The recipes of optical radiative properties manipulation are their materials chemistry, nano/microscale geometry, and transport properties of quasiparticle carriers such as photons, phonons, and electrons. The important technical element in optical properties is the dielectric function of materials, which is different for metals, dielectrics, 2D materials, and phase transition materials. Graphene has a unique electrical conductivity profile which have metallic nature depending on the frequency, but also has a negative thermal expansion coefficient that makes graphene unique. Hence, graphene creates wrinkles when deposited on the substrate as temperature decreases to room temperature from high substrate temperature. We also study phase transition material, particularly vanadium dioxide that transitions from insulating to metallic phase based on temperature change; we investigate its role in far-field thermal radiation. Other transition metal oxides are studied as a thermally and electrically tunable plasmonic gratings: Transition metal oxides include vanadium dioxide, tungsten trioxide, and molybdenum trioxide. The work demonstrates plasmonic phenomena and absorptance/emittance tunability. First, surface plasmon polariton along the graphene (SPPG) when wrinkles are formed above the plasmonic grating is studied. The resonance peak shift is modeled for both magnetic polariton (MP) with inductor-capacitor (LC) circuit and SPPG with Fabry-Perot phase change model. Second, the self-adaptive radiative coating is proposed using vanadium dioxide for high turn-down in emissivity spectrum. The Si high contrast grating (HCG) is introduced on the vanadium dioxide coating to prevent solar absorption by vanadium dioxide layer which have high extinction coefficient in visible to near-infrared region. Lastly, the switching in resonances, transitioning from MP resonance at metallic state to transmission mode obtained from concept of zero contrast grating (ZCG) is described. Overall, the work is aimed to tailor the optical radiative properties of gratings and multilayers used for thermal regulating applications.

Les lasers à cavité verticale émettant par la surface (VCSEL) à base d'antimoniures dans le moyen infrarouge permettent le développement et l'amélioration d'applications telles que la détection de gaz polluants. De nouveaux miroirs à réseaux à haut contraste d'indice (HCG) ont montré un pouvoir réflecteur comparable voire supérieur aux miroirs de Bragg conventionnels avec un gain d'épaisseur d'un facteur 10 tout en offrant un effet polarisant. L'insertion de ce nouveau type de miroir au sein d'une structure VCSEL présente ainsi des avantages prometteurs pour améliorer les propriétés de ces composants pour une émission dans le moyen infrarouge. Le travail présenté dans ce manuscrit de thèse concerne la conception de miroirs HCG qui répondent aux exigences d'une intégration VCSEL en prenant en compte les contraintes technologiques et la tolérance aux erreurs de fabrication. Pour cela, dans un premier temps, un algorithme d'optimisation global a été combiné à une méthode de simulation numérique de réseaux (RCWA) afin d'automatiser la conception de miroirs. L'étude précise des tolérances des paramètres géométriques du réseau a été menée pour pouvoir ensuite développer un algorithme d'optimisation robuste. Cet algorithme permet ainsi d'obtenir non seulement un miroir répondant aux exigences de réflectivités définies par l'utilisateur mais également de conserver ces performances pour de larges gammes de tolérances. Enfin, dans une dernière partie, l'intégration du miroir à réseau dans un VCSEL a été simulée par une méthode aux différences finies (FDTD) pour étudier le fonctionnement d'un composant complet. / In the mid infrared wavelength range, Vertical Cavity Surface Emitting Lasers (VCSEL) based on the antimony alloy is a promising solution to develop and enhance numerous applications such as polluting gas sensing. A new type of mirror based on High Contrast Grating (HCG) structures has shown similar reflectivities than the Bragg mirrors which are usually used in VCSELs. However, with a polarization selectivity and a reduction in thickness of a factor of 10, HCG mirrors can advantageously replace Bragg reflectors to enhance the properties of mid infrared VCSEL structures. The work presented in this manuscript is devoted to the design of high contrast grating mirrors for a VCSEL application and takes precisely into account the technological constraints and tolerance of fabrication. In a first part, a global optimization algorithm has been combined to a numerical analysis of grating structures (RCWA) to automatically design HCG mirrors for a VCSEL application. In a second part of this work, the tolerances of the grating dimensions have been precisely studied which has lead to the development of a robust optimization algorithm. This algorithm allows to design high contrast gratings which exhibit not only a high efficiency but also large tolerance values required by the manufacturing process. Finally, in a last part, a VCSEL structure using a high contrast grating as top mirror has been designed and simulated by FDTD to validate the use of HCG presented previously in a VCSEL structure.

