Application of liquid crystal (LC) devices for optoelectronic reconstruction of digitally stored holograms

A possible way to speed up the operation of liquid crystal structures based on nematic mixtures with a charge transfer complex between a fullerene and an organic molecule donor fragment is studied using pyridine and polyaniline monomers and polymers as systems with the donor?acceptor interaction. Self-organization is established to occur in such structures. A more than an order of magnitude reduction in switching time is shown to be achievable. A possible physical mechanism of accelerating the liquid crystal dipole reorientation stimulated with intermolecular complex formation is discussed.

https://iopscience.iop.org/article/10.1070/PU2005v048n04ABEH002101/pdf

Fullerene dispersed nematic liquid crystal structures: dynamic characteristics and self-organization processes

Surface-mediated director reorientation in a pure nematic liquid crystal (LC) cell in the presence of both a dc and low-power optical field has been observed. A surface-dependent lowering of the Friedericksz transition voltage in a planar cell upon light irradiation was found. It is believed that this effect is due to a light-induced change in the near-surface ion concentration in the presence of a dc field and a photosensitive surface. Enrichment in the ion concentration near the surface causes a redistribution of the electric field in the cell and its localization near the surface. As a consequence, the energy of interaction between the LC and the dc field near the surface overcomes the anchoring energy and results in the director reorientation.

Surface-mediated light-controlled Friedericksz transition in a nematic liquid crystal cell

Issues pertaining to the effect of quantum dots (QDs) on the properties of a nematic liquid-crystalline mesophase are briefly considered. The influence of nanoobjects representing CdSe/ZnS semiconductor QDs on the temporal characteristics of liquid crystals (LCs) belonging to the class of cyanobiphenyls has been studied for the first time. It is established that the presence of QDs leads to a significant decrease in the time of LC molecule reorientation from planar to homeotropic position in the nanoobject-sensitized medium.

Effect of CdSe/ZnS semiconductor quantum dots on the dynamic properties of nematic liquid-crystalline medium

We report a study of the crucial role of liquid-crystal–polymer interface on photoinduced transport and redistribution of charges in pure nematic liquid-crystal cells that exhibit a photorefractivelike effect. A stationary photocurrent that is 30% of the dark current has been measured for very low power illumination (few mW) and low applied dc electric field (about 0.1 V/μm). The experimental results indicate a clear dependence of the effect on the light wavelength. The absence of photocurrent in cells with only one component, liquid-crystal, or polymer, suggests that both are not intrinsically photoconductive, rules out light-induced charge injection by the electrodes, and indicates the polymer–liquid-crystal interface as the photoactive element in the effect. The photocurrent dynamics indicate the presence of various mechanisms. We suppose that the effect is due to photoinduced carriers injection through the liquid-crystal–polymer interface and recombination process with the counterions present on the o...

Charge transport due to photoelectric interface activation in pure nematic liquid-crystal cells

This paper describes low-molecular-mass liquid crystals doped with suitable dyes which can be used for real-time holographic purposes We describe the origins of the diffraction gratings or holograms induced by a light intensity pattern in a dye-doped nematic liquid crystal sandwiched between two conducting glass plates The mechanism is linked to electric-field-driven reorientation of the nematic director The modulation of the electric field is induced mainly by the bulk photoconductivity of the system Design and characterization (response time, diffraction efficiency) of the optically addressed spatial light modulator (OA-SLM) is presented Interesting applications of these materials enabling phase conjugation and optical correlation are discussed

http://iopscience.iop.org/article/10.1088/0963-9659/7/2/008/pdf

Januz Parka

Papers

Liquid crystals as materials for real-time holographic optical devices