The result of experimental studies of thermal mechanism of optical response of a c.w. He-Ne laser probe beam when a dye-activated nematic layer is irradiated with free-lasing radiation of a ruby laser are analyzed. Experimental geometry is such that planar-oriented nematic laser is perpendicular to the direction of the acting ruby laser beam, the electric field vector of this radiation forming an angle of 45 degrees with the layer director. Analysis of experimental oscillograms shows that, besides thermal impact whose intensity is determined by the number of oscillations, there is also variation in the oscillating signal amplitude. Their amplitude is determined by an azimuthal angle between vector E of acting laser beam and layer director. This angle can be induced only with action of electrical field of radiation.

THe paper considers the possibility of application of doped chiral systems with properties of dynamic optical hysteresis as optical limiters. The theoretical analysis of interaction of transmitted radiation with a resonant absorbing chiral system is performed using both two-level and multi-level models of the absorbing center. Experimental values of nonlinearity threshold obtained for the system of ketocyanine - nematochiral liquid crystal were approximately 250 (mu) J/cm² at the wavelength of 530 nm.

The study of photorefractive materials attracts a big interest due to large variety of their optical as well as electro-optical effects. As was shown by our investigations dye-doped ionic liquid crystal (DILC) appeared to be a promising medium for the said processes. Doping of ILC with electro-chromic additives leads to significant changes in both electrical and optical properties of ILC with electro- chromic additives leads to significant changes in both electrical and optical properties of ILC with respect to pure substances. Doped ILC was used as a medium for dynamic holography grating recording. Electric current passing through the DILC film induces the appearance of an absorption band in different spectral regions.Existence of self-diffraction during a single pulse as soon as its rather high efficiency pointed out that the mechanism of grating creation might include optical and electro-optical nonlinearity.

Light polarization measurements under magnetic field in the temperature region of the existence of the blue phases including the supercooling region for cholesteryl nonanoate are performed. Magnetic field has a strong influence on optical rotation in the pretransitional region of the supercooled blue phase. Negligible magnetic field influence was observed in the region of the blue phases stability. A high ellipticity of the light polarization in the supercooled blue phase in zero field was found. Magnetic field decreases the temperature region of supercooling. The possible mechanisms of the observed phenomena are discussed.

In a surface stabilized ferroelectric liquid crystal cell, optical transmission oscillations have been revealed accompanying mechanical vibrations caused by fast field reversal. Special bookshelf textures, so-called 'rainbow', were used in the experiments. Temperature dependences of the oscillation parameters have been studied. The temperatures dependence of the oscillation frequency suggests that the some oscillation resonance correspond to modes of the liquid crystals.

The temperature dependence of the complex dielectric permittivity in confined and bulk samples of the ferroelectric liquid crystals DOBAMBC in the bulk and adsorbed in ANOPORE membranes has been measured in the frequency range 10^-1 Hz to 10⁹ Hz. Several relaxations processes have been obtained for CE8 and DOBAMBC in the bulk. The spectra of the confined sample show that the molecular processes are nearly uninfluenced in restricted geometry. However, the Goldstone mode in the ferroelectric SmC* phase is not longer observed.

Relaxation of nematic liquid crystal (NLC) deformation near the pore in a metal-dielectric-NLC-ITO structure under the action of positive polarity of voltage is studied. Experiments indicate that deformation of NLC is observed over any size ores. Character time of relaxation depends on the size or pre and takes more than ten minutes for large (> 20 micrometers ) pores and less than a second for small (< 10 micrometers ) ones respectively. It is shown, that the electrically driven transferring of lecithin can be responsible for a long period of time relaxation.

The nonlinear electrooptic effect in the silicon substrate- nematic-ITO structure is described. It is supposed that a domain switching of a director is induced by a local accumulation and spreading of injected charge within a nematic layer. The exciting centers of a domain can be the defects of silicon surface and the laser irradiation.

Nematic cell in the field of light wave with spatially modulated intensity is considered. The influence of periodic spatial modulation of the director anchoring energy and the easy orientation axis at the cell surfaces on the director spatial distribution in the liquid crystal bulk under the action of light is investigated. It is shown that in both cases the director distribution takes the form of a superposition of the cosine gratings with periods that are the linear combinations of the light intensity and boundary condition periods. The diffraction of some gratings is estimated. The Frederiks transition threshold value is calculated for homeotropic cell with periodic modulation of the anchoring energy.

