Magnetic Fredericksz-like transition is theoretically investigated in a homeotropic ferronematic planeparallel cell with different director anchoring (strong and weak) on the cell walls. The optical birefringence of a ferronematic sample and its dependence on the value of applied magnetic field and anchoring energy is studied.

Light scattering cross sections caused by director inhomogeneities in the nematic liquid crystals filled with small spherical and cylindrical particles are calculated bothi n the Rayleigh-Gans approximation and within the anomalous-diffraction approach. The influence of the director anchoring conditions at the particle surface as well as the external electric field and the liquid crystal flexoelectricity on the light scattering cross sections is studied.

We describe the method to extend the generalized Mie approach to the case of light scattering by uniformly anisotropic spherical particles by relating the wave packet representation and expansions for electromagnetic field over spherical harmonics. As a result, we define quasi-spherical modes in anisotropic medium. For radially anisotropic layer we determine the region of validity of Rayleigh-Gans approximation by comparing approximate values of the scattering cross-section with the results computed from the exact solution. We study the relative error for the scattering cross section as a function of the particle size, the anisotropy parameter and the layer thickness.

We study theoretically interaction between the cylindrical particles immersed in a nematic liquid crystal, which is caused by the deformations of the director field. It is found that the orientation of the particles has a considerable influence on the pair interaction potential between them. Cylindrical particles inclined to the director turn out to be attracting on the Yukawa law. This leads to the origin of the cellular texture in the ferronematics in the presence of the external magnetic field.

Planar-aligned nematic liquid crystals cells with an array of parallel electrodes can perform phase modulation with profiles going from binary to blazed gratings. A nematic liquid crystal with high birefringence (BL006) allows reducing the thickness of liquid crystal cells and thus reducing switching times. But the discrete electrodes and the small thickness have negative consequences on the shape of the phase profile. Liquid crystal phase gratings with 192 separately controlled electrodes were fabricated. The electrode distances and widths were 3 or 4 micrometers at a cell thickness of 6 micrometers . Perpendicular and parallel alignment of the liquid crystal with respect to the electrode grating were investigated. Far field diffraction measurements and phase measurements with a Mach-Zehnder interferometer were performed to characterize the gratings. The director distribution was modeled in 2 dimension and the resulting phase profiles were calculated with a Jones matrix method. It allows a comparison with the measurements. It was found that in the liquid crystal grating cell the in- plane electric field has a large influence on the optical properties. The in-plane electric field between the high- and low-voltage electrodes forms an unfavorable director deformation that limits the diffraction efficiency to approximately 65% for linear polarized light. Both, the measured and the simulated phase profiles, show a typical structure where valleys appear and worsen the optical performances. The optimization of such a grating is a compromise of large thickness, that smooths the valley structures, and small thickness, that reduces the in-plane switching effect and the switching time.

Water solutions of metal alkanoates were shown to exhibit a certain range of concentration the liquid crystalline mesophase referred to as ionic lyotropic liquid crystalline phase. By means of introduction of different dyes the mechanisms of light interaction with dye-doped ionic liquid crystals were studied. Absorption and luminescence spectra of a number of dye-doped lyotropic liquid crystals on the base of caprilat-K water solutions were obtained and analyzed, their nonlinear optical properties were investigated also. Some conclusions concerning photorefractive properties of the studied systems were made and possibilities for their development and application are discussed as well.

The acoustic emission from liquid crystals during electric switching of these materials has been reported. Investigating the intensity and frequency of the sound emission, we have concluded that the sound is originated as a result of molecular motion when a liquid crystal is switched from one state to another.

The curing of polymer substrates with collimated beam of accelerated plasma is considered as a new method of LC alignment. As an aligning polymer we used polyninylcinnamate (PVCN), well known photoaligning material. Pretilt angle and anchoring energy of LC on PVCN substrates is investigated as a function of the incidence angle, beam energy and current density, and the time of irradiation. The parameters of LC alignment on the substrates treated with plasma beam are compared with the corresponding parameters of the UV cured PVCN substrates. It is shown that azimuth anchoring energy on the plasma treated substrates is close to that one obtained with UV curing. At the same time, generated pretilt angle is higher and much more thermally stable on the plasma treated PVCN layers. It is also considered possibility of the combined curing with plasma dn UV light.

Electrohydrodynamic instabilities arising with a.c. electric field applied to planar-oriented cells filled with anthraquinone dye-doped multicomponent nematic mixture have been studied by diffraction methods. It has been found that c.w. He-Ne laser radiation of small power (~1 mW) exerts ordering effect on the LC layer domain structure. The ordered structure can persist in the presence of the same a.c. electric field for a few tens of minutes. The size of periodic optical irregularity has been calculated.