The present work deals with the development and application of an acoustic long-period fiber grating (LPG) in conjunction with a special optical fiber (SF). The acoustic LPG converts selected optical modes of the SF. Some of these modes are characterized by complex, yet cylindrically symmetric polarization and intensity patterns. Therefore, they are the guided variant of so called cylindrical vector beams (CVBs). CVBs find applications in numerous fields of fundamental and applied optics. Here, an application to high-resolution light microscopy is demonstrated. The field distribution in the tight microscope focus is controlled by the LPG, which in turn creates the necessary polarization and intensity distribution for the microscope illumination. A gold nanoparticle of 30 nm diameter is used to probe the focal field with sub-wavelength resolution. The construction and test of the acoustic LPG are discussed in detail. A key component is the piezoelectric transducer that excites flexural acoustic waves in the SF, which are the origin of an optical mode conversion. A mode conversion efficiency of 85% was realized at 785 nm optical wavelength. The efficiency is, at present, mainly limited by the spectral positions and widths of the transducer’s acoustic resonances. The SF used with the LPG separates the propagation constants of the second-order polarization modes, so they can be individually excited and are less sensitive to distortions than in standard weakly-guiding fibers. The influence of geometrical parameters of the fiber core on the propagation constant separation and on the mode fields is studied numerically using the multiple multipole method. From the simulations, a simple mode coupling scheme is developed that provides a qualitative understanding of the experimental results achieved with the LPG. The refractive index profile of the fiber core was originally developed by Ramachandran et al. However, an important step of the present work is to reduce the SF’s core size to counteract the the appearance of higher-order modes at shorter wavelengths which would otherwise spoil the mode purity. Using the acoustic LPG in combination with the SF produces a versatile device to generate CVBs and other phase structures beams. This fiber-optical method offers beam profiles of high quality and achieves good directional stability of the emitted beam. Moreover, the device design is simple and can be realized at low cost. Future developments of the acoustic LPG will aim at applications to fiber-optical sensors and optical near-field microscopy. / Diese Arbeit behandelt die Entwicklung und Anwendung eines akustischen langperiodischen Fasergitters (LPG) in Verbindung mit einer optischen Spezialfaser (SF). Das akustische LPG wandelt ausgewählte optische Modi der SF um. Einige dieser Modi weisen eine komplexe, zylindersymmetrische Polarisations- und Intensitätsverteilung auf. Diese sind eine Form der so genannten zylindrischen Vektor-Strahlen (CVBs), welche in zahlreichen Gebieten der wissenschaftlichen und angewandten Optik zum Einsatz kommen. In dieser Arbeit wird eine Anwendung auf die hochauflösende Lichtmikroskopie demonstriert. Die fokale Feldverteilung wird dabei durch die Auswahl der vom LPG erzeugten Modi, welche zur Beleuchtung genutzt werden, eingestellt. Als Nachweis wird die entstehende laterale Feldverteilung mithilfe eines Goldpartikels (Durchmesser 30 Nanometer) vermessen. Aufbau und Test des akustischen LPGs werden im Detail besprochen. Eine wichtige Komponente ist ein piezoelektrischer Wandler, der akustische Biegewellen in der SF anregt. Diese sind die Ursache der Umwandlung optischer Modi. Die maximale Konversionseffizienz betrug 85% bei 785 nm (optischer) Wellenlänge. Die Effizienz ist derzeit hauptsächlich durch die Lage der akustischen Resonanzfrequenzen des Wandlers und deren Bandbreite begrenzt. Die benutzte SF spaltet die Ausbreitungskonstanten von Polarisationsmodi zweiter Ordnung auf, sodass diese individuell angeregt werden können und weniger anfällig gegen über Störungen der Faser sind, als das bei gewöhnlichen, schwach führenden Glasfasern der Fall ist. Das zu Grunde liegende Brechzahlprofil des Faserkerns wurde von Ramachandran et al. entwickelt. Für diese Arbeit wurde jedoch die Ausdehnung des Profils verkleinert – ein erster Schritt um Anwendungen bei kürzeren optischen Wellenlängen zu ermöglichen. Es werden numerische Simulationen mit der Methode der multiplen Multipole zur Berechnung der Modenfelder und den zugehörigen Propagationskonstanten vorgestellt. Diese zeigen u. a. den starken Einfluss von geometrischen Veränderungen des Faserkerns. Basierend auf den Simulationsergebnissen wird ein einfaches Kopplungsschema für die Modi entwickelt, welches ein qualitatives Verständnis der experimentellen Ergebnisse ermöglicht. In Kombination bilden die SF und das LPG ein vielseitiges Gerät zur Erzeugung von CVBs und anderen Strahlen mit komplexer Phasenstruktur. Die Methode besticht durch hohe Qualität des Strahlprofils, stabile Abstrahlrichtung, einfachen Aufbau, elektronische Steuerbarkeit und geringe Materialkosten. Zukünftige Weiterentwicklungen des akustischen LPGs zielen auf die Anwendung in faseroptischen Sensoren und in der optischen Nahfeldmikroskopie ab.

