Darbe pristatomi eksperimentiniai bei teoriniai rezultatai, susiję su skaidriųjų terpių lūžio rodiklio pokyčio indukavimu. Parodoma, kad lydytą kvarcą veikiant Yb:KGV lazerine sistema generuojamais impulsais, jame galima sukurti modifikuoto lūžio rodiklio sritis. Šios sritys pasižymi dvejopu šviesos lūžimu, atsirandančiu dėl medžiagos tūryje besiformuojančių nanogardelių, o modifikuotų sričių vienalytiškumas priklauso nuo akumuliacinių efektų. Pakitusio lūžio rodiklio sritis taip pat galima formuoti ir ličio niobato kristale. Priklausomai nuo spinduliuotės parametrų, šiame kristale galima įrašyti stabilius modifikuoto lūžio rodiklio darinius, o taip pat ir nestabilias modifikacijas, atsirandančias dėl fotorefrakcinio reiškinio. Pastarąjį efektą galima panaudoti daugkartiniam informacijos įrašymui. Pademonstruoti efektyvūs fotoniniai elementai, tūrinės Brego gardelės, įrašytos tiek lydyto kvarco, tiek ličio niobato kristalo tūryje. Pateikiama metodika, skirta lazerio indukuoto lūžio rodiklio pokyčiui nustatyti matuojant Brego gardelių difrakcinius efektyvumus. Taip pat tyrinėjama kaip modifikuoti dariniai lemia superkontinuumo ir šviesos gijos formavimosi reiškinius lydytame kvarce. / The study on refractive index modification of transparent materials with ultrashort laser pulses is presented in this dissertation. Based on experimental data it was demonstrated, that using ultrashort pulses, generated with Yb:KGW laser system, it is possible to produce modified refractive index zones in the fused silica glass, that possess birefringence. This effect is caused by nanogratings that form in the bulk of the material. Homogeneity of the modified zones is determined by the accumulation effects, mainly the number of pulses that affect each area. Refractive index variations can be created also in crystalline material such as lithium niobate. Depending on the writing pulse parameters different types of modifications can be created: permanent modification that is caused by crystal amorphization and non-stable modifications that originate from the photorefractive properties of the crystal. Latter modifications can be used for three-dimensional, rewritable data recording. Highly efficient photonic elements, such as volume Bragg gratings, recorded in fused silica and lithium niobate crystal are demonstrated. The technique allowing the evaluation of refractive index change applying Bragg gratings is described. Also modification influence on nonlinear processes that appear in fused silica such as filament formation and supercontinuum generation is experimentally investigated.

The study on refractive index modification of transparent materials with ultrashort laser pulses is presented in this work. Based on experimental data it was demonstrated, that using ultrashort pulses, generated with Yb:KGW laser system, it is possible to produce modified refractive index zones in the fused silica glass, that possess birefringence. This effect is caused by nanogratings that form in the bulk of the material. Homogeneity of the modified zones is determined by the accumulation effects, mainly the number of pulses that affect each area. Refractive index variations can be created also in crystalline material such as lithium niobate. Depending on the writing pulse parameters different types of modifications can be created: permanent modification that is caused by crystal amorphization and non-stable modifications that originate from the photorefractive properties of the crystal. Latter modifications can be used for three-dimensional, rewritable data recording. Highly efficient photonic elements, such as volume Bragg gratings, recorded in fused silica and lithium niobate crystal are demonstrated. The technique, allowing the evaluation of refractive index change applying Bragg gratings, is described. Also modification influence on nonlinear processes that appear in fused silica such as filament formation and supercontinuum generation is experimentally investigated. / Darbe pristatomi eksperimentiniai bei teoriniai rezultatai, susiję su skaidriųjų terpių lūžio rodiklio pokyčio indukavimu. Parodoma, kad lydytą kvarcą veikiant Yb:KGV lazerine sistema generuojamais impulsais, jame galima sukurti modifikuoto lūžio rodiklio sritis. Šios sritys pasižymi dvejopu šviesos lūžimu, atsirandančiu dėl medžiagos tūryje besiformuojančių nanogardelių, o modifikuotų sričių vienalytiškumas priklauso nuo akumuliacinių efektų. Pakitusio lūžio rodiklio sritis taip pat galima formuoti ir ličio niobato kristale. Priklausomai nuo spinduliuotės parametrų, šiame kristale galima įrašyti stabilius modifikuoto lūžio rodiklio darinius, o taip pat ir nestabilias modifikacijas, atsirandančias dėl fotorefrakcinio reiškinio. Pastarąjį efektą galima panaudoti daugkartiniam informacijos įrašymui. Pademonstruoti efektyvūs fotoniniai elementai, tūrinės Brego gardelės, įrašytos tiek lydyto kvarco, tiek ličio niobato kristalo tūryje. Pateikiama metodika, skirta lazerio indukuoto lūžio rodiklio pokyčiui nustatyti matuojant Brego gardelių difrakcinius efektyvumus. Taip pat tyrinėjama kaip modifikuoti dariniai lemia superkontinuumo ir šviesos gijos formavimosi reiškinius lydytame kvarce.