The paper deals with the application of statistical methods of experiments planning aimed at investigations of liquid crystal thermo-optic properties. To carry out the experiment the author has used the orthogonal central compositional planning. The experimental unit permitted to vary the controlled input factors on five levels. As a result of the experiment the statistical mathematics model of the second order was obtained. This model describes the dependence of the line thickness of LC cell on physical parameters of thermo-optic process of information recording.

It is reported about the first investigations of phenomena of light induced anisotropy in azo polymer introduce into micro porous glass. In contrast to the anisotropy induction in the polymer bulk practically pure 'hole burning' mechanism in a such system was realized. It means that light induced orientation of photo sensitive units is insufficient because of the restricted position in a porous matrices. Dipol-dipol interaction of azo fragments is also limited because of high dispersion of polymer in the pores.

The results of study of nonoriented nematic MBBA structural genesis at different temperature pre-history are reported. The temperature depended transformations of vibrational Raman spectra and their connections with the change of MBBA structure were investigated. Spectral region was 1100-1600 cm^-1, temperature interval was from 163 K to 333 K. The method allows to prognosticate structural evolution of MBBA and to identify phase states. In particular it is discovered that in dependence on cooling rate several coexisting fractions may be obtained at region lower than glass transition temperature.

Optical anisotropy induction and relaxation in azobenzene containing polymer films under polarized UV-light irradiation were investigated by UV and IR spectroscopy methods. The dependence of anisotropy relaxation on the exposure was established. The result are interpreted supposing the partial ordering of macrochains fragments in the irradiated films. The difference in dichroism and birefringence kinetics as well as IR spectra measurements support the model proposed.

The results of original investigations being in touch with regularities of the chiral components molecular structure effect on the properties of induced cholesteric mesophases were generalized. It was shown that presence of an elongate (pi) -electron fragment in the chiral dopants molecules is general requirement of high helical twisting power ((beta) ). (beta) values and the character of temperature dependences of induced helical pitch are significantly effected by molecular shape of chiral dopants. Variation of the extent of (pi) -electron fragment anisometry, and also incorporation and variation of terminal alkyl or alkoxyl groups at chiral dopants molecules are useful approach to a regulation of temperature dependences of induced cholesteric helix pitch. Influence on thermal stability of mesophases of different types of chiral dopants was analyzed.

Morphology, transmittance and dynamic characteristics of the liquid crystal composites with dispersed polymer and without have been studied. It is found that the introduction of 2 percent of polymer decreases threshold voltages and rise time, increases slope of the voltage-transmittance characteristic and contrast ratio.

The influence of added dyes of the naphthaquinone series on the morphology of liquid crystal composite droplets has been experimentally studied. It is shown that the size distribution of dye-free composite droplets is readily described by the gamma-distribution. An addition of dyes to these materials stipulates deviations from this distribution.

Present paper contains results of studies on TN LC mixture containing black dichroic dye. The effect of dye on temperature dependence of LC order parameter and optical anisotropy, is discussed. Contrast coefficients and transmission in on-site at room temperature are presented.

In the present paper definitions, procedures and measurements set-ups for characterization of LCDs are discussed. As the effect standardization of LCD electro- optical properties has been improved.

Present paper contains results of studies on TN LC mixture containing black dichroic dye. The general information concerning a principle of action of TN display with dye is presented. The effect of dye on temperature dependence of LC order parameter, optical anisotropy and dielectric properties is discussed. Transmissive characteristics of a display for different dye concentration are given. Contrast coefficients and transmission in on-state at room temperature are presented.

An analytical expression for the coherent transmittance of the polymer-dispersed ferroelectric liquid crystal monolayer at oblique illumination by linearly polarized plane wave has been obtained. Within the framework of the anomalous diffraction approach the conditions for coherent transmission quenching have been determined. It is shown that for the PDFLC monolayer on the basis of bistable smectic liquid crystals it is possible to provide a coherent transmittance equal to zero and unity for two stable states of droplet directors in the electric field.

