Second harmonic generation in ferroelectric LC when the waves propagate along the helical axis and in cholesteric LC for oblique wave propagation are studied taking into account the damping of pumping and SH waves, caused by absorption and scattering on the director fluctuations. The structural enhancement of SHG near Bragg reflection band is predicted.

We have investigated lasing mechanism for a Nd:YAG laser with cholesteric liquid crystal (CLC) end mirrors. The slope efficiency of a CLC-dielectric mirror resonator was measured and compared with a dielectric-dielectric mirror resonator. We considered influence of nonlinear bleaching of the CLC mirror on the operation of Nd:YAG laser. In cw operation we did not observe any difference in laser output power with a conventional dielectric-dielectric mirrors resonator. When we switched on the operation of laser from cw to 500 ns 4.5 kHz lasing, it disappeared in a 30 s - 10 min time interval, which depends on current on the lamp and the anchoring conditions on the sides of the CLC mirror (we tested four different CLC mirrors). It should be noted that this effect districts the use of the CLC mirrors in high- repetition rate lasers.

We have observed lowering of reflectivity (from approximately 90 to 95% up to approximately 50 - 70%) of the cholesteric liquid crystal (CLC) mirrors under the nonlinear action of circular polarized laser radiation. The possibility is considered of nonthermal but light-field induced helical pitch dilation and untwisting. It should be mentioned that it is the first experiment to our knowledge (the special laser operation was chosen, so that the changes of pitch can be accumulated) where such strong changes of reflectivity can be explained by nonthermal effects. We also observed defocusing of reflected beam with a near Gaussian spatial profile and changing of the CLC mirror curvature, but we consider that in these experiments thermal effects are more probable.

Wave-front conjugation (WFC) in four-wave interaction (FWI) of monopulse radiation of ruby laser in dye-activated nematics has been studied. The effect of the absorption saturation of the dye and change in the LC order parameter on the WFC energy efficiency is discussed.

Dependences of an irreversible response (memory effect) of suspension 'liquid crystal -- aerosol' on the ingredient's properties and electric field parameters are investigated. The experimental results are discussed in the frame of a model of a network organization of aerosol in a nematic liquid crystal.

The expression for light-induced Freedericksz transition threshold in nematic cell containing the chiral dopants and phototransformed molecules are obtained. The cases of linear and circular polarized light are considered. The dependence of threshold on the period of spatially modulated light intensity is found.

Due to its diffractive nature the light polarization plane rotation in cholesterical liquid crystals (CLC) is highly dependent on the parameters of a selective reflection (SR) band of liquid crystal matrix and possesses a number of qualitative peculiarities in contrast to usual liquids, solutions or crystals. The aim of the present work is to study the influence of such parameters as cell thickness, temperature and dye-doping on the optical activity of CLC. A method of precise calculation of the cell gyrotropy and elliptisity of light passed through CLC film is described. The square dependence of polarization plane rotation upon CLC film thickness was established. Abnormally strong light absorption of dye-doped CLC in the 'red' edge of SR band was observed for small dopant concentrations resulting in an asymmetry of polarization plain rotation with respect to the maximum of SR band. On the base of experimental data the possibility to create an electrically controlled two-color CLC light indicator with high color contrast is discussed.

The method of synchronous scanning fluorescence spectroscopy shows a presence of dimers of pyrene in a polymeric matrix. The results suggest that excimer formation takes place with dimers in liquid crystalline systems.

This paper gives an approximate theoretical model to forecast the noise spectrum of thin covers of polymeric material and analytical relation for Wiener's spectrum taking into account the near topological ordering of drop locations, the cooperative optical effects and the features of scattering by nematic drops allowing for the high electrical field. The relation for the spectrum is derived on the basis of the simulation of a thin polymeric film by an effective two- dimensional medium in the form of a stochastic amplitude-phase screen with the transmission function of an equivalent screen identified as a microdrop, the function being determined by illumination conditions and scattered radiation in the far field. The effective transmission function is inferred by comparing the results, obtained for the model proposed, with that of the anomalous diffraction. Approximation for scattering by a thin film of nematic drops that takes the configuration of a nematic director under high electrical field into account was used.

