Proceedings Volume 2967

Optical Inorganic Dielectric Materials and Devices

Andris Krumins, Donats K. Millers, Andris R. Sternberg, et al.
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Proceedings Volume 2967

Optical Inorganic Dielectric Materials and Devices

Andris Krumins, Donats K. Millers, Andris R. Sternberg, et al.
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 4 February 1997
Contents: 5 Sessions, 50 Papers, 0 Presentations
Conference: International Conference on Advanced Optical Materials and Devices 1996
Volume Number: 2967

Table of Contents

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Table of Contents

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  • Electronic Excitations
  • Radiation Effects in Optical Crystals and Glasses
  • Theory, Models, and Computer Simulation
  • Ferroelectrics
  • Optical and Fiber Optic Devices
Electronic Excitations
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Femtosecond photoelectron spectroscopy of II-VI and III-V semiconductors
M. Leblans, R. K. R. Thoma, J. L. LoPresti, et al.
Photoelectron spectra resulting from sequential or simultaneous absorption of two or three photons have been studied for ZnTe(110), ZnSe(110), and GaP(110) surfaces, with time resolution of the relaxation of carriers between the first and subsequent steps of excitation. Under 2.95 eV excitation and probing with 5.9 eV photons on ZnTe(110), we were able to follow the thermalization of conduction electrons, the subsequent trapping of electrons by surface defect states in the band gap, and the gradual relaxation toward defect states closer to the Fermi level. On GaP(110), the relaxation of photoexcited electrons and holes was studied by means of two-photon and three-photon photoelectron emission under 3.16 eV photon excitation.
Localized states in wide-gap oxide glasses
Anatoly N. Trukhin
Localized states manifest themselves by light absorption at the optical gap of a glass and by luminescence excited there with Stoke's shift. They are created by the minority structural motifs of one or many structural modifications in which a material can exist, and which can provide electronic states absorption at the optical gap. Their wavefunctions overlapping determine the luminescence intensity dependence on the temperature [I(T)on the order of magnitude exp(- T/T0)] and power law (t-1) of luminescence decay kinetics, which include intra-center processes due to triplet-singlet transitions and recombination processes due to a tunnel and overbarrier transitions, as well as a fast component of luminescence decay (some ns) due to singlet-singlet transitions.
Luminescent materials with photon multiplication
Marco Kirm, Eduard Feldbach, Aleksandr Lushchik, et al.
Multiplication of electronic excitations caused by hot photoelectrons has been examined for luminescent materials on the basis of metal halides and oxides. The results of the elaboration of luminophors with a quantum yield greater than one on the excitation by Ne (16.7 eV) or He (21.2 eV) gas discharge line sources, obtained by physicists and chemists of the Institute of Physics (Tartu, Estonia), have been generalized. The possibility to reduce the near-surface energy losses by using materials with self-trapping excitons (Y2O3, Zn2SiO4, etc.) in gas discharge devices has been revealed.
Optical properties of laser spinel
Nina Mironova-Ulmane, Vera Skvortsova, Andrejs Smirnovs, et al.
The present work summarizes the results of absorption and luminescence spectra investigation of natural and synthetic magnesium aluminum spinels (MgO*nAl2O3) containing chromium and manganese ions. The spectra have been analyzed with an aim to determine the effect of stoichiometry 'n' on distribution of emitting ions. The Mn2+ is observed in both tetrahedral and octahedral coordinations providing green or orange emission. Absorption bands have been explained in terms of the Mn2+ configuration model. Laser excitation of chromium-comprising magnesium aluminum spinel crystals has been carried out at 7 K with the purpose to detect the nearest neighbors of Cr3+ ions. Luminescence emission spectra have been obtained for natural sample and three synthetic samples (MgO*nAl2O3, n equals 1, 2, 2.8). Decay time has been measured at different wavelengths and compared for crystals of different stoichiometry. In case n equals 2 or 2.8, computer simulation has been used to decompose smeared luminescence spectra in the 680 - 700 nm region. Gaussian curves corresponding to R- and N-lines of natural spinel spectrum have been applied as components in the calculations of nonstoichiometric spinel spectra. This suggests that there aren't normally arranged Cr-occupied octahedral positions in nonstoichiometric spinel (n equals 2.8, e.g.).
Optical properties of novel phosphate glasses with embedded semiconductor nanocrystals
Andrey A. Lipovskii, Elene V. Kolobkova, Vladimir D. Petrikov
A novel high optical quality phosphate glass allowing doping with nanocrystals of CdS, CdSe, CdSxSe1-x solid solutions, CdTe and PbSe has been synthesized and studied. Thermal processing of the glass gives a possibility to vary both size and size distribution of the nanocrystals. High concentration of the semiconductors in the design glass provides observation of optical absorption peaks corresponding to nucleation of crystalline grains. Complicated structure of optical absorption spectra and multiple peaks related to different quantum transitions are also demonstrated for all doped glasses.
