The phenomenon of extraordinary ray refraction in a helical liquid crystal with large (compared to the light wavelength) pitch has been studied by theoretical and experimental methods. At a sufficiently large angle of incidence relative to the pitch axis, the extraordinary ray exhibits reflection (reversal) from a certain layer of the medium. The ordinary ray, for which the system is optically isotropic, exhibits no such reflection. The experimental dependences of the transmitted and reflected (reversed) rays are described using the geometrical optics approximation taking into account the optical losses for scattering inside the liquid crystal. 相似文献
Abstract A way of investigating dielectric relaxation phenomena occurring in the isotropic and liquid crystalline states by the use of monotropic mesogens is suggested. The application of common methods of dielectric spectroscopy in the radio frequency range (102-108Hz) to strongly supercooled samples for the investigation of the amorphous liquid and low temperature monotropic liquid crystalline states is described. The possibility of experimental separation and investigation of the different dipole polarization mechanisms responsible for the dielectric properties of the monotropic mesogen 4-cyano-3-chlorophenyl 4-hexyl-3-chlorobiphenyl-4′-carboxylate (CChEC), whose molecules have longitudinal and normal permanent dipole moment components, is established. 相似文献
Measurements of the refractive indices and optical anisotropy of a series of liquid crystalline coordination compounds based on lanthanides with an identical ligand environment have been carried out. It was found that the magnitude of the optical anisotropy of the investigated complexes was several times smaller than the anisotropy of organic liquid crystals. Analysis of the results showed that the variation of the ion complexing agent had little effect on the magnitude of the optical anisotropy in the mesogenic complexes containing the same ligands. The even-odd alternation of the optical anisotropy of lanthanidomesogens at the increasing the number of protons in the ions of the lanthanides has been observed.
The particular features of the propagation of light in uniaxial chiral liquid crystals with a large pitch of the spiral are considered. There exist forbidden zones in these systems for fairly large angles of incidence of an extraordinary ray. On the one hand, this results in an efficient reflection of the wave from the zone boundary, and, on the other hand, this causes the wave to decay inside the zone. A case of narrow forbidden zones is studied, and it is shown that optical effects that arise upon propagation of rays near turning points are equivalent to the tunnel and over-barrier reflection effects. The angular dependences of the intensities of rays that were refracted in a forbidden zone and transmitted through it are calculated. The percolation effect is experimentally studied in a mixture of a nematic liquid crystal with a chiral addition. The intensity of a transmitted extraordinary ray is studied as a function of the angle of incidence, which determines the width of the forbidden zone. Both the over-barrier reflection and the percolation effects are observed. The calculation results are shown to agree with experiment. 相似文献
The refraction of light, i.e., the turn of an extraordinary ray in the liquid crystal layer similar to total internal reflection at an interface between two media, has been studied in a cell with the homeoplanar orientation of the director. The rise, τon, and decay, τoff, times of optical responses have been obtained for various angles of incidence of light on a liquid crystal layer subjected to an electric field. The times τon and τoff of optical responses for the angles of incidence much larger than the angle of total internal reflection are 1–2 ms, which is three orders of magnitude smaller than the relaxation time of an optical response in the case of normal incidence of the ray. 相似文献
The values of optical anisotropy of two series of thermotropic nematic liquid crystalline complexes based on the ions Eu+3, Gd+3, Tb+3, and Dy+3 have been determined. Even–odd alternation of optical anisotropy with an increasing number of protons in ions of lanthanides has been observed. It is established that, in the considered series of lanthanidomesogens, optical anisotropy is more sensitive to changes in the ligand structure of complexes than to the variation of the complexing agent. 相似文献
Dielectric properties of a number of liquid-cry stalline comb-shaped copolymers with different ratios of side-chain mesogenic
cyanobiphenyl groups and acrylic acid units are studied. In the electric-field frequency range 300 Hz-100 MHz, temperature
dependences of dielectric permittivity are obtained for nematic and isotropic phases. The times of relaxation and the energies
of activation for processes responsible for dielectric-permittivity dispersion are measured. The quantitative relationship
between the dielectric characteristics and the content of acrylic acid units in the copolymer is established. 相似文献
The effect of an alternating electric field on the trajectory of an extraordinary light wave in a layer of a chiral liquid
crystal with a 180° turn of the director is studied. In this structure, in the absence of the field and at a large angle of
incidence of the light wave on the liquid crystal layer, the light undergoes refraction inside the layer. It is shown that
the deformation of the director that arises under the action of the electric field changes the character of refraction of
the extraordinary wave and the layer begins to transmit the light. The threshold voltage of this effect is determined. The
dynamics of the effect is studied. At large voltages, in addition to the extraordinary wave, an ordinary light wave is observed
in the light passed through the cell. The ordinary wave intensity is modulated by the initial frequency of the control signal,
whereas the extraordinary wave intensity is modulated by the double initial frequency. 相似文献