Photoinduced anchoring on a chalcogenide surface

Abstract

We present basic characteristics and a model of photoinduced anchoring of liquid crystals (LCs) on a chalcogenide surface. It was found that characteristics of the alignment strongly depend on the LC material for the same chalcogenide glass. The photoalignment is partially reversible and can be controlled by changing the light polarization direction. We propose a model in which the existence of dichroic units on the chalcogenide surface and competition between two mechanisms of the photoalignment is suggested. The first mechanism is related to the light-induced anisotropy on the chalcogenide surface and results in an easy orientation axes of a LC parallel to the polarization of the incident light. The second mechanism is attributed to an energy transfer from the dichroic units after the light absorption to the LC molecules adsorbed on the chalcogenide surface. The transferred energy causes polarization-sensitive desorption of the LC molecules from the chalcogenide surface and the light-induced easy orientation axis of a LC perpendicular to the incident light polarization. The competition between these mechanisms leads to the observed change of the direction of the easy axis with the exposure.

Photo-alignment control of topological defects in nematic liquid-crystal cells

“…According to Ref. [15], this time is associated with the time needed for settling equilibrium for the angular distribution of adsorbed LC molecules on the photosensitive surface during the irradiation process.…”

Recording of polarization holograms in a liquid crystal cell with a photosensitive chalcogenide orientation layer [Invited]

“…The easy orientation axis is either parallel or perpendicular to the polarization of the excitation beam [26][27][28]. In both cases, the light-induced easy axis on the chalcogenide surface ⃗ ex is described by the same expression as Eq.…”

“…The origin of this easy orientation axis can be either light-induced desorption of LC molecules from the chalcogenide surface [26] and/or light-induced anisotropy in the chalcogenide film [27,28]. The easy orientation axis is either parallel or perpendicular to the polarization of the excitation beam [26][27][28].…”

“…In this case, the problem of solubility of a hologram film can be serious and application of chemically stable and thermally robust photoaligning material is very desirable. In this concern, use of inorganic chalcogenide films, the photoaligning properties of which were recently reported in [25][26][27][28], is a good prospect. Here, we report on the recording of the polarization holograms in the chalcogenide layer that are amplified and electrically controlled by a nematic LC E7.…”

Liquid crystal photoalignment on As2S3chalcogenide thin films

“…Recently a new class of photoaligning materials based on chalcogenide glasses was introduced [17][18][19][20][21][22][23][24][25]. Kurioz et al observed photoalignment of a nematic LC on a chalcogenide surface upon polarized light irradiation through a layer of LC in the isotropic phase in a cell [17].…”