A theoretical model for the description of noise properties of polymer dispersed liquid crystal monolayers is proposed. A signal-noise ratio and a coherent transmittance of a monolayer with spherical nematic droplets have been analyzed as a function of a size parameter at different concentration of droplets and refractive index of polymer matrix. Radial and homeotropic uniformity oriented nematic director structures of droplets have been investigated. The radial distribution function is described in the hard discs approximation. Numerical result are obtained in the anomalous-diffraction approach.

Vibrational bands of DNA molecules from birds' erythrocytes, as well as Dunaliella viridis alga cells and Escherichia coli bacteria clinical strains in the weak microwave field were investigated with IR spectroscopy. Drastic changes were detected in the intensities and fine structure of C equals O and PL₂ bands for polarized spectra of irradiated samples of DNA molecules as compared with the reference samples in the 1700-1000 cm^-1 region. No essential changes were detected in the IR spectra in the region of PO₂ bands of DNA for the Escherichia coli, irradiated by the weak electromagnetic field, but essential redistribution of intensities and change in halfwidths of the PO₂ symmetrical bonds were detected for Dunaliella viridis alga cells.

The polarization state of light transmitted through the isotopic phase (IP) of cholesteryl nonanoate near the transition to the blue phase is experimentally examined. We have found that linearly polarized light, transmitted through the IP of cholesteryl nonanoate confined between untreated substrates, becomes slightly elliptically polarized. The dependence of the rotation of the light polarization plane on the magnetic field strength for the untreated substrates is nonlinear. For the substrates treated for a planar orientation this dependence is linear. These facts show the presence of the surface-induced optically active ordered layer on the interface between the IP and a solid substrate. The possible additional contributions to the anomalous dependence of the rotation of light polarization plane on temperature in the isotopic phase of cholesteric liquid crystal have been analyzed. The investigations of the optical rotation with two different polarimeters have been performed. The anomalous dependence of the azimuth of polarization of emergent light and linear dependence of small ellipticity of this polarization have been found. The birefringence of surface induced layer, as a source of appearance of ellipticity of polarization is posed. The results of studies of dependence of optical rotation on the magnetic field strong are agree with existence of the thin surface-induced layer.

The interface of the anomalous L₃ phase with the solid substrate is studied using the electroconductivity measurement, ellipsometry, total internal reflection of light, optical transmission spectra and interferometry. The results show the presence of the surface induced layer with the properties different from the properties of the volume L₃ phase. We conclude that this surface induced layer is the L_(alpha ) phase.

The role of the fatty acids in the biological membrane structure and properties is partially known. They can exhibit a mesogenic feature and behavior in terms of the temperature, the presence of many acids of cholesterol, or other important substances for the metabolism, of external stimuli etc. We studied the arachidic, lauric, elaidic, arachidonic and butiric acids. The most important seems to be the arachidonic acid, a forerunner of phospholipids. This is an unsaturated fatty acid,with four double bounds. We found that it displayed liquid crystalline properties between 4-20 grades centrigrades; in mixture with other fatty acids or cholesterol, these properties change. The paper present considerations on the biological role of the fatty acids and mixtures, in interactions with some physical fields experimental results and some theoretical considerations.

We report a novel azimuthal anchoring transition of nematic liquid crystal on a polysiloxane-cinnamate treated surface under the UV irradiation. It is found, that the direction of the light-induced easy axis strongly depends on the irradiation time. Under short exposure times the orienting surface provides an orientation of LC parallel to the direction of the uV light polarization. Longer times give the orthogonal to the UV polarization orientation of LC. There is region of exposure times that give a bistable anchoring conditions and domains with different directions of the director orientation. We propose a phenomenological model of this anchoring transition and surface bistability based on the competition between trans-cis isomerization of the side fragments of the polysiloxane-cinnamate material and cross-linking photoreaction of the transform of side fragments resulting in orthogonal molecular easy axes.

Feedback experiments by the Brazilian authors in lithium niobate [1, 2, 3] have shown that for a wide range of intensity ratios a grating with diffraction efficiency i = i can be achieved which seemingly does not change in time. Also holographic scattering is reduced in such experiments.

Contribution of different mechanisms to photorefractive light scattering (PRLS) is discussed. The main course of PRLS has been shown to be connected with instability of interaction of coherent light beam with a spatially inhomogeneous nonlinear medium.

