L'objectif de ce travail de thèse est l'élaboration d'un instrument de mesure optique dédié à la caractérisation de lentilles à gradient d'indice et d'asphériques de grandes dimensions. Pour parvenir à une caractérisation complète de la structure : variation spatiale de l'indice et de la topographie de surface, nous avons mis en place un banc d'interférométrie spectrale. Ce dispositif conduit à l'observation de spectres cannelés en lumière blanche (faible cohérence temporelle) porteurs d'une information de déphasage spectral entre les deux ondes qui interfèrent. <br />L'originalité de ce travail provient de l'utilisation d'une source supercontinuum de lumière blanche généré par pompage optique dans une fibre microstructurée. Cette source aux performances remarquables en termes de : largeur spectrale, de densité de puissance et de cohérence spatiale, permet d'analyser des composants peu étudiés jusqu'à présent.<br />L'exploitation des interférogrammes enregistrés nécessite la mise en place de traitements numériques adaptés. Ainsi les spectrogrammes périodiques associés aux mesures profilométriques sont traités par une méthode de décalage de phase 7 points, et les spectrogrammes non périodiques correspondant aux mesures de dispersion sont traités par une technique d'analyse simultanée temps-fréquence (transformée en ondelettes) couplée à une méthode d'ajustement de l'intensité par moindres carrés. <br />Les résultats expérimentaux mettent en évidence les différentes possibilités de l'interférométrie spectrale, la mesure de profil de surface avec une résolution nanométrique, la mesure de la variation spectrale de l'indice de groupe avec une résolution de 10-3, et la caractérisation simultanée des aberrations chromatiques et géométriques de systèmes imageurs.

Cette thèse concerne l'étude des propriétés linéaires des fibres optiques à bandes interdites photoniques et à coeur solide et l'utilisation de leurs caractéristiques singulières en optique non-linéaire guidée. La partie I est consacrée au calcul des bandes interdites photoniques que présente la gaine microstructurée. Nous avons mis en place un outil numérique de calcul de bandes par la méthode de décomposition en ondes planes en tenant compte de la dispersion des matériaux. Cet outil a été utilisé pour concevoir une fibre permettant la photo-inscription d'un réseau de Bragg. La méthode des perturbations stationnaires est ensuite appliquée pour déterminer les indices effectifs des modes autorisés aux grandes longueurs d'onde et identifier les modes linéairement polarisés vers lesquels ils évoluent. Dans la partie II, l'équation de Schrödinger non-linéaire généralisée est établie. Dans le cas d'une fibre effilée, il apparaît un terme supplémentaire permettant la conservation du nombre de photons. L'expression analytique usuelle du taux d'auto-décalage Raman est étendue au cas des solitons de courte durée jouant un rôle majeur dans le processus de génération de supercontinuum. La partie III est consacrée aux résultats obtenus en régime non-linéaire dans les fibres à bandes interdites photoniques à coeur solide. Nous montrons théoriquement que la forte valeur de la dispersion du troisième ordre est à l'origine de la suppression de l'auto-décalage Raman juste avant le bord de bande et sans pertes significatives. Cette suppression est ensuite utilisée pour limiter l'étendue spectrale et augmenter la stabilité tir-à-tir d'un supercontinuum.

