Atomic layer deposition of Al₂0₃ thin films on Si and Si0₂ substrates was investigated in the temperature range of 470- 1030 K. The films grown at 870-1030 K contained crystalline phase while those deposited at temperatures below 870 K were amorphous. The growth rate was 0.03 nm per cycle at 1030 K but it increased with decreasing temperature and reached 0.13 nm per cycle at 470 K. The densities of crystalline films were 3660-3670 kg/m³ while those of amorphous films ranged from 2820 to 3140 kg/m³. The refractive indices of crystalline films (1.75-1.77 at the wavelength of 500 nm) were significantly higher than the refractive indices of amorphous films. A disadvantage of crystalline films compared with amorphous films was somewhat higher surface roughness. Nevertheless, the extinction coefficient of the former films did not exceed 0.004 at the wavelength of 500 nm. Excitation of crystalline films at the wavelengths shorter than 175 nm resulted in a broadband photoluminescence peaking at 350-360 nm. The excitation spectrum indicated dominant excitation of this emission via interband transition. The intrinsic absorption edges of 7.2 and 6.6 eV were estimated for crystalline and amorphous films, respectively, from the long-wavelength edges of the excitation spectra measured at 10 K.

Alkali phosphate, phosphate-silicate, and phosphate-germanate glasses were studied by means of high-temperature acoustics and Rayleigh-Mandelstam-Brillouin (RMBS) and Raman scattering (RS) spectroscopies. Temperature-temporal dependences of the ultrasound velocity in the glass melts were measured at temperatures up to 1550°C. From the RMBS spectra the Landau-Placzek ratio and frequency shifts were found. A theory of the fluctuations fieezing at the cooling of the glass melt was applied to separate the contributions of the frozen-in density and concentration fluctuations to the Rayleigh scattering losses. A comparison was drawn with the losses in silica glass. The RS spectra allowed the identification of the constant-stoichiometry groups. The feasibility of the system xNa₂O-(40 - x)K₂0-30Al₂0₃-30P₂0₅ for the fabrication of low-scattering glasses was ascertained.

The structural microinhomogeneity of EuF₃ doped fluorophosphate glasses is studied to elucidate the influence of the Eu³⁺ ion environment on Rayleigh scattering. The measurements of Rayleigh and Mandelstam-Brillouin scattering, small-angle x-ray scattering, y-ray induced optical absorption, and fluorescence are used. It is shown that the introduction of Eu³⁺ ions into fluorophosphate glass with a small amount of phosphate decreases the Landau-Placzek ratio. Based on the analysis of the optical absorption and x-ray scattering spectra, the grouping of the Eu³⁺ ions with the phosphate groups is demonstrated. Applying the capture volume model, the maximum concentration of the Eu³⁺ ions in the phosphate environment is estimated to be 1.05x10¹⁸cm^-3. It is found that the capture volumes of the Eu³⁺ located in the phosphate and mixed environment differ by two orders of magnitude, which approves the discussion in terms of the doped ion segregation.

Manifestation of relaxor properties in the xPbZn_1/3Nb_2/3O₃-(1-x)PbSc_1/2Nb_1/20₃ ceramic solid solution system, similar to those observed in lead magnesium niobates, are reported. Dependence of the effective dielectric permittivity and dielectric loss on the temperature at frequencies of 0.1-10 Hz and different measuring field amplitudes E₀ are examined ceramic samples of 0.05PbZn_1/3Nb_2/3O₃-0.95PbSc_1/2Nb_1/20₃. It is demonstrated that the temperature at which the dielectric permittivity has a maximum, T_m, decreases with the increase of E₀. The dependence of T_m on the frequency in both strong and weak fields is shown to follow the Vogel-Fulcher law, with Voger-Fulcher temperature decreasing with the increase of E₀. The results of the dielectric studies in the xPbZn_1/3Nb_2/3O₃-(1-x)PbSc_1/2Nb_1/20₃ system are discussed in terms of the transition from the paraelectric to ferroelectric phase through the relaxor and glass states.

The cost-effective spray pyrolysis technique was applied to prepare ZnS thin films for large-scale applications. Aqueous solutions containing ZnCl₂ and SC(NH₂)₂ were deposited onto glass and n-type Si(100) substrates at 430-600°C. The structure and phase composition were studied by XRD and FTIR, the surface morphology by SEM. The optical properties were determined from the transmittance and reflectance measurements in the UV-visible and near-IR regions. The phase composition, crystallinity, and surface morphology of the films could be controlled by the Zn:S molar ratio in the stock solution and the deposition temperature. Highly (001) oriented ZnS films with wurtzite structure were grown at temperatures above 500°C using the Zn:S molar ratio 1:2 in the solution. The sprayed films had high optical transmittance in a wide spectral range and the refractive index of up to 1.9 at 632.8 nm. It was also found that the sprayed ZnS films are capable of being used as antireflection coatings in Si-based devices.

The optical properties of as-grown and electron-irradiated α-Al₂0₃ (corundum) single crystals were investigated at low temperatures, using vacuum-W (VUV) time-resolved luminescence spectroscopy under the synchrotron radiation excitation. It has been shown that in the electron-irradiated crystals the excitation of self-shrunk exciton emission extends to the region of interband transitions. The decay time of the 7.6-eV emission of the self-shrunk excitons in as-grown crystals was found to be about 7 and 23.8 ns respectively for the excitations in the excitonic band and at energies at which several electron-hole pairs are generated. In the irradiated crystals, these lifetimes were by about 2 ns longer than in the as-grown ones. For both crystal states, the nature and dynamics of the electronic excitations are discussed.

Precursor powders for yttrium gallium garnet (Y₃Ga₅O₁₂, YGG) were prepared by a simple sol-gel method based on the formation of metal chelates in aqueous solvents. A systematic study of sol-gel technique synthesized YGG samples is presented using different complexing agents. Six high-purity organic substances were used as complexing agents, namely, tartaric acid, 1,2-ethanediol, citric acid, ethylene diamine tetra-acetic acid (EDTA), malonic acid, and oxalic acid. These agents were found to influence the characteristics of the end products, in particular their homogeneity. The phase purity, composition, and microstructure of the polycrystalline samples were studied by thermoanalytical methods (TGADTA), x-ray diffraction (XRD) analysis, IR spectroscopy, and scanning electron microscopy (SEM). From the typical XRD patterns of different synthesis products it is concluded that only the use tartaric acid, 1,2-ethanediol, citric acid, and EDTA yields a single YGG phase.