Baigiamajame magistro darbe suprojektuotos ir pagamintos dviejų rūšių šviesos koncentratorinės sistemos: jungtinė parabolinė ir sistema su Frenelio lęšiu. Atlikta saulės elementų efektyvumo analizė, išnagrinėtos šviesą koncentruojančių sistemų rūšys bei aptarti jų optiniai parametrai. Frenelio lęšis ir koncentratorinių sistemų laikančiosios konstrukcijos pagamintos vakuuminio formavimo būdu, ieškant pigesnės gamybos technologijos. Baigiamajame darbe atlikti optinio pralaidumo ir lūžio rodiklio, matomos šviesos bangų ilgių ruože, tyrimai bei saulės elementų, esančių šviesos koncentratorinėse sistemose,voltamperinių ir voltvatinių charakteristikų tyrimai. Iš tyrimų rezultatų nustatyti šviesos koncentravimo laipsniai. Darbe diskutuojama apie pigių optinių sistemų galimus pritaikymus ir jų tobulinimo būdus. Išnagrinėjus teorinę ir praktinę dalis, pateiktos išvados ir pasiūlymai. Darbą sudaro 8 dalys: įvadas, saulės elementų efektyvumo ribos, saulės šviesos koncentratoriai ir jų panaudojimas fotoelektrinėse sistemose, eksperimentinių tyrimų metodika, prototipų gamyba, eksperimentiniai tyrimai, išvados, literatūros sąrašas. Darbo apimtis – 82 p. teksto be priedų, 95 pav., 13 lent., 22 bibliografiniai šaltiniai. Atskirai pridedami darbo priedai. / Concentrated PV systems (compound parabolic and Fresnel CPV) have been designed and investigated. The efficiency of solar cells and the types of light concentrated systems have been analyzed and their optical parameters have been discussed. Fresnel lens and the CPV system holding structure have been fabricated by means of vacuum forming machine in this way making the technology of production less expensive. Optical transmittance and refractive index of Fresnel lens were measured in the range of visible light wavelengths. Current-voltage and voltage-power characteristics of solar cells built inside the CPV systems were investigated, based on results the degree of light concentration by Fresnel lens and compound parabolic CPV has been determined. Some discussions regarding possible applications of concentrated PV systems containing the Fresnel lens as well as possible ways of CPV design improvements are given in current work. After analysed theoretical and practical parts, conclusions and suggestions are proposed. Thesis structure: introduction, theoretical and experimental parts, results of experiments, conclusions and references. Thesis consist of: 82 p. text without appendixes, 95 pictures, 13 tables, 22 bibliographical entries. Appendixes included.

