Etude théorique et expérimentale de transformations de phase par diffusion dans des aciers sous champ magnétique intense

The lithium niobate (LN) is one of the most interesting dielectrical materials for the applications in integrated optics because of its broad range of transparency and its great electro-optical, acousto-optical and nonlinear optical coefficients. The whole of these properties allows in particular the realization of weak losses (0.1 dB/cm) optical waveguides in the wavelengths of telecommunications, of electro-optical integrated modulators with weak order tension, and of integrated second harmonic generator. Our study carries out to characterization of the LN bulk crystals and waveguides by Raman spectroscopy and luminescence polaron. In its congruent composition ([Li] = 48,6 mol{rc) the LN presents specific defects of several species, in particular of the niobium ions in lithium site called antisites (Nbu). The concentration of these defects depends on the composition of the crystal. We studied in particular bulk crystals of composition under congruent ([Li]