We present an analytical model of dynamics of three spatial harmonics of 2D spatial grating profiles with taking into consideration both record mechanisms (polymerization and components diffusion, absorption, interference pattern contrast. On the base of numerical simulation we examined an influence of these parameters on 2D spatial profile along grating vector and along thickness of a film.

Liquid crystal displays in different modes are suitable due to their birefringence properties and wide transmission range. The paper discussed advantages amplitude-phase modulators and focused on boundary conditions for the application in digital holography (generation of 3D light wave) and for dynamic pattern generation. Implementation demands are discussed on the example of an optical system for parallel recording and optical reconstruction of digital hologram. Optical methods based on digital holography are highly effective for diffractive element synthesis. Modern production of digital hologram is characterized by high degree of flexibility and complexity. According to this the use of proposed method is useful for designing and developing an optical system able not only for fringe pattern fabric structures but as well to allow more complex pattern including singular for image forming. We report on a method for synthesis of digital holograms taken with interference of laser beams diffracted on a spatial light modulator. The proposed technique for modeling of adaptive diffractive elements computes the propagation of the complex optical wavefront diffracted by the object and used to determine the needed spatial light modulator (SLM) pattern. The extension of new method of modeling diffraction on amplitude-phase mask and possibilities of its practical application such as computer modeling of diffraction on a SLM, which consists of squared cells, for a wavefront reconstruction are considered. Conclusions regarding the possibilities the representation the arbitrary fields by using the discrete matrix of elementary diffractive aperture cell for enhancement of iteration algorithm of hologram synthesis and phase retrieval are arrived at. Proposed method for computer-generated holograms (CGH) enables one to synthesize CGH's and simulate digital image processing techniques for 3D image reconstruction. The process does not contain any Fourier transform calculations, and can thus be performed directly by grating recorder in line with recording. Nowadays miniaturized CCD and recent successes in optical spatial light modulator system devices allow building compact digital holographic system. Combining the original dot-matrix method with interferometric image forming allows obtaining new visual effects for hologram or diffractive elements synthesis. The new approach in this project is the idea of using the optical interference field is recorded at the same time in different areas to give multiple grating. Thus the image cell that are written are not separated into discrete dots of diffraction grating, like conventional dot-matrix spots, but form a continuous recording over relatively large area. Some advantages are that the basic cell, or pixel, is composed of not only a set of diffraction grating with various spatial frequencies but also may contain arbitrary pattern form and contain the hidden image or coding visual information. The result obtained by numerical and experimental means are presented together with a discussion of the limitations and further possibilities of this method.

We investigate the features of femtosecond laser pulses interaction with pure and dye-doped nematic liquid crystals. For femtosecond laser pulses interacting with dye-doped nematic liquid crystal we found the distinction between the efficiency of liquid crystal director reorientation in comparison to the continuous wave irradiation. The mechanisms responsible for such distinction associated with changes of intermolecular forces under two-photon absorption and light induced changes of anchoring conditions are discussed.

Light interaction with nematic liquid crystals doped with high-molecular polymer MEH-PPV (poly[2-methoxy-5-(2'-ethylhexyloxy)-l,4-phenylenevinylene]) has been studied. The director reorientation away from the light field was found within the absorption band of the polymer. The reorientation is explained by the appearance of the torque due to changing the intermolecular forces between the polymer macromolecules and nematic-host molecules under polymer excitation by light absorption.

Flat-parallel cells filled with several nematic liquid crystals of both planar or homeotropic steady-state alignments were exploited to study some of their properties. To make results of investigation more reliable wedge cells of the wedge angle of order of few milliradians were used to measure threshold electric and magnetic fields for the different kinds of Freedericksz transition. Nematic liquid crystals filling wedge cells were of planar orientation enforced by the treatment of flat boundary plates. A system of interference fringes appeared in a cell placed in normally incident light between analyser and polariser crossed. In the vicinity of each fringe a cell could be considered as a flat-parallel one and hence it was equivalent to a system of flat cells of different precisely determined thickness; the same relates to any cell of slowly varying thickness and flat cover plates. The threshold electric and magnetic field magnitudes were interpreted as the eigenvalues of the boundary eigenvalue problem for the operator of the second derivative; the interaction between the nematics and the substrates was described by the Rapini-Papoular formula (i.e. weak coupling was considered) or by a polynomials. The resulting formulae were used to determine the anisotropy of diamagnetic susceptibility and the splay and bend elastic constants of a few nematic liquid crystals (PCB, 6CHBT, DE) and the polar anchoring energy coefficient, after the measured threshold fields. The improved method exploiting a self-consistent director field was applied to determine all these parameters and the coupling between the nematics and the substrates made of some polyimides. The estimates of material parameters agreed pretty well with data taken from literature.

