Phase Coexistence in <$Eroman bold {Cs sub 3 Bi sub 2 I sub 9 }> Ferroelastics: Optical, Dilatation and Ultrasonic Velocity Studies. - ISSN 1609-1833

The results for dilatometric, ultrasonic velocity and the domain structure studies of <$Eroman {Cs sub 3 Bi sub 2 I sub 9 }> crystals in the course of ferroelastic phase transition are presented. It is shown that the phase transition in Cs3Bi2I9 is of the first order. Basing on the thermal expansion results and the data obtained for the elastic stiffness of <$Eroman {Cs sub 3 Bi sub 2 I sub 9 }> crystals, the latent heat Q = 79 J/kg at <$ET sub c> is calculated. The region between 183 K and 221 K (at cooling) is identified as a heterostructure region, where ferroelastic and paraelastic phases coexist.

Phase Transition in <$Ebold beta>-Alanine Amino Acid Crystals. - ISSN 1609-1833

Single <$Ebeta>-alanine crystals are grown by a triple cross-crystallization from the saturated aqueous solution of chemically pure <$Ebeta>-Ala powder and then dried in the vacuum thermostat at 340 K. <$Ebeta>-Ala single crystals belong to the point group of symmetry mmm at the room temperature. It is found that the temperature dependences of thermal expansion and the optical manifest anomalous behaviour at T = 204 K, thus testifying the existence of phase transition at this temperature. The temperature hysteresis of the Curie temperature <$ET sub c> means that the phase transition in <$Ebeta>-Ala crystals is of the first order. The spontaneous deformations and birefringence increments calculated by us depend linearly on temperature. It is shown that the phase transition in <$Ebeta>-Ala crystals could be ferroelectric or higher-order ferroic.

Role of Low-Frequency Modes in the Formation of Dielectric Function of <$Ebold beta>-Alanine Molecular Crystal. - ISSN 1609-1833

Dielectric permeability <$Eepsilon sub 0> of <$Ebeta>-alanine (<$Ebeta>-Ala) single crystals is studied with the IR spectroscopy technique and the appropriate calculations. We have calculated the dielectric permeability from the reflectance spectra, using the dispersive analysis and the harmonic multi-oscillator model. The calculations of <$Eepsilon sub 0> from the reflectance spectra of (010) <$Ebeta>-Ala crystal plane in the <$E400~-~4~000~ roman cm sup -1> region have earlier shown that it is impossible to achieve the <$Eepsilon sub 0> values experimentally measured in the microwave region (<$Eepsilon sub 0 sup { roman c } ~=~5,3,~ epsilon sub 0 sup { roman a } ~=~4,0>). The calculated data differ two times from those experimentally measured for one of the directions. The polarized IR reflectance spectra of <$Ebeta>-Ala single crystal and the transmittance spectra of the corresponding powder are detected in the <$E100~-~5~300~ roman cm sup -1> region. The account for the low-frequency modes (400, 321, 218, <$E180~ roman cm sup -1 }>) finally gives a possibility to obtain a good agreement between the calculated and experimental results. The large contribution to <$Eepsilon sub 0>, which is mainly due to the oscillator at <$E218~ roman cm sup -1>, is essential only for one of the alternative polarizations (E || the small axis of the (010) crystal plane). It seems to be associated with the H-bonded inter-molecular vibrations.

Optimization of Experimental Conditions for Ellipsometric Studies of ultra-thin Absorptive Films. - ISSN 1609-1833

The method for optimization of experimental conditions necessary for increasing the sensitivity and accuracy of ellipsometric measurements is presented. The method enables to organize an efficient searching algorithm for the optimum conditions. The substantiation of reliability of the method is accomplished. The correlation of results obtained using the present method and the other independent methods is found. The basic attention is devoted to a choice of refractive index of the immersion medium andthe angle of incidence of light, in order to ensure the most exact determination for the parameters of absorptive surface films. The technique for the choice of optimum experimental conditions is analyzed for the particular surface models. The areas of global minimum in the experimental error dependences are revealed. The existence of these areas is confirmed with numerical experiments.

Methods for the Studies of Piezooptic Effect in Crystals and Analysis of the Experimental Data. - ISSN 1609-1833

This review article deals with the analysis of works dedicated to studies of absolute piezooptic effect in crystals, which possess a symmetry lower than the cubic one. We demonstrate a possibility to construct indicative piezooptic surfaces, basing onthe completed matrices of piezooptic coefficients. The examples for analysis of the piezooptic effect anisotropy are given, which uses the indicative surfaces, as well as their sections and stereographic projections.