Size effects in CdS-nanocrystal doped glasses: luminescence under single-electron and plasma excitation
Saulius Jursenas, G. Kurilcik, M. Strumskis, et al.
Near-to-bandgap luminescence has been studied in bulk-like CdS nanocrystals as a function of the average radii ranging above the exciton Bohr radius (from 3.3 nm to 100 nm). The surface recombination was shown to be the main recombination route under experimental conditions. Comparing the size dependences of the luminescence under high and low excitation, a striking increase in the luminescence intensity of nanocrystals with one excited electron-hole pair was discovered for average radii below 10 nm. The small-volume enhanced bimolecular recombination was shown to account for the observed data.
Mechanisms of energy transport in BeO over the temperature region of self-trapped exciton transformation
I. N. Ogorodnikov, A. V. Kruzhalov
The specificity of mechanism of energy transport in BeO over the temperature region of self-trapped exciton transformation is considered in the framework of the model of a field fluctuation process (FFP). The paper discusses the results of the computer simulation of a perturbing effect of FPP on kinetics and parameters of thermally stimulated luminescence in comparison with the appropriate experimental data gained for beryllium oxide crystals. It was shown that the observed peculiarities of recombination processes in BeO over the temperature region between 150 and 180 K are due to the self-trapped exciton transformation.
Vibronic interactions in CsPbCl3xBr3(1-x) (x=0...1) and CsPbCl2J crystals
M. S. Pidzyrailo, S. V. Miagkota, Anatolii S. Voloshinovskii, et al.
Low temperature (T equals 5...80 K) reflection spectra at fundamental absorption edge and luminescence spectra have been measured for CsPbCl3xBr3(1-x) (x equals 0...1) and CsPbCl2J crystals. Some exciton parameters were estimated. Namely, the exciton binding energy for the crystal row varies from 71 to 31 meV and the ground exciton radius does in range 10.4 - 15.7 angstrom. It was found that disordering effects were insignificant for the above mentioned solid solutions. The exciton nature change condition is not satisfied in case of halide replacing. Relaxation of the intrinsic electron excitation for the investigated crystals excited in range of fundamental absorption occurs through the following ways. It is the free and trapped exciton emission and also their scattering on LO-phonons for CsPbX3 (X equals Cl,Br) single crystals, the trapped exciton emission for the CsPbCl3xBr3(1- x) (x equals 0...1) solid solutions and the trapped and self-trapped exciton emission for CsPbCl2J crystals.
Possible mechanism of energy storage in optically stimulable materials: doped alkali halides
Irena Plavina, Anatoli I. Popov, Aija Tale, et al.
Radiation-induced effects in doped alkali halides, mainly in KBr:In, are studied by the luminescence technique. The activator luminescence during a 10 s under UV-light or electron irradiation and, after it, the pulsed photostimulated luminescence on a phosphorescence background were investigated. The obtained results allow us to conclude that the main host lattice excitation relevant to both the luminescence processes mentioned above is a very mobile excitonic excitation including a photon phase and the self- trapped exciton in its composition. The photon phase, as we suppose, represents a free exciton luminescence at room temperature. In this phase, via multiple reabsorption in the low-energy exciton absorption band, the excitonic excitation can overcome large distances. In the phase of the self- trapped exciton, the induced decay within a perturbed region around the activator hole center takes place. As a result, the pairs of F-type electron and activator hole centers, contributing to the photostimulated luminescence under stimulation with light in the F absorption band, are formed. The above-mentioned defect formation process is dominant over the excitation of activator ion at low activator concentration. At high activator concentration, when strong competition between reabsorption in the exciton absorption band and absorption in the local center band connected with the activator takes place, the activator luminescence prevails. The activator luminescence spectrum is found to be sensitive to the F or F-aggregate centers formation in the region near the activator hole center.
Reflection, cathode, and photoluminescence studies of cadmium and zinc diphosphide
Ishtvan V. Fekeshgazi, G. Grischenko, P. Romanyk, et al.
Photoreflective, photo and cathodoluminescence investigations of the electron energy levels distribution in tetragonal cadmium and zinc diphosphide crystals at 4.2, 80 and 300 K temperatures and light polarizations parallel and perpendicular to optical axis were carried out. The obtained results confirm the calculated data of the band structure of these crystals, that indicate the presence of the complicated energy spectra states and majority different type of two-quantum transitions, provides of high efficiency of non-linear processes.
