Au cours de ce travail, essentiellement expérimental, nous nous sommes intéressés à la relaxation structurale dans un verre silicaté que nous avons analysé et interprété en terme de dynamique hétérogène. Expérimentalement, nous avons couplé les informations obtenues par différentes spectroscopies qui sondent des échelles spatiales allant du nm (Raman, Infrarouge) à une centaine de nanomètres (Brillouin). Numériquement, nous avons décomposé les fonctions de relaxation obtenues par les différentes spectroscopies et nous avons mis en évidence l’existence de plusieurs échelles temporelles ainsi existantes. A longue distance, les expériences in situ Brillouin effectuées le long d’une rampe de chauffage et des isothermes montrent que (i) les phonons acoustiques sont affectés par le recuit et (ii) la dynamique de relaxation est hétérogène à l’approche de la transition vitreuse. Ainsi, contre toute attente cette hétérogénéité est très fortement dépendante du parcours suivi en température. A courte et moyenne distance, les mesures in situ Raman à hautes température sur des rampes de chauffe et des isothermes, montrent que la relaxation structurale affecte l’ordre spatiale du réseau silicaté. Le couplage des analyses en composantes individuelles et principales a permis d’identifier deux processus de relaxation attribués respectivement à la relaxation du fond continu et des entités Qn. Par des mesures in situ d’Emissivité Infrarouge dans le liquide et grâce à un modèle proche du modèle binaire l’abondance des espèces Qn lors des processus de relaxation et cristallisation a été obtenue. Un mécanisme d’activation de la relaxation à grande distance par une re-polymérisation locale est mis en évidence. Ce même mécanisme est un précurseur de la cristallisation. / Résumé en cours de rédaction

This graduation thesis deals with use of unconventional optical fiber with the intention of photonic crystal fiber. There are described types of photonic crystal fiber, their physical, optical and transfer characteristics. There is explained what are the photonic crystals, principle of their function and possible types of crystals. There are also detailed types of photonic fiber commonly used in the optical fiber branch. There is also explained photonic crystal fiber its structure a hierarchy of its types. In this thesis are described and demonstrated different kinds of photonic optical fiber and their use. There is demonstrated principle of one-dimensional periodical structure of Bragg fiber using simulation software. There can be seen graphical comparison of the simulated optical fiber core to commonly obtainable fiber. Outcome of this graduation thesis should be explanation of function of photonic crystal fiber and possibility of finding new type of fiber with optimal dispersion characteristics for use in fiber optics.

The thesis is focused on physical principles of signal transmission by optical fiber and effects that may have influence on such transmission. This knowledge is acquired with regard to future usage of optical fiber as a sensor for detection and localization of mechanical vibration. In the thesis, mentioned knowledge is taken in account and also there are described methods, which allow mechanical vibration for dozens of km. At the conclusion the laboratory sollution is suggested, allowing detection and localization in vast distance with possibility of real test in practice.The testing curcuits are used for measurement and results are processed for purpose of detection and localization of source. The measurement itself was made by testing curcuits and results were processed for purpose of detection and localization of source.

Heterogenní katalýza hraje významnou roli pro zvy¹ování efektivity rùzných procesù. Vysokou katalytickou aktivitu vykazují oxidy ceru patøící k tzv. reducibilním oxidùm, je¾ snadno uvolòují èi (zpìtnì) pøijímají atomy kyslíku prostøednictvím procesù redukce a oxidace. Zámìrem pøedlo¾ené práce je vypoèítat pásové struktury a øezy plochami konstantní energie objemových a povrchových systémù oxidu ceru pomocí kvantovì-mechanické "ab initio"metody Teorie hustotního funkcionálu. Numerické simulace jsou provádìny pomocí programového balíèku Quantum ESPRESSO za u¾ití metod rovinných vln a pseudopotenciálu. Silná korelace elektronù v pøípadì atomù ceru je modelována pøidáním Hubbardova U-èlenu. Hlavní dùraz je kladen na mo¾nost porovnávání teoretických výsledkù s tìmi získanými pomocí experimentální metody úhlovì-rozli¹ené fotoelektronové spektroskopie umo¾òující pøímý zisk jak pásových struktur, tak øezù plochami konstantní energie zkoumaného materiálu. Porovnání pomù¾e jak poznat mo¾nosti a mo¾né hranice zmínìné experimentální metody, tak i roz¹íøit její teoretické zázemí vedoucí k prohloubení znalostí materiálù perspektivních pro katalýzu. Klíèová slova: Teorie hustotního funkcionálu, Hubbardùv U-èlen, pásová struktura, plocha konstantní energie, Brillouinova zóna 1

No description available.