The orientation of various types of liquid crystals (LC) on thin films of azobenzene polymers exposed to ultra-violet (UV) light has been investigated. The LC orientation depends on a concentration of azobenzene side-chains linked to a main polymer chain and on a heat treatment. Effects of homeotropic and planar orientations were observed when polymer films were irradiated by unpolarized light. A change of LC orientation types took place when LC was filled at applied electric field.

The reverse distributions of the director in the cell with nematic liquid crystal at arbitrary easy axes direction and anchoring energy value are considered. The transformation of the director distribution in the lowest reverse orientation modes under the change of an anchoring strength on one of the alignment surfaces is studied. A structural orientation transition from the tilted orientation on this surface to a planar one is found to be at definite value of the anchoring parameters.

The phase diagrams of the liquid crystalline systems which consisted of the achiral ester mesogen (the eutectic mixture of 4-n-hexyloxyphenyl 4-n-octyloxybenzoate and 4-n- octyloxyphenyl 4-n-hexyloxybenzoate) and the structurally similar chiral dopants are studied. The S-1-phenyl- and S-1-benzylethylamine N-arylidene derivatives including the ester group in arylidene fragment are used as chiral dopants. The twist grain boundary (TGB) region occurs in all investigated systems. This phase state is proved by small angle x-ray scattering and helical pitch measurements. The TGB states on the SmA side (TGB_A) and SmC* side (TGB_c) have different structure according to x-ray analysis data. The chiral dopants capacity for (theta) _c smectic tilt angle decreasing is considered as an important factor of the TGB state formation in the liquid crystalline systems investigated. The chiral dopant structure peculiarities influence the TGB phase topology and the phase boundary slopes. The boundaries of the TGB_c region are more sensitive to chiral dopants concentration changes in comparison with the TGB_A boundaries.

Liquid crystal composites, i.e., two phase polymer-liquid crystal systems, are very interesting from a scientific and application point of view. Amongst them the best known is PDLC (polymer dispersed liquid crystal) structure. In this material liquid crystal (LC) droplets, diameter of 0.1 - 10 micrometer are embedded in a polymer matrix. PDLC composites are used for construction of new information displays, image projectors and optical devices. In the presented work essential material requirements for PDLC are given from an application point of view. They concern mainly well-known electro-optical effect of electrically induced transmittance. The examples of experimental results are also presented.

The effect of the light-induced surface reorientation of the LC director in a cell filled with an LC-azo dye mixture is obtained. The surface reorientation is caused by LC director reorientation in the bulk, which is initiated by a consequent tans-cis-trans isomerization of azo dye molecules accompanied by a variation of their orientation with respect to the polarization of the exciting light. It is shown that the value and the kinetics of the effect depend on the type of the aligning surface.

The change of the molecular organization in the liquid crystal (5CB)-aerosol system under the influence of electric field is investigated with the use of IR spectroscopy methods. It is shown that aerosol A-300 addition (10 weight %) to 5CB leads to forming weak hydrogen bonds between the aerosol hydroxyl groups and the (pi) -electrons of benzene rings of 5CB (Si-O- H...(pi) ). Under the influence of electric field (U equals 60 V, f equals 2 kHz) these bonds undergo a rearrangement, the 5CB molecules in the aerosol pores align along a direction of the electric field and then form the new network of hydrogen bonds. In the case of the aerosol modified by the polymethylsyloxane the formation of new hydrogen bonds does not take place and in the electric field the 5CB molecules are easily oriented along the field direction.