The objective of the present work is to investigate the thermo-optical (TO) properties of the relaxor-type ferroelectric sodium-bismuth titanate (SBT) single crystals as a function of temperature, using the thermal lens and optical second harmonic generation (SHG) techniques with the emphasis on the TO response near the phase transitions (PT). Symmetry-forbidden SHG signals above 538 K in the [00l] cut SBT crystal are detected. The signals are related to the coexistence of the tetragonal and rhombohedral phases. Heating of the uniaxial strain poled SBT crystal revealed remarkable changes of the TO signal near the successive PT.

Processes of various intrinsic and impurity luminescence excitation by 4-32 eV photons or 18 and 300 keV electrons have been studied in pure and doped BaMgAl₁₀O₁₇ (BAM) and SrMgAl₁₀O₁₇ (SAM) phosphors at 6-300 K. In BAM:Eu (l0%), the quantum yield of Eu²⁺ center emission is QY = 1 in the region of exciting photon energies of hν_ec = 7-12 eV, the value of QY reaches 2 at 14-21 eV and sharply increases at hν_ec = 22-32 eV, where secondary electron-hole pairs are created by hot conduction electrons. The processes connected with the rise of QY for various types of emission in the region of 14-21 eV have been thoroughly studied for BAM and SAM phosphors. It has been suggested that such exciting photons cause the ionization of oxygen ions and form hot valence holes, the energy of which is partially used for the excitation of Eu²⁺ ions ->(4f⁷->4f⁶5d¹ transitions) due to nonradiative Auger transitions. The intensity of the Eu²⁺ emission increases after a single nanosecond electron pulse with a rise time of 50-150 ns. This rise is connected with the energy transfer from spinel blocks to Eu²⁺ ions located at cation planes of the β-alumina-type materials.

The limits of the hardening, and the effects of ion-induced internal and long-range stresses in LiF crystals irradiated with Bi, Ni, Kr, and S ions, having a specific energy of the order of 10 MeV/u and the fluence up to 10¹³cm^-2, are studied. A considerable hardness increase, bending of the crystals, formation of dislocations in distant nonirradiated parts of the crystals, and initiation of fracturing under the high-fluence irradiation are observed. It is shown that the irradiation with heavy ions (Bi) gives rise to dislocations and work hardening mainly in the region adjacent to the irradiated one. In the case of lighter ions (Ni and S), the work hardening takes place also inside the irradiated zone. The heavy ions that cause a severe track core damage generally induce a higher stress.

The recovery of optical and mechanical properties of LiF crystals irradiated with 790 MeV ⁷⁸Kr and 640 MeV ⁵⁸Ni ions at 10^l2 ions/cm² under annealing at temperatures up to 810 K is investigated. The optical absorbance and depth profiles of hardness before and after annealing were measured. A marked recovery of hardness and change in the optical absorption spectra were observed at temperatures above 520-530 K. An activation energy of 0.15±0.02eV, which is close to that for the thermal migration of H centers, is obtained from the annealing data. The results indicate a significant role of the H-center aggregates in the hardening and annealing processes. The maximum hardening is created and thermally most resistant defects are located around the Bragg maximum, where the threshold energy loss of about 10 keV/nm for track core damage is reached.

Irradiating nitrogen doped 6H-SiC(000l) crystals with a focused beam of an N₂ pulse laser, we could form discrete circularly placed nanohills on their surface. The necessary light intensities were close to the ablation threshold. The evidence was obtained by atomic force microscopy and photoluminescence. The measurements demonstrated that in the area acted upon, the surface morphology and the nitrogen concentration depended on the irradiation dose. Supplementary data was obtained from the numerical modeling of the temporal depth dependence of the temperature in SiC in response to an N₂ laser pulse. The appearance of the nanohills is accounted for by a temperature-gradient gathering of nitrogen into the subsurface focal area and by a rapid surface vaporization. The former process leads, via the melting point decrease, to a local area melting, and the latter, via the surface temperature decrease, to the capping of the melt with a thin solid lid. The interplay between the pressures exerted by the light and the liquid ends in a lid-peripheral extrusion of a portion of the liquid and formation of the nanohills. The whole process proceeds in a clearly distinguishable and repeatable two-stage mode.

Influence of radiation defects on the optical absorption spectrum of nickel oxide (NiO) was studied at 6 K in the near-IR energy range of 7750-8300 cm^-1 corresponding to the magnetic-dipole transition ³A_2g(F)->³T_2g(F) at nickel sites. NiO single crystals grown by the method of chemical transport reactions on the MgO(100) substrates were irradiated by the neutron fluences up to 5x10¹⁸ cm^-2. Two sharp lines were observed at the low-energy side of the band: the peak at 7805 cm^-1 is assigned to the pure exciton transition, whereas the peak at 7845 cm^-1, to the exciton-magnon excitation that occurs at the Brillouin zone-center (BZC). An increase of the defect concentration at higher fluences results in the lowering of the magnon-satellite-peak intensity. The long-wavelength BZC magnon absorption is sensitive to the long- range magnetic ordering, which becomes destroyed in the presence of the radiation defects. Therefore, the observed decrease of the peak intensity is attributed to the decrease of the spin-spin correlation length due to inhomogeneous broadening.

Raman spectroscopy (RS), x-ray dimaction (XRD), and reflection high-energy electron diffraction (RHEED) were applied for a structural analysis of ZrO₂ and HfO₂ thin films grown on Si substrates by chloride atomic layer deposition (ALD). The RS measurements were performed on freestanding ZrO₂ and HfO₂ films. In these conditions, high-quality micro-Raman spectra of 100-660-nm-thick films were obtained in the whole range of interest, 80-800cm^-1. The structural data determined by RS were complemented by the XRD and RHEED data. As a result, it has been ascertained that at the initial stage of the ALD growth of ZrO₂ and HfO₂ films at 500 and 600 °C, respectively, metastable phases form and dominate. In the case of ZrO₂ films, this phase has been identified as the tetragonal polymorph. Over the film thickness range of 56-660 nm, the absolute amount of the tetragonal ZrO₂ has been shown to be almost constant, with its relative amount decreasing and the amount of the monoclinic phase increasing when the film thickness increases. Neither RS nor XRD allowed any unambiguous identification of the metastable phase in the otherwise monoclinic HfO₂ films. According to the RHEED data, at the very initial stage of the HfO₂ growth, cubic HfO₂ is present.

