Compostos orgânicos constituem uma classe interessante de materiais para aplicações em óptica por apresentarem boa processabilidade, relativa facilidade para integração em dispositivos e, principalmente, pela possibilidade de otimização de suas propriedades ópticas através da engenharia molecular. Várias estratégias têm sido empregadas para sintetizar moléculas orgânicas, que exibam singificativos efeitos ópticos não lineares. Nesta direção, nos últimos anos moléculas multi-ramificadas vêm sendo produzidas com o objetivo de intensificar efeitos não lineares, já que estas podem exibir um forte efeito cooperativo entre seus ramos. Nesta tese estudamos a relação da absorção de dois fótons (A2F) e da primeira hiperpolarizabilidade com a estrutura molecular, para um conjunto de nove derivados de trifenilamina com diferentes grupos aceitadores de elétrons arranjadas em geometrias dipolar, quadrupolar e octopolar. O processo A2F foi estudados através da técnica de Varredura-Z, enquanto que a primeira hiperpolarizabilidade foi caracterizada pela técnica de espelhamento hiper Rayleigh. Os dados experimentais para a absorção de dois fótons revelaram espectros bem definidos, com valores razoáveis de seção de choque na região do visível e infravermelho próximo. Observamos ainda um engrandecimento para a seção de choque de A2F para as moléculas quadrupolares. Os resultados obtidos para a primeira hiperpolarizabilidade (β) mostraram que moléculas quadrupolares apresentam maior β do que as dipolares e octopolares, portanto, nossos resultados permitem concluir que o acoplamento eletrônico entre os ramos contribuem fortemente para a seção de choque por A2F e β nas moléculas quadrupolares, não sendo este processo relevante nas moléculas octopolares. Todos os resultados foram interpretados por meio de estudos teóricos empregando a teoria do funcional da densidade (DFT). / Organic compounds constitute an interesting class of materials for optical applications due to their excellent processability, easy integration into devices and, mainly, the possibility of optimizing its optical properties through molecular engineering. Several strategies have been employed to synthesize organic molecules, which exhibit significant nonlinear optical effects. In this direction, in the last few years multi-branched molecules have been obtained aiming at intensifying nonlinear optical effects, since they may exhibit a strong cooperative effect among their branches. On this thesis we have studied the relationship of two-photon absorption (2PA) and first hyperpolarizability with the molecular structure of a group of nine triphenylamine derivatives attached to distinct electron acceptor groups arranged in dipole, quadrupole and octopolar geometries. The 2PA process was studied by Z-scan technique, while the first hyperpolarizability was characterized by the hyper-Rayleigh scattering technique. The experimental data for two-photon absorption revealed well-defined spectra with reasonable cross section magnitude in the visible and near infrared range. We also observed an enhancement of the 2PA cross-section for the quadrupolar molecules in comparison to the dipolar and octopolar ones. The results obtained for the first hyperpolarizability (β) shown that the quadrupolar molecules present higher β than the dipolar and octopolar, suggesting that the electronic coupling between the branches strongly contribute to the 2PA cross-section and β in quadrupolar molecules, being not relevant in the octopolar molecules. All results were interpreted through theoretical studies based on the density functional theory (DFT).