The present work deals with the development and application of an acoustic long-period fiber grating (LPG) in conjunction with a special optical fiber (SF). The acoustic LPG converts selected optical modes of the SF. Some of these modes are characterized by complex, yet cylindrically symmetric polarization and intensity patterns. Therefore, they are the guided variant of so called cylindrical vector beams (CVBs). CVBs find applications in numerous fields of fundamental and applied optics. Here, an application to high-resolution light microscopy is demonstrated. The field distribution in the tight microscope focus is controlled by the LPG, which in turn creates the necessary polarization and intensity distribution for the microscope illumination. A gold nanoparticle of 30 nm diameter is used to probe the focal field with sub-wavelength resolution. The construction and test of the acoustic LPG are discussed in detail. A key component is the piezoelectric transducer that excites flexural acoustic waves in the SF, which are the origin of an optical mode conversion. A mode conversion efficiency of 85% was realized at 785 nm optical wavelength. The efficiency is, at present, mainly limited by the spectral positions and widths of the transducer’s acoustic resonances. The SF used with the LPG separates the propagation constants of the second-order polarization modes, so they can be individually excited and are less sensitive to distortions than in standard weakly-guiding fibers. The influence of geometrical parameters of the fiber core on the propagation constant separation and on the mode fields is studied numerically using the multiple multipole method. From the simulations, a simple mode coupling scheme is developed that provides a qualitative understanding of the experimental results achieved with the LPG. The refractive index profile of the fiber core was originally developed by Ramachandran et al. However, an important step of the present work is to reduce the SF’s core size to counteract the the appearance of higher-order modes at shorter wavelengths which would otherwise spoil the mode purity. Using the acoustic LPG in combination with the SF produces a versatile device to generate CVBs and other phase structures beams. This fiber-optical method offers beam profiles of high quality and achieves good directional stability of the emitted beam. Moreover, the device design is simple and can be realized at low cost. Future developments of the acoustic LPG will aim at applications to fiber-optical sensors and optical near-field microscopy.:Abstract / Kurzfassung iii Table of contents v 1 Introduction 1 2 Fundamentals of optical waveguides 5 2.1 Introduction 5 2.2 Maxwell’s equations and vector wave equations 5 2.3 Optical waveguides 7 2.3.1 Dielectric waveguides 7 2.3.2 Metallic waveguides 9 2.4 Numerical calculation of modes by the multiple multipole program 10 2.4.1 Representation of simulated mode fields 11 2.5 Overview of coupled mode theory 14 2.5.1 Coupled mode equations 14 2.5.2 Co-directional coupling 15 2.6 Summary and conclusions 16 3 Polarization control for fundamental and higher order modes 17 3.1 Introduction 17 3.2 Description of light polarization 18 3.2.1 Stokes parameters and the polarization ellipse 18 3.2.2 Polarization of light beams in free space 20 3.2.3 Polarization of light beams in optical fibers 21 3.3 Short overview of cylindrical vector beam generation 22 3.4 Excitation of cylindrical vector beams in optical fibers 27 3.4.1 Free-beam techniques 27 3.4.2 In-fiber techniques 29 3.5 Polarization control in optical fibers 30 3.5.1 Phase matching and the beat length 30 3.5.2 Polarization-maintaining single-mode fibers 32 3.5.3 Higher-order mode polarization-maintaining fibers 32 3.6 Summary and conclusions 34 4 Simulation of core-ring-fibers 36 4.1 Introduction 36 4.2 Model geometries for index-tailored optical fiber 37 4.2.1 Special fiber and fabrication 37 4.2.2 Elliptical core boundaries 39 4.2.3 Overview of the applied MMP Models 41 4.3 Simulation results for circular core geometry 43 4.3.1 Mode fields 43 4.3.2 Scaling of the core radii 43 4.3.3 Wavelength dependence 48 4.4 Simulation results for non-circular geometry 50 4.4.1 Mode fields 50 4.4.2 Effects of individual rotation angles 53 4.4.3 Wavelength dependence 56 4.5 Summary and conclusions 61 5 