Fronts et dynamiques spatio-temporelles dans l'expérience de la valve à cristaux liquides : effets de forçages spatiaux et rétroaction optique non locale

摘要

The appearance of spatial structures is a universal phenomenon. In nonlinear optics, generating transverse structures and controlling their dynamics is important not only from a fundamental point of view but also for potential applications. This work is carried out in this logic of characterizing and manipulating optical spatial structures, generated in a liquid crystal light valve experiment. The first part of the thesis is dedicated to the effects of spatial forcing on front propagation, which is done by using a spatial light modulator. A one-dimensional study, including the comparison with analytical models and numerical results, shows the existence of a pinning range inside which localized states of different size can be generated. A two-dimensional extension is also presented for different geometries of the spatial forcing. The second part deals with the effects of a nonlocal feedback on localized structures appearing in the simultaneous presence of diffraction and polarization interference. In the case of a translation effect, an advection phenomenon of structures is observed, associated with the appearance of phase singularities in their wake. Above a certain translation rate, another regime is attained, with periodicity along the direction of the drift. In the case where both translation and rotation are present, the self-organization modes of localized structures show analogies with certain modes occurring in the growing process of plants. The influence of the different parameters, in particular rotation, is characterized on the resulting patterns.