Au cours de ce travail, la génération de second harmonique optique des molécules biologiques a été étudiée. Cette technique optique non linéaire possède un caractère cohérent qui permet d’accéder aux propriétés de symétrie des molécules dont la taille est très inférieure aux longueurs d’onde optiques visibles utilisées et l’hyperpolarisabilité quadratique des acides aminés aromatiques a été mesurée en solution par diffusion non linéaire. L’hyperpolarisabilité des acides aminés non aromatiques a été obtenue de manière indirecte grâce à des mesures effectuées sur le collagène, une protéine ne contenant pas d’acide aminé aromatique. Le collagène possède en fait une très forte réponse non linéaire et fait l’objet d’études intenses en microscopie optique non linéaire. Par un modèle de sommation cohérente des champs harmoniques réémis, l’origine de la très forte efficacité non linéaire de cette protéine, liée à sa grande rigidité et à son organisation spatiale en triple hélice, a pu être obtenue. En parallèle, l’étude de plusieurs petits peptides synthétiques possédant de un à quatre tryptophanes a permis de comprendre la construction de la réponse optique non linéaire de ces objets à partir de motifs répétés. Par ailleurs, pour apporter des informations supplémentaires sur les nano systèmes, un nouveau montage expérimental a été développé. La grande sensibilité du montage a permis notamment d’atteindre la sensibilité d’une seule particule dans le volume sondé et de mettre en place un système de cartographie en trois dimensions par diffusion Hyper Rayleigh. La démonstration a été réalisée pour des nanoparticules métalliques uniques d’argent piégées dans une matrice de gélatine / This thesis presents an experimental study of second-harmonic generation of biological molecules. The coherent nature of this process allows obtaining the symmetries of molecules whose size is less than the wavelengths used. The hyperpolarizabilities of aromatic amino acids were measured in solution and the hyperpolarizability of non-aromatic amino acids was measured indirectly through measurements on the collagen molecule. Thus, all the building blocks of proteins are characterized. Among the biological molecules, collagen has a very strong non-linear response despite the absence of harmonophore. A model of coherent summation of the fields reissued to understand the origin of the very high non-linear efficiency from the rigidity and the spatial arrangement of amino acids in triple helix. In the same way, the study of several peptides with one to four tryptophans has enabled us to quantify the importance of conformation and the ionic environment of proteins in the nonlinear response. To provide additional information on nano systems, a new setup has been developed, combining two beams of excitation. Thus, the dipole and quadrupole radiation are differentiated to obtain the symmetry of molecular arrangements. Finally, the great sensitivity of the setup allows mapping in three dimensions, with the Hyper Rayleigh scattering, singles metal nanoparticles catch in a gelatin matrix.

La technique de la génération de second harmonique (SHG) a été employée pour étudier la réponse non linéaire des assemblées de nano particules métalliques aux interfaces liquides. Les nanoparticules ont d’abord été caractérisées en utilisant la génération de second harmonique incohérente, également nommée diffusion hyper Rayleigh. L’étude de particules d’or et d’argent, nanosphères et des nanobâtonnets, ont permis de mettre en évidence l’influence de la couche protectrice de surfactants sur l’hyperpolarisabilité quadratique de ces particules. Ces particules ont ensuite été placées à l’interface air/eau dans une cuve de Langmuir afin d’étudier le rôle des interactions entre les particules sur la réponse optique linéaire et non linéaire. Celle-ci a révélé dans ces films formés à l’interface la présence de couplages forts entre les particules lors de la compression de la surface. Cela conduit à une transition dans le film une fois que la distance entre les particules passe en dessous d’une distance critique. Ces études ont été complétées par des expériences réalisées à l'interface liquide/liquide et sur une électrode de carbone vitreux pour examiner plus en détail le rôle de la rugosité à l’échelle nanométrique dans l’exaltation de la réponse non linéaire SHG / In this work, the nonlinear optical response of assembled metallic nanoparticles at interfaces was studied using Second Harmonic Generation. First, the nanoparticles were characterised using incoherent second harmonic generation, a technique also called Hyper Rayleigh Scattering. Thioalkane-capped silver and gold nanoparticles, both nanospheres and nanorods, were investigated and the role of this capping layer on the quadratic hyperpolarisability of these particles was underlined. The particles were then deposited at the air/liquid interface in a Langmuir trough to investigate the role of the interparticles interactions in large assemblies. Both the linear and the nonlinear optical response of these metallic films formed at the surface of the trough provided evidence of a strong coupling between adjacent particles upon compression leading to a phase transition of the film once the interparticle distance is less than a critical value. These studies were complemented with experiments performed at the liquid/liquid interface and at the glassy carbon/electrolyte interface to examine in greater details the role of roughness at the nanoscale on the enhancement of the SHG response

No description available.

