Alta concentração de lipoproteína modificada de baixa densidade (LDL) é um dos fatores que aumentam o risco de doenças cardíacas. As concentrações mais elevadas de LDL modificada estão associadas à aterosclerose nas veias de sangue. A técnica de Z- scan (ZS) foi utilizada para investigar a resposta óptica não-linear da lipoproteína modificada de baixa densidade (moLDL). As características estruturais do mLDL foram estudadas por espalhamento dinâmico de luz. Nesta pesquisa, os experimentos foram realizados em amostras de LDL de 24 pacientes com diabetes e gengivite (grupo 1) e 24 pacientes com diabetes e periodontite (grupo 2). Os experimentos foram repetidos após 6 meses sem qualquer tratamento para o grupo 2 e com um tratamento periodontal para o grupo 1. Os resultados mostram que a amplitude da curva Z-scan no grupo 1 é menor que a do grupo 2. Após 6 meses de tratamento periodontal a amplitude é maior do que antes, depois a concentração de LDL modificado é reduzida nos pacientes tratados. Portanto, o risco cardiovascular para aterosclerose é diminuído após o tratamento periodontal. Além disso, os resultados do espalhamento dinâmico de luz mostram que não há nenhuma mudança estrutural significativa no moLDL entre os dois grupos antes e após 6 meses. / High-concentration of modified low-density lipoprotein (LDL) is one of the factors that increases the risk of heart disease. The higher concentrations of modified LDL are associated with the atherosclerosis in the bloodstream. The Z-scan (ZS) technique was used to investigate the nonlinear optical response of modified low-density lipoprotein (moLDL). The structural characteristics of moLDL were studied by dynamic light scattering. In this work, the experiments were carried out in LDL solution from 24 patients with diabetes and gingivitis (group 1) and 24 patients with diabetes and periodontitis (group 2). The experiments had been repeated after 6 months without any treatment for group 1 and with a periodontal treatment for group 2. The results show that the amplitude of Z-scan curve in group 2 is lower than that of group 1. After 6 months of periodontal treatment the amplitude is getting higher than before, then the concentration of modified LDL is reduced in the patients treated. Therefore, the cardiovascular risk for atherosclerosis is decreased after the periodontal treatment. Also, dynamic light scattering results show that there is not a significant structural change in moLDL between the two groups before and after 6 months.

Ce travail concerne la mise en oeuvre de la technique de la « lentille thermique » pour l'étude des phénomènes d'absorptions multiphotoniques dans les matériaux organiques. La technique de la lentille thermique utilisée ici, est dans son principe une technique pompe-sonde où le faisceau pompe provient d'un laser pulsé (25ps, 532nm ou 1064nm) tandis que le faisceau sonde est issu d'un laser continu (He-Ne : 632nm). Cette technique s'apparente aussi à la technique de z-scan dans la mesure où l'échantillon est déplacé de part et d'autre du point focal d'une lentille convergente disposée sur le trajet du faisceau pompe. Selon le rapport des diamètres des faisceaux pompe et sonde, on distingue deux variantes principales de la technique de la lentille thermique en régime pulsé : la variante dite en « modes accordés » (les diamètres des deux faisceaux sont identiques) et la variante en « modes désaccordés » (les diamètres des deux faisceaux sont différents). Pour des raisons de simplicité de mise en oeuvre et de sensibilité, nous avons choisi la variante en modes désaccordés. Cette variante de la technique de la lentille thermique, ayant été peu utilisée jusque là, a été utilisée pour mesurer le coefficient et la section efficace de l'absorption à deux photons dans différents matériaux organiques. Ces résultats sont comparés à d'autres mesures provenant de technique de mesure plus connue comme « transmission non linéaire » ou la technique de z-scan.