The investigation of light propagation in the polymer dispersed liquid crystal film in its isotropic phase is carried out. The propagation of coherent (direct) component of the transmitted and reflected light in the film with high concentration of spherical scatters is considered by using the adding method. The calculation results of coherent transmittance, reflectance, and phases of transmitted and reflected waves are presented.

A method for calculation ellipsometrical parameters of light transmitted through a polymer dispersed liquid-crystal film is proposed. It is based on the Rayleigh-Gans approximation for independent scattering regime. Functional dependencies of ellipticity and azimuth of polarization ellipse of scattered light on liquid-crystal droplets' order parameter are presented.

Unwinding (winding) of a helix in thin planar cholesteric layers induced by the varying external parameters (temperature, electric or magnetic field) and its dependence on the surface anchoring are theoretically investigated for the defectless mechanism of the cholesteric pitch jumps connected with a slipping of the director on the surface through the anchoring potential barrier. Earlier investigations of the problem performed for the case of the temperature variations showed strong dependence of the relevant phenomena on the anchoring potential (two sets of model anchoring potentials were considered). However the field dependence of the pitch variations was examined only for the Rapini-Papoular (R- P) anchoring potential. We performed investigation of the problem for two types anchoring potentials, R-P - potential and so called B-potential and found a qualitatively different behavior of the pitch in applied field for the different types of potential. The parameter S_d = K₂₂/(dW) (where K₂₂ is the twist constant, W is the height of the anchoring potential and d is the sample thickness) governs the "pitch versus applied field (temperature)" dependence. The field dependences of the pitch are calculated for a planar cholesteric layer with infinite strength of anchoring at one surface and finite strength of anchoring at the second one for the R-P and B-surface anchoring potentials. It is found that for the B-potential the pitch jumps and hysteresis of these jumps exists at any strength of anchoring opposite to the case of the R-P-potential for which the jumps and hysteresis exist for sufficiently strong anchoring only when S_d<1. In particular it is shown that the critical field of the complete helix unwinding E_c, in a thin layer may be as essentially lower than the critical field in a bulk cholesteric so larger than this field and for some range of the relevant to the problem parameters the helix unwounded by the field remains to be unwounded after removing of the field.

Dynamic holographic recording is investigated in novel class of liquid crystals namely in ionic metal-alcanoic smectics, which contain photosensitive impurities. A design of a heterostructure cell that consists of at least two layers: the first layer is a solid dye film and a second layer is an ionic smectic matrix, is proposed for dynamic holographic applications. Fast temporal relaxation of dynamic holograms in investigated cells is provided due to high values of both thermal and electric conductivities in the ionic smectic matrix. The high aggregation of molecules in the dye film affords strong light absorption and changes of polarizability in the cells. The structural features of lyotropic both potassium caproate and potassium caprilate are investigated by small angle X-ray scattering. Proposed LC cells can find applications in ultra-fast all-optical switchers.

Smectic glasses of ionic thermotropic liquid crystals (system based on cobalt (11) decanoate) were investigated. Holographic properties of these systems were observed. Electronic absorption spectra of Co²⁺ in the isotropic melt, ionic smectic mesophase and smectic glass phase were studied as a function of temperature. On the base of small angle X-ray scattering was determined structure of cobalt decanoate mesophase.