Long period fiber gratings 63 5.1 Introduction 63 5.2 Principle of long-period fiber gratings 64 5.2.1 Results from coupled mode theory 64 5.2.2 Types of long-period gratings 65 5.2.3 Properties of acoustic long-period fiber gratings 67 5.3 Acoustic long-period grating setup 68 5.3.1 Transducer 69 5.3.2 Mechanical coupling 72 5.3.3 Acoustic dispersion of an optical fiber 75 5.3.4 Optical setup 77 5.3.5 Comparison to other acoustic LPG geometries 81 5.4 Experimental results 82 5.4.1 Transmission spectra 82 5.4.2 Discussion of transmission results 88 5.4.3 Direct mode field observation 93 5.4.4 Discussion of mode field observations 97 5.4.5 Time behavior and grating amplitude modulation 99 5.5 Summary and conclusions 101 6 Application of higher order fiber modes for far-field microscopy 104 6.1 Introduction 104 6.2 Complex beams in high-resolution far-field microscopy 104 6.3 Theoretical considerations 106 6.4 Experimental details 111 6.5 Results 114 6.6 Discussion 118 6.7 Summary and conclusions 122 7 Summary and outlook 124 Acknowledgments 139 Publications related to this work 142 List of figures 144 List of tables 150 List of acronyms 151 / Diese Arbeit behandelt die Entwicklung und Anwendung eines akustischen langperiodischen Fasergitters (LPG) in Verbindung mit einer optischen Spezialfaser (SF). Das akustische LPG wandelt ausgewählte optische Modi der SF um. Einige dieser Modi weisen eine komplexe, zylindersymmetrische Polarisations- und Intensitätsverteilung auf. Diese sind eine Form der so genannten zylindrischen Vektor-Strahlen (CVBs), welche in zahlreichen Gebieten der wissenschaftlichen und angewandten Optik zum Einsatz kommen. In dieser Arbeit wird eine Anwendung auf die hochauflösende Lichtmikroskopie demonstriert. Die fokale Feldverteilung wird dabei durch die Auswahl der vom LPG erzeugten Modi, welche zur Beleuchtung genutzt werden, eingestellt. Als Nachweis wird die entstehende laterale Feldverteilung mithilfe eines Goldpartikels (Durchmesser 30 Nanometer) vermessen. Aufbau und Test des akustischen LPGs werden im Detail besprochen. Eine wichtige Komponente ist ein piezoelektrischer Wandler, der akustische Biegewellen in der SF anregt. Diese sind die Ursache der Umwandlung optischer Modi. Die maximale Konversionseffizienz betrug 85% bei 785 nm (optischer) Wellenlänge. Die Effizienz ist derzeit hauptsächlich durch die Lage der akustischen Resonanzfrequenzen des Wandlers und deren Bandbreite begrenzt. Die benutzte SF spaltet die Ausbreitungskonstanten von Polarisationsmodi zweiter Ordnung auf, sodass diese individuell angeregt werden können und weniger anfällig gegen über Störungen der Faser sind, als das bei gewöhnlichen, schwach führenden Glasfasern der Fall ist. Das zu Grunde liegende Brechzahlprofil des Faserkerns wurde von Ramachandran et al. entwickelt. Für diese Arbeit wurde jedoch die Ausdehnung des Profils verkleinert – ein erster Schritt um Anwendungen bei kürzeren optischen Wellenlängen zu ermöglichen. Es werden numerische Simulationen mit der Methode der multiplen Multipole zur Berechnung der Modenfelder und den zugehörigen Propagationskonstanten vorgestellt. Diese zeigen u. a. den starken Einfluss von geometrischen Veränderungen des Faserkerns. Basierend auf den Simulationsergebnissen wird ein einfaches Kopplungsschema für die Modi entwickelt, welches ein qualitatives Verständnis der experimentellen Ergebnisse ermöglicht. In Kombination bilden die SF und das LPG ein vielseitiges Gerät zur Erzeugung von CVBs und anderen Strahlen mit komplexer Phasenstruktur. Die Methode besticht durch hohe Qualität des Strahlprofils, stabile Abstrahlrichtung, einfachen Aufbau, elektronische Steuerbarkeit und geringe Materialkosten. Zukünftige Weiterentwicklungen des akustischen LPGs zielen auf die Anwendung in faseroptischen Sensoren und in der optischen Nahfeldmikroskopie ab.:Abstract / Kurzfassung iii Table of contents v 1 Introduction 1 2 Fundamentals of optical waveguides 5 2.1 Introduction 5 2.2 Maxwell’s equations and vector wave equations 5 2.3 Optical waveguides 7 2.3.1 Dielectric waveguides 7 2.3.2 Metallic waveguides 9 2.4 Numerical calculation of modes by the multiple multipole program 10 2.4.1 Representation of simulated mode fields 11 2.5 Overview of coupled mode theory 14 2.5.1 Coupled mode equations 14 2.5.2 Co-directional coupling 15 2.6 Summary and