Orientation of a liquid crystal on an aligning surface is characterized by the direction of an easy axis, e and anchoring energy, W. Traditional rubbed aligning layers provide a rigid surface and a strong anchoring of LC (W>10^-1 erg cm^-2). Therefore, magnetic or electric field usually does not reorient director on the aligning surface, and both of these parameters remain constant during the application of the field to the LC cell. Novel aligning materials, such as photoaligning and brush- like orientants possess very soft surface, containing flexible groups and usually provide much smaller anchoring energy (W<10^-2 erg cm^-3). In this case the reorientation of the director on the aligning surface is essential. In this report we show that the surface director reorientation can result in the realignment of flexible fragments of a weak anchoring photoaligning surface, i.e. in the modification of the aligning surface. Therefore, both the easy axis and the anchoring energy of the soft aligning layer can be changed during the application of external field to LC cell. The effect of the aligning surface modification induced by director reorientation on a soft surface of polyvinylcinnamate (PVCN) was found in a cell filled with LC 5CB. Namely, we observed that application of electric field results in the producing of a transient pretilt angle of 5CB on the PVCN surface, which relaxed to the initial state after switching off the external field during about 10 min. To describe the obtained results we propose to consider the interface containing LC molecules and flexible fragments of the aligning layer as an LC with effectively high orientation viscosity (gamma) _s. Anchoring energy and easy axis of the LC corresponds to its equilibrium state. In the studied case the value (gamma) _s approximately =5 P is appeared to be in fifty times greater than the value (gamma) ₁ of 5CB.

We studied alignment of dye-doped liquid crystal (LC) on non-photosensitive aligning surfaces after the irradiation with polarized light of the cell with LC being in a nematic phase. The stable planar alignment of LC 5CB doped with a dye Methyl Red (MR) was observed in the irradiated areas. Light sensitivity, direction of easy axis and thermal stability of the light-induced alignment of LC were different for ITO and fluoro-polyvinyl-cinnamate (PVCN-F) aligning surfaces. The characteristics of the alignment also differed from that obtained with the irradiation of the cells with LC being in the isotropic phase. These results point out at a crucial role of both LC orientational ordering and the nature of the aligning surface in the effect the light-induced anchoring. The ordering of dye molecules results in a formation of an anisotropic dark- adsorbed MR layer on the aligning surface after the cell filling. Therefore, the light-induced easy axis is forming on the background of the dark-adsorbed anisotropic layer of dye molecules, and the final anchoring is determined by the cumulative effect of the dark and light-induced anchoring. The difference in the light-induced anchoring on ITO and PVCN-F surfaces is explained by different mechanisms of light-induced anisotropy in adsorbed MR layer. In the case of ITO surface this mechanism is the isomerization of MR molecules, while the MR molecules desorption/adsorption processes provide light-induced anisotropy in the adsorbed on the PVCN-F surface layer.

Polar electrooptic effect in M-nematic-silicon structure has been investigated. In hybrid oriented nematic (MBBA) under the action of dc voltage with polarity - U on silicon substrate a transition of nematic to homeotrop states takes place. This effect is explained by an influence of the surface electric field on nematic director which changes due to ion adsorption. It is shown that this effect may be used for visualization of regions on silicon surface which have different types of conductivity.

Director reorientation threshold in the field of electromagnetic wave in round cylindrical metallic waveguide loaded with nematic liquid crystal is theoretically studied. The dependence of threshold on the frequency and type of electromagnetic wave in waveguide as well as director anchoring energy with waveguide surface is analyzed.

We present a theoretical study of the possibility of optical singularity birth in a wave front of a laser beam passing through a homeotropically aligned nematic liquid crystal (LC) cell. There is not any distortion in the initial homogeneous homeotropic LC alignment at intensities below some threshold value. When light intensity becomes higher than this threshold value, LC director deviates from its initial orientation. Strong director anchoring at the cell walls is assumed. Inhomogeneous director profile leads to the modulation of refractive index which in its turn may be considered as a Gaussian lens formed in the LC cell. This lens gives birth to the phase singularities in coherent beam with initially smooth wave front. One can find the light field just after the LC cell at small values of director deviation in geometrical optics approximation, and utilizing the Huygens-Fresnel principle calculate spatial position of the phase singularity at near field as a function of intensity of the input beam. It was found that both radius of circular edge dislocation and its distance form the cell boundary decrease with increase of intensity of an incident beam.

