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Neste trabalho foram produzidos e caracterizados filmes finos de óxido de zinco (ZnO) e de dióxido de titânio (TiO2) e dos metais puros (Zn e Ti), em substratos de vidro e em fibras ópticas, por pulverização catódica DC assistida por magnetrão, para aplicações em sensores de fibra óptica. Os parâmetros de deposição como a pressão parcial de oxigénio, a pressão de trabalho e a potência aplicada, foram otimizados de modo a obter filmes espelhados maximizando a reflectância. Os filmes depositados em substratos de vidro foram caracterizados por espectroscopia UV-Vis, difracção de raios-X (XRD) e microscopia electrónica de varrimento (SEM). No que diz respeito aos parâmetros de deposição, para os filmes de Zn e ZnO, a pressão de trabalho e a potência aplicada foram mantidas constantes, sendo apenas alterada a percentagem de oxigénio presente em cada filme. No entanto, para os filmes de TiO2, foram testados os três parâmetros em simultâneo. Para os filmes de Ti e TiO2 foi possível concluir que pressão de trabalho mais baixa e potência aplicada mais elevada conduz a filmes com reflectância superior. Através da análise dos filmes finos feita por difracção de raios-X confirmou-se que foram depositados filmes de Zn, ZnO, Ti e TiO2. Nas imagens de SEM foi possível verificar que a superfície dos filmes de óxido de zinco é mais rugosa que a superfície dos filmes de dióxido de titânio. Com o objectivo de desenvolver sensores de fibra óptica, foram depositados nas fibras ópticas clivadas os revestimentos mais promissores. No entanto, devido à rugosidade descrita anteriormente dos filmes de Zn e ZnO, apesar das fibras revestidas com estes filmes apresentarem reflectividade mais elevada, as cavidades formadas pelas fibras ópticas com estes revestimentos não apresentam o comportamento característico de uma cavidade Fabry-Perot. Por outro lado, conseguem ser formadas cavidades Fabry-Perot com sucesso, utilizando uma fibra monomodo e uma fibra com qualquer revestimento de Ti ou TiO2 estudado. Finalmente, foram selecionadas fibras ópticas revestidas por filmes de ambos os óxidos produzidos com diferentes condições de deposição para analisar a sua sensibilidade à temperatura. In this work, thin films of zinc oxide (ZnO) and titanium dioxide (TiO2) and of the pure metals (Zn and Ti) were produced and characterized on glass substrates and on optical fibers, by DC magnetron sputtering, for applications in optical fiber sensors. The deposition parameters such as oxygen partial pressure, working pressure and sputtering power were optimized to obtain films with the maximum possible reflectance. The films deposited on glass substrates were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Regarding the deposition parameters, in the zinc and zinc oxide films, the working pressure and the applied power were kept constant, with only the percentage of oxygen present in each film being changed. However, in titanium dioxide films, all three parameters were tested simultaneously, changing the working pressure, the sputtering power, and the oxygen percentage. For Ti and TiO2 films, it was possible to conclude that lower working pressure and higher applied power lead to films with higher reflectance. Through the analysis of thin films made by X-ray diffraction, it was confirmed that Zn, ZnO, Ti and TiO2 films were deposited. In SEM images it is possible to verify that the surface of zinc oxide films is rougher than the surface of titanium dioxide films. To develop optical fiber sensors, the most promising coatings were deposited on the cleaved optical fibers. However, due to the previously described roughness of Zn and ZnO films and although fibers coated with ZnO films have shown higher reflectivity, the cavities formed by optical fibers with these coatings do not present the characteristic behavior of a Fabry-Perot cavity. On the other hand, Fabry-Perot cavities can be successfully formed using a single-mode fiber and a fiber with any studied Ti or TiO2 coating. Finally, optical fibers coated with films of both oxides produced with different deposition conditions were selected to analyze their temperature sensitivity.