conclusions 16 3 Polarization control for fundamental and higher order modes 17 3.1 Introduction 17 3.2 Description of light polarization 18 3.2.1 Stokes parameters and the polarization ellipse 18 3.2.2 Polarization of light beams in free space 20 3.2.3 Polarization of light beams in optical fibers 21 3.3 Short overview of cylindrical vector beam generation 22 3.4 Excitation of cylindrical vector beams in optical fibers 27 3.4.1 Free-beam techniques 27 3.4.2 In-fiber techniques 29 3.5 Polarization control in optical fibers 30 3.5.1 Phase matching and the beat length 30 3.5.2 Polarization-maintaining single-mode fibers 32 3.5.3 Higher-order mode polarization-maintaining fibers 32 3.6 Summary and conclusions 34 4 Simulation of core-ring-fibers 36 4.1 Introduction 36 4.2 Model geometries for index-tailored optical fiber 37 4.2.1 Special fiber and fabrication 37 4.2.2 Elliptical core boundaries 39 4.2.3 Overview of the applied MMP Models 41 4.3 Simulation results for circular core geometry 43 4.3.1 Mode fields 43 4.3.2 Scaling of the core radii 43 4.3.3 Wavelength dependence 48 4.4 Simulation results for non-circular geometry 50 4.4.1 Mode fields 50 4.4.2 Effects of individual rotation angles 53 4.4.3 Wavelength dependence 56 4.5 Summary and conclusions 61 5 Long period fiber gratings 63 5.1 Introduction 63 5.2 Principle of long-period fiber gratings 64 5.2.1 Results from coupled mode theory 64 5.2.2 Types of long-period gratings 65 5.2.3 Properties of acoustic long-period fiber gratings 67 5.3 Acoustic long-period grating setup 68 5.3.1 Transducer 69 5.3.2 Mechanical coupling 72 5.3.3 Acoustic dispersion of an optical fiber 75 5.3.4 Optical setup 77 5.3.5 Comparison to other acoustic LPG geometries 81 5.4 Experimental results 82 5.4.1 Transmission spectra 82 5.4.2 Discussion of transmission results 88 5.4.3 Direct mode field observation 93 5.4.4 Discussion of mode field observations 97 5.4.5 Time behavior and grating amplitude modulation 99 5.5 Summary and conclusions 101 6 Application of higher order fiber modes for far-field microscopy 104 6.1 Introduction 104 6.2 Complex beams in high-resolution far-field microscopy 104 6.3 Theoretical considerations 106 6.4 Experimental details 111 6.5 Results 114 6.6 Discussion 118 6.7 Summary and conclusions 122 7 Summary and outlook 124 Acknowledgments 139 Publications related to this work 142 List of figures 144 List of tables 150 List of acronyms 151

Quantitative Planar Laser Induced Fluorescence (QPLIF) is developed as a diagnostic technique and then applied to a prototype Jaguar optical internal combustion engine. QPLIF derives quantitative, two-dimensional, spatially-resolved measurements of fuel concentration. This work reports the first demonstration of a fully-fractionated surrogate fuel which exhibits all the characteristics of a typical gasoline. This 'pseudo' fuel, developed in association with Shell UK, is blended to accept a fluorescent tracer which may track one of the light, middle or heavy fractions of the fuel, each of different volatility. The traditional weaknesses of PLIF for quantitative measurements are addressed by use of a fired in-situ calibration method, which maps the quantum efficiency of the tracer and concurrently corrects for window fouling and exhaust gas residuals (EGR). Fuel distributions are presented with an estimated super-pixel accuracy of 10% at different operating conditions, and then compared to the computational fluid dynamics (CFD) predictions of an in-house Jaguar model. Fuel/Air Ratios by Laser Induced thermal Gratings (FARLIG) is developed theoretically, and results of validation experiments conducted in a laboratory setting are reported. FARLIG conceptually enables the measurement of fuel concentration, oxygen concentration and temperature within a spatially-localised probe volume. Uniquely, the technique exploits the dominant influence of molecular oxygen on non-radiative quenching processes in an aromatic tracer molecule. The changing character of a model quenching mechanism potentially allows the oxygen concentration in the measurement volume to be derived. Absolute signal strength is used to determine fuel concentration, while the oscillation period of the signal provides a precise measurement of temperature (~0.3% uncertainty), with accuracy limited by knowledge of the gas composition.