The real-time detection of trace species is key to a wide range of applications such as on-line chemical process analysis, medical diagnostics, identification of environmentally toxic species and atmospheric pollutant sensing. There is a growing demand for suitable techniques that are not only sensitive, but also simple to operate, fast and versatile. Most currently available techniques, such as spectrophotometry, are neither sensitive enough nor fast enough for kinetic studies, whilst other techniques are too complex to be operated by the non-specialist. This thesis presents two techniques that have been developed for and applied to liquid-phase analysis, with supercontinuum (SC) radiation used for liquid-phase absorption for the first time. Firstly, supercontinuum cavity enhanced absorption spectroscopy (SC-CEAS) was used for the kinetic measurement of chemical species in the liquid phase using a linear optical cavity. This technique is simple to implement, robust and achieves a sensitivity of 9.1 × 10−7 cm−1 Hz−1/2 at a wavelength of 550nm for dye species dissolved in water. SC-CEAS is not calibration-free and for this purpose a second technique, a time-resolved variant called broadband cavity ring-down spectroscopy (BB-CRDS), was successfully developed. Use of a novel single-photon avalanche diode (SPAD) array enabled the simultaneous detection of ring-down events at multiple spectral positions for BB-CRDS measurements. The performance of both techniques is demonstrated through a number of applications that included the monitoring of an oscillating (Belousov-Zhabotinsky) reaction, detection of commercially important photoluminescent metal complexes (europium(III)) at trace level concentration, and the analysis of biomedical species (whole and lysed blood) and proteins (amyloids). Absorption spectra covering the entire visible wavelength range can be acquired in fractions of a second using sample volumes measuring only 1.0mL. Most alternative devices capable of achieving similar sensitivity have, up until now, been restricted to single wavelength measurements. This has limited speed and number of species that can be measured at once. The work presented here exemplifies the potential of these techniques as analytical tools for research scientists, healthcare practitioners and process engineers alike.

The aim of the presented work is to investigate the angle-resolved scattering characteristics of biological nano- and micro-scaled cell structures. The scattering results of cellular structures were compared to measurements of ideal spherical nano- and micro-particles. A monolayer of mouse fibroblasts L929 cells was cultivated in a Dulbecco's Modified Eagle Medium (DMEM) in a standard 24 well cell culture plate. The system allows an in situ measurement directly in the standard cell culture plate and a contaminant-free investigation of the viability of the cell cultures. Of particular interest was whether changes in the tumor characteristics occur in necrosis or other cell-harming effects. Because of the size ratios between wavelength and the scattering particles, all observations were investigated using Mie scattering theory. A setup for reliable measurements was developed and the scattered angle dependent intensity obtained was compared with simulated scattering characteristics. A homemade supercontinuum (SC) light source was filtered by an optical bandpass filter with a central wavelength of 500 nm. The scattered portion of the pulsed SC light behind the sample was recorded in a time-resolved manner at defined angles. A specimen holder adapted to standard cell culture plates allows detection of scattered radiation at angles between ±80° without angle-dependent Fresnel reflection losses and a Snell’s law bending of the propagation direction. Finally, the system was tested to detect structural changes of mouse fibroblast L929 cells before and after poisoning the cells with the cell detergent Triton X100 and the data clearly shows changes in the scattering characteristics when the cells were destroyed.

No description available.