A novel pair of the E- and Z-isomeric 1R,4R-2-)4- heptyloxyphenyl)-benzylidene-p-menthan-3-ones has been prepared and the influence of distinctions in their molecular geometry on macroscopic properties of liquid crystal systems with the induced supra-molecular helical structure has been studied. The significantly lower helical twisting power of the chiral Z-isomer in comparison with that of E- one has been confirmed in the case of induced cholesteric systems based on 4-pentyl-4-cyanobiphenyl. The phase behavior and ferroelectric characteristics have been investigated for smectic-C* compositions based on the eutectic mixture of the homological 4-hexyloxyphenyl-4'- hexyloxy- and 4-hexyloxyphenyl-4'-octyloxybenzoates containing the novel isomeric chiral dopants. The spontaneous polarization of the opposite signs induced by the isomeric chiral components has been revealed for the compositions studied. Distinctions in phase states, absolute values of the spontaneous polarization, smectic tilt angle and rotation viscosity of the systems obtained are discussed.

By X-ray diffraction has been obtained the information concerning molecular structure of three chiral compounds, p- menthane-3-one derivatives, containing biphenyle fragment (Ia, Ib) and OH-group (II). The cinnamoyl group C₆H₄-CH=C-C=O is non planar in all compounds investigated but to different degrees. A dependence of the non-planarity of this fragment as well as of the cyclohexanone ring flattening on the substituents X and Y nature is discussed.

The dyperchlorates of N,N'-dy(2-dygydroxyethyl)-4,4'- dipyridylium (IX) and of N,N'-dy(carbethoxymethyl)-4,4'- dipyridylium (X)(such named viologenes) are the perspective dye-dopants to work out the new photorefractive materials. The X-ray investigation of single crystals of IX and X was carried out. It has been shown that in the charge transfer absence the flat structure of dipiridilium core at IX, X are determined by electronic effects of hydroxyl and ether groups which contain non-separated electronic pairs. Such structure flatness is favor for effective cation-radicals formation.

The features of low-threshold limitation are observed. It is shown, that one of the solutions of this task is usage of effect of two-photon absorption in an impurity liquid crystal. It is stipulated by large cross-section of two- photon absorption in cyanobiphenyls. The strategy of usage of mesomorphic microlenses as structural elements of optical limiters is discussed. The experiments on optical limitation in constructions using mesomorphic microlenses are realized.

The advantages of use the problems of optical limiting of impurity mesomorphic systems are discussed. These advantages are caused by existence of the excitonic mechanism of the transport energy electronic excitation in liquid crystals. A dynamic range of optical limiting in such systems can be essentially extending using of two- photon absorption.

Geometric type of liquid crystal (LC) lens can be obtained by using the spherical substrate in a liquid crystal cell. The LC lens can have a potential application to a kind of light wave controlling device by utilizing the electronic variable focusing properties. However, it shows a particular aberration properties induced by the molecular orientation related with a curved substrate structure. In this study, LC molecular orientation states in the LC lens and the optical properties are investigated by the experimental and the theoretical approaches. Interference fringe patterns induced by the LC layer are observed and optical path distribution properties are compared between the rubbing direction and the direction perpendicular to the rubbing. One dimensional model is applied to the molecular orientation calculation, and the optical path difference in the 2D area and the wave aberrations are calculated for normal incidence. It is confirmed that a particular wave aberration dependent upon the rubbing direction appears, and the influence of the curved substrate strongly depend upon the thickness of the LC layer. Therefore, the aberration phenomena of the convex and concave lens are quite different even though they have the spherical substrate with the same magnitude of curvature. When a voltage is applied to the LC lens, reverse tilted disclination lines tend to appear and they usually cause a fatal degradation of lens properties. The disclination lines can be eliminated by introducing a small pretilt angle to the alignment layer within a smaller inclination of substrate. However, even in the disclination free state, there is some influence on the wavefront through the LC lens; that is, large inclination of the wave front causes in the lower applied voltage.

Liquid crystal (LC) molecular orientations and optical properties of LC polarization-converting devices are discussed. It is found that two stable LC molecular orientation states appear (we define them at the +/- 90 degree(s) and +/- 180 degree(s) twist modes), and the switching method between the two modes are discussed. Fourier transforms (FT) of the transmitted light of the LC polarization- converting device are performed by computer simulations. It is confirmed from the simulated FT results that both distribution profiles of the transmitted light beams in the +/- 90 degree(s) and +/- 280 degree(s) twist modes can be regarded as wavelets. Wavelet transforms using the LC polarization- converting device are simulated and feature extraction properties are discussed. It is found that the +/- 90 degree(s) and +/- 180 degree(s) twist modes can perform corner and edge extractions, respectively.