La spectroscopie Raman est un outil non destructif fort utile lors de la caractérisation de matériau. Cette technique consiste essentiellement à faire l’analyse de la diffusion inélastique de lumière par un matériau. Les performances d’un système de spectroscopie Raman proviennent en majeure partie de deux filtres ; l’un pour purifier la raie incidente (habituellement un laser) et l’autre pour atténuer la raie élastique du faisceau de signal. En spectroscopie Raman résonante (SRR), l’énergie (la longueur d’onde) d’excitation est accordée de façon à être voisine d’une transition électronique permise dans le matériau à l’étude. La section efficace d’un processus Raman peut alors être augmentée d’un facteur allant jusqu’à 106. La technologie actuelle est limitée au niveau des filtres accordables en longueur d’onde. La SRR est donc une technique complexe et pour l’instant fastidieuse à mettre en œuvre. Ce mémoire présente la conception et la construction d’un système de spectroscopie Raman accordable en longueur d’onde basé sur des filtres à réseaux de Bragg en volume. Ce système vise une utilisation dans le proche infrarouge afin d’étudier les résonances de nanotubes de carbone. Les étapes menant à la mise en fonction du système sont décrites. Elles couvrent les aspects de conceptualisation, de fabrication, de caractérisation ainsi que de l’optimisation du système. Ce projet fut réalisé en étroite collaboration avec une petite entreprise d’ici, Photon etc. De cette coopération sont nés les filtres accordables permettant avec facilité de changer la longueur d’onde d’excitation. Ces filtres ont été combinés à un laser titane : saphir accordable de 700 à 1100 nm, à un microscope «maison» ainsi qu’à un système de détection utilisant une caméra CCD et un spectromètre à réseau. Sont d’abord présentés les aspects théoriques entourant la SRR. Par la suite, les nanotubes de carbone (NTC) sont décrits et utilisés pour montrer la pertinence d’une telle technique. Ensuite, le principe de fonctionnement des filtres est décrit pour être suivi de l’article où sont parus les principaux résultats de ce travail. On y trouvera entre autres la caractérisation optique des filtres. Les limites de basses fréquences du système sont démontrées en effectuant des mesures sur un échantillon de soufre dont la raie à 27 cm-1 est clairement résolue. La simplicité d’accordabilité est quant à elle démontrée par l’utilisation d’un échantillon de NTC en poudre. En variant la longueur d’onde (l’énergie d’excitation), différentes chiralités sont observées et par le fait même, différentes raies sont présentes dans les spectres. Finalement, des précisions sur l’alignement, l’optimisation et l’opération du système sont décrites. La faible acceptance angulaire est l’inconvénient majeur de l’utilisation de ce type de filtre. Elle se répercute en problème d’atténuation ce qui est critique plus particulièrement pour le filtre coupe-bande. Des améliorations possibles face à cette limitation sont étudiées. / Raman spectroscopy is a useful and non-destructive tool for material characterization. It uses inelastic light scattering interaction with matter to investigate materials. The major part of the performances in a Raman spectroscopy system comes from two light filter units: the first shapes the light source (usually a laser) and the other attenuates the elastic scattered light in the signal beam. In resonant Raman spectroscopy (RRS), the excitation energy (wavelength) is tuned to match an electronic transition of the sample. When in resonance, the Raman cross section is increased by a factor up to 106. Current RRS setups are limited by filtering devices technology. RRS is a complex technique which, for the moment, remains tedious to implement. This master thesis presents the construction of a tunable Raman spectroscopy system based on volume Bragg gratings light filters. The setup is designed to operate in the near infrared region so as to study carbon nanotubes resonances. Steps leading to the operation of the system are described. They cover conceptualization, fabrication, characterization and optimisation of the setup. Collaboration with a local small company, Photon etc, led to the building of two new light filters that allow to tune easily the excitation wavelength. These filters have been adapted to work with a tunable titanium-sapphire laser (tunable from 700 to 1100 nm) and assembled with a homemade microscope and a detection system combining a CCD camera with a grating spectrometer. This document is arranged as follow: First are presented the theoretical aspects surrounding RRS. Carbon nanotubes (CNT) are than described to illustrate the relevance of such technique applied to material science. Principles behind the use of the Bragg filters are described to be followed by a scientific paper in which the main results of this work are presented. These include the optical characterisation of the filters and measurements with the system. Low frequency limits of the system are demonstrated using a sulphur powder where the 27 cm-1 line is clearly resolved. The tunability of the setup is also demonstrated using a bulk carbon nanotube sample. By changing the excitation wavelength, different nanotube chiralities become resonant, leading to different signals in the Raman spectra. Finally, clarifications regarding the alignment, optimisation and operation of the system are described. Low angular acceptance has been found to be the main drawback of the system leading to attenuation problems especially critical for the notch filter. Possible improvements on this limitation are discussed.