Salinity and turbidity are two important seawater properties for the physical oceanography. The study of physical oceanography requires a compact high-resolution in-situ salino-turbidi-meter. The main objective of this work is to propose, design and implement an optical solution to simultaneously measure the seawater salinity and turbidity. Our first study is carried out to design a high-resolution refractometer based on a laser beam deviation measurement by a Position Sensitive Device (PSD). The refractive index measurements obtained by the voltage value delivered by PSD have been evaluated to quantify the performances of the sensor. According to the obtained results, it is clear that this PSD-based refractometer is attractive for innovative applications in metrology. However, PSD lacks the capability to retrieve the power distribution information of laser beam, which is related to the turbidity measurements. On the contrary, Charge-Coupled Device (CCD) gives much more information of laser beam than PSD. In the second part of the thesis, a performance comparison between PSD and CCD combined with a centroid algorithm are discussed with special attention paid to the CCD-based refractometer. According to the operating principle of CCD-based system, five factors of CCD-based system: image window size, number of processed images, threshold, binning and saturation are evaluated to optimize the CCD-based refractometer. By applying the optimized parameters, the performance of CCD-based refractometer is better than PSD-based refractometer in measuring the refractive index. Furthermore, by applying different post-processing algorithms, CCD-based system possesses the capability of measuring the power distribution sensitive quantities. To show this advantage of CCD-based system, the attenuation measurement method is used to measure turbidity without modifying the refractometer configuration. The turbidity measurement and salinity measurements influence each other in a refractometer. To overcome these influences, a CCD combined with a new location algorithm is used to measure both the refractive index and the attenuation. Several simulations and experiments are carried out to evaluate this new method. According to the results, the way to improve the resolution is discussed as well. Comparing to the nephelometer specified by the NTU standard, our method has been proved as a valid method to measure turbidity. By studying the performances of CCD-based refracto-turbidi-meter, 3 new prototypes are proposed to improve the salinity and turbidity measurement performance at the end of this thesis.

Various carbon content hydrogenated amorphous silicon carbide (a-Si1&iexcl / xCx:H) and hydrogenated amorphous silicon (a-Si:H) thin films have been deposited on various substrates by using plasma enhanced chemical vapour deposition (PECVD) technique. Transmission spectra of these films have been determined within UV-Visible region and the obtained data were analysed to find related physical constants such as / refractive indices, thicknesses, etc. Fourier transform infrared (FT-IR) spectrometry technique has been used to determine transmission &amp / reflection type spectra of these films. Obtained data were analysed to determine bond structures of the films. E&reg / ects of relative concentration of ethylene (C2H4) gas on thin film bond structure and on optical constants have been questioned.

The eye lens grows continuously throughout life and changes its shape as the eye changes focus from a distant to a near object (the process of accommodation). These changes are complex because they may affect not only the shape of the lens, but also its refractive index distribution. To date there has been no satisfactory technique for directly and non-invasively measuring these changes. In this study the refractive index distribution through the isolated lens was measured non-invasively using a novel MRI technique. The dependence of the refractive index value of lens tissue on its transverse relaxation rate (R2) was determined empirically from measurements on lens homogenate samples. Using a multi-spin-echo imaging sequence, data were acquired for constructing R2 maps of a central slice through the isolated lens. These R2 maps were transformed to refractive index maps using the empirically determined dependence of refractive index on R2. Using a standard algorithm for ray tracing through gradient index media, the propagation of light rays through the index map were simulated. The optical properties of the lens, such as focal length, were then measured. The technique was validated by also directly measuring the focal length of each lens using laser ray tracing. The subtle changes in refractive index distribution that are responsible for the dramatic change in the optical properties of the isolated lens with age, were observed for the first time. The decrease in surface power of the isolated lens with age accounted only partially for the decrease in total lens power with age, the remainder resulting from a reduction in the gradient of refractive index (GRIN) power. It is likely that this reduction in GFUN power is the mechanism by which the eye maintains emmetropia (good distant vision) with age despite the increasing curvature of its surfaces. The reduction in the GRIN power of the lens was found to be mainly due to a flattening of the refractive index profile in the central region of the lens, accompanied by steepening of the profile near the edge of the lens. In agreement with a previous MRI study of the isolated human eye lens, this study found a decrease in the refractive index of the nucleus with age. However the age related change in this study was not as large and not found to be statistically significant. The results demonstrate that existing simple models for the optics of the eye lens are inadequate to accurately describe its properties. Several more sophisticated models were considered in an attempt to describe better the age-dependent changes that occur in both the power of the lens and its longitudinal aberration. Mathematical modelling was also used to simulate the accommodative process and investigate possible changes in the index distribution of the lens that may occur with accommodation. A preliminary in vivo study was performed aimed at observing the change in the refractive index distribution of the eye lens with age and accommodation. These results demonstrated the feasibility of the technique for in vivo applications and showed that within experimental error there is little change in the central refractive index of the lens with age. However the resolution achievable with standard clinical imaging sequences and signal detection hardware was not optimal for in vivo refractive index mapping of changes in the human eye lens with accommodation. Finally therefore, methods for refining the technique for in vivo applications are discussed which may make it possible to directly and simultaneously measure both the shape and refractive index distribution of the lens with age and accommodation.