Supercontinuum (SC) generation, oftentimes referred to as white-light continuum (WLC), has been a subject of interest for more than 40 years. From the first observation of WLC in condensed media in the early 1970s to the first observation of WLC in gases in the mid-1980s, much work has been devoted to developing a framework for understanding the complex nature of this phenomenon as well as discovering its utility in various applications. The main effort of this dissertation is to develop a WLC for the purpose of broadband nonlinear spectroscopy and use it in spectroscopic measurements. The ability to generate a high-quality, high-spectral-irradiance source of radiation confined in a single beam that spans the visible and near-infrared spectral regimes has great utility for nonlinear measurement methods such as the Z-scan technique. Using a broadband WLC instead of conventional tunable sources of radiation such as optical parametric generators/amplifiers has been shown to increase the efficiency of such measurements by nearly an order of magnitude. Although WLC generation has many complex processes involved, and complete models of the process involve highly complex numerical modeling, simple models can still guide us in the optimization of systems for WLC generation. In this dissertation the effects of two key mechanisms behind WLC generation in gaseous media are explored: self-phase modulation (SPM) and ionization leading to plasma production. The effects of SPM are largely dependent upon the third-order nonlinear refractive index, n2, of the gaseous medium whereas the effects of plasma production are dependent upon many parameters including the initial number density, ionization potential/energy, and the rate of ionization production. It is found that in order to generate a stable WLC suitable for nonlinear spectroscopy, the phase contributions from SPM and plasma production should be nearly equal. This guided our experiments in inert gases using mJ level, 150 fs-FWHM (full-width at half-maximum) pulses at 780 nm as well as 40 fs-FWHM pulses primarily at 1800 nm to create a stable, high-spectral-irradiance WLC. The generated WLC is shown to have sufficient spectral energy and spatial quality suitable for nonlinear spectroscopic measurements. In addition to extending the WLC bandwidth by using a long wavelength (1800 nm) pump source, it is found that by using a secondary weak seed pulse with a peak irradiance three orders of magnitude less than the main pulse, the spectral energy density is enhanced by more than a factor of 3 in Krypton gas for a WLC spectrum that spans over 2 octaves. Numerical simulations are presented which qualitatively describe the experimental results. The spectral enhancement of the WLC by seeding is also demonstrated for other inert gases and condensed media. Other efforts described in this dissertation include the development of the Dual-Arm Z-scan technique and its extension to measuring thin film nonlinearities in the presence of large substrate signals as well as predicting the n2 spectra of organic molecules (where we can approximate their behavior as if they were centrosymmetric) from knowledge of the one-photon and two-photon absorption spectra using a simplified sum-over-states quantum perturbative model by utilizing a quasi 3-level and quasi 4-level system.

Zuerst wird die Idee einer gechirpten photonischen Kristallfaser vorgestellt. Aus einem stark vereinfachten Modell, die qualitativen Eigenschaften dieses neuen Fasertyps abgeleitet. Hier gelingt es, alle wichtigen Designparameter zu bestimmen. Die hervorragenden Leitungseigenschaften dieser Fasern werden dann in Experimenten demonstriert. Ohne jegliche Dispersionskompensation wird die Übertragung eines 25 fs Impulses in einer 1 Meter langen Faser gezeigt. Wird zusätzlich eine Dispersionskompensation verwendet, lassen sich sogar Impulse mit weniger als 20 fs Dauer übertragen. Im Anschluss daran wird eine photonische Kristallfaser untersucht, die mit einer Flüssigkeit gefüllt ist. Die hergestellte Faser ist dahingehend optimiert, einen hoch effizienten Soliton-Fission Mechanismus zu ermöglichen, der zur Erzeugung von Weißlicht genutzt wird. Diese Weißlicht-Impulse haben eine mit Soliton-Fission bisher noch nie erreichte Energie von 390 nJ. Auf Grundlage einer guten Übereinstimmung mit den experimentellen Resultaten lässt sich aus numerischen Simulationen der zugrunde liegende Effekt bestimmen. Abschließend wird über ein Experiment berichtet, das die nichtlineare Wechselwirkung zwischen zwei Impulsen verschiedener Wellenlänge ausnutzt, um einen optischen Schalter zu verwirklichen. Dieses Experiment erfordert genaueste Kontrolle der Dispersion und der Nichtlinearität in der Faser. Bei der gleichzeitigen Propagation von zwei Impulsen wird ein neuartiger Schalteffekt beobachtet. Beide Impulse haben nahezu die gleiche Gruppengeschwindigkeit, und ihre nichtlineare Wechselwirkung basierend auf Kreuz-Phasen-Modulation wird dadurch deutlich verstärkt. Hiermit wird ein voll funktionsfähiger optischer Transistor mit gutem Schaltkontrast experimentell demonstriert, der insbesondere einen schwachen Impuls einen stärkeren Impuls schalten lässt. / First, the concept of a novel chirped photonic crystal fiber is introduced. The qualitative dispersion and loss properties of this new fiber are theoretically derived. The calculated results agree excellently with experimental data obtained from fabricated fiber samples. The superior guiding properties of this new photonic fiber are demonstrated in two experiments. The delivery of 25 fs pulses over a 1 meter distance is realized without any dispersion compensation. Moreover, using dispersion compensation, the delivery of even sub-20-fs pulses becomes possible. Subsequently, a photonic crystal fiber with a liquid core is investigated, work presents effective methods for the preparation and explains a scheme for successfully reducing the insertion loss. The fiber is optimized to support the highly efficient soliton-fission mechanism at unprecedented pulse energies in white-light supercontinuum generation. Because of the liquid core, the supercontinuum generation scheme can be scaled beyond the peak-power limitations of solid-core fibers. The generation of a two-octave spanning supercontinuum with 390 nJ pulse energy is demonstrated. The experimental results are compared to a numerical simulation and the underlying mechanism is identified. Finally, an experiment is presented that exploits strong nonlinear interaction of two pulses inside a photonic crystal fiber for all-optical switching. A novel effect is observed during the co-propagation of two ultrashort pulses with different wavelengths. Because of the dispersion properties in the chosen fiber, these pulses are propagating at nearly identical group velocities, which dramatically increases the nonlinear interaction via cross-phase modulation between the two pulses. Based on this interaction, a fully functional optical transistor is experimentally demonstrated with good switching contrast. In particular, the demonstrated optical transistor enables switching of a strong pulse by a much weaker pulse.