Optical-Refractometric Synthesis of Transmission Spectra and Optical Parameters of <$Eroman bold {0,5TiO sub 2 ~ cdot ~0,5Nd sub 2 O sub 3 }> Thin Films. - ISSN 1609-1833

An original method for determining the optical parameters of thin films with the optical-refractometric synthesis of their transmission spectra is suggested. The proper choice of dispersion relation for refractive indices is substantiated. Experimental studies and computer simulations are performed for the quartz-glass optical element with <$Eroman {0,5TiO sub 2 ~ cdot ~0,5Nd sub 2 O sub 3 }> film. The advantages of the suggested method are discussed.

Luminescent-kinetic parameters of <$Eroman bold {CsPbCl sub 3 }> nanocrystals dispersed in wide-band perovskite-like matrices. - ISSN 1609-1833

<$Eroman CsPbCl sub 3> nanocrystals are obtained in perovskite-like <$Eroman CsBCl sub 3> (B = Sr, Ca, Mg) matrices doped with Pb ions (<$Eroman {C sub Pb } ~=~0,05> and 1 mol. %). The luminescent-kinetic parameters of the <$Eroman CsPbCl sub 3> nanocrystals dispersed in <$Eroman CsBCl sub 3> (B = Sr, Ca, Mg) matrices are studied underthe pulsed UV and X-ray excitation. The conclusion about the formation of <$Eroman CsPbCl sub 3> nanocrystals is confirmed with the data of their luminescence decay kinetics and a short-wavelength shift of the exciton luminescence maximum, when compared to that of an excitonic luminescence in a bulk single <$Eroman CsPbCl sub 3> crystal. Under the pulsed X-ray excitation, re-absorption of core-valence luminescence of <$Eroman CsBCl sub 3> (B = Sr, Ca, Mg) matrices with the <$Eroman CsPbCl sub 3> nanocrystals is registered.

Influence of Ba-Sr Substitution on the Optical Properties of <$Eroman bold {BaB sub 2 O sub 4 }> Single Crystals. - ISSN 1609-1833

The results of studies for the optical transmission spectra, radiation hardness and the refractive indices of <$Eroman Ba sub {1~-~x } roman Sr sub x roman {B sub 2 O sub 4 }> (x = 0,1) single crystals grown with the Czochralsky technique are presented. The investigations have shown that the substitutiveSr impurity improves the technological process of single-crystal growth, though leads simultaneously to worsening the transmittance and the radiation hardness. The assumption about the additional influence of incontrollable Na impurity on the mentioned properties of <$Eroman {Ba sub 0,9 Sr sub 0,1 B sub 2 O sub 4 }> single crystals is made.

Influence of Non-Linear Recording of Thick Hologram on the Effective Value of Modulated Refractive Index. - ISSN 1609-1833

Diffraction of a plane electromagnetic wave falling onto a thick hologram at the first-order Bragg angle at the non-linear recording conditions is analyzed using the coupled-wave equations. It is shown that, under the non-linear conditions, one can use double-wave approximation and the effective values for the modulated refractive index. Analytical dependences of the hologram diffraction efficiency on thickness are obtained. A possibility is revealed for using the effective value of the refractive index for the case of slight deviations from the Bragg angle.

Laser Polarimetry of Birefringence of Architectonics of Biotissues. - ISSN 1609-1833

The features of polarization tomography of optically anisotropic architectonic nets of biotissues (BT) of different morphological structures have been investigated. The peculiarities of phase mapping of skin derma, muscular and bone BT have been experimentally studied. The interrelation between the BT structure and physiological state of BT has been determined. The criteria of early diagnostics of the appearance of degenerative-dystrophic and pathological changes in the structure of BT optically anisotropic architectonics have been revealed.

Polarizable Optical Bistability of Frenkel Excitons. - ISSN 1609-1833

Optical spectra of molecular crystals with two molecules in their elementary cell are investigated. Depending on the polarization angle one or two exciton excitation bands can be realized in the spectrum. The bands are separated by the terminal frequency interval. The exciton absorption bands genesis and the peculiarities of the function of their form at the change of the laser radiation polarization have been analyzed and the regularity of arising bistable states in organic benzol-type crystals has been established.