The effect of uncertainty in gas composition on the accuracy of gas-phase thermometry using Laser-Induced Thermal Grating Spectroscopy, LITGS, is studied. Temperatures are obtained from measurements of the sound speed derived from the frequency of oscillations ƒ_OSC imposed upon the LITGS signal arising from the transit of acoustic waves across the density modulation feature. The dependence of the sound speed, c_s on √γ/m, where γ is the ratio of specific heats and m is the mean molecular mass leads to a dependence upon gas composition. LITGS signals were generated in acetone vapour in a variety of gas mixtures in a temperature controlled cell at 4 bar total pressure using pump pulses from a frequency quadrupled Q-switched Nd:YAG laser at 266 nm and a cw diode pumped solid state probe laser at 671 nm. Studies were undertaken of the variation in ƒ_OSC with gas composition using gas mixtures of O₂ and N₂ with component concentrations in the range 0-100 %, and was found to agree with theoretical predictions. Measurement precision of the data (one standard deviation in 50 measurements) was found to be typically ± 1.7 % for measurements at 4 bar total pressure. The effect of varying concentrations in exhaust gas residuals (EGR) typical of pre-ignition gases in a spark ignition internal combustion engine were studied using synthetic air (N₂/ O₂ mixtures) containing variable amounts of simulated EGR components, CO₂ and H₂O. The effect of variation in CO₂ concentration in dry synthetic air was measured at 4 bar and 30°C and found to agree with theoretical predictions. Experiments conducted at 30°C, with the addition of a saturated vapour pressure of water indicate that the effect of a saturated vapour pressure of water on the oscillation frequency in synthetic EGR is on the borderline of resolution. The effect of variable amounts of typical hydrocarbon fuel vapour on ƒ_OSC was studied using 2,2,4-trimethyl-pentane in gas mixtures composed of synthetic air and variable amounts of EGR and water vapour at 80°C. Kinetic theory was used in order to model the dependence of the oscillation frequency ƒ_OSC on various gas compositions containing fuel and EGR, in order to construct an error surface for comparison with experimental measurements. Experimental data were found to agree with the model predictions to within experimental error for a representative data set within the range of calculated values. The results indicate that uncertainties in temperature values derived from LITGS thermometry can be estimated with confidence within reasonable estimates of composition variations in an internal combustion engine, and should lead to absolute temperature accuracy of within 2-3 %.

Ce manuscrit de thèse porte sur la formation de masques de réseaux denses de nanopiliers ou nanotrous à partir de l’auto-assemblage de copolymères à blocs (CPB) à haute force de ségrégation, pour des applications dans la micro-électronique. Des copolymères à blocs, de type ABA, constitués d’un bloc central de polydiméthylsiloxane (PDMS) et de deux blocs terminaux de polylactide (PLA) ont été synthétisés par polymérisation par ouverture de cycle. Les caractérisations de deux CPB d’intérêt en masse et sous forme de film mince montrent une mesostructure hexagonale sphérique et cylindrique de PLA dans la matrice de PDMS,avec des périodes de 14,3 et 15,5 nm respectivement. Afin de contrôler l’organisation des domaines, les autoassemblages des films minces des deux CPB ont été étudiés en fonction de plusieurs facteurs : paramètres de dépôt et post-traitements (exposition à des vapeurs de solvant et recuit thermique). Dans le cas du réseau hexagonal cylindrique, le contrôle des énergies interfaciales entre le film et le substrat de silicium a été obtenu grâce au greffage d’une couche de copolymères statistique ayant des blocs chimiquement différent des blocs contenus dans le CPB. Par ailleurs, à des fins industrielles, les mesostructures doivent montrer une organisation à grande échelle (plusieurs micromètres) dépourvue de défauts. Dans cette perspective, l’auto-assemblage des CPB a aussi été étudié sur des surfaces à topographie contrôlée (graphoépitaxie) montrant un relief sinusoïdal. / This manuscript is related to the formation of high density masks of nanoholes or nanodotsmade from high segregation strength block copolymer (BCP) for applications in the microelectronicindustry. Two block copolymers, ABA type with a polydimethylsiloxane (PDMS) center block and twoterminal polylactide (PLA) blocks, where synthetized by a ring opening polymerization. BCP characterizations inbulk and in thin film show a hexagonal array of PLA spheres and cylinders in a PDMS matrix, with 14,3 and 15,5nm pitches respectively. In order to control the domain organization, thin film BCP self-assembly were studiedin function of several parameters : spin coating process and post-treatments (vapour and thermal annealing). Inthe case of the hexagonal array of cylinders, the control of the interfacial energy between the film and thesilicon wafer has been obtained by grafting a random copolymer layer. Due to their microelectronicapplications, the mesostructures need to be defectless at a large scale (several micrometres). In this way, theself-assembly of one of the two BCP has also been studied by graphoexpitaxy on a sinusoidal surface-reliefgratings.

