Pattern forming instability induced by light in pure and dye-doped nematic liquid crystals

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.Comment: 8 pages, 7 figures, LaTeX, accepted to Phys. Rev.

Hysteresis in the dependence of transparency on light intensity in a nematic liquid crystal

Hysteresis in the dependence of transparency on light intensity, in a nematic liquid crystal (NLC) layer, is experimentally observed The phenomenon is connected with the light scattering on disclinations in unoriented layers of NLC and with the difference of scattering cross sections in the homogeneously oriented phase and in isotropic phase.Une hystérésis de la transparence d'une couche de cristal liquide nématique fonction de l'intensité de la lumière a été découverte expérimentalement. Ce phénomène est relié à la diffusion de la lumière par des disinclinaisons dans la couche de cristal liquide non orientée et à la différence de section efficace de diffusion entre phase orientée de façon homogène et phase isotrope

Orientational optical non-linearity near the instability of nematic liquid crystal flow over an inclined plane

The problem of the gravity flow of nematic liquid crystal (NLC) mesophase over an inclined plane is investigated. In the case when the director of NLC is strongly anchored on the inclined plane surface perpendicular to the gravitational force and flow direction, a specific orientational instability arises for which the flow threshold value is obtained. Orientational optical non-linearity at the threshold of NLC flow instability is investigated.On étudie le problème de l'écoulement d'un nématique sur un plan incliné. Dans le cas où le directeur est ancré sur la surface du plan incliné perpendiculairement à la direction de la gravité et à celle de l'écoulement, on prédit une instabilité spécifique de l'orientation dont on calcule le seuil. On étudie la non-linéarité optique d'orientation du nématique au voisinage du seuil de l'instabilité d'écoulement

A new kind of photo-polymerisation induced diffraction gratings in liquid crystalline composite materials

In this paper we report on the first results of a new technique used to obtain good quality holographic diffraction gratings. This technique represents an improvement with respect to the traditional one, the so called polymerisation induced phase separation technique. Gratings are obtained by exposing the initial homogeneous mixture of liquid crystal and monomer molecules to the pattern produced by two interfering UV laser beams. The polymerisation process, which is photo-induced by this pattern, is thus spatially inhomogeneous: It leads to a redistribution of the mixture components and hence to the grating formation

The Decay of Unstable Orientational States of Nematic Liquid Crystals Interacting with a Laser Field

We show that the rate of relaxation is an important characteristic of the dynamics of critical systems undergoing second order phase transition, which are, in fact, still in effective motion even after the order parameter is reaching its steady state value. As a model system, we investigate the instability of the orientational state of a nematic liquid crystal acted on by a laser field and present the measurement of the initial fluctuations that start up the decay of the unstable state

Azodyes for liquid crystal photoalignment in displays and diffraction optical elements

Photoalignment on azo dye films is a simple and efficient way to achieve anisotropic ordering of molecules, which is promising to achieve ultra-thin high-performance dichroic polarizers. Besides, the photoalignment technique shows a unique advantage on patterned alignment applications, and enables the realization of advanced optical elements such as liquid crystal (LC) Dammann grating, LC Fresnel lens, holographic polarizers and bifocal optical-vortex lens. © 2022 SPIE