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1.
Raman and luminescence spectroscopies are used for non destructive characterization of titanium-diffused LiNbO3 waveguides at the classical resolution of confocal microscopy (0.5×0.5×3 m). The broadening of Raman lines near the surface permits one to measure the depths of lithium out-diffusion and titanium in-diffusion. The contrast of polaron luminescence makes it possible to control routinely the waveguides just after the diffusion process. Vertical scans give the thickness of the chemically-reduced layer near the surface of the wafer, whereas horizontal scans across the waveguides reveal screening effects by the titanium stripes against surface reduction. PACS 78.55.-m; 78.30.-j; 42.79.-e 相似文献
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A. Alcázar de V. J. Rams J.M. Cabrera F. Agulló-López 《Applied physics. B, Lasers and optics》1999,68(5):989-993
The overall power and far-field pattern of the beam out-coupled from a single-mode planar proton-exchanged LiNbO3 waveguide in the α-phase have been studied for in-coupled intensities within the range 20–700 W/cm2. The steady-state output versus input power response shows three definite stages designated as I, II, and III in order of
increasing input intensity. In stage I the output varies linearly with input and the far-field pattern does not show appreciable
changes. In stage II, the pattern is considerably broadened and displays a number of steady peaks and dips indicative of a
filamentary structure of the beam. As in bulk LiNbO3, these damage features are explained in terms of parametric processes involving the amplification of scattered (noise) light. An additional broadening is observed in stage III together with the occurrence of a fluctuating profile (chaotic
response) attributed to random fluctuations in the coupling parameters. The threshold input intensity separating stages I
and II is related to the intensity-dependence of the photovoltaic field.
Received: 18 November 1998 / Revised version: 13 January 1999 / Published online: 12 April 1999 相似文献
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A model of the grain-boundary self-diffusion process in metals undergoing phase transitions in the solid state is proposed. The model is based on the ideas and approaches of the theory of nonequilibrium grain boundaries. It is shown that the range of application of basic relations of this theory can be extended, and they can be used to calculate the parameters of grain-boundary self-diffusion in high-temperature and low-temperature phases of metals with phase transition. Based on the constructed model, activation energies of grainboundary self-diffusion in titanium and zirconium are calculated, and their anomalously low values in the low-temperature phase are explained. The calculated activation energies of grain-boundary self-diffusion are in good agreement with experimental data. 相似文献
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P. K. Manna S. M. Yusuf M. D. Mukadam J. Kohlbrecher 《Applied Physics A: Materials Science & Processing》2012,109(2):385-390
We report the evidence of a core?Cshell structure in the antiferromagnetic La0.2Ce0.8CrO3 nanoparticles by using a combination of neutron diffraction, polarized neutron small angle scattering (SANSPOL), and dc magnetization techniques. The neutron diffraction study establishes that the present nanoparticles are antiferromagnetic in nature. The magnetic scattering in the SANSPOL study arises from the shell part of the nanoparticles due to the disordered surface spins. The analysis of the SANSPOL data shows that these nanoparticles have a mean core diameter of 12.3±1.1?nm, and a shell thickness of 2.8±0.4?nm, giving a core?Cshell structure with an antiferromagnetic core, and a shell with a net magnetic moment under an applied magnetic field. 相似文献
6.
Temporal evolution of absorption induced by single femtosecond pulse (13Ors, 800nm) with high intensity in LiNbO3 is obtained using the probe shadow imaging technique in order to investigate light-induced electron relaxation processes. By saturating the polaron density with a high intensity laser pulse, ultra-fast decay process on picosecond time scale is observed. The decay time constant is about 141 ps and it is attributed to the direct interband electron-hole recombination process. 相似文献
7.