Photoluminescence (PL) of TiO₂:Sm³⁺ thin films was studied at RT. The films were prepared by the sol-gel spin-coating technique or by atomic layer deposition (ALD) followed by ion implantation. The PL was excited with a Nd:YAG pulse laser emitting at 355 nm. The spectrum of PL consists of intense Sm³⁺-specific emission lines with a well-pronounced fine structure. The influence of different gaseous environments (air, oxygen, nitrogen) or vacuum on the Sm³⁺ emission was investigated. In the case of a permanent irradiation of sol-gel films in an oxygen-containing environment, the PL intensity increased. The increase was significantly large but slow. The subsequent evacuation of the measurement chamber led to a rapid decrease of the emission below the detection limit. When the oxygen-containing gas was without any intermediate evacuation replaced by nitrogen, the PL intensity descended to an almost vacuum level. The subsequent exposure to oxygen led to a rather fast emission recovery. The ALD-prepared films exhibited a similar but markedly slower response. The fast response observed was attributed to the adsorption of oxygen on the surface, and the slower one, to the diffusion of oxygen vacancies taking place under the irradiation in the bulk.

Fluoride crystals with the perovskite structure doped with rare-earth ions and other activators are interesting materials for laser hosts, scintillators, and detectors of ionizing radiation. Therefore, an actual task is to clarify the structure of the radiation-induced defects and recombination processes in these crystals. Compared to other fluoroperovskites, considerably less information is available concerning to the radiation-induced processes in the CsCdF₃ crystals. We present a study of photostimulated luminescence (PSL) in the previously x-irradiated CsCdF₃ crystal doped with Mn (0.05%). After the x-irradiation of the crystal, optical stimulation at 320 nm leads to the appearance of 300- and 550-nm luminescence bands. Previous studies of the fluoride crystals doped with Mn²⁺-like ions let us ascribe the luminescence at 550 nm to the Mn²⁺ luminescence. Analysis of the temperature dependence, spectral position, and stimulation spectrum of the PSL band at 300 nm allows us to suggest that it appears because of the electron recombination with self- trapped holes. According to the Mollwo-Ivey relation for halide crystals the stimulation band at 325 nm seems to be F- type center absorption band.

The iron-containing silica films on Si substrates were prepared by sol-gel technique from precursors composed of tetraethoxysilane (TEOS) solution in ethanol and FeCl₃ water solution. The colloid solutions were deposited by spinning on cleaned Si substrates and annealed in air, Ar, or H₂ atmosphere. The samples were characterized by optical parameters determined using spectroscopic ellipsometry (1-5 eV) and magnetic properties by measuring the temperature (4-300 K) and field (up to 50 kOe) dependences of magnetic moment. The physical properties were correlated with sample structure, which has been examined by atomic force microscope (AFM) and scanning electron microscope (SEM).

Atomic layer deposition (ALD) of SnO₂ thin films from SnI₄ and either H₂O₂ or O₂ on the α-Al₂0₃(1 ₁^- 2) substrates is studied. Reactor temperature is varied from 100 to 750 °C. X-ray diffaction, x-ray reflection, x-ray fluorescence, x-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and UV-visible spectroscopy are used to obtain the growth and structural data. The SnI₄-H₂0₂ precursor pair brings forth the film growth even at temperatures as low as 100°C with a wholly amorphous outcome up to 150°C. For the pair SnI₄-0₂, the films grown nearby the process initiation temperature of 400°C are also amorphous. When the temperature is raised respectively above 250 and 500°C, both pairs make epitaxial growth happen, generally in three-dimensional mode. Exceptionally, in a limited range of grown thicknesses in the proximity of 50 nm, the growth from SnI₄ and O₂ at 750°C appears to be driven by the predominantly two-dimensional nucleation, as the films grow extremely flat. The SnI₄-0₂ precursor pair gives at 600- 750°C the highest growth per cycle of about 0.085 nm. The epitaxially grown tetragonal (cassiterite) films are (1 0 1)- oriented. The iodine contamination in them is below 0.1%. All the film-substrate structures are highly transparent in the visible region.

A novel Laponite-lithium iodate nanocomposite has been synthesized for nonlinear optical applications. The elaboration starts with the addition of a lithium iodate aqueous solution to a colloidal suspension of Laponite JS. Thin layers, elaborated using the dip-coating technique, form waveguides and the linear dependence between the lithium iodate concentration and the refractive index and the control over the thickness allow one to optimize waveguiding properties. Waveguides show an attenuation of about 2 dB/cm and easily detectable second harmonic generation. For the nonlinear effective coefficient a value of 1.6 pm/V has been measured. X-ray structural characterization shows that after drying and heat-treatment between 150 and 200°C, lithium iodate crystallizes in the matrix with the crystallite size ranging from 20 to 50 nm. Due to the natural dipole moment of lithium iodate, the orientation of nanocrystals could be controlled using external electric field. The influence of the orientation on the nonlinear optical properties has been determined and compared with the simulations based on a matrix model considering the nanocomposite as a stack of linear and nonlinear 1D layers with fixed or random orientation. A good agreement is achieved between the experiment and the simulation.

We describe the synthesis of two-dimensional {[Mn^IICr^III(C₂O₄)₃]C} bimetallic networks that include as template cations C stilbazolium salts 4-[4-(N,N-dimethylamino)-α-styryl]-N-alkylpyridinium with alkyl = methyl (DAMS), 4-[4-methoxy- α-styryll-N-isopentylpyridinium (MIPS), and DAZOP, which is a DAMS analogue with the central [C=C] core replaced by an azo N=N] moiety. These networks are obtained in their optically active forms, using the resolved - or Λ- [Cr^III(C₂0₄)₃]^3- anionic bricks as chiral-inducing reagents. The UV-visible properties of the networks and their natural circular dichroism (Cotton effects) demonstrate that the MIPS, DAZOP, and DAMS become chiral in [Mn^IICr^III (C₂0₄)₃]^- anionic matrices. The absolute configurations of the template cations inside the anionic framework depend on the configuration of the starting anionic reagent.

