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The optical activity of DNA liquid-crystalline dispersions is being investigated based on a theory for absorption of electromagnetic waves by large molecular aggregates. The impact on the dispersions-optical properties, exerted by the interaction between the complexes of nucleic acid molecules and nanoparticles, is being considered.

We extend further the theoretical and experimental studies of the actual surface anchoring potential restoration by polarization microscope technique in a wedge-shaped cell with weak surface anchoring forces filled by a chiral nematic liquid crystal (in Grandjean-Cano Wedge). To realize the theoretically predicted options of observation of large director deviation angles from the easy axes the experimental studies of director distribution in Grandjean-Cano zones were performed for differing easy axes orientations at the wedge surfaces. A weak surface anchoring at one wedge surface was obtained by a photo-alignment technique. A strong surface anchoring at the second wedge surface was also obtained by a photo-alignment technique with an enlarged irradiation dose. There were observed walls with weak jumps of the director orientation between first neighboring Grandjean-Cano zones. Some experimentally obtained polarization microscope images demonstrate partially unwound director structures in zero Grandjean-Cano zone. To ensure optimal parameters of the further experiments on the actual surface anchoring potential restoration theoretical calculations of the director distribution in individual Grandjean-Cano zones were performed for various model surface anchoring potentials. It was found that especially promising for description of the experimentally found director distribution is the D-potential. As a result of the present studies the angular range of a model-independent actual azimuthal surface anchoring potential restoration was enlarge (up to π/3) and the ways of an actual surface anchoring potential restoration in a whole angular range of its determination are discussed. [ABSTRACT FROM AUTHOR]

We extend further the theoretical and experimental studies of the actual surface anchoring potential restoration by polarization microscope technique in a wedge-shaped cell with weak surface anchoring forces filled by a chiral nematic liquid crystal (in Grandjean-Cano Wedge). To realize the theoretically predicted options of observation of large director deviation angles from the easy axes ϕ at a wedge surfaces (up to π/2) the experimental studies of director distribution in Grandjean-Cano zones were performed. A weak surface anchoring at one wedge surface was obtained by photoalignment technique. A strong surface anchoring at the second wedge surface was obtained by rubbing. The measurements were performed using polarizing microscope. The experimentally found director distributions in Grandjean-Cano zones were compared with theoretical ones calculated for various model surface anchoring potentials. As a result of the present studies the ways to enlarge (compared to the previous studies) angular range of the actual surface anchoring potential restoration were proposed and it was found that the experimentally found surface potential is nicely fitted by a new model surface anchoring potential, the so called model D-potential WD(ϕ) ∼ϕ2. [ABSTRACT FROM PUBLISHER]

Experimental and theoretical studies of the chiral liquid crystal (CLC) director distribution in a wedge shape cell with a weak surface anchoring as well in a planar layer with a gradient of the pitch are performed. The theory predicts that the director distribution in individual Cano-Grandjean zones as well in narrow walls dividing the zones are dependent on the strength and shape of the anchoring potential. The performed calculations for a wedge and a planar layer of variable thickness show that the experimentally distinguishable details of the director distribution in the wedge area between two consequent walls (Cano-Grandjean zone) allow one to obtain information on the shape of the surface anchoring potential and especially favorable for the measurements are several first individual Cano-Grandjean zones. The measurements of the director orientation at the wedge surface with weak surface anchoring versus the coordinate along wedge surface carried out by means of optical polarized transmission spectra were used to reconstruct the director distribution at this surface for the second Cano-Grandjean zone. The relevance of the obtained director distribution to the different model surface anchoring potentials is discussed. [ABSTRACT FROM AUTHOR]

An analytic approach to the theory of the optical defect modes in chiral liquid crystals (CLC) is developed. The analytic study is facilitated by a special choice of the problem parameters. The dispersion equation determining connection of the defect mode frequency with the isotropic (defect) layer thickness is given. Analytic expressions for the transmission and reflection coefficients of the defect mode structure (CLC-defect layer-CLC) are presented and analyzed for nonabsorbing, absorbing and amplifying CLC. The effect of anomalously strong light absorption at the defect mode frequency is revealed. It is shown that in DFB lasing in a defect structure adjusting of the lasing frequency to the DM frequency results in a significant lowering of the lasing threshold. Numerical solutions of the DM dispersion equation are performed for typical values of the related parameters. [ABSTRACT FROM AUTHOR]

An analytic theory of localized edge modes in chiral liquid crystals (CLCs) is developed. Equations determining the edge-mode frequencies are found and analytically solved in the case of low decaying modes and are solved numerically for the problem parameter values typical for the experiment. The discrete edge-mode frequencies specified by the integer numbers n are located close to the stop-band edge frequencies outside the band. The expressions for the spatial distribution of the n’s mode field in a CLC layer and for its temporal decay are presented. The possibilities of a reduction of the lasing threshold due to the anomalously strong absorption effect are theoretically investigated for a distributed feedback lasing in CLCs. It is shown that a minimum of the threshold pumping wave intensity may be reached, generally, for the pumping wave propagating at an angle to the helical axis. However, for lucky values of the related parameters, it may be reached for the pumping wave propagating along the helical axis. The lowest threshold pumping wave intensity occurs for the lasing at the first low-frequency band-edge lasing mode and the pumping wave propagating at an angle to the spiral axis corresponding to the first angular absorption maximum of the anomalously strong absorption effect at the high-frequency edge of the stop band. The study is performed in the case of the average dielectric constant of the liquid crystal coinciding with the dielectric constant of the ambient material. Numerical calculations of the distributed feedback lasing threshold at the edge-mode frequencies are performed for typical values of the relevant parameters. [ABSTRACT FROM AUTHOR]

An analytic theory of the localized edge modes (EM) in chiral liquid crystals (CLC) is developed. Equations determining the edge mode frequencies are found and analytically solved for the case of low decaying modes and solved numerically for the problem parameters values typical for the experiment. The discrete EM frequencies specified by the integer numbers n are located close to the stop band edge frequencies outside the band. The expressions for space distribution of the n's mode field in CLC layer and for its temporal decay are presented. The possibilities of reduction of the lasing threshold due to the anomalously strong absorption effect are theoretically investigated for a distributed feedback lasing in CLC. It is shown that a minimum of the threshold pumping wave intensity may be reached, generally, for the pumping wave propagating at an angle to the helical axes. However, for lucky values of the related parameters it may be reached for the pumping wave propagating along the helical axis. The lowest threshold pumping wave intensity occurs for the lasing at the first low frequency band-edge lasing mode and the pumping wave propagating at an angle to the spiral axes corresponding to the first absorption maximum of the anomalously strong absorption effect at the high frequency edge of stop band. The corresponding analytical study is performed for the case of the average dielectric constant of LC coinciding with the dielectric constant of the material limiting LC. Numerical calculations of the DFB lasing threshold at EM frequencies are performed for the typical values of the related parameters. [ABSTRACT FROM AUTHOR]