Electron-hole processes in nonstoichiometric J- and Br-sodalite powders and optical ceramics
Viktor Denks, Tiit Karner, Vladimir Murk
Electron relaxation have been studied by means of luminescent methods in nonstoichiometric J- and Br- sodalites. The processes of 'intrinsic' electron-hole trapping were investigated at low temperatures. Electron- hole and ionic processes at elevated temperatures and the role of strong molecular coupling between halogens are discussed.
Luminescence of intrinsic defects in YAG polycrystalline powder
A. Pujats, A. Veispals, Janis Jansons
In the present work we have investigated luminescence properties of the fine, well-crystallized undoped YAG polycrystalline powders and thermochemically treated YAG polycrystalline powders. Presented work give evidence of significant role of 'antisite' defects (AD), i.e., where some portion of one type of cations (Y3+) occupy another cations (Al3+Oh) sites and vice versa in YAG structure, on the creation and structure of luminescence centers in complex multi-component oxides.
Efficiency and dynamic range of the photostimulable x-ray storage material KBr:In
Irena Plavina, Anatoli I. Popov, Aija Tale, et al.
By calibrating the photostimulated luminescence (PSL) response with the known intensity of a standard light source, efficiency of the KBr:In powder material to the x- ray bremsstrahlung exposure at room temperature is estimated. At 44 and 85 kV voltages on the x-ray tube, the values of (8 plus or minus 2) multiplied by 105 and (18 plus or minus 4) multiplied by 105 photons from 1 mm2 area of the 1 mm thick material are obtained as PSL responses on a 1 mR x-ray exposure, respectively. Under an assumption of the uniform x-ray excitation within the material, the maximum values for the x-ray irradiation dose and the PSL response both corresponding to the upper limit of linearity range are tentatively appraised, using the data for PSL response saturation under UV-irradiation.
Performance data of optically stimulable irradiated materials (doped alkali halides) oriented for imaging and dosimetry purposes
Aija Tale, Irena Plavina, A. Kalnins, et al.
Performance characteristics of a doped alkali halide (KBr:In)-based imaging plate (IP) and dosemeter (D) both the devices utilizing optically stimulated luminescence (OSL) and suitable for UV-light and x-ray energy recording are described. By exploiting (silicon) photodiode array as a photodetector, the detective quantum efficiency of 0.1 for IP (KBr:In) can be achieved. A very wide dynamic range, 1010:1 for UV (6.35 eV) and 1011:1 for x-ray (44 kV tube voltage) OSL recording at the spatial resolution of 1 mm2, is favorable for digital imaging and considerably improves image quality. These possibilities are illustrated by presenting available information capacities, energy consumption per bit as a function of the spatial resolution, and signal contrast ratio as a function of the input energy if using the KBr:In material with optimum characteristics (the activator concentration of 1017 cm-3, the 245 nm UV-light sensitization of UV detecting, minimum concentration of Ca+2 ions, etc.). Both the radiation dose storage is stable only up to 18 degrees Celsius and 200 s after an x-bremsstrahlung write at this temperature. When used for dose measuring, KBr-In monocrystals can be exploited for low-intensity x-ray detection and provide a possibility of the space background measuring in a second time interval.
Spectral properties of AIN ceramics
L. Trinkler, Baiba Berzina, Janis Sils, et al.
Spectral properties of oxygen-related defects are studied in AIN ceramics at room temperatures. Original results concerning the photoluminescence under ultraviolet irradiation are obtained; they include the excitation spectrum and irradiation dose effects. The ultraviolet light energy storage and its release under irradiation with visible or infrared light in the form of the photostimulated luminescence has been observed in AIN ceramics. The properties of the photostimulated luminescence such as creation, emission and stimulation spectra are reported. For the explanation of the experimental results the mechanism of the recombination luminescence involving the oxygen-related defect is proposed.
Radiation Effects in Optical Crystals and Glasses
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Two-photon processes in wide-gap materials of short-wavelength laser optics
Vladimir Murk
Intrinsic two-photon excitation and absorption processes have been studied in Al2O3, YAP and YAG crystals in the temperature interval 80 - 300 K. The comparison with the one-photon processes in the same region of energies of electron excitations has shown, that different electron excitations are responsible for the absorption in both these cases. Specific relaxation features of electron excitations are discussed in the frame of model taking into account non- bonding states of oxygen.