An essential factor for the creation of oxygen sensors based on luminescence quenching is the long-term stability of the parameters determining the luminescence decay. In the present work, the effects of material aging and photobleaching on decay parameters are studied for Pd-tetraphenylporphyrin and Pd-pentafluoro-tetraphenylporphyrin molecules embedded into different polymer films. In polymethylmethacrylate host the decay was well described by stretched exponent function. During annealing of PMMA films at different temperatures between 20 and 70 °C during 9 months a logarithmic decrease of the material sensitivity occurred due to the physical aging of the polymer. The photostability studies of PMMA films showed an opposite effect: the photobleaching was accompanied by a decrease in natural decay time, whereas the oxygen sensitivity remained practically constant. Luminescence quenching in polystyrene and polycarbonate films had different character as compared to PMMA, and was interpreted with a two-site model, combined with a nonlinear gas transport model. In these polymer hosts the oxygen sensitivity increased during the first stage of aging, which was ascribed to the changes in the Langmuir component of gas transport, i.e., to the evaluation of microvoids in these glassy polymers.

Electroabsorption (EA) or Stark effect spectroscopy is a widely used method for characterizing the dopant molecules in polymer films and the films themselves. In this method the spectrum of a small (~0.1%) absorbance change induced by a strong (~1 MV/cm) electric field is measured. Analysis of the spectra provides information about the change in dipole moment and the change in polarizability accompanying an electronic transition. We measured near-UV absorption and EA spectra of indole-doped poly (methy1 methacrylate) (PMMA) film prepared by a spin coating method. In the normal-incidence EA spectrum a negative contribution, being proportional to the absorption, was observed. In the case of magic angle between the electric vectors of the absorbed light and the applied field this contribution disappeared. These observations have been explained by field-induced orientation/alignment of the ensemble of polar indole molecules. Since the ground state dipole of indole is nearly parallel with the transition dipole, the absorption rate of light, which is polarized perpendicularly to the applied field, should be smaller. Our study demonstrated that the angular movement of indole-sized molecules in PMMA at room temperature is hindered, but not stopped.

A humidity sensitive membrane with a good linearity and sensitivity was fabricated. Its moisture sensitivity is based on the hyperchromic effect and the hypsochromic shift in the absorption spectrum of poly(methy1 methacrylate) (PMMA) doped with a solvatochromic Reichardt's betaine dye. A 20-μm-thick self-standing film exhibited a good linearity in the absorbance dependence on the humidity at the wavelength of 667 nm and the humidity level sensitivity to within 0.002%. The membrane had similar reaction rates for the sorption and desorption of moisture without any hysteresis. The conventional dual-mode gas sorption model is applicable to describe water dynamics in glassy PMMA. From the analysis of the temperature dependent sorption data, the activation energy of the diffusion coefficient ΔE = 53 kJ/mol and the enthalpy of the water sorption in PMMA ΔH_s = 22 kJ/mol have been estimated.

During the last years, there has been an increasing interest in the photoinduced switching effects. Among the objects of concern azobenzene derivatives, isomerizing under UV and visible light, occupy a prominent position. To understand the photoresponse of these materials in the condensed phase, their spectroscopic and electrical properties are studied. It is shown that the photoresponse depends on the orientation of the molecules and their packing. A number of novel azobenzene derivatives containing a N,N-dicyclohexyl sulfonamide moiety is synthesized. The derivatives differ in the length of alkyl chains between the azobenzene moiety and SH or COOH groups. The morphology and the photoinduced switching of the surface potential of the self-assembled monolayers and Langmuir-Blodgett multilayers are investigated.

Many organic compounds in solid state have nonlinear optical properties due to the orientation of the molecules in a polymer matrix. In this work, all-optical poling and second harmonic generation in a composition consisting of 1 mass% of N,N-dimethylaminobenzylidene 1,3-indandione (DMABI) compound in poly(methyl methacrylate) (PMMA) matrix were studied. Thin films were prepared by solvent casting. The 1.064-μm fundamental and 532-nm second harmonic wavelengths of a Nd:YAG laser were used. It is shown that DMABI molecules can be oriented by the method of all- optical poling, and that the process is related to the photoinduced switching between two equally stable states of the molecule.

We study an optical transition in a center with strongly reduced local elastic springs in the excited electronic state. In this case the transition takes place to the vicinity of a flat minimum of the potential energy in the configurational coordinate space. The existence of such a minimum results in the resonant increase of the local density of states of low-frequency phonons, i.e., in the appearance of the resonant (pseudo-local) mode of a low frequency in the excited state. Existence of such a mode in this state means that the strong mode mixing takes place at the transition. To take this effect into account, we apply an operator transform method (V. Hizhnyakov, J. Phys. C, 20,6073, 1987). We find that if a parameter of the quadratic vibronic coupling is close to its critical value, corresponding to the dynamical instability of the excited state, then the zero-phonon line is practically absent in the spectrum and the long-wave part of the phonon sideband is strongly enhanced, resulting in formation of so-called lambda-shaped absorption spectrum. The measurements of the optical spectra of this type have been reported in the literature.

The spontaneous emission rate (SER) of a single impurity molecule for the electric dipole transition has been found in the case where the birefringence of a host crystal is taken into account. SER depends on the orientation of the dipole moment with respect to the principal axes of the dielectric (permittivity) tensor of the host crystal and on the principal refractive indices of the crystal. We use the model where the average electromagnetic field in the crystal is classical and effective electric field vectors at the site of the impurity molecule are found for the interstitial impurity which is located in the center of the crystal cell. The results of calculations for seven biaxial host crystals (anthracene, chrysene, diphenyl, fluorine, naphthalene, phenanthrene, terphenyl) are presented. It is shown that values of SER form in the space a three- axial ellipsoid. Differences in the values of SER for the electric dipole transition in the same host crystal are up to 34%.

Persistent spectral hole burning (PSHB) has remarkable applications in optical data storage and processing, including space-frequency and space-time domain holographies. Experiments have proven practically everything predicted and proposed by theory. The bottleneck between laboratory experiments and commercial applications is the need in low (liquid He) temperatures, as the main parameter of the data storage efficiency-the ratio between the inhomogeneous and homogeneous zero-phonon line (ZPL) widths α(T) = Γ_inh/Γ_hom(T)-- decreases owing to the rapid increase of Γ_hom(T) with temperature. A few optical and Mossbauer ZPLs are narrow even at RT, but they have usually also narrow Γ_inh. It is proposed to enlarge Γ_inh by making use of the Doppler effect. Two possible manifestations of the Doppler effect in the Universe are also discussed.