Made available in DSpace on 2016-12-12T20:27:39Z (GMT). No. of bitstreams: 1 Renan Sebem.pdf: 14781648 bytes, checksum: 1c30002408823e0116831038c8c98e8c (MD5) Previous issue date: 2015-09-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work explores the potential and shows the implementation of the long period gratings as refractive index sensors. It is proposed a sensor design where the refractive index sensitivity is improved. The design includes the use of the sensor with simple and low cost interrogation. Several manufacturing parameters are investigated and the process is enhanced to meet the design specifications, and also to obtain repeatability in the process. New ideas were proposed to manufacture tilted gratings and to control the index modulation duty cycle in a practical way with inexpensive equipment. The inscription of the fiber sensor is made by CO2 laser, point to point, with a uniform index modulation. The gratings were interrogated by an optical spectrum analyzer and also by edge filter demodulation in the 1550 nm region through an electronic board, developed in this work with automatic normalization of the signal. Results show that the refractive index sensitivity is influenced by several design and manufacturing parameters of the fiber grating. Performed experiments show a considerable increase in the refractive index sensitivity of the grating. / Este trabalho explora o potencial e demonstra a implementação das redes de período longo em fibra como sensores de índice de refração. É proposto um projeto do sensor em que a sensibilidade ao índice de refração é aperfeiçoada. O projeto contempla a utilização do sensor com interrogação de maneira simples e de baixo custo. Diversos parâmetros de fabricação são investigados e o processo é aprimorado para atingir as especificações de projeto, e também a fim da obtenção de repetibilidade no processo. Novas ideias foram propostas para fabricação de redes inclinadas e para o controle do duty cycle da modulação de índice da rede de maneira prática com equipamentos de baixo custo. A fabricação do sensor em fibra é feita através de laser de CO2, ponto a ponto, e com modulação de índice uniforme. As redes foram interrogadas através de analisador de espectro óptico e também por demodulação de borda de filtro na região de 1550 nm através de uma placa eletrônica, desenvolvida neste trabalho com normalização automática do sinal. Resultados mostram que a sensibilidade ao índice de refração é influenciada por alguns parâmetros de projeto e fabricação da rede em fibra. Experimentos realizados mostraram um aumento considerável na sensibilidade da rede ao índice de refração.