Esta tese descreve a demonstração experimental de dispositivos baseados em fibras de cristal fotônico (PCFs), que aproveitam a flexibilidade estrutural oferecida pela matriz de capilares que compõe a seção reta da fibra, de forma a preencher estes capilares com líquidos e materiais nanoestruturados. Para o caso de materiais nanoestruturados, uma vez preenchida a fibra, os materiais nela inseridos interagem eficientemente com a luz guiada. Essa arquitetura diferenciada em relação às fibras ópticas convencionais abre novas perspectivas no desenvolvimento de aplicações como óptica não-linear e sensoriamento. PCFs de núcleo líquido, por outro lado, impõe dificuldades para a implementação de dispositivos práticos, devido às altas taxas de evaporação dos líquidos inseridos. Por esta razão, foi desenvolvida uma nova técnica para vedar seletivamente ambas as faces externas do núcleo líquido de uma PCF, utilizando um polímero curável. Estes tampões poliméricos evitam a evaporação, causando um impacto mínimo no guiamento da luz, tornando o dispositivo usável por semanas. Esta nova técnica de vedação foi empregada em um experimento para a geração de supercontínuo em uma PCF com núcleo de água destilada, proporcionando uma estabilidade de pelo menos 1 hora. Combinando líquidos e materiais nanoestruturados, foi também foi desenvolvido um sensor de temperatura baseado no preenchimento do núcleo de uma PCF por uma amostra coloidal de nanopartículas semicondutoras de CdSe/ZnS, dispersas em óleo mineral. O espectro de luminescência destes pontos quânticos coloidais é fortemente dependente da temperatura e os resultados obtidos mostraram que a grande interação entre a luz e o colóide, aliada a geometria da fibra, proporcionando uma sensibilidade ~5,5 vezes maior que a apresentada por uma rede de Bragg escrita em uma fibra óptica padrão, com boa relação sinal-ruído. / This thesis describes the experimental demonstration of devices based on photonic crystal fibers (PCFs). PCFs are optical fibers whose core is surrounded by a regular matrix of holes, which runs longitudinally across its length. This singular configuration allows the insertion of liquids and nanostructured material into the fiber. Nanostructured materials embedded inside the fiber efficiently interact with the guided light, opening up possibilities of novel applications regarding the fields of non-linear optics, as well as optical sensing. On the other hand, liquid-core PCFs suffer from some disadvantages concerning practical device applications, on account of the high evaporation of the inserted liquids. In order to address this issue, we developed a novel technique to selectively seal the external faces of a liquid-core PCF, by using a polymer plug. These polymer plugs avoid evaporation while causing a minimum impact on the light guiding characteristics of the PCF. This novel sealing technique was employed in a supercontinuum generation experiment, by using a PCF whose core was water-filled. A temporal stability of at least one-hour on the resulting spectrum was achieved. Combining the above techniques, we also developed a temperature sensor based on the core-filling of a PCF by a colloidal ensemble of CdSe/ZnS semiconductor nanoparticles dispersed in mineral oil. Those colloidal quantum-dots display a luminescence spectrum which is strongly dependent on temperature and the experimental results indicated that the greater interaction between the guided light and the colloidal sample, provided by the fiber geometry, allowed a sensitivity which is approximately 5.5 times than possible with a conventional Bragg grating, while keeping a satisfactory signal-to-noise ratio.