The positions of atoms in glasses or nanocrystals deviate from those in a perfect crystal. At a distance exceeding the equilibrium value merely by 11%, the second derivative of a Lennard-Jones 6-12 potential is reduced to zero, causing the intermolecular force constant to vanish. This circumstance can explain, qualitatively, the softening and localization of phonons in disordered solids in the presence of free volume. Large density of localized, low frequency vibrations is responsible for well-known anomalies in thermal, acoustic, and spectral properties of glasses. Optical transitions in impurity centers can serve as sensitive probes for the disorder and dynamics of solids. The frequency-dependent, temperature- or pressure-induced shifts of zero-phonon lines can be expressed in terms of the first two derivatives of Lennard-Jones potentials of the ground state and the excited state. The applicability of the pair potential model is illustrated for spectral hole burning in the inhomogeneous spectra of pigments in polymer host matrices.

Ternary semiconductor compound CuInSe₂ is one of the most promising absorber material used in solar cells. In this study, we used CuInSe₂ powder materials synthesized in molten salts. Modifying the preparation conditions, we studied the relationships between the initial and final composition, and determined the preparation conditions for the single- phase growth of CuInSe₂. The as-grown samples were annealed in selenium or sulfur vapor at various temperatures for a different time period to change the CuInSe₂ material properties. Se vapor treatment has been found to influence the bulk composition. Sulfur vapor treatment has been found to improve the open-circuit voltage of the completed cells by about 100 mV. It could be attributed to an increase of the band gap at the surface of the absorber due to the formation of a wider band gap CuIn(S,Se)₂ material. The incorporation of sulfur into CuInSe₂ reduces the carrier recombination in the interface region, which was indicated as an improvement of the fill factor of the cells.

Hybrid solar cells based on a combination of conductive polymer poly (3,4-ethylenedioxyth1ophene) (PEDOT) doped with polystyrenesulfonate (PSS) and inorganic semiconductor CuIn(S,Se)₂ (CISSe) were investigated. The CuInSe₂ (CISe) absorber layers were electrodeposited on IT0 covered glasses from aqueous solutions with various ratios of elements. The ITO/In(O,S)/CISSe photovoltaic (PV) junctions were prepared by the sulfurization of ITO/CISe precursors at 450 °C in the H₂S atmosphere. A PEDOT-PSS layer of p-type is considered as an alternative for the traditional window top layer on the CISSe absorber layer in the cell structure. The polymer deposition was performed using spin-casting technique. The PV properties of the prepared ITO/In(O,S)/CISSe and ITO/In(O,S)/CISSe/PEDOT- PSS structures were investigated, with special attention paid to the role of the conductive polymer layer in the cell structure.

Ternary chalcopyrite semiconductor CuInSe₂ (CIS) is a promising material for the fabrication of high-efficiency low-cost solar cells. However, various recombination losses decrease the efficiency of the cells and deteriorate their other characteristics. To identify the recombination channels and to obtain information about the related defects, we conducted current-voltage measurements at various temperatures, followed by admittance spectroscopy measurements and bias dependent quantum efficiency measurements. Two types of solar cells were studied: the ones based on the CIS monograin layers, and the others based on CuInGaSe₂ thin films. The temperature dependence of the open-circuit voltage of the monograin cells demonstrated that the dominant recombination channel involves CIS-CdS interface states. According to the admittance spectroscopy data, the states lie at 150-166 meV below the conduction band of CIS. In some samples, a defect state at about 45 meV was observed. The quantum efficiency measurements revealed the influence of the sulphur post-treatment on the band gap of the absorber material. The derivative curves brought out the influence in the best possible way.

In the Department of Materials Science of the Tallinn University of Technology, an EU project with the same title as the present communication is carried out. The aim of this paper is to summarize the results of the research and development of the different materials and polycrystalline solar cells obtained within the project. The topics addressed are: photoluminescence of different ternary compounds, thin films and thin film structures by different chemical methods, photovoltaic structures based on electrically conductive polymers and copper-indium-chalcogenide materials, monograin powders with a tailored composition and structure, and the technology of monograin layer solar cells.

This paper presents the state of the art of photovoltaics in the new member and candidate states of the European Union, namely, Bulgaria, the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania, the Slovak Republic, and Slovenia. A brief survey of the research, including its organization and potentials, and the development, industry, markets, demonstration installations, education, policies, support mechanisms, barriers, challenges, and needs is given.

We measured the photoreflectance (PR) and wavelength-modulated differential surface photovoltage (DSPV) spectra of δ-doped GaAs/AlAs multiple quantum wells (MQW) with different well widths and doping levels. We demonstrated that PR and DSPV are powerful contactless tools for the characterization of MQW structures. We observed Franz-Keldysh oscillations in the PR spectra, which enabled us to determine the built-in electric fields in the GaAs/AlAs MQW structures. As it turned out, in the GaAs buffedcap layers the field strength is in the range of 18-20 kV/cm. It was found that a buried interface rather than the structure surface very probably governs the SPV effect. Sharp features associated with excitonic optical transitions were revealed in both, PR and DSPV spectra. From the line shape analysis of the modulation spectra, we estimated optical transition energies and broadening parameters. The energy levels and interband transition energies calculated by the transfer matrix method are in good agreement with the experimental values. The influence of the doping on the broadening of exciton resonances was observed and investigated.

Quantum-dot Si/Ge superlattice structures with the Ge amount slightly above the critical for island formation are prepared by molecular beam epitaxy. The structures grown under optimized conditions are defect-free. Their structural and optical properties are described. A significant increase in the RT luminescence efficiency is obtained by adjusting such parameters as the growth temperature, growth rate of Ge, the number of the Ge quantum-dot sheets, their thickness, the level of Sb doping at specific planes, and the thickness of Si spacers. An intensive RT electroluminescence from the structures in the fiber optic communications 1.6-μm range is demonstrated. The approach opens new routes to the fabrication of Si-based RT light emitters.

GaAs nanowhiskers are grown by molecular beam epitaxy (MBE) on the GaAs(111)B surface activated by Au at different conditions (Au layer thickness, GaAs flux, substrate temperature, effective thickness of deposited GaAs) and characterized by scanning electron microscopy technique. The dependence of the nanowhisker height on the size of Au- GaAs alloy drops is investigated. A kinetic model of nanowhiskers formation in the vapor-liquid-solid growth mechanism is proposed. In particular, the nanowhiskers growth rate is found as a function of the drop size, system energetics, and MBE growth conditions. The predictions of a theoretical model are compared to the results of experimental observations. It is demonstrated that the MBE method enables one to fabricate nanowhiskers ensembles with tunable structural properties (height, lateral size distribution, surface density) by changing the Au layer thickness, the amount of deposited GaAs, and MBE growth conditions.