After nearly 100 years of particle acceleration, particle accelerator experiments continue providing results within the field of high energy physics. Particle acceleration is used worldwide in practical applications such as radiation therapy and materials science research. Unfortunately, these accelerators are large and expensive. Dielectric Laser Acceleration (DLA) is a promising technique for accelerating particles with high acceleration gradients, without requiring large-scale accelerators. DLA utilizes the electric field of a high energy laser to accelerate electrons in the proximity of a nanostructured dielectric surface.The aim of this project was limited to laser beam routing and imaging techniques for a DLA experiment. The goal was to design the laser beam pathway between the laser and the dielectric sample, and testing a proposed imaging system for aiming the laser. This goal was achieved in a test setup using a low-energy laser. In the main setup including a femtosecond laser, the result indicated lack of focus. For a full experimental setup, a correction of this focus is essential and the beam path would need to be combined with a Scanning Electron Microscope (SEM) as an electron source.

[pt] Redes de Bragg em fibras ópticas (RBF) são formadas por modulações periódicas introduzidas no índice de refração do núcleo de fibras ópticas. Estes componentes comportam-se como filtros espectrais de banda passante, ou seja, quando iluminados por um sinal óptico de banda larga, refletem apenas uma fina fatia espectral de luz, cujo centro, o comprimento de onda de Bragg, é proporcional ao período espacial da modulação no índice de refração. As RBF têm encontrado aplicações importantes no sensoriamento das mais diversas grandezas, sendo hoje utilizadas em sistemas de monitoramento para vários segmentos industriais, tais como os setores de petróleo e gás, construção civil e aeroespacial, que, estima-se, respondem em conjunto por cerca de 70% destas aplicações. Em diversas situações o sensoriamento com RBF baseia-se em medidas indiretas da grandeza de interesse, sendo empregados mecanismos de transdução que transformam variações do mensurando em deformações na fibra óptica. Nestes casos, um problema que deve ser tratado com atenção é o acoplamento entre temperatura e deformação, uma vez que as RBF são sensíveis a estas duas variáveis. Não raro, a alternativa é utilizar simultaneamente duas RBF para obter-se a compensação de temperatura na medida de deformação. Este trabalho apresenta um estudo sobre deformações não homogêneas em redes de Bragg e discute aplicações de duas técnicas que podem ser utilizadas como alternativas para eliminar o efeito da temperatura no sensoriamento de deformação com apenas uma RBF. A primeira delas explora a birrefringência óptica induzida na RBF por carregamentos transversais à fibra óptica. A segunda baseia-se nos efeitos sobre o espectro refletido pela rede de Bragg quando submetida a um campo de deformações longitudinais não uniformes ao longo da direção axial da fibra óptica. No trabalho são apresentados protótipos e dispositivos que exploram tais técnicas para a medida simultânea de pressão e temperatura. Esses protótipos foram projetados com auxílio de ferramentas CAD e modelados utilizando-se o método de elementos finitos em conjunto com a teoria de modos acoplados da Rede de Bragg. As previsões obtidas utilizando-se estes modelos mostraram-se bastante próximas dos resultados das implementações experimentais dos protótipos, indicando que a metodologia de modelagem desenvolvida pode ser aplicada nos projetos de transdutores baseados nas duas técnicas estudadas. / [en] Fiber Bragg gratings (FBG) are modulations in the effective refractive index of optical fibers, introduced in a small length along the fiber core. Such components operate as narrow band reflective filters, that is, when illuminated by a broad-band light source, they reflect a narrow spectral band centered at a specific wavelength, the Bragg wavelength. This wavelength is proportional to the spatial period of the refractive index modulation. Fiber Bragg gratings have find an increasing number of applications as sensors for different quantities, and today are being employed as part of permanent, real time monitoring systems in various industrial segments. The oil and gas sector, together with civil infrastructure and aeronautics and aerospace, account for almost 70% of this applications. In a number of situations, FBG sensing is based on indirect measurements of the quantity being monitored, and a transduction mechanism is employed to transform changes in the measured quantity in strain sensed by the optical fiber. Since the FBG is sensitive to strain and temperature, proper temperature compensation is always necessary. Usually, a second grating is employed to simultaneously measure temperature and strain, performing the required compensation. This thesis presents a study on effects due to non- homogeneous strains in the Bragg grating and discusses application of two different techniques, based on these effects, to allow temperature compensated strain measurement using a single FBG. The first technique explores strain induced optical birefringence when the fiber is loaded transversely. The second technique is based on changes in the spectral shape of the light signal reflected by the grating when subjected to non homogeneous axial strain fields. Prototypes of pressure and temperature transducers based on these techniques have been developed. These prototypes have been designed by employing CAD techniques and modeled using the finite element method in conjunction with the theory of coupled modes for fiber Bragg gratings. Comparisons between results provided by theoretical models and experimental realizations of the prototypes are very close, demonstrating that the developed approach can be applied to design transducers based on the discussed techniques. Results obtained with the proposed pressure and temperature sensors are also encouraging indicating that the two techniques are suitable for industrial applications.