[pt] Nessa tese é analisada a dinâmica dos modos de lasers aleatórios à fibra com feedback distribuído. Um rigoroso estudo é feito sobre o mecanismo de feedback distribuído, i.e., o espalhamento Rayleigh, que é um dos principais elementos contribuindo para emissão laser. É desenvolvido um modelo teórico para previsão do retro espalhamento Rayleigh de luz coerente, o qual é baseado na ordem de médio alcance da sílica, e na tensão residual de fibras ópticas. As previsões do modelo são comparadas com resultados experimentais, levando a conclusão de que o retro espalhamento Rayleigh em fibras ópticas é um processo ergódigo nos domínios do tempo e da frequência óptica. O modelo mostrou-se eficaz na previsão das flutuações de intensidade do retro espalhamento Rayleigh de luz coerente, e foi utilizado para explicar a emissão de luz laser numa nova configuração de laser aleatório à fibra, que faz uso de um amplificador óptico a semicondutor (SOA) como meio de ganho. É demostrado que operação monomodo só é possível em emissão pulsada e com bombeio próximo ao limiar laser, enquanto operação multimodo é dominante para bombeio acima do limiar. Resultados experimentais indicam que potência dos modos é limitada pela competição entre modos por ganho. A operação em regime pulsado é atribuída a um efeito de cintilação da luz Rayleigh retro espalhada, que equivale a um fenômeno de chaveamento de perdas (Q-switching) aleatório na cavidade. O tempo de vida dos modos é ~ 1 ms e larguras de linha estreitas, no intervalo entre 4 e 7 kHz, foram obtidas experimentalmente. Lasers aleatórios à fibra com ganho Brillouin também foram analisados, mostrando semelhante dinâmica dos modos. Entretanto, por conta da estreita banda espectral do ganho Brillouin a competição entre modos não limitou a potência dos modos, a qual foi observada ser limitada por luz Stokes proveniente do espalhamento Brillouin de segunda ordem. Por último, experimentos com modulação de fase intra-cavidade foram avaliados, e mostraram que emissão laser pode ser controlada a partir da supressão da condição de fase ou ganho. / [en] In this thesis, it is provided a thorough analysis of mode dynamics of random distributed feedback fiber lasers. A rigorous investigation is proposed for the feedback mechanism, Rayleigh backscattering, which plays a key role in laser action. Based on the intermediate range order of silica glasses, and on residual stress of optical fibers, a theoretical model was built to predict intensity fluctuations of Rayleigh backscattered coherent light. Model predictions were compared to experimental results, strongly supporting the conclusion that Rayleigh backscattering in single mode fibers is an ergodic process exhibiting ergodicity in the time-frequency sense so that the model can be used to predict the statistical behavior of backscattered intensity fading. The model was used to explain laser action in a novel configuration of random fiber laser, with a semiconductor optical amplifier (SOA) employed as the gain medium. It is here demonstrated that single-mode operation is only possible in pulsed regime at SOA driving currents close to the threshold, whereas multimode regime dominates under higher currents. Experimental results indicate that the mode power is limited by mode competition, which is observed under high SOA currents. Pulsed regime is shown to be due to randomly driven Q-switching induced by a scintillation effect in the Rayleigh backscattered light, which effectively translates as a time-varying cavity loss. Mode lifetimes of ∼1 ms and narrow linewidths ranging from 4 to 7 kHz were experimentally obtained. Brillouin-based random fiber lasers were also analyzed, showing similar mode dynamics, but due to the much narrower gain spectral width, mode competition did not limit the mode power, which was rather limited by the second order Brillouin-Stokes light. Last, intra-cavity phase-modulation experiments showed that laser action can be efficiently controlled by breaking either phase or gain conditions.

