométrique. À cette fin, nous explorons les faisceaux ultracourts de Bessel non-diffractifs d'ordre zéro et les facteurs qui contribuent au confinement de l'énergie au-delà de la limite de diffraction. Le traitement par laser de matériaux transparents à l'aide de faisceaux non diffractifs offre un avantage important pour les structures sub-microniques en volume de haut rapport d'aspect à des fins applicatives en nanophotonique et en nanofluidique. Nous présentons l'effet de différentes conditions de focalisation et de paramètres laser sur la modification de la silice fondue, explorant ainsi les différents régimes d'interaction. Cette thèse aborde essentiellement des conditions modérées de focalisation car elles offrent un régime d'interaction stable sur une large gamme de paramètres laser, permettant l'ingénierie de la dispersion. La durée de l'impulsion laser s'est révélée être essentielle dans la définition du type de modification de l'indice de réfraction ou de modification structurale. Par exemple, l'usinage utilisant des impulsions laser femtosecondes entraîne une augmentation des structures d'indice de réfraction alors que les impulsions laser picosecondes engendrent une cavité uniforme i.e., des structures de faible indice. Pour acquérir un meilleur contrôle et une meilleure précision du dépôt d'énergie laser, un ensemble de mécanismes physiques responsables des dommages induits par laser dans des conditions d'excitation non-diffractives a été observé expérimentalement et examiné par des simulations indiquant le rôle essentiel de la diffusion de la lumière sur les électrons. Des mesures de microscopie pompe-sonde résolues en temps avec une résolution temporelle sub-picoseconde et spatiale sub-micronique donnent accès à l'excitation et à la relaxation dynamique instantanées. La transmission optique dynamique et le contraste de phase offrent des informations complémentaires sur la réponse électronique ou sur celle de la matrice vitreuse. La dynamique ultrarapide des porteurs libres a été particulièrement étudiée puisque le transfert d'énergie des électrons vers le réseau est la clé de transformation ultérieure du matériau. Le rôle de l'excitation instantanée pour différentes durées et énergie d'impulsion laser est exposé. Ainsi, la dynamique complète des porteurs de charge est présentée pour différents paramètres du laser. En particulier, la dynamique d'obtention de structures d'indice de réfraction positif et des cavités uniformes indique deux chemins différents de relaxation électronique et de dépôt de l'énergie: une relaxation rapide par l'intermédiaire de défauts pour les structures d'indice positif et une relaxation thermomécanique lente pour les cavités nanométriques. Enfin, en corrélant les résultats des études résolues en temps, les simulations et les résultats de photoluminescence après irradiation, nous formulons des scénarios potentiels de formation de l'indice de réfraction positif ainsi que des structures d'indice faible ou de vides uniformes / This thesis is focused on the controllability of laser-induced refractive index changes at sub-micron level over long dimensions i.e., with high aspect ratios and sections on the nanoscale. To this end, we explore non-diffractive zerothorder ultrafast Bessel beams and factors contributing to energy confinement beyond the diffraction limit. Laser processing of transparent materials using non-diffracting beams offers a strong advantage for high aspect ratio submicron structures inside the bulk in view of nanophotonics and nanouidics applications. We present the role of various focusing conditions and laser parameters on material modification in bulk fused silica and explore the different interaction regimes. This thesis tackles mostly the moderate focusing conditions as they offer a stable interaction regime backed up dispersion engineering over a large range of laser parameters. The laser pulse duration was found to be key in defining the type of laser induced refractive index or structural modification. For instance, machining using femtosecond laser pulses results in increased refractive index structures whereas picosecond laser pulses result in uniform void i.e., low index structures. To acquire better control over the laser energy deposition and precision, a range of physical mechanisms responsible for the laser induced damage in non-diffractive excitation conditions have been observed experimentally and further interrogated by simulations indicating a critical role of light scattering on carriers. Time-resolved pump-probe microscopy measurements with a sub-picosecond temporal and sub-micron spatial resolution allow access to the instantaneous excitation and relaxation dynamics. Dynamic optical transmission and phase contrast o_er complementary information of either electronic and glass matrix response. Primarily, ultrafast dynamics of free carriers was studied as the electron mediated energy transfer to the lattice is key to the subsequent material transformation. Role of instantaneous excitation at different laser pulse durations and energies is outlined. Then complete carrier dynamics is presented at different laser parameters. Particularly dynamics in conditions of positive refractive index structures and uniform voids is indicating two different paths of electronic relaxation and energy deposition: a fast defect mediated relaxation for positive index structures and slow thermomechanical relaxation for nanosize void structures. Finally, by correlating the results of time resolved studies, simulations and post-irradiated photoluminescence results, we formulate potential formation scenarios for the positive refractive index and low index or uniform void structures