In this work we investigated structural, optical and non-linear optical properties of lyotropic liquid crystal (LC) composition with the electrochromic admixture of viologen. X-ray investigations showed the presence of smectic A liquid crystal phase in samples. We calculated the main values, which characterize samples' structure, and made conclusions about the influence of the admixture at LC matrix Under the action of static electric field we observed colouring of the samples, which depends on the value of the voltage applied and influences the absorption spectra. We provided an analysis of the dependence of colour intensity of LC composition on the admixture concentration. Basing on our previous works we interpreted processes running inside the samples under the action of the electric field and leading to colour change. We registered holographic recording for the composition of LC-viologen and made suggestions about the mechanism of recording.

We present the results of the investigations of photo galvanic effect in Methyl Red (MR) doped nematic liquid crystal (LC). The photocurrent appears under the action of the active pulsed irradiation. The photocurrent amplitude depends on the cell thickness, temperature, concentration of MR, cell's lifetime and beam propagating direction. Our investigations showed the appearance of the adsorbed MR molecules layer on the boundary surface. We suppose the spatial charge separation in the adsorbed layer of dye molecules.

In the work the approximate analytical relations describing the director distribution in depth of a plane-parallel layer of nematic liquid crystal are presented. The analytical expression determining the orientational effect of the periodic surface in a system "relief grating - liquid crystal" is derived. Its diffraction characteristics are studied theoretically. Relaxation kinetics of the director in a plane-parallel layer of nematic liquid crystal is considered taking account of the microscopic inertia moment.

The methods for the optical signal conversion based on the optoelectronic system "relief grating - liquid crystal" and liquid-crystal (LC) cells using S- or twist-effect have been presented. New schemes forming the basis for realization of bistable LC devices, optoelectronic logic elements and systems of electrically-coupled LC elements intended for the production of laser oscillations at the constant input intensity have been proposed. It has been demonstrated that with the use of varying parameters of optoelectronic feedback one is enabled to set up both regular and chaotic intensity oscillations, to control the frequency and form of these oscillations, to realize functional changes of logic elements. The developed LC systems have been introduced into the educational practice of students mastering modem information techniques.

Response of cholesteric sensor materials to biologically active UV radiation has been studied. The sensor mixture comprised a cholesteric liquid crystalline matrix doped with provitamin D, and changes in the maximum selective reflection wavelength λ_max caused by the photochemical reaction of provitamin D → vitamin D transformation were recorded. Using a UV source (DRT-240 lamp) calibrated accounting for the specific irradiation geometry, λ_max shifts were obtained as function of UV illuminance dose (in J/cm²). Using a set of optical filters cutting off specified parts of the provitamin D absorption spectrum, effects of the spectral composition of UV radiation upon the response characteristics of sensor were determined. The results obtained support our earlier considerations of the developed sensor material as "bioequivalent".

We have developed a model to explain the phenomena of electron focusing by pyroelectric and photogalvanic crystals. The pyroelectric crystals used to compare experiments with theory were Fe doped and un-doped LiNb0₃. The crystals were either heated from the +z end or illuminated with a laser (to test photogalvanic effect). Heating the crystals by passing a current through a resistor attached to the +z end produced the pyroelectric effect: a change in polarization in response to a change in temperature. Illuminated with a CW solid-state diode pumped laser (532 nm, 100 mW) produces the photogalvanic effect: the build up of charge on the polar surfaces of the crystal. In both cases the polar ends of the crystal becomes electrically charged and produced self-focusing electron beams that were imaged on a ZnS screen. Using different targets we have produced x-rays, and demonstrated x-ray imaging of metal masks.

We study theoretically arid generate experimentally two-dimensional nonlinear optically-induced photonic lattices with periodic phase modulation of different geometries in a photorefractive medium, including the periodicnonlinear waves with an internal energy flow or vortex lattices. We demonstrate that the light-induced periodically modulated nonlinear refractive index is highly anisotropic and nonlocal, and it depends on the orientation of a two-dimensional lattice relative to the crystal axis. We discuss stability of such optically-induced photonic two-dimensional structures and demonstrate experimentally their waveguiding properties.

The possibility of micro-domains origin in photoreffactive ferroelectric crystals near charged mesoscale defects inside the crystal has been studied. For simplicity this defect is simulated by electrically charged sphere, but the micro-domain is considered as a cylinder with infinitely thin domain walls. It has been shown that the charge of defect must exceed the threshold value for micro-domain appearance. Depending on electrical and geometrical parameters of charged defect the needle-like or lens-like micro-domains can be generated.