Cavity enhanced spectroscopies (CES) are currently amongst the most sensitive spectroscopic techniques available for probing gas-phase samples, however their application to the liquid-phase has been more limited. Sensitive analysis of submicrolitre liquid samples is highly desirable, as miniaturisation allows for the reaction and analysis of scarce or expensive reagents, produces less waste, and can increase the speed of separations and reactions, whilst having a small footprint and high throughput. Absorption spectroscopy is a particularly desirable technique due to its universal, label-free nature, however its application to small volume liquid samples is hampered by the associated short absorption pathlengths, which limit sensitivity. CES improve sensitivity by trapping light within a confined region, increasing the effective pathlength through the sample. Three distinct types of optical cavity were constructed and evaluated for the purposes of making optical absorption measurements on liquid samples. The first incorporated a high optical quality flow cell into a "macrocavity" formed from two dielectric mirrors separated by 51.3 cm. Cavity losses were minimised by positioning the flow cell at Brewster's angle to the optical axis, and the setup was used to perform a single-wavelength cavity ringdown spectroscopy experiment to detect and quantify nitrite within aqueous samples. The detection limit was determined to be 8.83 nM nitrite in an illuminated volume of only 74.6 nL. Scattering and reflective losses from the flow cell surfaces were found to be the largest barrier to increased sensitivity, leading us to focus on the integration of cavity mirrors within a microfluidic flow system in the work that followed. In the second set of experiments, cavity enhanced absorption spectroscopy (CEAS) measurements were performed on Thymol Blue using custom-made microfluidic chips with integrated cavity mirrors. Unfortunately, due to the plane-parallel configuration of the mirrors and the corresponding difficulty in sustaining stable cavity modes, the results were underwhelming, with a maximum cavity enhancement factor (CEF) of only 2.68. At this point, attention was focussed toward a more well-defined cavity geometry: open-access plano-concave microcavities. The microcavities consist of an array of micron-scale concave mirrors opposed by a planar mirror, with a pathlength that is tunable to sub-nanometer precision using piezoelectric actuators. In contrast to the other experimental setups described, themicrocavities allow for optical measurements to be performed in which we monitor the change of wavelength and/or amplitude of a single well-defined cavity mode in response to a liquid sample introduced between the mirrors. In the first microcavity experiment, we used 10 μm diameter mirrors with cavity lengths from 2.238 μm to 10.318 μm to demonstrate refractive index sensing in glucose solutions with a limit of detection of 3.5 x 10^-4 RIU. The total volume of detection in our setup was 54 fL. Thus, at the limit of detection, the setup can detect the change of refractive index that results from the introduction of 900 zeptomoles (500,000 molecules) of glucose into the device. The microcavity sensor was then adapted to enable broadband absorption measurements of methylene blue via CEAS. By recording data simultaneously from multiple cavities of differing lengths, absorption data is obtained at a number of wavelengths. Using 10 μm diameter mirrors with cavity pathlengths from 476 nm to 728 nm, a limit of detection, expressed as minimum detectable absorption per unit pathlength, of 1.71 cm^-1 was achieved within a volume of 580 attolitres, corresponding to less than 2000 molecules within the mode volume of the cavity. Finally, a new prototype was developed with improved cavity finesse, a much more intense and stable light source, and improved flow design. Using a single plano-concave microcavity within the array with a cavity pathlength of 839.7 nm, and 4 μm radius of curvature mirror, absorption measurements were performed on Methylene Blue. Analysis of this data indicated a CEF of around 9270, and a limit of detection based on the measured signal-to-noise ratio of 0.0146 cm^-1. This corresponds to a minimum detectable concentration of 104 nM Methylene Blue, which given the mode volume of 219 aL, suggests a theoretical minimum detectable number of molecules of 14.