Analyzing the low and infralow frequent dispersion component of complex dielectric permittivity (epsilon) ' and (epsilon) ', the possibility of evaluation of parameters of liquid crystal-solid substrate interface is shown. For the planar oriented liquid crystal at least two regions of (epsilon) ' and (epsilon) ' were found. First the low frequent region of dispersion is defined by redistribution of ion between volume and interface and by formation of the double electric layer the thickness of which is described by Debye equation with a one dielectric relaxation time, the value of which is tens ms and strongly depends on the thickness of the liquid crystal layer. Second, the low frequency region of dispersion (epsilon) ' and (epsilon) ' is defined by transit ions processes between electrode and interface. The setting of the permanent process for transit ions is described by Debye equation with symmetric distribution of relaxation time, the value of which is tens s and does not depend on thickness of liquid crystal layer.

The conditions for transitions between the possible structures in nematic liquid crystals with spherical particles (SPs) are studied. It has been shown that the divergent terms (K₁₃ and K₂₄) in Frank energy play an important role in such structures. The influence of charge of the SP and of an external electric field on the transitions between the structures is investigated.

We study hydrodynamic instability of nematic liquid crystal (NLC) in a biharmonic electric field. The instability is found to strongly depend on the frequency difference; namely, if the applied frequencies of the electric field are close one to another, the critical voltage of Williams domains behaves as the square root of the frequency difference. The 'germination' and 'winking' of the generated structure is exhibited also by the same condition. In the special case of a significant frequency difference, the threshold field of the instability increases with the higher frequency and eventually tends to a constant value. Theoretical explanation of the observed phenomena is given.

A color sequential projection system has some distinct advantages over conventional systems which make it uniquely suitable for consumer TV as well as high performance professional applications such as computer monitors and electronic cinema. A fast responding light-valve is, clearly, essential for a good performing system. Response speed of transmissive LC lightvalves has been marginal thus far for good color rendition. Recently, Sevchenko Institute has made some very fast reflective LC cells which were evaluated at Philips Labs. These devices showed sub millisecond-large signal-response times, even at room temperature, and produced good color in a projector emulation testbed. In our presentation we describe our highly efficient color sequential projector and demonstrate its operation on video tape. Next we discuss light-valve requirements and reflective light-valve test results.

This lecture provides an introduction to flat panel displays technologies for graphic and imagery applications. The main displays technologies are cathode ray tubes (CRT) and liquid- crystal displays (LCDs), but not far behind them on development and product status are plasma display panels (PDP) and electroluminescence displays (EL). The status of the development achievements, trends and prospects for each of the technologies, are presented. The intention of this lecture is to identify a significance and prospects of each technology and their comparison with LCD.

We report experimental and numerical investigation of optical vortices nucleation in a wavefront of a laser beam passed through LiNbO₃ crystal with light-induced self- defocusing nonlinear lens and through SBN crystal with self-focusing nonlinear lens.

A transient photo-electric current was investigated in photorefractive crystals of Sr_1-xBa_xNb₂O₆ (SBN) and Bi₁₂TiO₂₀ (BTO) as a response to a step-like modulation of the light grating phase. Different dependencies of the photocurrent relaxation time on the grating period were observed for SBN and BTO crystals. It is explained theoretically taking into consideration kinetics of the photoexcitation of carriers, charge transfer and trapping. A number of important parameters characterizing the crystals are estimated.

Light influence on LiNbO₃:Fe crystals has been found to induce appearance of needle-like microdomains with average length of 1 - 2 mm and diameter of 1 micrometer. Light scattering by photoinduced microdomain array has been investigated and found to be a seeding source of polarizationally anisotropic photorefractive light scattering. The effect of unlocality of forming the microdomains has been revealed. Photoinduced charge redistribution at the crystal surface has been found to cause the domain formation and rebuilding the crystal structure.

The results of the detailed investigation of influence of the composition compound variation on photorefractive effect in nominally pure LiNbO₃ crystals at continuous-wave illumination are reported. The investigation indicates clear photorefraction amplitude (Delta) n_s increase with the growth of the light intensity J for any studied crystals. The main result of our investigation consists in discovering of a direct linear correlation between (delta) ((Delta) n_s)/(delta) J and density N of such intrinsic defects as Nb_Li. This effect is independent from the accidental iron contamination. Therefore at low J the (Delta) n_s value decreases with growth N while at high J the opposite dependency is observed. The threshold intensity value of such transformation correlates with the crystal optical quality. It has been established that these photorefraction changes are connected with the light induced absorption on the secondary centers caused by the existence of the metastable small polarons at room temperature during illumination.