Solid-state broadband lasers emitting in the 2-4 μm region are of interest for a variety of applications. However, conventional lasers for these wavelengths have limitations, such as the complexity and cryogenic operation. Recently, alternative materials for the mid-IR lasers--Cr²⁺-doped II-VI chalcogenide crystals-have been proposed. The RT mid- IR absorption in these crystals is due to the effective Cr²⁺ intracenter transitions. We present the results of an investigation of the Cr²⁺ crystals. The crystals were grown from the CdSe source by seeded physical vapor transport in the helium atmosphere with a wafer of CdSe_xS_1-x as a seed. A CrSe source was used for the growth-time doping. The changing sulfur content along the growth axis was determined by energy dispersive x-ray microanalysis. An absorption peak in the IR range of 1.5-2.2 μm due to the Cr²⁺ intracenter transition ⁵T₂->⁵E of ions was revealed. The maximum peak absorption was determined to be 4.5 cm^-1. The concentration of the ²⁺ ions in the samples calculated from the IR absorption was found to vary fkom 1x10¹⁷ to 3x10¹⁸ cm^-3. With the sulfur content, the intracenter absorption peak shifts to shorter wavelengths.

Electrical and optical low frequency noise characteristics of different quality InGaAsP Fabry-Perot and distributed feedback buried-heterostructure 1.55-μm laser diodes with the multiple-quantum-well active region are investigated keeping in view the use of the peculiarities of the characteristics for the assessment of the quality and reliability of LDs. The noise characteristics are shown to give the most informative result when measured at the threshold. In parallel to the noise measurements the current-voltage characteristics are measured and analyzed. In the use of this combination an alternative to the reliability tests by accelerated aging is seen. The mode hopping effect exhibited by the Fabry-Perot laser diodes is suppressed by the facet coating with an antireflection layer.

Dynamic characteristics of partly gain-coupled multiple-quantum-well InGaAsP distributed feedback laser diodes (LD) have been investigated. Relative intensity noise measurements were done and key dynamic parameters (differential gain, K-factor) were estimated. From time-resolved frequency chirp measurements, the chirp components and the chirp parameter were extracted. Several tens of devices were characterized. Although all the devices were of the same structure and dimension, their dynamic parameters were spread in values. It is believed, that the spread is due to the limited device processing accuracy. The correlation between the dynamic parameters was observed. The K-factor and differential lifetime were found to be correlated mutually and with the differential gain, which indicates that the latter plays an essential role in determining the variance of dynamic parameters. It was shown that the increase of the coupling coefficient results not only in both the oscillation and damping frequency increase, but also in the decrease of the amplitude of the time-resolved frequency chirp oscillation. LDs were subjected to the accelerated aging by applying at 100 °C the 150-mA bias for 1800 h. The degradation of the threshold current, the efficiency, and the amplitude ,of the time-resolved frequency chirp oscillation was observed.

Quantum dot (QD) diode lasers attract currently much attention due to their ability to emit light in the advanced near- infrared region at extraordinarily low threshold current densities. A vertical-cavity surface emitting laser (VCSEL), having a superior beam quality, improved temperature stability, low threshold current, and cost-effective planar fabrication, is also an attractive device variant. Here we discuss the state of the art of these lasers intended for the use in 1.3-μm fiber-optic communications. The discussion is centered on an InAs/GaAs semiconductor QD system. Basic issues of the QD synthesis in the system are addressed. The achievement of the control over the 1.3-μm QD emission is demonstrated. Both, wide-stripe and single-mode edge-emitting lasers are described. The lasers designed have a very low threshold current density, high differential efficiency, and a high output power. Narrow-stripe 1.3-μm QD lasers generate in a single mode, have a record-low threshold current, and produce the continuous-wave (CW) power output in excess of 100 mW. Also, we report on QD VCSELs emitting at 1.3 μm. The design of their cavity and active region are described. The room-temperature CW output power of these lasers is as high as 2 mW. Both, the edge- and surface-emitting lasers satisfy the demands of the fiber optical communication technology.

Recent achievements in self-organized quantum dots (QDs) have demonstrated their potential for long-wavelength laser applications. However, the wavelength of QD structures pseudomorphically grown on GaAs substrate is typically not longer than 1.3 μm. In this work we study a novel approach for extension of the spectral range of GaAs-based diode lasers up to 1.5 μm. We use a sensitivity of QD emission to the band gap energy of surrounding matrix. The method is based on formation of a QD array inside a metamorphic InGaAs epilayer. Growth regimes of metamorphic buffer that enable mirror-like surface morphology in combination with effective dislocation trapping are discussed. Structural and optical properties of metamorphic InAs/InGaAs QDs are presented. It is shown that the wavelength of QD emission can be controllably tuned in the 1.37-1.58 μm range by varying the composition of metamorphic InGaAs matrix. Details of formation, fabrication, and characterization of metamorphic-based diode lasers are also presented. We demonstrate a lasing wavelength as long as 1.48 μm in the 20-80 °C temperature interval. The minimum threshold current density is 800 A/cm² at RT. The external differential efficiency and pulsed power maximum exceed 50% and 7 W, respectively.

The reflection of s- or p-polarized electromagnetic plane waves from an N-layer system of inhomogeneous ultrathin dielectric films in the vicinity of the classical Brewster angle is investigated analytically in the long-wavelength limit. The second-order approximate formulas for principal and polarizing angles are derived and their accuracy is estimated by using exact numerical methods for calculating the reflection characteristics of inhomogeneous films. It is shown that expressions obtained for characteristic reflection angles are of immediate interest to the solution of the inverse problem for nanoscopic-layered structures. A few novel straightforward methods for optical diagnostics of ultrathin layers are established.

Thermochromic laminated glazing (TLG) aids in reducing the energy needs of a building and providing indoor comfort. The polymeric interlayer of TLG is doped with transition metal (Fe, Cr, W, etc.) complexes, which change their coordination and the transmission or color of TLG under the influence of light and heat fluxes. At present we have conversions from light gray or brown to dark gray or brown and from rosy or yellow to blue or green at our disposal. TLG is able to sense changes in the light and adjust accordingly. It can block out the sunlight during the brightest parts of the day or capitalize on the available light during overcast days. As evaluated on the basis of tests, TLG has a good UV stability. It offers practical benefits of a low cost and easy fabrication. No electrical or any other driving power is needed to operate TLG. The energy modeling of the heat transfer in ventilated facades showed that TLG can provide a 15-30% decrease of the building energy consumption during the winter heating time in the climatic conditions of some regions in Russia. During the summer season the reduction of the solar energy gain reaches 30-40%; this is enough to give up air- cooling systems altogether.