Les matériaux nanocomposites formés à partir de particules métalliques incluses dans une matrice diélectrique présentent des propriétés inusitées que l'on ne retrouve pas dans les matériaux massiques étant donné la taille nanométrique des particules métalliques. Notamment, la résonance des électrons de conduction du métal sous l'excitation d'une lumière incidente, appelée résonance plasmon de surface (spr), donne lieu à l'apparition d'une bande d'absorption dans le visible ayant une influence drastique sur les propriétés optiques du nanocomposite. La position, la largeur et l'amplitude de cette bande d'absorption sont des fonctions complexes des caractéristiques nano-structurales du nanocomposite, notamment : la nature et la concentration du métal, la taille des nanoparticules, leur forme, l'indice de réfraction de la matrice, etc. Spécifiquement, la présence de particules asymétriques, comme par exemple des particules de forme nano ellipsoïdale, permet l'observation de bandes d'absorption spr multiples résultant en un matériau non-symétrique possédant des propriétés anisotropes. Dans cette thèse, nous présenterons le développement et l'analyse de techniques avancées de fabrication permettant le contrôle précis de la synthèse d'un nanocomposite formé de nanoparticules d'or incluses dans une matrice de silice. Nous avons développé une technique en trois étapes permettant de fabriquer des couches nanocomposites comprenant des particules de tailles et de formes contrôlées. Ces étapes sont : 1) dépôt hybride pulvérisation/dépôt chimique en phase vapeur assisté par plasma, 2) recuits thermiques, 3) irradiation à l'aide d'un faisceau d'ions de haute énergie. Subséquemment, la performance optique des matériaux fabriqués a été testée par différentes techniques afin d'en évaluer les propriétés linéaires et non-linéaires. Les premières ont été étudiées par ellipsométrie et spectrophotométrie alors que les deuxièmes l'ont été par les techniques P-Scan et Z-Scan. Plus précisément, nous nous sommes intéressés à la métrologie et au contrôle de l'anisotropie des propriétés du système nanocomposite formé par faisceau d'ions. Une nouvelle approche de mesure des propriétés optiques non-linéaires anisotropes sera présentée. Dans ce document, le lecteur retrouvera une description théorique exhaustive des propriétés optiques (linéaires et non-linéaires) des matériaux nanocomposites métal/diélectrique incluant des modèles détaillés pour la description des propriétés de chacun des constituants du nanocomposite : métal (Drude, Lorentz) et diélectrique (Cauchy).

Polymer liquid crystal possesses advantages of polymer in chemical industry and liquid crystal in display industry,so it is attracted more attention in science and technology. Diacrylate is a polymer liquid crystal with photosensitive property, so ,it can be applied to optical storage . He-Ne laser induced polymerization in diacrylate mesogen RM257 and RM82 had been verified in previous study. Furthermore, holography pattern can be recorded in RM257 and RM82 by controlling both the temperature of sample and the time of exposing. In this study, we consider the study of nonlinear optical properties of diacrylate using Z-SCAN techeique.¡¨Z-SCAN¡¨ is a simply yet highly sensitive single-beam experimential technique ,it can be used to measure both nonlinear absorption and nonlinear refraction.In this study ,we measured effect of absorption of diacrylate in irradiation of He-Ne laser using Z-SCAN technique.To investigate the reason that He-Ne laser induced polymerization in both RM257 and RM82.

Ο όρος μη-γραμμική οπτική αντιπροσωπεύει τον κλάδο της οπτικής ο οποίος μελετά την αλληλεπίδραση της ύλης με ακτινοβολία πολύ ισχυρής έντασης. Όταν ένα υλικό εκτεθεί σε ακτινοβολία υψηλής έντασης όπως αυτή του laser, οι οπτικές του ιδιότητες αλλάζουν εξαιτίας της πόλωσης που επάγεται στα δομικά υλικά του και το αποτέλεσμα είναι η αλλαγή των οπτικών του ιδιοτήτων. Αυτό με τη σειρά του οδηγεί σε μια πληθώρα φαινομένων τα οποία μας βοηθούν στη κατανόηση της δομής του υλικού αλλά και των φυσικών μηχανισμών που κρύβονται πίσω από αυτά. Στην παρούσα μεταπτυχιακή εργασία μελετώνται οι μη γραμμικές οπτικές ιδιότητες χρωμοφόρων τύπου BODIPY υπό μορφή διαλυμάτων. Η σύνθεση των μορίων έγινε στο Ινστιτούτο Φυσικοχημείας του ΕΚΕΦΕ ΔΗΜΟΚΡΙΤΟΣ από την ερευνητική ομάδα του κ.Πιστόλη στα πλαίσια ενός έργου ΘΑΛΛΗ. Η διάρθωση της εργασίας είναι η εξής: Στο πρώτο κεφάλαιο γίνεται μια εισαγωγή και παρουσιάζονται κάποιες βασικές έννοιες της μη γραμμικής οπτικής. Ενώ ταυτόχρονα αναπτύσσονται αναλυτικότερα μερικά φαινόμενα τα οποία οφείλονται στη μη γραμμική επιδεκτικότητα τρίτης τάξης. Στο δεύτερο κεφάλαιο γίνεται η παρουσίαση της πειραματικής τεχνικής Z-scan, που χρησιμοποιήθηκε για τη διεξαγωγή των πειραμάτων, αλλά και η διαδικασία που ακολουθήθηκε για την εξαγωγή των μη γραμμικών οπτικών ιδιοτήτων από τα πειραματικά δεδομένα. Στο τρίτο κεφάλαιο παρουσιάζονται τα πειραματικά αποτελέσματα των συστημάτων που μελετήθηκαν. Αρχικά, παρουσιάζεται μια περιγραφή των ιδιαίτερων φωτοφυσικών ιδιοτήτων των μορίων BODIPY που μελετήθηκαν. 'Επειτα, ακολουθεί η μη γραμμική οπτική απόκριση των συστημάτων για διέγερση στα 532nm και 1064nm με παλμούς χρονικής διάρκειας 532ps και 4ns. Τέλος, ακολουθούν τα συμπεράσματα από τη μελέτη των συστημάτων και μια πρόταση για μελλοντική μελέτη. / Nonlinear optics (NLO) is related to laser-matter interactions, as well as the changes which are induced in materials during their interaction with intense laser fields. Laser beams can provide strong enough electromagnetic fields, capable of inducing optical changes. In these cases the response of the material is not linearly dependent on the intensity of the electric field. The primary objective of this thesis was the investigation of the non-linear optical properties of BODIPY derivatives. In particular, we focused on the determination of the second-order hyperpolarizability in order to correlate the magnitude and the sign of the observed nonlinearities with their photophysical characteristics. The main experimental technique used was the Z-scan technique, employing 35 ps and 4 ns laser pulses at both 532 nm and 1064 nm. The molecules were synthesized by the research group of Dr. Pistolis at the Institute of Physical Chemistry NCSR ''Demokritos" as a part of the ''THALIS" programme. The structure of the thesis is as follows: In Chapter 1, the basic NLO phenomena and the corresponding related nonlinear optical parameters are introduced. In Chapter 2, the theoretical background of the Z-scan technique is briefly presented, while the Z-scan experimental set-up is fully described. In Chapter 3, experimental results on the NLO properties of the Bodipy derivatives are presented. The relationship between the nonlinear optical properties and photophysical properties of the derivatives is also considered. The conclusion summarizes the results of the NLO response of the BODIPY derivatives and details a proposal for future work..