Radiation-induced electrical conductivity in MgO, Al2O3, and Gd3Ga5O12 single crystals
Uldis Ulmanis
The radiation-induced electrical conductivity (RIC) of single crystals MgO, Al2 O3 and Gd3Ga5O12 (GGG) has been measured during gamma-neutron irradiation at dose rates between 102 and 106 Gy/h and temperature from 20 to 400 degrees Celsius. The RIC for these crystals varied in a linear manner with dose rate in temperature region 60 - 300 degrees Celsius. The activation energy of conductivity before irradiation above 230 degrees Celsius is 1.4 eV for MgO, 0.75 eV for Al2O3 and 0.57 eV for GGG. The activation energy decrease during irradiation and at high dose rates (greater than 105 Gy/h) electrical conductivity does not depend on temperature. Single crystal MgO irradiation at 320 degrees Celsius and dose rate 500 kGy/h in electrical field 10 kV/m shows no noticeable radiation-induced electrical degradation (RIED).
Single-crystalline oxide films of the Al2O3-Y2O3-R2O3 system as optical sensors of various types of ionizing radiation: significant advantages over volume analogs
Yuri V. Zorenko, M. Batenchuk, V. Gorbenco, et al.
This investigation is dedicated to studying of peculiarities of luminescent properties of the single crystalline films (SCF) of Al2O3-Y2O3-R2O3 oxide system with alpha-Al2O3 and garnet structure, which are used as various types of ionizing radiation luminescent detectors. These peculiarities define the number of nontrivial advantages over their volume analogues. It is shown that SCF are characterized by the low concentrations of vacancy type defects and substituent defects, and the high concentration of Pb ion as dopant. This allows us to substantially increase the spatial resolution and selectivity of cathodoluminophores on the base of these compounds.
Correlation of PbWO4 scintillation and termo stimulated luminescence (TSL) data
A. E. Borisevich, O. V. Kondratiev, M. V. Korzhik, et al.
The correlations between parameters of slow component in PbWO4 (PWO) scintillation afterglow and presence of different traps centers has been investigated. Obtained correlations are based on the comparison of scintillation and termo stimulated luminescence (TSL) data obtained from crystals grown from the different raw materials with variation of growth conditions.
Photostimulated processes in the CsI-Tl crystal after UV irradiation
S. A. Chernov, L. Trinkler, Anatoli I. Popov
The photostimulated luminescence is studied for CsI-Tl crystal after irradiation with ultraviolet light in the 80 - 300 K temperature range. The PSL creation spectrum coincides with the D absorption band at 80 K. Three bands are observed in the stimulation spectra at 80 K: 1400, 950, and 600 nm. The 1400 and 950 nm stimulation bands are presumably explained as optical transitions in the Tl0 and Vk centers situated in the spatial correlated pairs. The stimulation at 600 nm band is ascribed to the unperturbed Tl0 centers.
Self-trapped exciton formation through photo-induced recombination of F and H centers in alkali iodides
Baiba Berzina
The photo-induced conversion of the primary F, H center pairs into self-trapped excitons have been proposed and studied in alkali iodides.
Radiation resistance of nonlinear LiB3O5 crystals: optical properties
I. N. Ogorodnikov, A. V. Kruzhalov, A. V. Porotnikov
This paper presents the results of study of the radiation stability of LiB3O5 (LBO) crystals with regard to optical properties. LBO crystals of the high optical quality were studied under action of an electron beam with energy of 0.2 - 10 MeV, x-rays, and polarized synchrotron radiation of a high intensity. Both the trapped electron (B2) and hole (O-) centers were revealed and their optical manifestations were studied in detail. In particular, the strong radiation-induced optical absorption band at lambda equals 306 nm, extending up to the spectral region of the second harmonic (at about 532 nm), was attributed to the optical transitions inside the O- center. The accumulation of defects over the dose region between 1010 and 5 multiplied by 1016 electrons per cm2 was measured. The accumulation curve at 77 K exhibits two well-defined flux regions: 1010-1014 and 1014- 1016 electrons per cm2. The paper discusses the origin of radiation degradation of LiB3O5 optical properties.
Mechanoactivated processes on metal oxide interfaces at room temperature
Solid state bonding of metal with oxide at room temperature have been studied. The properties of Al/SiO2, Al/glass, Al/MgO, Mg/SiO2, In/glass interfaces as well as to ascertain the mechanism of formation of interfaces. Structure, composition and mechanical properties were investigated using auger-spectroscopy (AES), secondary-ion mass-spectrometry (SIMS), electron microscopy and precision microindentation. The results showed marked adhesion not all over contact area but only at zones of the maximum shear stress. The effect of mechanoactivation is considered from the viewpoints of both structure formation and physico- chemical interaction of nonequilibrium systems. As a result of relaxation, formation of a narrow metal/O reaction zone spreading in the metal and being characterized by oxygen concentration gradient occurred. The reaction zone exhibits high hardness and brittleness in comparison with those of pure metals.