Recent measurements revealing new aspects of the nature and physics of space-charge waves in photorefractive Bi₁₂SiO₂₀ crystals are presented. A Bessel-function family of space-charge wave resonances are shown to exist for excitation by a frequency modulated running interference pattern. It is also demonstrated that space-charge waves may continue into regions of the crystal not subjected to the driving light field. Subharmonic space-charge gratings are shown to have an internal structure that for running waves moves with a group velocity opposite the driving optical interference pattern, which is moving with the phase velocity of the space-charge field and the associated refractive-index grating. We also describe how the subharmonics evolve dynamically from a speckle-like pattern towards a regular wave structure. Finally, self-excitation of spontaneous scattered beams ins described, and it is demonstrated that space-charge waves with a long decay time and a high Q-factor are associated with this phenomenon.

It is presented the result of two experiments for excitation of dynamic phase grating in the photorefractive KD*P crystal putted in the cavity of YAG:Nd³⁺ laser. In the first experiment the control by a spectrum of the pulse laser generation is carried out by an external radiation of YAG:Nd³⁺ CW-laser. It was found that the influence of the external radiation to a spectrum of the pulse laser generation is existed for a long time after injection switched off. In the second one a passive selection of transversal modes of CW-laser was automatic. It is marked, that in both experiments the energy and the power of radiation are less than the threshold of effective excitation of the dislocation subsystem resulting to photorefraction in the KD*P crystal at the room temperature. Additional polarizing measurements point to excitation of impurity centers in the KD*P crystal.

We demonstrate a photorefractive scheme that demultiplexes two signals carried on a multimode fiber. The signal channels must be spatially and temporally uncorrelated. This method is based on selective energy transfer in photorefractive two-beam coupling. Under two-beam coupling in photorefractive crystal the energy exchange between beams take place only for signal carrier which form a speckle pattern modulated with frequency equal to the frequency detuning between two beams. Extraction of each signal was performed by the measurement of difference of beam intensities. The modulation of two speckle patterns with different frequencies was obtained by rotation of light polarization at the entrance of fiber.

Grating recording by phase modulated light beams in photorefractive Bi₁₂TiO₂₀ crystal under external AC field is studied experimentally. It was shown that maximum grating amplitude or energy exchange are achieved for regime of modulation corresponding to intermediate case between two usually used methods of recording in ac field: by standing and running interference pattern.

A scheme of light coupling into optical fiber was proposed and studied theoretically. Light coupling is realized by excitation of photorefractive oscillator. It consist of fiber facet and phase conjugate mirror based on four wave mixing. The scheme is self-adaptive and can tolerate rather large angular and lateral displacement of fiber end. As a result of numerical simulation we obtain that about 50 percent of reading pump wave intensity can be injected into the fiber. Coupling efficiency is decreased by factor of two when the lateral displacement of fiber end about 1000 micrometers .

Simple analytical expressions of diffraction efficiency, maximum diffraction efficiency, relative intensity and maximum relative intensity for the uninclined transmission hologram in photorefractive optically active crystals of (110)-cut are obtained with regard to piezoelectric effect at different orientations of the gratin vector in approximation of small coupling constants and small Bragg angles. The approximate expression for calculation of optimum azimuths of incident light, at which the maximum diffraction efficiency of holographic grating and maximum relative intensity of subject wave take place, are found. The applicability limits of the derived formulas for a Bi₁₂SiO₂₀ crystal are determined and the dependence of relative errors on crystal orientation is investigated.

The dependence of the maximum diffraction efficiency (eta) ^m of hologram, which has been recorded in a BSO crystal, and also the dependence of an orientation angle (theta) ^m at which (eta) ^m is reached on the crystal thickness d are investigated. It is shown, that the optical activity and piezoelectric effect qualitatively change the form of dependences (eta) ^m(d) and (theta) ^m (d).

Bismuth tellurite single crystals undoped and B,P-doped by Czochralksi method were grown. The analysis of the contents of the impurity in received single crystal was carried out. The results of the electrical and optical investigations on the undoped and doped single crystals are presented and discussed. It is determined that change of the compound does not exert significance influence on conductivity of bismuth tellurite single crystal. Considering CVC behavior we may suppose that energy trap distribution in the band gap has Gauss character. The optical measurements have showed that B impurity makes more transparent Bi₂TeO₅ single crystal.