No description available.

No description available.

Laser induced damage is of interest in studying the transmission of large amounts of optical energy through step-index, large core multimode fibers. Optical fibers often have to be routed around objects when laser light is being transmitted between two locations which require the fiber to bend into a curve. Depending on how tight the bend is, this can result in transmission losses or even catastrophic damage when the energy density of the laser pulse exceeds the damage threshold of silica glass. The purpose of this study is to: Establish a minimum bend radius that would allow high energy (GW/cm2 ) to be transmitted through multimode fiber. Evaluate unique fiber routing configurations including loops, 180 bends, and S-bends. Develop optical modeling simulations backed with experimental data that can serve to predict critical areas for future systems. Waveguide theory predicts that light traveling through a bend will form whispering-gallery modes that propagate through total internal reflection bounces along the inside of the outer edge of the bend. This is critical since in these locations the energy density of the light will increase significantly, raising the potential of laser damage, nonlinear effects, and transmission losses. This loss is especially problematic when two 90° bends going in opposite directions are in close proximity to each other, forming an ‘S-bend’. Light that is grouped along the outer edge going through the first bend will enter the second bend at a sharper angle which causes much high transmission losses and raises the possibility of failure. iv Models using R-Soft BeamProp and Zemax were developed to study transmission losses, investigate light interactions at critical areas, and predict under which conditions laser damage would occur. BeamProp presents a clearer view of the modal distribution of light within the core of the fiber and is used to analyze how a plane wave with a Gaussian intensity distribution excites the fiber modes. Zemax provides a tool to perform non-sequential ray tracing through the fiber cable and stray light analysis within the core and once the light exits the fiber. Intensity distributions of the cross sectional area of the fiber shows the whispering gallery modes forming as the light propagates around bends and disburses as it propagates afterwards. It was discovered using R-Soft that if the separation distance between bends in an S-bend is approximately 3 mm there exists a condition where maximum transmission occurs. For 365 µm diameter core fiber it was calculated that the difference in output power could be as high as 150%. This was initially completely unexpected; however ray tracing using Zemax was able to verify that this distance allows the light to transition so that it enters the 2nd bend at the optimal angle to enter the whispering gallery mode. Experiments were performed that validated the models’ predictions and images were captured clearly showing the spatial distribution shift of the light within the core of the fiber. Experiments were performed to verify light grouping together to form whispering gallery modes as predicted by Zemax. Microscope images were taken as a function of distance from various bends to observe the periodic nature in which the laser light fills up the fiber. Additionally, a configuration was setup to examine stimulated Brillioun scattering and determine the onset of laser damage in the fiber. Fibers were tested as a function of bend radius and number of shots v and recommendations for future systems were made. Lastly, mechanical failure tests were performed to determine the relationship between stress placed on the fiber through bending and fiber lifetime in a static environment. This allowed a minimum safe bend radius to be calculated for a 30 year lifetime that agreed with previous calculated values.

Acontecimientos como el colapso de las dos torres del Skyline Center Project en Virginia (1973), el colapso del puente I-35W sobre el río Mississipi en Mineapolis (2007) y, más recientemente, del puente colgante Kutai Kartanegara en Indonesia (2011) ponen de manifiesto la gran importancia y necesidad de monitorizar ciertas estructuras para poder evaluar su seguridad estructural en tiempo real. El éxito de esta tarea depende fundamentalmente de dos aspectos. Por un lado, los sistemas y sensores empleados deben ser precisos y fiables a la vez que posibiliten una instrumentación segura, fácil y económica. Por otro lado, es necesario contar con pautas generales de monitorización de distintas tipologías estructurales que proporcionen una guía sobre cómo debe instrumentarse una estructura. En este contexto general, esta tesis diseña y propone nuevos sensores para la monitorización estructural basados en la tecnología de la fibra óptica por las ventajas comparativas que ofrece este material. La investigación se justifica por las limitaciones de las tecnologías actualmente disponibles y ha comprendido las fases siguientes: - Desarrollo de un sensor óptico puntual basado en redes de Bragg para medir deformaciones y temperaturas. - Desarrollo de un sensor óptico de longitud basado en redes de Bragg para medir deformaciones - Estudio y calibración de sensores distibuidos para medir deformaciones, basados en el fenómeno de dispersión de la luz. - Ensayos con probetas en laboratorio de los sensores desarrollados. - Comprobación y optimización del funcionamiento de los sensores mediante modelos numéricos realizados con el método de elementos finitos. - Comprobación del comportamiento de los sensores en estructuras reales y mejora en su caso de su diseño. Las estructuras monitorizadas abarcan una gran variedad de materiales y tipologías como son el tablero de un puente empujado, una losa postesa de edificación, el encepado de cimentación de un puente atirantado de 318 m. de luz o / Torres Górriz, B. (2012). Definición de las pautas y condiciones de monitorización, encapsulado y fijación de sensores de fibra óptica para la medida de deformación y temperatura en estructuras [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/17802