Theory, Models, and Computer Simulation
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Formation, diffusion, and aggregation of radiation-induced defects in MgO and alpha-Al2O3
Patrick W. M. Jacobs, Eugene A. Kotomin, R. A. Evarestov
This paper describes computational simulations of some atomic and electronic defects in MgO and alpha-Al2O3, using ab initio, semi-empirical, and pair-potential methods.
Modeling of trapped charge effects in ferroelectrics: application to piezoactuators
E. Klotins, K. Kundzins, A Sternberg, et al.
The strain response of lead zirconate titanate piezoelectric multilayer actuators have been measured up to 107 N/m2 stress and the 3.106 V/m periodic unipolar driving voltage. An additional nonstationary strain component is detected. This effect is explained in terms of a simple solution of polarization kinetics specific for unipolar driving voltage. Preliminary experimentally assertions are given for space charge effects which manifest itself in the strain as well as charge plot after removing the mechanical load. It demonstrates that the static load free equilibrium of the actuator is not complete and the charge recently supported by the piezo voltage and then trapped forms a nonuniform space charge field confining the strain relaxation.
Semi-empirical Hartree-Fock calculations for KNbO3 and KTaO3
R. I. Eglitis, A. V. Postnikov, G. Borstel
As a first step in modeling the electronic structure of Perovskite-type ferroelectric mixed crystals K(Nb,Ta)O3, semiempirical calculations for pure KNbO3 and KTaO3 are performed with the intermediate neglect of the differential overlap (INDO) quantum chemical method. The calculations are mostly done for 40-atom supercells. The choice of the INDO parameters based on the comparison of results with ab initio and experimental data is discussed. INDO results for the equilibrium geometry and the (Gamma) -TO phonon frequencies are given. The results show that the accuracy of the INDO method is sufficient for reliably reproducing the energy differences on the order of 1 mRy (per formula unit) scale which are typical when dealing with ferroelectric instabilities.
Calculations of F centers in KNbO3 ferroelectric crystals
R. I. Eglitis, Eugene A. Kotomin
Semi-empirical method of the intermediate neglect of the differential overlap (INDO) combined with the supercell model is applied to the calculations of the F center optical properties in ferroelectric KNbO3 perovskite crystals. It is shown that two electrons of the defect are weakly localized inside the O vacancy, unlike similar defects in ionic alkali halides, but are considerably spread over two nearest Nb atoms. For the orthorhombic phase stable at room temperatures three absorption bands are predicted to be at 2.72 eV, 3.04 eV and 3.11 eV, respectively. The first energy is close to the band at 2.7 eV observed in electron- irradiated crystals. In the high temperature, cubic phase only two bands, 2.67 eV and 3.04 eV, are expected to arise due to higher local symmetry of the defect.
Quantum chemical simulations of bound hold polarons (V Mg centers) in corundum crystals
Yu. F. Zhukovskii, Eugene A. Kotomin, R. M. Nieminen, et al.
The semi-empirical INDO method has been applied to the calculations of the bound hole small-radius polarons in corundum. Results for optimized atomic and electronic structure using two different approaches (molecular cluster and periodic, supercell model) are critically compared. Both models find that two-site configurations of bound hole polarons have the lowest energy (which does not exclude existence of one-site polarons also characterized by essential relaxation energies). Experimental ENDOR data on VMg defects are discussed in the light of the calculations.
Computer modeling of light collection processes in scintillators of arbitrary shape
Ivan V. Konstankevych, M. Dzikovska, M. Batenchuk, et al.
This paper is devoted to creation of mathematical model that describes light propagation processes in arbitrary shape scintillators. Created software was used to evaluate light collection coefficient for different scintillators on the basis of PbWO4 (PWO), Y3AlO12 (YAG) and Bi4Ge3O12 (BGO).
Ferroelectrics
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Optical nonlinear properties and structural phase transitions in a new promising ferroelectric family LnBXO5 (Ln-La, Pr; X-Ge, Si)
B. A. Strukov, B. V. Mill, Eleva L. Belokoneva, et al.
The new family of ferroelectric oxides presented and some of its properties including nonlinear optical properties of LaBGeO5 (LBGO) are considered. It is shown that these oxides have high Curie temperatures, symmetry change P3121 yields P31 and the mixed displacive and order- disorder type of the phase transitions. All second harmonic generation (SHG) tensor components are determined for LBGO crystals and the magnitude of the spontaneous polarization is evaluated from the vector part of SHG tensor as 2.4 plus or minus 0.8 (mu) C/cm2. The phase transitions in PrBGeO5 and LaBSiO5 crystals are considered taking into account SHG data for powder samples.