Generalized fractional Fourier transform in optical systems. - ISSN 1609-1833

We investigate the properties of intensity distribution of the two optical signals, which are shifted and modulated by a plane wave and correspond to the generalized fractional Fourier transform (FFT). The results of analytic and numerical calculations show the possibilities for designing new systems for the processing of information. As an example, the correlator based on the generalized FFT is considered. The domains of the generalized FFT in the practicable optical systems are obtained and analyzed. A principal possibility for the formation and recording of the interference pattern is demonstrated for the case when the images of the FFT, starting from the general form of the cascade matrix, are optically superimposed.

Possible Principles of Optical 3D Tensor Stress Field Tomography . - ISSN 1609-1833

In the present paper the approach for solving the problem of 3D stress tensor field tomography is suggested. It is shown that the stress tensor field tomography can be based on the imaging polarimetry. The problem can be divided into three separate stages. In case of 2D stress distribution, one can easy obtain experimentally the distribution of the difference of stress tensor components (<$Esigma sub 1 ~-~ sigma sub 2>) and the shear component <$Esigma sub 6>. In case of 3D stress distribution, our approach is based on searching equi-stressed surfaces (if such the surfaces are non-closed) with the imaging polarimetry methods and using the rotation of sample in the index-matching liquid. Reconstruction of these surfaces allows one to reconstruct the 3D stress distribution in the sample. When the equi-stressed surfaces are closed, we suggest the cell model of the stressed medium and the approach based on the Jones matrices. We show that solving the system of 6N nonlinear equations of <$E( roman N) sup {1"/"3 }> power with 6N variables (N being the number of cells, into which the stressed sample is divided) requires sample probing by a broad beam in <$E2( roman N) sup {1"/"3 }> different directions.

Hyper-Rayleigh Scattering Characterization of the Movement of Lithium Ions in <$Eroman bold {Li sub 2 B sub 4 O sub 7 }> Crystals .. - ISSN 1609-1833

The integral intensity of hyper-Rayleigh scattering from the bulk of nominally pure ionic conducting <$Eroman {Li sub 2 B sub 4 O sub 7 }> crystals is studied as a function of temperature in the range where a break in the temperature dependence of ionic conductivity expressed in the coordinates ln (<$Esigma sub 33 roman T)> = f (1/T) is observed. Characteristics of jump-diffusive movement of lithium ions are determined. The movement activation energy for the temperatures <$Eroman {T~ symbol У ~400~ roman K}> is estimated from the temperature dependences of hyper-Reyleigh scattering intensity. Its value <$Eroman {E sub am ~=~0,46~eV}> is close to that obtained from the measurements of temperature dependence of the ionic conductivity.

Determination of 2D Stress Distribution in Semiconductor Glass <$Eroman bold {As sub 2 Se sub 3 }> with Infrared Imaging Polarimeter. - ISSN 1609-1833

In this paper the optical polarimetric method for determination of inhomogeneous 2D stress distribution in semiconductor samples is presented. The infrared imaging polarimeter is tested on the example of <$Eroman {As sub 2 Se sub 3 }> semiconductor glass possessing the induced inhomogeneous stresses. The reconstructed distribution of the shear stress tensor component <$Esigma sub 6> and the difference (<$Esigma sub 1 ~-~ sigma sub 2>) of the principal tensor components are in a satisfactory agreement with those predicted theoretically.

The spectroscopy of <$Eroman bold {4SrO~ cdot ~7B sub 2 O sub 3 :RE sup 3+ }> (<$Eroman bold {RE~=~Eu sup 3+ ,~Pr sup 3+ ,~Nd sup 3+ }>) glasses=Спектроскопія стекол <$Eroman bold {4SrO~ cdot ~7B sub 2 O sub 3 :RE sup 3+ }> (<$Eroman bold {RE = Eu sup 3+ ,~Pr sup 3+ ,~Nd sup 3+ }>). - ISSN 1609-1833

In this paper the spectroscopic properties of boron glasses <$Eroman {4SrO~ cdot ~7B sub 2 O sub 3 :RE sup 3+ ~(RE~=~Eu sup 3+,~Pr sup 3+ ,~Nd sup 3+ )}> are described. The transmissions and luminescence spectra are presented. The earlier known absorption bands of <$Eroman {Eu sup 3+ ,~Pr sup 3+ }> and <$Eroman Nd sup 3+> are detected. The luminescence of <$Eroman {4SrO~ cdot ~7B sub 2 O sub 3 :Pr sup 3+ }> (under the laser pumping), <$Eroman {4SrO~ cdot ~7B sub 2 O sub 3 :Eu sup 3+ }> (under the light-emitting diode pumping) is investigated. All the transmissions and luminescence lines are characterized.