Two-beam coupling is observed in the planar Bi₁₂TiO₂₀/Bi₁₂GeO₂₀ waveguide in the presence of external square-wave field. The enhancement of the two-beam gain coefficient to the value of 0.77 cm^-1 at (Lambda) equals 2.7 micrometer is achieved. The one level band transport model is extended for two-beam interaction in the waveguide in the presence of external field. From a set of experimental data, an acceptor density, an effective electro-optic coefficient, and a multiplication of carrier mobility and recombination time of the waveguide is estimated.

The investigation of the photorefractive effect in crystals Pb₅Ge₃O₁₁:Cu and Pb₅Ge₃O₁₁ that we started earlier is continued. The lead germanate crystal doped by copper demonstrated the photorefractive properties at the wavelength of 496.5 nm with diffraction efficiency of the recorded hologram of 0.4%. The crystal Pb₅Ge₃O₁₁ exhibited the photorefractive effect at the wavelength 496.5 nm and 514.5 nm. In this case the grating diffraction efficiency was 5.3%. As for two investigated crystals the total intensity of writhing beams kept at the level of 100 mW/cm². There was no external electric field applied to crystals. We studied the temporal characteristics of recording and of erasure of holographic gratings and the crystal response time as a function of the total light intensity.

Gaussian beams' diffraction on the computer synthesized holograms permits formation of the optical vortices. Using this method we can obtain optical vortices with different topological charges and different laser beams. Although, technology used to obtain such optical transparencies determined a static optical vortex structure depending on the hologram type. As a rule they ought to be thin holograms. The obtaining of thick holograms of high quality demands the use of a special technique. Strip structure based on magnetic domain films considerably better permits the precise adjustment of optical vortices.

The phenomenon of a light topological birefringence in a multimode fiber has been discussed in papers. The physical mechanism of the topological birefringence, as expected earlier is determined by the interaction of the two effects, namely, the topological Berry's phase and the optical Magnus effect. So, for a square distribution of a refractive index in a fiber cross section the near-meridianal local waves propagate along ray trajectories represented by strongly stretched ellipses of an elliptical helix. A plane made by a fiber axis and a major axis of a ray elliptical helix undergoes a rotation into the fiber, and the rotation hand of this plane is defined by a sign of the wave polarization circularity. If a linear polarized light drops into a fiber input its left-hand polarized component will rotate the major axis of the elliptical helix counterclockwise, and the right-hand polarized component rotates clockwise. Since the angular rates of this rotation are slightly different one from another forthcoming the local waves having counter circulation of a polarization should be collapsed in a single linear polarized local wave. However if the local wave trajectory doesn't lie in a plane then it is a space curve.

A determined chaos of a polarized light field in multimode fibers could be defined by a diversity of physical processes. There is a mode and polarized dispersion, birefringence of a material core and also the topological Berry's phase and the optical Magnus effect (OME) which destroy an evolution of a polarized light in multimode fibers. In the present paper I would like to draw your attention to the interesting phenomenon, namely, the optical Magnus effect in an inhomogeneous medium. The stochastic pattern of the determinate chaos is in essence caused by this effect. Many assumptions on the behavior of an inhomogeneous wave due to total reflections of a plane wave appeared just after the discovery of the longitudinal shift of Gooss and Hanchen. However only in 1955 the paper by F. Fedorov about a transverse energy electric wave flow due to a total reflection was published.