Joining of semiconductive n-BaTiO3 with Si single-crystal, electrical, and optical properties
S. Sugihara, T. Andoh, S. Suzuki
Semiconductive n-BaTiO3 film on Si single crystal (100) was studied on the electrical optical properties by solar beam and its simulator. The film was spin-coated on the Si with a buffer layer in which Pt or Ceramace G (commercial name -- SnO and Sb2O3 as the base materials) was employed. The electrode Pt or Ceramace G was put on the film as the top one and Ag for the lower one. The temperature for joining of the film and Si were 700, 800 and 1000 degrees Celsius. The solar beam irradiated on the film to measure the photovoltage and photocurrent and also transmittance of the film on the glass was investigated. Furthermore, the interfaces between n-BaTiO3 film and Si were discussed by the results of electron probe microanalyzer and the microstructures were also reported.
Modification of LiNbO3 optical properties by He+ implantation
Irena Hruba, Jaroslav Kral
Ion beam modified layer on x- and z-cuts of LiNbO3 single crystal has been produced by 100 keV He ions implantation with doses from 1.1016 to 1.1017 at/cm-2. Using ellipsometry, the complex refractive index [n-i.(lambda) .k/(4(pi) )] was measured for ordinary and extraordinary rays. The effect of ion beam modification depends on the ion beam orientation with respect to the crystal axes. Bombarding along the z-axis conserves the optical anisotropy of the material, both of the refractive index and the absorption coefficient.
Radiation effects in transparent ferroelectric ceramics
Andris R. Sternberg, A. Spule, L. Shebanovs, et al.
Radiation of different types ((gamma) -rays, electrons, neutrons) and fluence has been used to study the defect processes as well as the change of physical parameters in PLZT X/65/35 (X equals 4.5 - 11 at.%) and PbSc0.5Nb0.5O3 (PSN) ceramics and to evaluate critical irradiation conditions. Effects on optical (extinction) spectra and dielectric characteristics (polarization, thermal and frequency dependences of dielectric permittivity (epsilon) and losses), dependent on composition and state of phase and polarization have been analyzed by means of annealing in isochronic and prolonged time regimes. A gradual shift of extinction edge to longer wavelengths, reduction of polarization and (epsilon) values, and a progressive diffusion of the phase transition including a defect-stimulated phase transformation from the rhombohedral to quasicubic structure in PLZT 6.5-8.5/65/36 compositions with the increase of irradiation fluence are observed in neutron irradiated ceramics. First radiation-induced electrical conductivity studies in PLZT ceramics are presented.
Production and properties of doped PSN electro-optical ceramics
M. Dambekalne, K. Bormanis, Andris R. Sternberg, et al.
Due to multifunctionality the transparent ferroelectric ceramics is attractive to solid state chemistry and physics as a promising material for active electro-optic elements. To study doping effects on the technological processing and properties, ceramic samples of Pb1-xZxSc1/2Nb1/2O3, have been prepared, where Z: (1) Ba (0 less than or equal to x less than or equal to 1), (2) rare-earth elements: Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu (x equals 0.1), (3) PbSc1/2Nb1/2O3 doped with 5 wt.% of rare-earth oxides. Ceramic characteristics, dielectric and electro-optical parameters have been measured. Differential thermal analysis (DTA), and x-ray diffraction are used to study the influence of doping on the solid state reactions and to determine the sequence of phases formed during the processes in oxide mixtures in the 500 degree to 950 degree Celsius interval. The pervoskite structure of PbSc1/2Nb1/2O3 (PSN) is found to be formed in a complicated multistage process with several intermediate products during the reaction.
Long-term effect of bias field on dielectric properties of SBN optical crystals with diffused phase transition
A. I. Burkhanov, A. V. Shil'nikov, R. E. Uzakov, et al.
The infralow frequency dielectric response of SBN single crystals with different electrical prehistory has been investigated. The data on the temporal dependencies of (epsilon) '(lgt) and (epsilon) '(lgt), and field dependencies of (epsilon) '(E) and (epsilon) '(E) after long time aging determined by dc field allow us to propose some conclusions about kinetics of the glasslike state of a material in the relaxor phase.
Microscopy studies of the surface of high-temperature superconductor films
M. Livinsh, M. Kalnberga, L. Chakare, et al.
The surface morphology is studied by use of optical and electron microscopes with respect to production regime (rate and temperature of crystallization) of the 50 - 125 micrometer thick doped YBa2Cu3O7 films obtained by Stokes sedimentation on SrTiO3 ceramic substrate (size 20 mm by 5 mm by 0.5 mm) and firing in air or oxygen following the MTG procedure, performed in the gradient tube furnace. Evolution of thick film structure with regard to temperature and cooling rate is studied.