The given paper considers the process of computer modeling of temperature field in LC layer, resulting from thermooptic effect. Prior the heat conduction equation for the source of hear having Gaussian distribution of intensity along beam section was solved. Dimensions and shape of temperature field in LC layer are shown to depend on concentration coefficient of Gaussian laser beam.

The paper presents the results of investigation of bleachable dichroic dye-doped liquid crystal (LC) cells operating as intra-cavity (passive shutter) and extra-cavity (wave-front conjugation mirror) laser elements. Regularities in the saturation of bleachable dichroic eye absorption in a LC have been established taking into account the order parameter. Control of monopulse parameters from free-running spiking mode to monopulse mode by changing the working temperature of the passive LC shutter or the layer director orientation has been achieved. It was shown that in case of wave-front conjugation of nanosecond pulses in LC's doped with bleachable dyes the thermal nonlinearity is considerably higher than the resonance nonlinearity in the range of temperatures close to the phase transition point ((delta) T degree(s)=3 degree(s)C), which results in higher total conjugation coefficient as compared with isotropic bleachable dyes solutions.

In the inplane-switching (IPS) mode an electric field is applied to the liquid crystals along the direction that is parallel to the plane of the substrates with interdigital electrodes. The threshold behavior and response characteristics of the liquid crystals in the IPS mode were studied by Oh-e et al. Assuming uniform electric field and strong director anchoring at the cell boundaries. We found an electric field profile of the electric field in the IPS mode. We found there exists an optimal ratio between the cell thickness, electrode width and electrode gap which corresponds to minimal value of the threshold voltage.

The coherent transmittance of polymer dispersed liquid crystal monolayer with bipolar nematic droplets have been investigated. Two kinds of electrooptical response (S- formed response and oscillation response) at transition of droplets directors structure from planar to homeotropic have been found. The influence of the order parameter of droplets and droplet polydispersity on the quenching conditions are analyzed.

We have derived adequate system of equations for description of pattern formation and optical limiting effects due to dynamic reflection gratings, formed by the counter propagating beams in the photorefractive-photogalvanic crystals. Approximative solutions related to pattern formation and optical limiting are analyzed.

Theoretically we investigate the operation of a novel nonlinear system, feedback controlled photorefractive beam coupling. It is shown that the feedback conditions used earlier ((pi) /2 phase shift between the diffracted and transmitted beam components) are satisfactory only during a relatively short initial stage of development. We have generalized these conditions by taking into account the inertia inherent any real feedback loop. The inertial feedback conditions ensure the permanent operation of the nonlinear system and lead to a variety of periodic and quasi-periodic regimes. We investigate the distinctive features of these regimes and transitions between them for moderately thick crystals.

Tin is shown to be a suitable dopant that makes it possible to grow cadmium telluride crystals with considerably reduced conductivity (semi-insulating material) and ensures a well pronounced photorefractive response both for cw and Q- switched Nd³⁺:YAG laser radiation.

The new holographic scheme with a photorefractive crystal, which is based on the interference of two identical object beams, are studied for the purpose of multiplex image storage. It is shown, that every image recorded by the proposed method possesses a property of associative readout. The proposed scheme can be applied in optical implementation of associative network, all-optical associative memory, template matching, optical interconnection.

Absorption saturation features and the correspondent nonlinear change of refractive index in a Cr⁴⁺:YAG crystal are studied applying the Z-scan technique in steady- state at wavelength 1.06 micrometers with taking into account of the crystal nonlinear absorption anisotropy.

Z-scan technique is applied to a saturable medium described by a generalized three-level scheme of photoexcitation. Correctness of the Z-scan data interpretation is analyzed in framework of the model. The approach is applied for measuring the refractive indices (delta) n and n₂ in polymer films containing Bacteriorhodopsin.

The present paper is devoted to detailed investigation of the low-temperature optical and photoelectric properties of Cd_1-xHg_xTe:V (x<EQ0.088) crystals which provided information on the optical quality of these crystals and the nature of their inhomogeneity, and also the nature and the position of the energy levels of deep V²⁺ and V³⁺ (single and complex) impurity centers and singly charged complex acceptors. It was shown that the anisotropy of complex impurity centers is determined by the nature of the donor atom and its position in the crystal lattice. It should be noted that such crystals were grown for the first time by the Bridgman method. Transport measurements (T=300K) showed that the samples were highly compensated with a dark resistivity greater than 10⁶(Omega) $CTR cm. It was shown that the anisotropic V²⁺ centers may be caused by formation of complex impurity (V²⁺_Cd+ X_Te) centers, where X are the accidental impurities of group VII atoms positioned at anionic sites. The appearance of rhombohedral V²⁺ centers may be caused by the formation of the complex (V²⁺_Cd+ X_Te) centers whose axis is oriented in one of the <110> direction. In the case of the tetragonal V²⁺ centers the Z atoms are positioned at cationic sites in one of the equivalent <001> directions. In the case of the Cd_1-xHG_xTe:V crystals Z may be the Hg Atoms.