The self-induced rotation of the plane of light polarization of the pulse ruby and neodymium lasers was studied as a function of value 2hv-E_g in CdP₂ and ZnP₂ single crystals. This phenomenon is known as nonlinear optical activity (NOA) in crystals which have a pronounced two-photon absorption of the laser radiation of the investigated wavelengths. intensity of the pulse laser radiation transmitted through crystal and analyzer plotted against intensity of the radiation incident on crystal has a nonlinear character because of both the display of the two-photon absorption (2hv greater than E_g greater than hv) and the self-induced rotation. These results offer to the determination of the specific value of NOA. The temperature dependence of the specific value of NOA and its dependence from intensity of the laser radiation are determined. The likely mechanisms and application of the investigated phenomenon are discussed.

We study experimentally the photorefractive gratings decay in semi-insulating germanium doped cadmium telluride crystals. The estimates for the diffusion length of free carriers L_D and for Debye screening length l_s, for dark and photoconductivities of the sample are done from the angular and intensity dependences of the time constant.

Rigorous coupled-wave diffraction theory is used to analyze two and multi-wave mixing in diffusion-controlled photorefractive barium titanate which is modeled by the Kukhtarev equations. The transmitted and reflected optical fields, the dielectric modulation, the electrostatic electric field, and the electron density are studied for the cases when the interfering, incident optical fields have equal and unequal amplitudes, for different values of the linear refractive index mismatch and for different values of photorefractive crystal length. Our computations are extended to include longitudinal variations of the electrostatic field. Temporal instabilities and higher order generation are examined.

BGO and BSO single crystals, pure and doped, have been grown by the Czochralski technique. The influence of natural and forced convection flows in the melt on the distribution of dopants in as grown single crystals has been discussed. Strong photochromic effect for such dopants as Cr, Mn and Cu has been observed. The change of the coloration from pale yellow to colorless has been found in case of sulphur doping.

The technological procedure of the manufacturing of the LiNbO₃ single crystals doped with 5 mol.% MgO is described in this paper. The results of the investigation of the crystal optical properties and optical homogeneity are presented. The refractive index dispersion in the 300 - 700 nm region and their temperature dependences in the 20 - 500 degree Celsius range are measured. The dispersion curve is approximated by the two oscillator Sellmeier formula. The data on the LiNbO₃:MgO crystal optical resistance are presented. The phenomenon of optical damage in LiNbO₃ (LN) restricts considerably the application of the crystals in devices that control powerful laser beam. Crystal doping by MgO suppresses photorefractive characteristics of LN and leads to considerable increase of the threshold of crystal optical damage. Hence it is of vital importance to receive optically homogeneous LiNbO₃:MgO (LN - Mg) crystals of big size and to study their optical characteristics. The concentration dependence of MgO influence on optical characteristics is threshold like and the threshold concentration of MgO ranges within 5 - 7% mol according to the ratio of Li/Nb in the crystal.

The LiKSO₄ (LPS) and (NH₄)₂BeF₄ (AFB) crystals belong to ferroelectrics with incommensurate phase and birefringence inversion. Birefringence inversion point (lambda) ₀ in LPS crystals was observed in spectral ranges 240...360 nm within 180...430 K. Two regions of (Delta) n_i sign change of AFB crystals were observed (76 K and 312 K) for spectral range 400...1000 nm. The purpose of the paper is to investigate the influence of ancienting, annealing and x-ray irradiation on temperature and spectral dependences of birefringence (isotropic point) of LPS and AFB crystals.

Spectral dependences of optical absorption coefficient of the bismuth tellurite single crystals grown by Chohralsky method have been observed. The investigations were carried out on the fresh-prepared samples of the different thickness after annealing up to 400 degrees Celsius in the air and in the vacuum and also after illumination by the intensive light with various wavelengths. The value of the forbidden band for indirect transition (E_gi) is approximately 3.11 eV at room temperature and it decreases with the coefficient about 10^-3eV multiplied by K^-1. On the absorption spectra of the fresh-prepared sample the broad bands were observed in the region of fundamental edge and in the longwave region (hv equals 1.5 - 1.9 eV). Photochromic effect was found in the Bi₂TeO₅. The nature of optical absorption bands and photochromic effect is analyzed.