Dielectric spectra of electron-irradiated PSN ceramics
A. I. Burkhanov, A. V. Shil'nikov, S. Yu. Shishlov, et al.
The influence of electron-irradiation on the dielectric properties of transparent PSN ferroelectric ceramics is studied by low (LF) and infralow (ILF) frequency spectrum analysis. Redistribution of relaxation frequencies caused by electron-irradiation has been discovered and is related to pinning impacts of the radiation-induced defects.
Optical and Fiber Optic Devices
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Monograin layers as optoelectronic devices
Enn Mellikov, Dieter Meissner, Tiit Varema, et al.
The possibility is demonstrated to manufacture by the recrystallization of initial powders in different molten fluxes different A2B6 powders with the qualities acceptable for monograin layer construction. Several technologies of formation of monograin layers and optoelectronic devices were developed and studied. It is shown, that insufficient electronic parameters of semiconductor sensors and solar cells designed as monograin layers are connected with the insufficient cleaning of surfaces of crystals in the monograin layer.
Acceleration of a photorefractive response in Bi12TiO20 crystals
Erik Raita, Alexei A. Kamshilin
Significant acceleration of a photorefractive response has been obtained in a thin and long Bi12TiO20 waveguide-like crystals using the nonlinear self-channeling of a laser beam. Total internal reflections of strong fanning beams and their coupling with the pump beam result in the light intensity redistribution inside the crystal and in the generation of the photorefractive surface wave of high intensity, which speeds up the photorefractive response by enhancing both the beam intensity and the interaction length. The exceptionally fast photorefractive response as well as its anomalous acceleration with the increasing amplitude of ac electric field applied to the crystal were experimentally demonstrated. The photorefractive surface wave can be used as the energy source for the amplification of weak signals in two-wave mixing experiments. This fact may lead to a fabrication of fast photorefractive devices operating with low power laser-diodes.
Thermal imaging in artificial nonlinear media
Guntis Liberts, Vismants Zauls
A method has been developed to determine the temperature distribution of ferroelectric surfaces and volumes. Based on the nonlinear optical effect of second harmonic generation (SHG) in highly nonlinear ferroelectric coating, demonstration of 2D thermosensing has been performed in the wide temperature range (77 K - 600 K). Physical concept of SHG thermal imaging, design of thermosensitive coating and experimental verification of the method has been discussed.
Glowing optical fiber designs and parameters
Janis Spigulis, Daumants Pfafrods, Maris Stafeckis, et al.
Side-emitting optical fiber designs and main parameters have been studied. A simplified model to describe emission of the 'glowing' fiber is developed. Basic expressions for the emission parameters as functions of the input radiation intensity, distance along the fiber axis and scattering efficiency longitudinal distribution are given for several design modifications. The model assumptions have been checked experimentally by testing silica core side-glowing optical fiber samples.
Aging of evaporated MgF2 described by a various number of parameters
Aarne Kasikov, Anatoli S. Kuznetsov
The MgF2 layers were vacuum evaporated on fused silica substrates using a crystalline and a pressed sintered evaporation materials. The transition spectra of the specimens were recorded in the wavelength range 240 - 830 nm and changes in it monitored during storage of the specimens in atmosphere. The results were analyzed using an envelope method and a fitting of Lorentzian dispersion model with various number of parameters. A rise of the computed indices of refraction and absorption during storing in the air was seen. A heating in vacuum resulted in the temporal descending of refraction and rise of absorption indices. Fitting of the dispersion equation showed a drop of the absorption index moving from 4 to 7 fitting parameters in the red side of the spectra. On the blue side (UV) both indices rose moving from 4 to 5 parameters and descended again at 7 parameters. This shows a need of proper selection of the dispersion model for describing the real coatings. The negative values for the indices of absorption obtained by envelope method displayed the inhomogeneity of the refractive index in the fresh coatings.
Antireflection coating of cesium iodide optical windows for average IR range
I. Houd, Roman Didyk, R. Leshchuk
The method of optical surface antireflection and protection of CsJ single crystals has been elaborated. The material and methods of coating covering on the cesium iodide laser windows for IR-range of spectrum were proposed. The analysis of the reflected ray interactions from the optical surface and of the coated transparent film which have different refraction indexes shows that it is possible to change of the reflection coefficient of light from that system. The necessary material and its thickness was chosen. The sodium fluorine film with refraction index n1 equals 1.32 was covered on the optical cesium iodide surface with refraction index n2 equals 1.71 (the film thickness is about 20 micrometers). That's why the reflection coefficient decreased in IR-range (to 16 micrometer). Owing to this transparent of cesium iodide surface increases in that wavelength range. The microstructure of covered film and connected with its transparency and adhesion depend on covering conditions: crystal's temperature and film covering speed. The parameters of the covered coating processes are chosen. The offered methods permits us to produce monocrystalline cesium iodide windows which are transparent in visible and average IR-range of the spectrum.