Nonlinear transmission wave-mixing problem in a photorefractive medium that include both local and non-local responses is solved not traditionally but with using a new variable namely the dynamic grating amplitude. The dynamics of the wave-mixing is described by a modified sine-Gordon equation that have soliton-like solutions for the dynamic grating amplitude. For the first time the solution for the grating amplitude distribution in a medium with complex response is obtained. The shape of the grating amplitude profile is determined only by the value of the non-local response in the steady state, and both by local and by non-local components of the response in a transient process. Complete analytical solutions with taking into consideration the complex medium response as well as the absorption in two-wave mixing are obtained. The described theoretical predictions can be a base for a novel topographical method to material characterization of photorefractive crystals that allows one to study contributions local and non-local components of the medium response more precisely.

A theoretical model which can describe the dynamics of spatial bright discrete solitons in photovoltaic photorefractive media is suggested. Four different types of staggered solitons, symmetric odd and even, twisted and antisymmetric odd one are observed numerically and their behavior is investigated with respect to small transverse phase offsets. A first experimental observation of steering of such symmetric odd staggered solitons in lithium niobate waveguide arrays is presented.

Results of low- and high-frequency modulation of laser beam, propagating both in the direction of optical axis and along three crystallographic axes in Fe-doped KNb0₃ crystal, are presented. It was found, that the high-frequency electro-optical constants of Fe:KNb0₃ are: r₃₃ = (5353) pm/V, r₁₃ = (21±3) pm/V, and r₅₁ = (88±11) p d V . The difference between high- and low-frequency values is about 20% and this is in good accordance with known data for nominally pure crystal. We found also, that there was no twinning effect in this crystal under the electrical fields up to 2.5 kV/cm. The half-wave voltage was only 800 V at the wavelength of 633 nm in a longitudinal configuration of modulator. We measure also that bandpass of light modulation in Fe:KNb0₃ is equal to at least 6 MHz. In our experiments we also determined the speed of acoustic waves, created in the crystal by inverse piezoelectric effect, when fast HV electrical pulse is applied to it, these values are v_l=(56001100) d s and v₂=(6400±100) m/s along Oz and Ox axes correspondingly.

Femtosecond laser radiation self-channeling and second harmonic generation under plasma formation conditions were investigated. Laser pulses with sub- and microjoule energy were tightly focused into the volume of a KDP crystal, Estimated laser pulse intensity was of the order 10¹³ W/cm² in the focal spot exceeding damage and plasma ignition thresholds in the crystal. Threshold of plasma channel formation measured in the experiment corresponds to critical power of self-focusing 1.5f0.1 MW for KDP crystal. Plasma channels with length up to 150 μm were observed in the volume of the KDP crystal. We developed an algorithm allowing estimating electron density and temperature in the plasma channel using experimental dependence of laser energy transmittance through the crystal on incident laser energy. For laser pulse energy 1 μJ estimated electronic density in the plasma channel is of the order of l0²⁰ cm^-3 (that is about one tenth of the critical plasma density value) and mean electronic temperature is about 3 eV. Free plasma electrons leaded to refraction index increasing by 5 %, extinction coefficient was -25 cm^-1. The maximum measured efficiency of second harmonic generation was 1.2 %.

This paper is devoted to growth and doping of semiconductor photorefractive cadmium telluride (CdTe) crystals as well as to the investigation into their spectroscopic and non-linear optical properties. The crystals are doped with vanadium, iron, and titanium. Two methods have been used for the production of doped crystals: diffused post-growth doping and growth of doped crystals from melt. Non-linear optical properties of the samples were studied at a wavelength of 1.06 μm for a four-wave mixing geometry and 1.54 μm for a two beam coupling. Maximum 2% diffraction efficiency at 1.06 μm was revealed with the convergence angle of light beams approximating 8" for the grating period of 7 μm. In this case the dynamic grating lifetime was found to be about 0.2 μs. Under beam coupling at ~ 1.5 μm, the conditions of maximum gain (0.7 cm^-1) were observed in the experiment for a minimum grating period of 1 μm; and the gain could be slightly enhanced by application of a dc electric field (~ 2 kV/cm) up to 40%.