This thesis descibes a theoretical study of nonlinear self-focusing as applied to the metrology of the nonlinear optical parameters of a medium. It also studies the phe- nomenon of optical power limiting which utilizes self-focusing e ects. As an analytical tool, a mode decomposition method which uses an orthogonal and complete set of Gaussian-Laguerre modes as a basis set is used to treat these problems. Nonlinear media both in the thin and thick limits are investigated. For thin media, a closed form expression is derived which describes the optical eld of an initally Gaussian beam that is perturbed by a thin nonlinear material which exhibits nonlinear absorption as well as nonlinear refraction. This result is valid for any regime of nonlinearity in the thin medium approximation. Thick media are treated using a numerical extension of the Gaussian-Laguerre Mode Decomposition technique. Spatial scanning techniques such as the Z-scan that rely on self-focusing e ects and that are used to measure the nonlinear optical parameters of a material are studied in detail. Optical limiting in both thick and thin media is also investigated.

This thesis descibes a theoretical study of nonlinear self-focusing as applied to the metrology of the nonlinear optical parameters of a medium. It also studies the phe- nomenon of optical power limiting which utilizes self-focusing e ects. As an analytical tool, a mode decomposition method which uses an orthogonal and complete set of Gaussian-Laguerre modes as a basis set is used to treat these problems. Nonlinear media both in the thin and thick limits are investigated. For thin media, a closed form expression is derived which describes the optical eld of an initally Gaussian beam that is perturbed by a thin nonlinear material which exhibits nonlinear absorption as well as nonlinear refraction. This result is valid for any regime of nonlinearity in the thin medium approximation. Thick media are treated using a numerical extension of the Gaussian-Laguerre Mode Decomposition technique. Spatial scanning techniques such as the Z-scan that rely on self-focusing e ects and that are used to measure the nonlinear optical parameters of a material are studied in detail. Optical limiting in both thick and thin media is also investigated.