Ce travail est financé par le fond européen Interreg VA (projet "PowderReg"). L'optimisation du transport, du stockage et du mélange des dispersions granulaires passe par le contrôle de leur écoulement, par exemple en ajoutant des vibrations mécaniques. Ce travail permet d'apporter une meilleure compréhension de l'influence des vibrations sur la rhéologie apparente de dispersions granulaires modèles dans le régime quasi-statique. Des travaux expérimentaux et numériques sont réalisés afin de sonder les modifications de la dynamique locale ainsi que les hétérogénéités qui apparaissent lors de leur mise en écoulement. Deux géométries présentant des intérêts fondamentaux, géophysiques et industriels sont étudiées : la cellule de type Couette et le plan incliné. Dans un premier temps, des mesures iso-indice couplées à de la fluorescence induite par laser ont été réalisées sur des suspensions granulaires dans une cellule de type Couette sous vibrations. Les vibrations rendent la rhéologie locale en homogénéisant le système. Elles suppriment la contrainte seuil apparente et font apparaître un plateau Newtonien à bas gradient, intrinsèque à la dynamique locale qui est de nature diffusive. Il est apparu que le temps de réarrangement des particules, dépendant de l'intensité des vibrations, est relié au volume libre disponible autour de chaque particule. L'étude numérique de cette géométrie dans le cas d'une dispersion granulaire sèche a mis en évidence des résultats similaires. Dans un second temps, des écoulements de dispersions de grains secs sur un plan incliné vibrant ont été réalisés. Des travaux numériques sur cette même géométrie ont permis d'enrichir cette étude. Les résultats mettent en évidence l'existence de deux régimes sous vibrations. Le comportement dans le régime dominé par la gravité n'est pas influencé par les vibrations, et un profil de Bagnold est observé. Les vibrations permettent principalement de baisser la friction basale, influant alors la hauteur des dépôts. Dans le régime dominé par les vibrations, les écoulements sont déclenchés par les vibrations elles-mêmes. Il est apparu qu'elles induisent des fluctuations de vitesses, qui créées alors une température granulaire. Cette température permet d'activer les réorganisations à l'échelle de la particule, éliminant le seuil apparent responsable du blocage des écoulements et permettant leur contrôle au travers du taux de cisaillement / This work is funded by the European Founds Interreg VA ("PowderReg" project). The optimization of the transport, storage and mixture of granular dispersions involves their flow control, by adding mechanical vibrations, for example. The present work enables a better understanding of the influence of the vibrations on the apparent rheology of model granular dispersions in the quasi-static regime. Experimental and numerical studies were carried out in order to probe the modifications of the local dynamic and heterogeneities that appear during the flow. Two geometries, interesting for diverse applications in fundamental science, geophysics and industries, were studied: the Couette cell geometry and the inclined plane. In the first step, refractive-index matching technique, coupled to the planar laser induced fluorescence was used to make measurements in granular suspensions in a vibrated Couette cell geometry. Vibrations make the rheology local by homogenizing the system. They suppress the yield stress and result in the appearance of a Newtonian plateau at the low shear, intrinsic to the local dynamic, which is diffusive in nature. It appears that the rearrangement time of the particles, depending on the intensity of the vibrations, is linked to a free volume available around each particle. The numerical study of this geometry in the case of a dry granular dispersion shows similar results. In the second step, flows of dry granular dispersions down the inclined and vibrated plane were realized. This study was completed with a numerical work. The results demonstrated the existence of two distinct regimes under vibrations. The behavior in the gravity-driven regime is not affected by the vibrations and a Bagnold profile is observed. The vibrations mainly cause the decrease of the basal friction and thus influence the height of the deposits. In the vibration-driven regime, however, flows are triggered by the vibrations themselves. It appears that they induce velocity fluctuations that create a granular temperature. That temperature allows the activation of the reorganizations at the grain scale. This suppresses the apparent yield responsible for the flow jamming, and thus enables their control through the shear rate