Research towards the development of a gas-discharge fibre laser using noble gases, with target emission wavelengths in the mid-IR. Additional and separate work on gas treatment methods for managing the formation of photo-induced defects in silica glass.

Cette thèse porte sur l'utilisation du processus d'amplification paramétrique dans le fibres optiques dans le cadre d'applications en télécommunications (collaboration avec Alcatel) et sur la génération de supercontinuum spectraux. Les Amplificateurs Paramétriques à Fibres Optiques (FOPA) possèdent un potentiel intéressant en vue d'applications en télécommunications, en raison des larges bandes de gain disponibles, de leur accordabilité en longueur d'onde et de leurs propriétés de conversion de fréquence. Nous proposons un travail principalement théorique afin de vérifier la compatibilité de cette nouvelle famille d'amplificateurs avec les performances que requièrent les systèmes de télécommunications actuels. Différents formats de modulation de phase de la pompe sont étudiés afin de s'affranchir de la diffusion Brillouin stimulée, susceptible d'être engendrée par les puissantes pompes continues mises en oeuvre dans ces amplificateurs. Les performances de ces pompes sont ensuite évaluées sur des signaux monochromatiques et sur des signaux modulés en intensités. Ces résultats théoriques, en accord qualitatif avec des essais expérimentaux réalisés par Alcatel, montrent que la modulation de phase de la pompe induit des variations d'intensité pénalisantes pour des applications en télécommunications. Plusieurs solutions permettant de s'en affranchir sont alors proposées. D'autre part, nous démontrons qu'une mesure correcte de la figure de bruit de ces amplificateurs doit être effectuée dans le domaine des radiofréquences. L'amplification de signaux WDM est ensuite étudiée et nous démontrons qu'un positionnement spectral particulier du peigne WDM par rapport à la longueur d'onde de pompe permet de minimiser les interactions paramétriques parasites entre signaux et pompe. Par ailleurs, nous illustrons l'impact des fluctuations longitudinales de la longueur d'onde de dispersion nulle sur l'allure des courbes de gain d'un FOPA. La sensibilité des FOPAs à ces fluctuations nous a d'ailleurs permis de développer une nouvelle méthode de cartographie de la longueur d'onde de dispersion nulle d'une fibre optique de quelques centaines de mètres seulement. Enfin, une étude plus prospective de l'impact de la cohérence partielle d'ondes continues et intrinsèquement spectralement larges de type lasers à fibres sur le processus d'Instabilité de Modulation (MI) est proposée. D'une part nous démontrons que ce processus combiné à l'émission d'ondes dispersives permet d'expliquer l'élargissement spectral asymétrique observé expérimentalement. D'autre part, que l'utilisation de lasers à fibres pour pomper des FOPAs serait envisageable sous certaines conditions. Concernant la génération de supercontinuum spectraux dans les fibres optiques, nous proposons un dispositif expérimental simple, composé d'un micro-laser et d'une fibre de télécommunication standard, qui permet d'obtenir un supercontinuum monomode spatialement de plus de 1100 nm.