Uranus is one of the least explored planets in our solar system. Event though the Uranian Ly-α emission has been a subject of study for decades, there is not a consensus on the sources contribution to the total signal. This thesis aims to analyse the contribution from scattering of the solar flux to the Uranian Ly-α dayglow by solving the radiative transfer equation in a parameter study for the atmosphere. The sources are solar Ly-α resonant scattering and Rayleigh scattering by atomic and molecular hydrogen respectively. The radiative transfer equation is solved using the Feautrier Method Program, a program written by Randall G. Gladstone. The program was adjusted to the Uranian atmosphere and modelled with different variations in parameters, including the atmospheric temperature and particle density of Ly-α scatterers and absorbers. A parameter study is performed to investigate the dependency on the Ly-α signal on these parameters. The results showed a significant Ly-α limb brightening with a maximum intensity located around 400 km outside one planetary radius as seen from the disk center. The contributions to the Ly-α dayglow from Rayleigh scattering by H2 was calculated to be 160 R whereas the contribution from resonant scattering by H was 550 R. One feature that prevents direct comparison to observed data with this thesis is that some sources that contributes to Uranus Ly-α signal are omitted in the simulations. / Uranus är en av solsystemets minst utforskade planeter. Även om dess Ly-α-strålning har undersökt, råder ännu inte konsensus kring de olika källornas bidrag till den totala Ly-α signalen. Genom att lösa ekvationen för strålningstransport i en parameterstudie ämnar examensarbetet att studera bidraget från solens två källor till Uranus Ly-α- signal. De två källorna är resonant- och Rayleigh strålningsspridning från atomärt och molekulärt väte. Ekvationen för strålningstransport beräknas av ett program som heter Feautrier Method Program, skapat av Randall G. Gladstone. Programmet har justeras till Uranus atmosfär för att kunna beräkna strålningstransport för olika atmosfärersmodeller i en parameterstudie. Parameterna som ändras är temperaturen, partikeldensiteten hos spridare och absorberare i atmosfären. Från resultaten kan parameterstudien svara på beroendet av de olika källorna till Ly-α-signalen från Uranus. Resultaten visar en tydlig ökning av ljusintensitet vid Uranus kanter med maximum runt 400 km utanför planetens radie, sett från planetens mitt. Bidraget till Ly-α-signalen från Rayleigh stålningsspridning beräknades till 160 R och från resonant strålningsspridning till 550 R. En egenskap som hindrar direkt jämförelse med resultaten från detta examensarbete och observerad data är att alla bidragande källor till Uranus Ly-α signal inte simulerats.

The aim of master's thesis is to get familiarized with the problems of measurement and analysis of seismic waves. Theoretical part deals with the description of seismic waves, especially their types, sources and properties. Attention was afterwards focused on the measurement systems of these waves, emphasis was placed on their principles and advantages. The practical part discusses methods of noise reduction and highlighting of significant events in measured data. At the end, individual methods are implemented into user-friendly graphical interface.

This thesis explores and evaluates the temperature measuring capabilities of a phase-sensitive optical time-domain reflectometer (φ-OTDR), which exploits Rayleigh backscattering in normal single mode optical fibers. The device is constructed and its setup explained, and a protocol for making temperature measurements with it is developed. Performance tests are made and the device is shown to achieve fully distributed temperature measurements on fibers hundreds of meters in length with a spatial resolution of 1 m and a temperature resolution of 0.1 K. In addition, the capabilities of the device to measure normal strain in the measurement fiber are tested using the same approach, albeit with less success. The device is capable of very precise measurements, making it very sensitive to the environmental conditions around the measuring fiber but also susceptible to disturbances. Some discussion is had on how to avoid or deal with these disturbances. Furthermore, the technique is shown to be able to run in conjunction with other φ-OTDR measurement techniques from the same device simultaneously. / Det här examensarbetet utforskar och utvärderar förmågorna att mäta temperatur hos en fas-känslig optisk tidsdomän-reflektometer (φ-OTDR), som utnyttjar bakåtriktad Rayleigh-spridning i vanliga optiska singelmodfibrer. Anordningen konstrueras och dess komponentstruktur förklaras, och ett protokoll tas fram för att utföra mätningar med den. Prestandatester utförs och anordningen visas kapabel att göra fullt distribuerade temperaturmätningar längs hundratals meter långa fibrer, med en rymdsupplösning på 1 m och en temperaturupplösning på 0.1 K. Dessutom testas förmågan att mäta normaltöjning hos testfibern med samma metod, dock med mindre framgång. Anordningen är väldigt känslig för förhållandena i omgivningen runt mätningsfibern, vilket gör den kapabel till mätningar med mycket hög precision, men också mottaglig för störningar. Lite diskussion hålls kring hur dessa störningar kan undvikas eller hanteras. Vidare visas att mätningstekniken kan köras samtidigt som andra φ-OTDR-baserade tekniker från samma anordning.