Semiconductor p-n and metal-insulator-semiconductor structures containing a capacitive element were investigated under pulsed ir laser irradiation. It is shown that the carrier heating in the structures is responsible for the rise of the photosignal. A direct correlation between the photosignal and the capacitance of the structures is confirmed. Possible applications of the effect are discussed.

We discuss a number of aspects of a novel flexible electrochromic foil capable of varying its optical transmittance. The foil includes thin films of tungsten oxide and nickel oxide laminated together by a polymer electrolyte. Starting with scientific issues, we discuss the dominating defects in amorphous tungsten oxide and how they may yield a consistent picture of the optical properties of tungsten oxide films versus nonstoichiometry and ion intercalation. We also present a detailed model for the coloration/bleaching due to proton extraction/insertion in thin surface sheaths of nanocrystallites of nickel oxide. Next we consider aspects of technology and treat options to enhance the bleached-state transmittance by mixing the nickel oxide with another oxide having a wide band gap. We also cover pre-assembly charge insertion/extraction by facile gas treatments of the films as well as practical device manufacturing. The final part of the paper deals with a number of applications, with emphasis on architectural "smart windows" which can improve indoor comfort at the same time as they accomplish significant energy savings due to lowered requirements for air cooling. Applications concerning electrochromics-based eyewear are introduced; these may be approaching market introduction.

The work of a MEMS-technology compatible thin-film thermoelectric IR radiation sensor with multiple PbTe thermocouples is simulated. The sensitivity up to 350 V/W is predicted. PbTe thin films are grown on the BaF₂(111) buffered Si(111) substrates, using the hot-wall-beam epitaxy technique. Indium and zinc ion implantation is applied to transform the as-grown p-PbTe films into the n-type thermocouple counterpart films. With a dose of 10^l6 cm^-2 and exposition time of 3-4 h, a 4-μm-thick film is homogeneously reversed, retaining the high epitaxial quality.

Acousto-optic tunable filters (AOTF), besides their other functions, allow a multispectral processing of images. It means that AOTFs process the information in time, space, and wavelength domain. The optimization of the information treatment with the devices requires a specific approach to the metrology. In the present work, the approach, developed preliminarily for other acousto-optic devices, is extended to AOTF. It is shown that the wavelength selectivity of AOTF can be defined as a distance between two resolvable spectral lines in which a certain number of gray scale levels can be recognized with a preassigned probability. The experimental determination of the wavelength selectivity is much more complicated than the determination of the spatial or temporal selectivities. An apparatus for performing this complicated task is designed. The results of the measurements are presented.

Pulp consists of distinguishable particles, the refractive indices of which differ from the index of the employed medium, water. We are thus dealing with an optically scattering material. Particle distribution in pulp is nowadays a focus of interest. This parameter is related to the photon path length distribution (PPLD) determined by the inhomogeneity of the scatterer. In order to assess PPLD, we use two methods. In the first, the particle properties in pulp are estimated by means of a microscope. A model for Monte Carlo simulation is then built to obtain PPLD. In the second, the signal generated by a laser pulse passing the cuvette filled with water or pulp is detected with a streak camera and the assessment of PPLD accomplished by a deconvolution procedure. To obtain the particle distribution, the two methods may be used together, so that the streak-camera measurements give PPLD, and in the following simulation process the particle distribution is found, which corresponds to the determined PPLD. The number and diversity of the sample sets currently used do not fulfill the statistical requirements of the industry. Nevertheless, the results achieved encourage us to develop the methods further.

M-lines spectroscopy (MLS) is an accurate, to within 10^-3-10^-4, nondestructive technique for measuring optogeometric parameters (refractive index and thickness) of thin planar step-index waveguide films. Two exciting polarizations can be used and information about the film anisotropy derived. Usually, MLS uses only one wavelength, which may be disadvantageous in some cases. We have developed an MLS setup that includes a set of lasers emitting in the range of 405 to 1550 nm to conduct multi-wavelength MLS (MWMLS). MWMLS offers an opportunity to obtain more detailed optical information, e.g., index profiles and dispersion curves, especially important for sol-gel prepared waveguide thin films that are relatively porous and whose structure depends on the annealing treatment. The paper presents a detailed description of the MWMLS setup. By using sol-gel prepared waveguide thin films of Y₂O₃, HfO₂:Eu³⁺, and TiO₂, optical measurements are exemplified. Proceeding from the measurements, the advantages and limitations of the method are discussed.

The features of the media acceptable for hologram recording as well as their difference as concerns the recording mechanism and characteristics are considered. Special attention is paid to the performance of the recording processes in time domain. The variations occurring during the hologram storage and image reconstruction from the recorded holograms are also the objects of our attention. The differences in the hologram recording mechanisms and kinetics allow holographic solving of different problems.

Bragg and asymmetric-relief gratings and their formation in the amorphous As-S-Se films are discussed. Due to the high refractive index and its photoinduced change, the films are useful in holography. The thickness of the As_0.4S_0.15Se_0.45 and As_0.4S_0.3Se_0.3 films used in the Bragg gratings is optimized. The dependence of the dimaction efficiency of the asymmetric-relief gratings on the conditions of recording, chemical treating, and reading out (polarization and angle) is studied.

The angular selectivity of thin gratings is studied both experimentally and theoretically. The concepts of thick and thin gratings are analyzed. Thin holographic gratings recorded in a-As-S-Se films have exhibited pronounced and oscillatory diffraction efficiency angular dependences. These results are explained by the obliquity factor in Fresnel-Kirchhof diffraction integral and by finite beam and grating sizes. It is also shown that oscillatory diffraction efficiency angular dependences, most probably, arise due to the interference of diffracted waves of different orders because dephasing can be significant for small grating strengths and large enough readout angles. Fabry-Perot resonator effect can contribute as well. Thick gratings in a-As₂S₃ and a-As-S-Se films are also studied for comparison. The conclusion is made that normally all gratings possess angular selectivity and existing criterions underestimate the angular selectivity of thin gratings because they neglect factors other than dephasing.

The processes of light-induced thermal field modulation of the optical parameters in the media for photothermic recording are surveyed. The applicability of the technique for the recording of holograms is considered. Attention is also paid to the processes involved in the bit-by-bit photothermic and magnetophotothermic recording.