The amplitude of the transmission dynamic grating recorded due to the backward four-wave mixing (BFWM) in the non-local response photorefractive crystal is investigated theoretical. The grating's amplitude distribution is described as a motionless soliton. Both the soliton localization degree and its location can be control by varying of input intensity's ratio or/and input waves' phase differences. When waves' phase differences equal to 0 of (pi) the steady stage double-phase-conjugation mirror is formed. The BFWM dynamic is described by sin-Gordan-like equation.

For the first time to our knowledge, the results of the investigation of some photorefractive characteristics of lead germanate crystals doped by neodymium (PbsGe3011 :Nd) are reported along with those of Pb5Ge3011 :Cu and Pb5Ge30 11 crystals. The furnace charge concentration for Nd and Cu amounts 0.2% and 0.5% respectively. We have not used any monodomained crystals. There was no external electric field applied to crystals. All the crystals under study have exhibited the photorefractive properties when irradiated by a He-Ne laser. The total intensity of the irradiation was about 2 mW/mm2. The diffraction efficiency of the gratings recorded on PbsGe3011 :Nd, Pb5Ge30 11 :Cu, and Pb5Ge30 11 crystals was equal to 2.8, 2.5, and 2.2%, respectively. The holograms were recorded in counterpart beams, too. So, the crystal resolution appears to be not less than 3175 lines/mm. The response time for the crystals have ranged from a few seconds up to several minutes depending on mutual orientation of the optical axis of the crystal and the grating vector the recorded hologram, and upon the grating constant. The time of photoinduced erasure of the crystals when effectuated by one of the recording beams, has appeared to depend on the above parameters and ranged from 5 sec to 30 min. The grating on Pb5Ge30 11 :Nd, once recorded, have preserved its properties, if stored in the dark, for about 10 days. The gratings recorded in counterpart beams have lost their properties in the dark in 10 seconds. Only minor photorefractive effect has been registered under the irradiation by green line (A.=4880 A) of an Arlaser.

Keywords: holographic gratings, formation and erasure time. diffraction efficiency, holographic image processing

The low-temperature thermoluminescense (TSL) technique has been applied for probing the energetic disorder of localized states in poly(methyl-phenylsilylene) (PMPSi) combining the TSL studies and transport properties as determined by photocurrent transients. The results are described in terms of the disorder model and the energetic relaxation of photogenerated charge carriers within a manifold of the states of Gaussian distribution. Analysis both of the energetic position of the TSL peak maximum and the shape of its high energy wing allowed to extract a parameter characterized the intrinsic energetic disorder in PMPSi, the value of which coincided well with the width of the density-of-states determined from transport measurements. The interpretation of results leads to conclusion that although the disorder is the dominant factor, the polaron contribution should be taken into account for the description of the charge carrier transport in PMIPSi. The problem of the photochemical stability of PMPSi as well as the appearance of new trapping centers, is briefly outlined.

Keywords: organic polymeric photoconductors, poly(mcthyl-phenylsilylene), energetic disorder, charge carrier transport, thermoluminescence.

The kinetic of holographic recording in photopolymer compositions is considered in the terms of Abrami-Erofeev equation. It has been shown for composition with polymerization-diffusion mechanism of recording it is possible to realize the conditions, at which the kinetic of recording and consequently, light sensitivity of a material and efficiency of recording will be determined by the parameters of the polymerization process.

Poly(2-methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene and copolymers with fragments of 1 ,4-phenylene , 1,4-naphthylene, 9, 10-anthrylene and model compounds is one of the most interesting polymers, which have a high third-order non-linearity optical activity. We have investigated spectral luminescent characteristics (absorption, excitation and fluorescence spectra) ofthis compounds. The quantum chemical calculation of electronic structure model compounds were carried out in an AM1, PM3 approximation. It was founded the relationship between the structure of polymer and its spectral -luminescent properties and shown that creation intramolecular hydrogen bond and intermolecular complexes such as excimer - dimer plays significant role in formation of electronic structure polymer and consequently their non-linearity optical activity.

We have suggested a mathematical model of bio-optical nonlinearities for the suspensions of motile microorganisms (MO). Modeling of photophobic and photokinetic types of the photoresponse of MO suspensions allow us to predict effects of aggregation and 'hole burning' in the spatial distribution of MO concentration. Theoretical description of nonlinear diffraction may help with the diagnosis of the vitality of MO culture and for characterization of photomovement.