Significant magnitude of the dual beam refraction and gyrotropic characterized CdAs2 and ZnAs2 monocrystals are observed. Nonlinear effects, for example self -inducted rotation of the plane of polarization, exist for these materials due -to crystals symmetry and connect with spatial dispersion. These crystals is very important for following applications: light modulator, frequency reduplicator, optical filters, lenses and polarize prisms for IR region of the spectrum. Optical surface state of the photoreflective CdAs2 and ZnAs2 monocrystals were investigated by electroreflectance (ER) in dependence from surface treatment. The metods of elkectroreflectance modulation spectroscopy (ERMS) make it possible to investigate direct transitions in peculiar points of the Brillouin zone. The parameters of broadening of these transitions F, which can be calculated from the ERMS spectra, are integral characteristics of scattering of carriers on lattice defects. The shift of optical transitions and change of the parameter F are sensitive indicators of the state of the reflecting surface with respect to the mechanical stresses, electrical charge, presence of adsorbed molecules and oxide films, presence of microdefects. For this reason, the study of the zone structure of these materials and the influence of treatment of their surface on their physical properties became the subject of this to work. For this aim, monocrystals of CdAs2 (spase group D , tetragonal structure) and ZnAs2 (spase 4 5 group C , monoclinic structure) were for the first time investigated by the ERMS method.

Absorption and refractive index dispersion spectra of porous silicon (por-Si) samples with different porosity were measured for energy interval 1.5-3.5 eV at room temperature. Experimental data were compared with dependencies calculated using Bruggemann formula for dielectric function of multicomponent medium consisted of crystalline silicon. SiO₂, amorphous silicon and voids. The best agreement between experimental data and theory was obtained for the comparatively large concentration of SiO₂ in the por-Si samples.

The refined results of the specified dispersion of refractive indexes, birefringence, optical activity of anisotropic (beta) -CdP₂ single crystals and the components of both the gyration tensor G₃₃ and the optical activity tensor (gamma) ₁₂₃ in a wide spectral band of polarized light under normal conditions are presented. The influence of temperature and radiation intensity of neodymium and ruby lasers on these characteristics of CdP₂ single crystals is studied and analyzed.

Nonlinear optical medium with periodically modulated refractive coefficient is considered. New two-parametric soliton solutions are found with frequencies, lying near the gap of linear waves spectrum of the system. Such near-gap solitons propagate with velocity varying from zero to its maximum value, which is defined by medium properties. The evolution of the system phase portrait with change of the nonlinear excitation frequency (Omega) is also studied. Moving algebraic solitons, which separate two types of two- parametric solitons, namely gap and near-gap, are also considered.

We investigate the problem of nonlinear waves propagation in modulated nonlinear systems. The nonlinear optical medium with periodically changed in space refractive index represents the example of such modulated system. It is shown, that the dynamical equations for this system are similar to those for other modulated systems, e.g. diatomic elastic chain, two-sublattice ferromagnet and easy-plane antyferromagnet. The general type of dynamical equations for modulated systems with third-order nonlinearity is studied. The main result of our work is the qualitative analysis of all kinds of the small amplitude soliton excitations with frequencies lying in the gap and near the gap of the linear waves spectrum. We also study the evolution of the system phase portrait and bifurcation picture of the soliton solutions under changes of the medium parameters and nonlinear excitation frequency.

As it is known polystyrene is the most stable transparent mould for production of scintillators, luminescent solar concentrators, active mediums of hard bodied lasers. At present problems of polystyrene scintillates aging attract a particular attention because of the development of high- energy physics and creation of devices for ionization radiation registration.

Two approaches to the analysis of fluorescence spectra of pyrene have been considered. In the first case, the profile of excimeric bands is investigated. The influence of defects in pyrene crystals over their fluorescence spectra is described by the potential of the monomer-dimer interaction, which is determined by the treatment of derivative fluorescence spectra. Second technique is based on the study of temperature dependencies in pyrene excimeric spectra and leads to the determination of some energetic parameters for excimeric potentials.

The structure of the corundum monocrystals subjected heat treatment in medium of oxide of cobalt is studied. It is obtained that the monocrystals of the spinel CoAl₂O₄ are generated at the surface of (alpha) -Al₂O₃.