Conception et réalisation d'un banc automatisé de caractérisation du comportement temporel des miroirs auto-pompés à conjugaison de phase photoréfractive : cartographie d'échantillons et modélisation physique

Abstract : This dissertation deals with photorefractive self-pumped phase-conjugate mirrors and more precisely with the so-called CAT mirror. The large diversity of temporal behaviour that can be observed with CAT mirrors and the great difficulty in understanding how they actually work, compared with the relative simplicity of obtaining efficient reflections, lead us to undertake a systematic study of mirrors of that kind. The first step was to design and build a fully automated measurement bench that can perform the digital acquisition of the phase conjugate wave, while controlling relevant physical parameters such as the temperature of the sample, the incidence angle, and the transversal position of the incident beam on the crystal. Then a software (for PC and MacIntosh), capable of finding the best experimental conditions in order to optimize a given quality criterion, has been developped. Such a criterion, carefully chosen with respect to the actual use of the mirror, will be mapped automatically versus relevant physical parameters. Experimental results, got from two different barium titanate samples, helped us make physical modelling. We first performed a model for steady state reflectivity, based on the "two coupled four-wave-mixing regions" model, but taking into account a fanning distribution inside of the crystal and the influence of geometrical parameters. Computered calculations are in good agreement with experimental results. A second model describe the temporal behaviour of the reflectivity by means of a ramdom function governed by a probability law. Furthermore, the measurement bench we designed is capable of testing other assumptions or working hypothesis about the physical processes involved in CAT mirrors. It also could be an useful apparatus for crystal growth scientists to characterize thoroughly their samples
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Michel Goetz. Conception et réalisation d'un banc automatisé de caractérisation du comportement temporel des miroirs auto-pompés à conjugaison de phase photoréfractive : cartographie d'échantillons et modélisation physique. Autre [cond-mat.other]. Université Paul Verlaine - Metz, 1994. Français. ⟨NNT : 1994METZ040S⟩. ⟨tel-01776743⟩

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