Today, medical imaging is playing an important role in medicine as it provides the techniques and processes used to create images of the human body or parts thereof for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and function). Modalities are developing over time to achieve the highest possible resolution, speed of image acquisition, sensitivity, and specificity. In the past decade, advances in optics, fiber, as well as laser technology have enabled the development of noninvasive optical biomedical imaging technology that can also be applied to endoscopy to reach deeper locations in the human body. The purpose of this dissertation is to investigate a full system design and optimization of an optical coherence tomography (OCT) system to achieve high axial and lateral resolution together with an extended depth of focus for endoscopic in vivo imaging. In this research aimed at advancing endoscopic OCT imaging, two high axial resolution optical coherence tomography systems were developed: (1) a spectrometer-based frequency-domain (FD) OCT achieving an axial resolution of ~2.5 µm using a Ti:Sa femtosecond laser with a 120nm bandwidth centered at 800nm and (2) a swept-source based FD OCT employing a high speed Fourier domain mode locked (FDML) laser that achieves real time in vivo imaging with ~8 µm axial resolution at an acquisition speed of 90,000 A-scans/sec. A critical prior limitation of FD OCT systems is the presence of mirror images in the image reconstruction algorithm that could only be eliminated at the expense of depth and speed of imaging. A key contribution of this research is the development of a novel FD OCT imager that enables full range depth imaging without a loss in acquisition speed. Furthermore, towards the need for better axial resolution, we developed a mathematical model of the OCT signal that includes the effect on phase modulation of phase delay, group delay, and dispersion. From the mathematical model we saw that a Fourier domain optical delay line (FD ODL) incorporated into the reference arm of the OCT system represented a path to higher performance. Here we then present a method to compensate for overall system dispersion with a FDODL that maintains the axial resolution at the limit determined solely by the coherence length of a broadband source. In the development of OCT for endoscopic applications, the need for long depth of focus imaging is critical to accommodate the placement of the catheter anywhere within a vessel. A potential solution to this challenge is Bessel-beam imaging. In a first step, a Bessel-beam based confocal scanning optical microscopy (BCSOM) using an axicon and single mode fiber was investigated with a mathematical model and simulation. The BCSOM approach was then implemented in a FD OCT system that delivered high lateral resolution over a long depth of focus. We reported on the imaging in biological samples for the first time with a double-pass microoptics axicon that demonstrated clearly invariant SNR and 8 um lateral resolution images across a 4 mm depth of focus. Finally, we describe the design and fabrication of a catheter incorporated in the FD OCT. The design, conceived for a 5 mm outer diameter catheter, allows 360 degree scanning with a lateral resolution of about 5 um across a depth of focus of about 1.6 mm. The dissertation concludes with comments for related future work.

Ce travail consiste en l'étude et la mise en oeuvre d'une microscopie optique en champ proche utilisant des nano-antennes annulaires dans le but de distinguer les composantes électriques et magnétiques du champ électromagnétique, détectées au voisinage d'un échantillon.<br />Nous présentons la genèse de la microscopie en champ proche en mettant en avant l'importance des caractéristiques intrinsèques du système d'éclairage employé mais également le rôle primordial du nanocollecteur en interaction avec le champ électromagnétique. Les antennes étant un des enjeux majeurs dans l'art de détecter les champs électromagnétiques, nous donnons ensuite une cartographie des antennes dans différents domaines de fréquences ainsi que leurs applications respectives en champ proche. Puis nous exposons les étapes nécessaires à la fabrication d'une nano-antenne annulaire métallique aux dimensions spécifiques, à l'extrémité d'une fibre optique.<br />La description du système d'éclairage et du montage général de caractérisation nous amène enfin à présenter l'étude d'un nouveau type de sonde que constitue une nano-antenne annulaire usinée à l'extrémité d'un micro-axicon fibré. En exploitant les propriétés d'un faisceau de Bessel polarisé polychromatique, nous accédons aux propriétés de collection de la structure annulaire. Nous mettons en évidence le fait que ces antennes peuvent collecter spécifiquement la composante longitudinale du champ électrique en polarisation radiale ou du champ magnétique en polarisation orthoradiale. L'analyse des propriétés magnétiques et électriques d'échantillons en microscopie optique champ proche<br />s'annoncent, de ce fait, sous un nouveau jour.

Continuing advances in laser and photonic technology has seen the development of lasers with increasing power and increasingly short pulsewidths, which have become available over an increasing range of wavelengths. As the availability of laser sources grow, so do their applications. To make better use of this improving technology, understanding and controlling laser propagation in free space is critical, as is understanding the interaction between laser light and matter. The need to better control the light obtained from increasingly advanced laser sources leads to the emergence of beam engineering, the systematic understanding and control of light through refractive media and free space. Beam engineering enables control over the beam shape, energy and spectral composition during propagation, which can be achieved through a variety of means. In this dissertation, several methods of beam engineering are investigated. These methods enable improved control over the shape and propagation of laser light. Laser-matter interaction is also investigated, as it provides both a means to control the propagation of pulsed laser light through the atmosphere, and provides a means to generation remote sources of radiation.