Thermomechanical effects in hybrid and cylindrical-hybrid oriented nematic liquid crystals (NLC), as well as thermomechanical effects in NLC with a homogeneous director distribution induced by quasistatic or light electric fields, are observed and investigated theoretically and experimentally. It is postulated that these effects arise from a horizontal hydrodynamic flow in the NLC due to the vertical temperature gradient. There is good agreement between the theoretical calculations and the experimental results. The thermomechanical coefficient is measured. In the case where the hydrodynamic flow tends to strain the curvature of the “flexible ribbon,” an oscillatory motion is observed.

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2014 On étudie à la fois théoriquement et expérimentalement la multistabilité et les instabilités temporelles de processus ondulatoires non linéaires dans les conditions de transfert d'énergie et de compétition entre les différentes composantes de polarisation, pour un milieu anisotrope inhomogène présentant une non-linéarité à seuil. Dans de telles interactions, il se produit un couplage rétroactif lorsque le rayonnement laser induit un réseau d'indice de réfraction dans le milieu, à cause de la réponse non locale du milieu élastique anisotrope au champ extérieur. Abstract. 2014 The multistability and temporal instabilities of nonlinear wave process with an energy transfer and competition between different light polarization components have been studied both theoretically and experimentally for a nonhomogeneous anisotropic medium with threshold nonlinearity. A feedback for such wave interactions, when the laser radiation induces the bulk-gratings of refractive index, arises because of the non-local response of the anisotropic elastic medium on the external field.

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