Atomic-layer-deposited TiO2 dielectric coatings
A. Rosental, A. Tarre, A. Gerst, et al.
The possibilities of the in situ real-time Brewster-angle interferometric reflectance probe to follow cycle-dependent film-quality changes during the atomic layer deposition (ALD) are investigated. Experiments are centered around the growth of amorphous TiO2 thin films on fused quartz substrates in a traveling-wave reactor using TiCl4 and H2O as reactants. It is concluded that ALD has prospects for the preparation of microstructurally homogeneous low- optical-loss TiO2 films in case the precise thickness control is needed. The main problem is the microporosity of the films and as a result their moderate refractive index.
Plasmon-type CO sensor based on In2O3(Sn) films
Viktoras V. Vaicikauskas, Regimantas Januskevicius, Erimijus Radavicius, et al.
In2O3(Sn) film CO senors in the Kretschmann configuration were investigated using a rotating analyzer spectrometer. From the experimental surface plasmon resonance (SPR) angular dependencies, applying the best fit method complex dielectric permitivity of In2O3(Sn) films ((epsilon) equals 2.4-i0.2) were obtained. Under exposition of sensor by CO gas at 134 degrees Celsius temperature, SPR shifted to higher angles and sufficiently broadened. Most significant change possesses an imaginary part of dielectric permitivity -- after 0.8% CO exposition it becomes 4.1, whereas a real part equals to 1.2.
Photochromatic and other optical effects in HTSC films
Sergei I. Tiutiunnikov, Valerii N. Shaliapin, N. I. Balalykin, et al.
The measurement results of transmission spectra through super-conducting films are given. Used were: YBCO(123) - Tc equals 77 K; BSCCO(2212) - Tc equals 80 K; TBCCO - Tc equals 87 K, in a light energy range E equals 1.4 divided by 3.2 eV and T equals 5 divided by 300 K. The YBCO transmission spectra present an anomaly at T less than 70 K, E equals 1.9 eV. All HTSC films have a maximum of the absorption band at E approximately equals 2 eV. The photochromatic effect (light-induced photo-absorption) was observed in all films. The quantity of this effect depends on the type of the sample and critical temperatures (Tc). Remnant optic radiation was detected after film light irradiation.
Thermo-optical mirror on a free ferrofluid surface
Vismants Zauls, Guntis Liberts, J. Shakars, et al.
Here we report on the first, to our knowledge, direct experimental observation of giant thermo-optical mirror effect on the free surface of ferrofluid under He-Ne laser excitation. In our experiment a slightly focused laser beam of power in mW range is incident nearly normally to the surface, and a characteristic diffraction ring pattern has been observed in reflection mode. Concave surface deformation has been clearly observed at laser irradiated spot and has been explained in terms of lubrication theory approach for laser driven thermocapillary motion in thin layer of light absorbing fluid.
Specific UV and VUV spectra light sources
Arnolds Ubelis, Juris Silinsh, Ib Trabjerg
The report contains information about laboratory made radiofrequency powered electrodeless discharge sources (lamps) of resonance atomic spectra radiation for various elements (e.g. Hg, Cd, Zn, O, S, Se, Te, As, Sb, Bi, J, Br, Kr, Xe, H) having main spectral lines in UV and VUV region. There are known, and can be found a lot of new specific applications of such sources in laboratory made or commercial optical devices.
Optoelectronic eye tracking system
Saulius Navikas, Jonas Verkelis
The eye movement monitor measures both vertical and horizontal eye movements by employing an optoelectronic noncontact technique with a high updates rate. The monitor is controlled by an IBM AT or compatible computer and basically consists of a sensor assembly and two cards, connected to the PC bus: an amplifier and synchronous detection unit and a 12 bit AD/DA converter. The sensor assembly is mounted to spectacle frames and connected with the computer by a flexible cable. All the measurement data are stored in the hard disk and can be represented as vertical and horizontal coordinates of the gaze at selected time moments. The monitor does not interfere with the subject's head movements nor does it obstruct significantly his view of vision. The pulsed bias and synchronous detection make the device insensitive to the background illumination artifacts.
Nonlinear optical losses in medical fibers
Andris O. Ozols, Girts Ivanovs, Guntars Coders
Attenuation intensity dependences of 1064 nm and 532 nm picosecond pulses in multimode optical fibers produced for medical purposes by 'Anda' factory in Livani, Latvia are experimentally studied. A strong linear growth of inverse transmittance with intensity is found. The possible mechanism of nonlinear losses are analyzed and the conclusion is made that the observed effect is mainly due to the two-photon absorption involving defects levels. Strong attenuation intensity dependence can be used to make such fiber optical devices as light power limiters, optically driven light modulators and dynamic holographic frequency filters.