Electrical and optical properties of CdTe doped by Vanadium in the concentration range from 5.10¹⁸cm^-3 to 5.10¹⁹cm^-3 are studied with the use of a set of experimental methods: EPR, photoluminescence, photoconductivity, and thermostimulated conductivity. It is shown that doping CdTe by Vanadium leads to formation of defect that manifests itself as deep donor center with optical and thermal activation energies equal to 1.30 eV and 0.71 eV respectively.

The equation of the electric field of light diffracted on space charge waves is obtained. The interaction of light with space charge waves in some semiconductors can be used to control the laser radiation.

A generalized photorefractive model, that includes influence of the electric field on photoconductivity and birefringence is presented. This model is applied for description of Bragg and non-Bragg self-diffraction in photorefractive polymers in the schemes, suitable for holographic electro-optic modulation.

Processes of phase hologram recording in binary photopolymeric media have been considered. These media are based on two monomers having different polymerization rates and forming polymers with different refractive indexes. The mechanism of inhomogeneous structures formation in such media includes two main processes: radical polymerization and diffusion mass transfer. The general equations systems has been theoretically investigated, which describes the dynamics of inhomogeneous photopolymerization in complex polymeric compositions.

In aminoacid crystals ((alpha) -glycine, (beta) -alanine, L-histidine) a gigantic growth of nonlinearity at simultaneous action of two resonance fields (Omega) _m and (omega) $i) (double resonance conditions) was found. If frequency (omega) _i responds to one of the infrared (IR) transitions (600 - 2000 cm^-1) and (Omega) _m is in resonance with the absorption lines which are in extremely high frequency (EHF) range ((Omega) _m approximately equals 37.5 - 53.5 GHz), the value of third order nonlinear polarization coefficient (chi) ⁽³)((Omega) _m, - (Omega) _m, (omega) _i) amounts to 10 cm/erg. Despite small EHF radiation power (Pm less than 10 mW) such nonlinearity may result in essential (up to 10%) change of reflection coefficient R((omega) _i). A change of the orientation and form of reflection coefficient polarization indicatrix for resonance field in IR range was also observed. The most pronounced nonlinear effects appear at resonance frequencies connected with deformational vibrations of NH₃⁺ group and valent vibrations of COO^- group.

We designed experimental equipment realizing one of the time-spectroscopy methods for detail investigation of photorefractive process in the DKDP single crystal at room temperature. A non-steady-state optic-polarization technique with a pulse pumping (pulse duration of Q- switched YAP:Nd³⁺-laser was approximately 20 ns, energy density of pulses varied from 0.2 J/cm² up to 1.6 J/cm²) has been used in experiments. This allowed us to achieve temporal resolution for responses of various components of photorefractive (PR) effect with different characteristic times (acoustic component is approximately 12 ms, fast component is approximately 1 ms and slow component is from 4 ms up to 100 ms). As a result a linear dependence of the pumping-induced internal field magnitude on pumping pulse energy at the 1.08 mm is established. It was shown for the first time that mechanisms of excitation of fast and slow components are independent. The present results may create basis for detail PR effect investigations of the KDP group crystals above the Curie point with prospect of further holographic applications and a new technique to measure laser pulses energy.

The problem of new methods of temperature measurements has become vital recently. One of the trends in the search of non-contact methods of temperature measurement is based on changes of optical characteristics caused by temperature changes. One of these methods is the interference-optical method based on recording of the changing interference pattern caused by the light transmission through the anisotropic crystal when temperature is changed.

Narrow bandwidth gratings, recorded using volume holography in photorefractive materials such as LiNbO₃, have been demonstrated for use as filters, wavelength selective couplers, and optical data storage elements. Sub-angstrom bandwidths have been demonstrated in the visible and infrared. Reflectivities of up to 95% have been obtained. Applications in filtering, instrumentation, telecommunications, and optical storage are discussed.