Appearance of Optical Vortex at Conical Refraction. Examples of <$Eroman bold {NaNO sub 2 }> and <$Eroman bold {YFeO sub 3 }> Crystals. - ISSN 1609-1833

In the present paper it is shown that effect of conical refraction is accompanied by a generation of vortex due to the existing singularities on the surfaces of phase and group velocities in biaxial crystals. This fact is confirmed experimentally by the studies of conical refraction in <$Eroman YFeO sub 3> and interference patterns in <$Eroman NaNO sub 2> crystals. The angle of external conical refraction in <$Eroman YFeO sub 3> crystals determined by us is equal to <$E4,2 symbol Р>.

Baric Changes in the Optical Indicatrix of TGS Crystals with L-threonine Admixture. - ISSN 1609-1833

The influence of uniaxial mechanical stresses, applied along the principal crystal-physical axes, on the principal values of birefringence Дni is studied for TGS crystals with 5 % L-threonine admixture. It is revealed that <$EDELTA n sub i> are quite sensitive to themechanical stresses. The baric coefficients <$Edel roman {T sub c } "/" del sigma sub { roman m }> for the phase transition temperature appear to be less than those for the pure TGS. Temperature dependences and dispersion of the piezooptic coefficients are calculated. The jump-like changes in all of the piezooptic coefficients occurring at the Curie temperature in the doped crystals are explained with the contributions of a secondary electrooptic effect.

X,T-Phase Diagram of the <$Ebold { roman {Cu sub 6 PS sub 5 J} sub x roman Br sub {(1~-~x) } }> Mixed Crystals. Optical, Dilatation and Ultrasonic Velocity Studies. - ISSN 1609-1833

On the basis of studies of the domain structure and the temperature dependences of thermal expansion and the ultrasonic velocity, the x,T-phase diagram of <$Eroman {Cu sub 6 PS sub 5 I} sub x roman Br sub {1~-~x }> mixed crystals is obtained. It is shown that all the compounds possess the first-order superionic (SI) phase transitions (PTs). Their temperatures are determined with the aid of thermal expansion measurements. The mixed crystals with the concentration <$Ex~=~0~ symbol Ш ~1> possess the second-order structural PTs into a ferroelectric-ferroelastic (FF) phase. In the composition range <$Ex~=~0~ symbol Ш ~0,75>, the temperature of the structural PT slowly decreases and the line of <$ET sub C> crosses the line of <$ET sub S> approximately at x = 0,75 (at heating) and at x = 0,9 (at cooling). Due to a wide temperature hysteresis of <$ET sub S> in therange of <$EDELTA x~=~0,75~-~0,9>, the sequence of PTs should depend on the particular temperature scan process - cooling or heating. In this range of the composition the polycritical point exists, in which the crossed curves of PTs separate the following phases: paraelectric-paraelastic-SI (the symmetry <$E{43} bar m>), paraelectric-paraelastic-nonSI (<$E{43} bar m>), ferroelectric-ferroelastic-SI (m) and ferroelectric-ferroelastic-nonSI (m). The coordinates of the polycritical point are determined as (x;T) = (0,76; 217 K).

Optical properties of <$Eroman bold {SnO sub 2 ~-~As sub 2 Se sub 3 ~-~ZnS(Mn, Cu)~-~Al}> structure with intermediate chalcogenide-glass. - ISSN 1609-1833

Introducing of <$Eroman {As sub 2 Se sub 3 }> as a contrasting intermediate layer into <$Eroman {SnO sub 2 ~-~As sub 2 Se sub 3 ~-~ZnS(Mn,~Cu)~-~Al}> structure allows one to increase 1,5 times the light contrast range of the device that facilitates the perception of symbol-alphabetic information. The bleachingof <$Eroman {As sub 2 Se sub 3 }> film under the action of moisture allows to control the state of the structure air-tightness. The absorption edge of As - Se film and the electrooptical characteristics of <$Eroman {SnO sub 2 ~-~ZnS(Mn,~Cu)~-~Al}> active structure are investigated.