Characteristics of a holographic interferometer with photorefractive media that includes a regime of real time registration of holograms are considered. The interferometer arranges an optical fiber bunch that allows one to use this scheme for delivery of optical information from hard accessible places. Distortions coming from changes of mode structure of the probe fiber bunch during hologram recording are decreased significantly owing to the features of the proposed optical setup and the method of registration.

We have proposed the phenomenological description of dielectric hysteresis loops in ferroelectric semiconductors with impurity centers charged under photo- or UV excitation. Exactly we have modified Landau-Ginsburg approach and shown that the macroscopic state of the aforementioned inhomogeneous system can be described by three coupled equations for three order parameters. Both the experimentally observed coercive field values well below the thermodynamic one and the various hysteresis loop deformations (constricted and double loops) have been obtained in the framework of our model.

In the given work researches of spectral characteristics of thin-film structures have been lead on the basis of amorphous silicon. The number of laws connected to increase of absorption, and also by improvement of electric parameters films is revealed due to change of concentration of hydrogen in a film that entails creation of cheap sources of nonconventional power, that is solar elements.

The new method for measuring the eigen mode "weights" in a radiation emitted from a weakly guiding optical fiber with a strong birefringence is discussed. The method is based on the detection of geometrical parameters of the diffractive pattern of the field after the optical fiber. The mode "weights" are plotted as a function of the fiber excitation parameters. The analysis showed a good agreement between the theoretical results and the experimental data.

We investigate the propagation of optical vortices in strongly elliptic weakly guiding fibres. A novel method of the perturbation theory developing is suggested based on the simple change of variables that effectively makes it possible to take account of the field amplitude corrections in higher orders of perturbation theory. The form of a generic elliptic vortex in elliptic fibres is found to be a mixture of partial circular vortices.

The aim of the given report is experimental and theoretical research of the diffraction of a Gaussian beam by the optical wedges system. It is shown that this system is able to form high-order optical vortices. The effectiveness of system is about 90%. It was shown, that each wedge changes a charge of phase singularity as a result of edge diffraction. The value topological charge of the optical vortex formed after system is defined by the number of wedges in the system. Changing mutual orientation corners of wedges we can select required conditions of the vortex core. It was revealed that the optical vortex appears structurally steady if the comer of mutual orientation of wedges equals α = πn (where n-number of wedges).

Experimental showed that a monochromatic singular beam emitted from a crystal has three focal planes. The distances between additional focuses of the beam depends both on the focal distance of the lens, a lens position relative to the crystal and the beam and the crystal parameters.

We experimentally investigate some features of the self-defocusing of light beams as well as the relaxation of waveguide channels induced by dark spatial solitons at wavelength of 632.8 nm within slab optical waveguides formed in lithium niobate by iron diffusion or combined diffusion of titanium, iron and copper. We also study an influence of the externally applied electric field on both, spatial self-action of single beam within such waveguides and external focused beam which propagates in direction normal to the waveguide surface. Experiments show that for lowest TE modes the photovoltaic nonlinearity results in the fast but not very strong beam defocusing and for modes of higher order this effect is slower but much stronger. It is also demonstrated that at suitable light intensity the screening of the external electric field significantly contributes to the beam self-action at its initial stage even for mediate value of applied electric field.

We experimentally investigate the photorefractive nonlinearity within lithium niobate samples with surface doping by combinations of copper (Cu) and iron (Fe). In the configuration of closed Z-scan we use either helium-neon laser irradiation with wavelength of 633 nm or continuous wave semiconductor laser with wavelength of 650 nm. Light power in experiments ranges from 1 to 4 mW. We observe very strong Z-scan response in the closed scheme at the transient stage and the different temporal behavior of this response for different locations of the light beam waist with respect to the doped surface of samples studied. The approach of thin light-induced nonlinear lens is used to estimate the Z-scan response in the steady state in dependence on the nonlinear sample position. We also use this approach to compare the observed distortions of the light beam due to its spatial self-action with expected change of the beam profile.