Made available in DSpace on 2015-05-14T12:14:02Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 4030478 bytes, checksum: 03b24ba7a8957d1ad2df45e0035eccad (MD5) Previous issue date: 2011-10-13 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The z-scan technique consists in measurement of the variation of the radial intensity of a Gaussian laser beam induced by self-focusing or self-defocusing while propagating through a nonlinear medium. These variations are deduced through detection of the beam transmitted through a small, fixed aperture. After the seminal work by Sheik-Bahae et al. [30] in 1990, a lot of work has been done studying the nonlinearity of solids. By comparison, very little has been done with resonant atomic vapors, but rich results were obtained due to the very high atomic susceptibilities at resonance [33, 42]. In this work we report our measurements using a focused laser beam sent through a thermal cesium vapor. We have carried out many runs of z-scan for different frequencies of the laser tuned in the wings of the cesium Doppler-broadened D2 transition (6S1/2-6P3/2 at 852 nm) and observed the changes in the radiation transmitted through a fixed aperture. / A técnica de z-scan (varredura z) consiste na medição da variação da intensidade de um feixe laser Gaussiano induzida por auto-focalização ou auto-desfocalização quando o feixe se propaga através de um meio não-linear. Estas variações são medidas através da detecção do feixe transmitido por uma abertura pequena, fixa. Após o trabalho seminal de Sheik-Bahae e outros [30] em 1990, muitos trabalhos foram feitos estudando a não-linearidade de sólidos com esta técnica. Por comparação, muito pouco tem sido feito com vapores atômicos ressonantes, mas resultados ricos foram obtidos devido às susceptibilidades atômicas muito elevadas na ressonância [33,42]. Neste trabalho relatamos nossas medições utilizando um feixe laser focalizado enviado através de um vapor térmico de césio. Nós realizamos muitas varreduras z para diferentes freqüências do laser nas asas da transição D2 com alargamento Doppler do césio (6S1/2 6P3/2 em 852 nanômetros) e observamos as mudanças na radiação transmitida através de uma abertura fixa.

A técnica de varredura-z tem sido bastante utilizada para a determinação do índice de refração não-linear (n2) em meios transparentes. Apresentamos neste trabalho uma análise teórica e resultados da técnica de varredura-z por reflexão, visando o estudo de efeitos térmicos em amostras que possuem coeficientes de absorção muito grandes. Extensões à técnica, tais como: a varredura-z resolvida no tempo e varredura-z resolvidas em freqüência puderam ser aplicadas para medir efeitos térmicos, pois estes são relativamente lentos nos materiais que medimos (água, polímero e vidro). Das componentes linear e quadrática da evolução temporal da transmitância, ou, da segunda componente de Fourier de curvas obtidas em duas freqüências, pode-se extrair parâmetros térmicos como: a capacidade térmica por unidade de massa e a difusividade térmica. Propriedades térmicas são de grande interesse na usinagem de peças, e em estudos sobre tensões estruturais e novos materiais. Pela teoria aqui desenvolvida, dada as constantes térmicas, é possível distinguir os efeitos térmicos e eletrônicos nas amostras que apresentam os dois. / The Z-Scan technique is the most popular one for the determination of the nonlinear index of refraction (n2) of transparent media. In this work we present a theoretical analysis and results of the reflection z-scan technique, aiming the research of thermal effects in highly absorbing materials. Extensions of the technique, such as the time resolved z-scan and the frequency resolved z-scan could be applied to measure thermal effects because they are relatively slow in the materials that we have measured (water, polystyrene and glass). From the linear and quadratic terms of the transmittance time evolution, or, from the second Fourier component of curves obtained in two frequencies, one can extract thermal parameters like: the heat capacity per unit mass and the thermal diffusion coefficient. Thermal properties are of great interest in the manufacture of pieces, and in the study of structure strains and new materials. By the theory presented here, if thermal constants are given, one can distinguish between thermal and electronic effects in samples that present both.

Neste trabalho são estudadas algumas propriedades ópticas de tetrâmeros de anilina em solução, usando o dimetil sulfóxido (DMSO) como solvente. Os espectros de absorção e emissão permitiram uma determinação aproximada dos níveis de energia do tetrâmero. Para a caracterização das propriedades ópticas não lineares foram utilizadas as técnicas de varredura-Z resolvida em freqüência e com trem de pulsos. Com a primeira foram determinados os parâmetros térmicos relacionados ao solvente, enquanto que com a segunda foram caracterizadas as não linearidades eletrônicas associadas aos estados excitados das moléculas. Além disso, foi possível obter a dinâmica das não linearidades presentes nas soluções, que apresentam um processo acumulativo relacionado à formação de uma lente térmica induzida pelo perfil gaussiano do laser. / This work reports on the optical properties of aniline tetramers in dimethyl sulfoxide (DMSO) solutions. Absorption and emission spectra allowed a rough estimate of the energy levels of the aniline tetramers. Nonlinear optical properties were studied with the frequency resolved Z-scan technique and with the Z-scan technique with pulse trains. The former determined the thermal parameters of the solvent, while the latter characterized electronic nonlinearities associated to molecular excited states. Moreover, we could analyze the dynamics of the optical nonlinearities and verify the presence of an accumulative process related to thermal lensing.