L’objectif principal de ce travail est d’étudier in-situ et ex-situ l’interaction du dioxyde de carbone (CO2) avec les films minces de polystyrène et les surfaces par deux techniques principales : la réflectivité des rayons X (RRX) et l’ellipsométrie.Dans cette thèse, nous abordons l’étude des propriétés physiques de films de polystyrène (PS) à l’état confiné (films minces) et leur évolution lors de leur exposition à du CO2 sous pression. Nous démontrons par RRX et par ellipsométrie sur les mêmes films que la densité et l’indice de réfraction augmentent quand l’épaisseur du film diminue. Nous confirmons la diminution de Tg pour des films de PS d’épaisseur inférieure à 70 nm selon la loi empirique de Keddie [1]. Ces deux résultats pourraient signifier que les films ultraminces présentent une certaine organisation des chaines.Nous abordons ensuite le comportement des films ultra minces de PS exposés à du CO2 en fonction de la pression de CO2 par réflectivité de rayons X (RRX) faite au rayonnement synchrotron (ESRF ligne ID10B). Nous suivons in-situ le gonflement et le dégonflement du film mince d’épaisseur 7 nm lors de la pressurisation et la dépressurisation du CO2. Par calcul de l’évolution de la densité électronique dans le film, nous mettons en évidence l’existence d’une pression de transition vitreuse Pg et d’un gonflement rémanent lié à la présence de molécules de CO2 piégées dans le film [2].Nous proposons par la suite une étude ex-situ par RRX du gonflement et de l’évolution au cours du temps des films de PS gonflés. Nous observons que les films minces présentent une plus grande capacité de gonflement et dégonflement au cours du temps par opposition aux films plus épais. Nous constatons que ce phénomène est fortement dépendant du taux de dépressurisation. En effet, nous constatons que la dépressurisation rapide renforce considérablement, non seulement le gonflement du film, mais aussi son dégonflement au cours du temps. Nous mettons alors en évidence que le taux de dépressurisation régit clairement l'état final des films gonflés, à savoir l’état métastable ou l’état vitreux.Finalement, nous étudions l’influence du gonflement du film par le CO2 sur l’évolution de la température de transition vitreuse. Cette étude est effectuée principalement par ellipsométrie. Nous montrons que ces films qui ne présentaient qu’une valeur unique de Tg avant exposition, présentent après exposition trois valeurs de Tg. En suivant l’évolution de l’épaisseur de ces films gonflés en fonction de la température, nous proposons des réponses qui peuvent expliquer les différentes Tg observées. En outre, nous mettons en évidence l’existence du CO2 stocké dans les films. Après un recuit au dessus de 150°C, les films reprennent le même comportement qu’avant exposition au CO2 qui est loin d’être l’état d’équilibre du polymère massique. Nous confirmons par ce fait l’existence de fortes forces de rappel dans les films ultraminces qui les ramènent vers leurs états initiaux de non équilibre. Ce résultat est à rapprocher de celui concernant l’évolution de la Tg due au confinement dans les films ultraminces avant exposition. / The aim of this work is to study in-situ and ex-situ interaction of carbon dioxide (CO2) with thin films of polystyrene and surfaces by two main techniques: the X-ray reflectivity (XRR) and ellipsometry.In this thesis, we address the study of the physical properties of polystyrene films (PS) in the confined state (thin films) and their evolution when exposed to CO2 pressure. We demonstrate by XRR and ellipsometry in the same films that the density and the refractive index increase when the film thickness decreases. We confirm the decrease of Tg for PS films of thickness less than 70 nm according to the empirical law of Keddie [1]. Both results could mean that ultrathin films have a certain organization of channels.We then discuss the behavior of PS ultra thin films exposed to CO2 as a function of CO2 pressure by XRR made at synchrotron radiation (ESRF ID10B line). We monitor in situ the swelling and deswelling of the 7 nm thin film thickness upon pressurization and depressurization of CO2. By calculating the evolution of the electron density in the film, we highlight the existence of a glass transition pressure Pg and a residual swelling due to the presence of CO2 molecules trapped inside the film [2].We propose then an ex-situ XRR study of swelling and kinetic of deswelling for PS swollen films. We observe that the thin films have a higher swelling and deswelling capacity compare to the thicker films. We note that this phenomenon is highly dependent to the depressurization rate. Indeed, we find that the rapid depressurization greatly enhances not only the swelling of the film, but also its deswelling over time. We then highlight that the rate of depressurization clearly governs the final state of swolen films, to say the metastable state or glassy state.Finally, we study the effect of film swelling by CO2 on the evolution of the glass transition temperature. This study is carried out mainly by ellipsometry. We show that these films which showed only a single Tg value before exposure, after exposure has three values of Tg completely independent of film thickness. By following the thickness evolution of these swollen films as a function of temperature, we offer answers that can explain the different Tg values observed. In addition, we highlight the existence of CO2 stored in these films. After annealing above 150 ° C, the films show the same behavior as before exposure to CO2 which is far from the equilibrium state of the bulk polymer. We confirm therefore the existence of strong restoring forces in ultrathin films that bring them back to their initial states of non-equilibrium. This result presents similarities to that concerning the evolution of the Tg due to confinement in ultrathin films before exposure.