Holographic recording of surface-relief and refiactive-index-modulated gratings with a period ranging from 0.15 to 1 μm in thin amorphous chalcogenide films of As-S-Se and As₂S₃ is studied. The profile of the surface-relief gratings is measured by atomic force microscopy. By structuring the As-S-Se films with the subwavelength-period surface-relief gratings their reflectivity is decreased from 25-30% to less than 2%. In the refractive-index-modulated As₂S₃ films polarization effects are revealed. It is shown that the angular selectivity of the holographic recording in amorphous chalcogenide thin films can be substantially improved by decreasing the grating period.

A review of the recent advances and developments in the practical application of amorphous chalcogenide materials is presented, focusing special attention to holography and lithography. The main functional principles and practical application of amorphous chalcogenide photoresists for production of the embossed rainbow holograms and holographic optical elements are discussed. The laser interference lithography can be used as a low-cost method for the exposure of large surfaces with regular patterns like subwavelength-gratings and microsieves. The surface-relief and reftactive-index modulated gratings with a period of about 50 nm and less can be fabricated by immersion holographic method. The Bragg reflection gratings were recorded and studied in amorphous As₂S₃ and As-S-Se films. The possibility to use the amorphous chalcogenide films as a media for holographic recording and storage of information with high density is discussed.

A four-channel photoplethysmography device was designed and built at University of Latvia to detect signals from different body parts and to analyze the signal shapes. The device consists of optical contact probes, interface, and a standard PC. Clinical tests were performed with occlusion patients having vascular problems at arm or leg arteries. Results showed significant difference in the pulse wave transit time in occluded and nonoccluded part of the body.

Laser photoacoustics (PA) and optical coherence tomography (OCT) are versatile and sensitive techniques for biomedical diagnostics, imaging, and measurements. In this paper, the fundamentals of PA and OCT are considered and the applications in biomedicine reviewed. The properties of the two techniques are compared to find the proper technique for a specific application. The problems and restrictions, dependent on the factors of the human body, which have to be reduced before the clinical utilization of the techniques, are pointed out. The PA technique is more suitable for measuring or imaging the objects located in deep tissue or organs and for sensing the physiological changes caused by compositions with larger absorption variation, such as hemoglobin, blood oxygenation, and melanin. OCT is more suitable for imaging tissue surface and subsurface structures and fine structures and for sensing the physiological changes caused by compositions with larger scattering and refractive index variation, such as skin water, tissue glucose, and sweat.

The aim of this study was to evaluate the simulation of eye pathologies, such as amblyopia and cataracts, to estimate the stereovision in artificial conditions, and to compare the results on the stereothreshold obtained in artificial and real- pathologic conditions. Characteristic of the above-mentioned real-life forms of a reduced vision is a blurred image in one of the eyes. The blurring was simulated by (i) defocusing, (ii) blurred stimuli on the screen, and (iii) occluding of an eye with PLZT or PDLC plates. When comparing the methods, two parameters were used: the subject's visual acuity and the modulation depth of the image. The eye occluder method appeared to systematically provide higher stereothreshold values than the rest of the methods. The PLZT and PDLC plates scattered more in the blue and decreased the contrast of the stimuli when the blurring degree was increased. In the eye occluder method, the stereothreshold increased faster than in the defocusation and monitor stimuli methods when the visual acuity difference was higher than 0.4. It has been shown that the PLZT and PDLC plates are good optical phantoms for the simulation of a cataract, while the defocusation and monitor stimuli methods are more suitable for amblyopia.

Combining features of optical coherence tomography and Doppler flowmetry, Doppler optical coherence tomography (DOCT) gives a possibility of noninvasive assessment of turbid highly scattering media with a high space and velocity resolution. This and the relative simplicity of the hardware lend to DOCT clinical and biomedical importance in investigating, e.g., the blood microcirculation. Using the developed apparatus based on a fiber-optic Michelson interferometer and a superluminescent diode, experiments on the determination of the velocity of the Intralipid flow in turbid (silicone) tubes are carried out. In the paper, the apparatus is described in some detail. The feasibility of the measurements is demonstrated. It is shown that the measured Doppler shift is proportional to the infusion rate and the experimental velocity profile in the conduit is parabolic as expected for the laminar flow.

The study concerns the Monte Carlo simulation of the optical coherence tomography (OCT) signal from blood and Intralipid layers. We show that in the case of the hematocrit values of 5 , 10, and 35%, the rear border of a 0.5-mm-thick blood layer is clearly distinguishable in the signal. The finding is in line with the fact that the least-scattering component gives a major contribution to the signal. In the case of Intralipid, the major contribution comes from the multiple- scattering component, and the signal from the rear border is not visible. The scattering properties of Intralipid, a highly scattering medium, can be ascertained fiom the slope of the downward slanting part of the signal. As it has been proved, the change of the detector radius strongly influences the shape of the signal. The larger the radius is, the larger is the contribution from multiple-scattered photons. On the contrary, the change of the numerical aperture (NA) of the detector does not change the shape of the signal, as the contributions from diversely scattered photons respond in a similar way. Hence, to optimize the determination of the properties of the media from the OCT signal slopes, a small detector radius and large NA should be used.

The paper reports on the development of the equipment for studies of the eye dominance and ocular stereoprevalence by using black-and-white and color stereostimuli. The stereostimuli are separated either by color-filter goggles or phase separating liquid-crystal-shutter goggles. The stability of the stereoprevalence is studied by artificial step-by-step deterioration of the retinal image quality, particularly in the dominant eye. The stimuli are blurred using spatial Gaussian filtering. The polymer-dispersed-liquid-crystal cell placed in front of the dominant eye induces a controllable light scattering. The stimuli-blurring and light-scattering methods exhibit different influence on the eye ocular prevalence. Blurring causes a smooth change of the prevalence towards the nonblurred stimuli eye. The influence of moderate scattering depends heavily on stimuli color. At a sufficiently high scattering level the instable switching from the prevalence of one eye to the prevalence of the other occurs.

Time resolved detection and analysis of the skin backscattered optical signals (remission photoplethysmography or PPG) provide rich information on skin blood volume pulsations and can serve for reliable cardiovascular assessment. The single- and multi-channel PPG concepts are discussed in this work. Simultaneous data flow from several body locations allows one to study the heartbeat pulse wave propagation in real time and evaluate the vascular resistance. Portable single-, dual- and four-channel PPG monitoring devices with special software have been designed for real-time data acquisition and processing. The clinical studies confirmed their potential in the monitoring of heart arrhythmias, drug tests, steady-state cardiovascular assessment, body fitness control, and express diagnostics of the arterial occlusions.