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Experimental bounds on induced vacuum magnetic birefringence can be used to improve present photon-photon scattering limits in the electronvolt energy range. Measurements with the Polarizzazione del Vuoto con Laser apparatus [E. Zavattini et al., Phys. Rev. D 77, 032006 (2008)] at both $\ensuremath{\lambda}=1064$ and 532 nm lead to bounds on the parameter ${A}_{e}$, describing nonlinear effects in QED, of ${A}_{e}^{(1064)}l6.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\text{ }\text{ }{\mathrm{T}}^{\ensuremath{-}2}@1064\text{ }\text{ }\mathrm{nm}$ and ${A}_{e}^{(532)}l6.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}21}\text{ }\text{ }{\mathrm{T}}^{\ensuremath{-}2}@532\text{ }\text{ }\mathrm{nm}$, respectively, at 95% confidence level, compared to the predicted value of ${A}_{e}=1.32\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}24}\text{ }\text{ }{\mathrm{T}}^{\ensuremath{-}2}$. The total photon-photon scattering cross section may also be expressed in terms of ${A}_{e}$, setting bounds for unpolarized light of ${\ensuremath{\sigma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}^{(1064)}l4.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}62}\text{ }\text{ }{\mathrm{m}}^{2}$ and ${\ensuremath{\sigma}}_{\ensuremath{\gamma}\ensuremath{\gamma}}^{(532)}l2.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}60}\text{ }\text{ }{\mathrm{m}}^{2}$. Compared to the expected QED scattering cross section these results are a factor of $\ensuremath{\simeq}2\ifmmode\times\else\texttimes\fi{}{10}^{7}$ higher and represent an improvement of a factor about 500 on previous bounds based on ellipticity measurements and of a factor of about ${10}^{10}$ on bounds based on direct stimulated scattering measurements.

IIn 2006 the PVLAS collaboration reported the observation of an optical rotation generated in vacuum by a magnetic field. To further check against possible instrumental artifacts several upgrades to the PVLAS apparatus have been made during the last year. Two data taking runs, at the wavelength of 1064 nm, have been performed in the new configuration with magnetic field strengths of 2.3 T and 5 T. The 2.3 T field value was chosen in order to avoid stray fields. The new observations do not show the presence of a rotation signal down to the levels of $1.2\cdot 10^{-8}$ rad at 5 T and $1.0\cdot 10^{-8}$ rad at 2.3 T (at 95% c.l.) with 45000 passes in the magnetic field zone. In the same conditions no ellipticity signal was detected down to $1.4\cdot 10^{-8}$ at 2.3 T (at 95% c.l.), whereas at 5 T a signal is still present. The physical nature of this ellipticity as due to an effect depending on $B^2$ can be excluded by the measurement at 2.3 T. These new results completely exclude the previously published magnetically induced vacuum dichroism results, indicating that they were instrumental artifacts. These new results therefore also exclude the particle interpretation of the previous PVLAS results as due to a spin zero boson. The background ellipticity at 2.3 T can be used to determine a new limit on the total photon-photon scattering cross section of $\sigma_{\gamma\gamma} < 4.5 \cdot10^{-34}$ barn at 95% c.l.., Comment: 25 pages, 7 figures Main changes rel. to v.2: minor changes to abstract, replaced Figures 4,5,6, corrected typographical errors. Paper submitted to Physical Review D

We study wave transport through a chaotic quantum billiard attached to two waveguides via barriers of arbitrary transparencies in the semiclassical limit of a large number of open scattering channels. We focus attention on the ergodic regime, which is described by using a random-matrix approach to chaotic resonance scattering together with an extended version of Nazarov’s circuit theory. By varying the relative strength of the barriers’ transparencies a reorganization of the relevant resonances in the energy interval where transport takes place leads to a full suppression of high transmission modes. We provide a detailed quantitative description of the process by means of both numerical and analytical evaluations of the average density of transmission eigenvalues. We show that the density of Fabry-Perot modes can be used as a kind of order parameter for this quantum transition. A diagram is presented as a function of the transparencies of the barriers exhibiting the transport regimes and the transition lines.