Spin waves and their quanta, magnons, are the wave-like excitations of a magnetically ordered medium. The technological prospect of utilizing them as low-loss information carriers has driven various research efforts in the field of magnonics. Spin waves arise further interest due to their inherently strong nonlinear behavior which results from their interaction with the surrounding magnetic texture. Hence, magnons are subject to a variety of nonlinear effects and allow for extensive studies of such phenomena. In this work, the propagating spin-waves in micro structured Co25Fe75 conduits have been investigated by means of micro focused Brillouin light scattering spectroscopy. Due to the low intrinsic damping of this metallic compound, spin-wave decay lengths in the order of 20 μm can be observed which have not been reported elsewhere for other ferromagnet thin film materials. Furthermore, nonlinear four-magnon scattering processes can be observed when increasing the spin-wave amplitudes applying a sufficiently strong microwave excitation. This phenomenon introduces additional losses for propagating waves as it diverts energy into the parametric generation of secondary states. It is shown that the reduction of the spin-wave decay lengths reaches up to 50 %. In the second part, a novel approach for the utilization of four-magnon scattering is presented. It is shown that an additional driving signal at a secondary driving frequency can steer the nonlinear process in such a way, that a set of secondary parametric states with a well-defined frequency spacing is populated. This process is referred to as stimulated four-magnon scattering, as it enhances specific nonlinear scattering events. As a result, frequency combs with multiple equidistant modes are observed, which exhibit frequency spacings of 400 MHz up to 2 GHz. These complex spin-wave spectra can actively be tuned in various ways using external parameters such as the driving signals. These results advance the understanding of nonlinear spin waves in general and expands the range of possible technological applications of magnons.:List of Figures List of Tables List of Abbreviations and Acronyms List of Symbols 1 Introduction 2 Theoretical background 2.1 Interactions in microstructured thin film ferromagnets 2.1.1 Exchange interaction 2.1.2 Dipolar interaction and demagnetizing fields 2.2 Magnetization dynamics in ferromagnetic thin films 2.2.1 The Landau-Lifshitz and Gilbert equation 2.2.2 Spin waves 2.3 Nonlinear phenomena 2.3.1 Four-magnon scattering 3 Materials and Methods 3.1 Materials and sample fabrication 3.1.1 The low damping alloy Co25Fe75 3.1.2 Patterning: electron beam and optical lithography 3.1.3 Microwave antenna structures 3.2 Brillouin light scattering 3.2.1 Magnon-photon interaction 3.2.2 The Tandem Fabry Pérot interferometer 3.2.3 BLS microscopy (μBLS) 3.2.4 Phase-resolved BLS (PR-μBLS) 3.2.5 Temporal resolution (TR-μBLS) 3.3 Micromagnetic simulations in MuMax3 3.3.1 Mesh and material parameters 3.3.2 Simulation of magnetization dynamics 4 Results 4.1 Magnon transport in Co25Fe75 micro-conduits 4.1.1 Low external fields and magnetic groundstate 4.1.2 Magnon transport at low driving powers 4.1.3 Impact of nonlinear four-magnon scattering on magnon transport 4.2 Magnon frequency combs 4.2.1 Introduction on stimulated four-magnon scattering 4.2.2 Experimental realization 4.2.3 Amplitude-dependent observations 4.2.4 Tunability of spin-wave frequency combs 4.2.5 Variations of the excitation geometry 5 Summary and outlook Own publications Bibliography 109 Acknowledgement A Appendix A.1 Fabrication of Co25Fe75 microstructures A.2 Atomic Force Microscopy measurement on a 5 μm wide conduit A.3 BLS measurement of spin-wave decay lengths in a 5 μm wide conduit A.4 Calculations: Temporal profile of stimulated four-magnon scattering A.5 Power dependent frequency comb formation measured at positions II & III A.6 Averaged frequency comb mode numbers at reversed magnetic field polarity