We compare the optical properties of Er3? in LiNbO3 waveguides produced by different techniques and find by confocal luminescence microscopy characteristic differences in the excitation and emission transitions. Besides a small redistribution among the regular defect sites, essentially no direct Er3?—Ti4? interaction can be observed in Ti4? diffused waveguides. However a significant shift in transition energies is found, which increases with Ti4?concentration. Based on earlier results we associate this shift with a decrease in the intrinsic electric field. In addition to a similar shift, we find in Zn2? diffused waveguides new defect types which suggest a change in direct environment. Finally, in annealed proton exchange waveguides we find no interaction effects at all. 相似文献
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K. E. Rammutla J. D. Comins R. M. Erasmus T. T. Netshisaulu P. E. Ngoepe A. V. Chadwick 《辐射效应与固体损伤》2013,168(6-12):783-788
High temperature Raman and Brillouin light scattering experiments have been combined with molecular dynamics simulations to provide a comprehensive study of the superionic state of BaF 2 ( x v mol% LaF 3 ) over a particularly wide range of LaF 3 dopant concentrations from x =0 to 50. Room temperature Raman spectra for x =0, 5 and 10 show the usual T 2g symmetry mode at 241 v cm m 1 , but for samples with x =20, 30 and 50 the dominant Raman mode is at higher frequencies and of E g symmetry. The temperature dependence of the Raman line-widths show initial near linear increases followed by substantial increases above temperatures ( T c ) at 1200, 850, 800, 975, 950 and 920 v K for x =0, 5, 10, 20, 30 and 50. In the Brillouin scattering experiments, the acoustic modes respectively related to elastic constants C 11 and C 44 initially showed a quasi-linear decrease in frequency with increasing temperature. Above the same characteristic values of T c , where the Raman line-widths show marked increases, there are substantial decreases in the elastic constant C 11 for all samples with x =0 to 50. Only the doped samples showed significant decreases in C 44 at corresponding values of T c . Molecular dynamics (MD) simulations have been carried out on the same systems. From the calculated mean square displacements, the diffusion coefficients ( D ) of the mobile fluorine ions were calculated as a function of temperature for each of the samples. Substantial increases in the values of D occur above the respective values of T c determined in the light scattering experiments. The MD simulations also provide details of the mechanisms of diffusion of the mobile fluorine ions. The results emphasize the role of motional effects as an explanation of the mechanisms responsible and provide a self-consistent explanation of the dominant processes in the superionic phase of doped fluorites. 相似文献
9.
The present work cites the investigation results of local magnetic fields on 1H and 19F nuclei and spin ordering in β-FeF3·3H2O. In the structure of this compound (space group P42/n, a=7.846 Å, c=7.754 Å, z=41,2) Fe atoms are bonded via bridged F atoms (1) in infinite chains along the /001/ axis. With such positioning, in which two paramagnetic atoms are separated by a diamagnetic atom (F, O, C1 and others) there is a possibility for indirect (superexchange) interaction. Linear chains … Fe - F - Fe - F - Fe - F … are separated from each other by F(2) atoms and water molecules H2O (1) and H2O (2), so that exchange between neighboring Fe atoms from various chains is ostensibly much encumbered. 相似文献
10.
《Solid State Communications》1987,61(12):779-784
The constitutional and thermal defect formation in the Co100-xGax alloys (42⩽x⩽53) and Ni100-xGax alloys (47⩽x⩽52) was studied by Mössbauer spectroscopy. The formation of both constitutional and thermal defects in the CoGa alloys was observed by the appearance of resolved quadrupole split spectral components. The influence of these defects in the NiGa system was detected only by the broadening of the absorption line. The 57Fe probe atoms were found to populate the Nisublattice in these alloys. The highest concentration of thermal defects was found in the equiatomic composition of the NiGa alloys. 相似文献
11.
Dynamic Phase-Mapping of Domain Nucleation in MgO:LiNbO3 Crystal by Digital Holographic Interferometry
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The quantitative phase-mapping of the domain nucleation in MgO:LiNbO3 crystals is presented by using the digital holographic interferometry. An unexpected peak phase at the beginning of the domain nucleation is observed and it is lowered as the spreading of the domain nucleus. The existence of the nucleus changes the moving speed of the domain wall by pinning it for 3 s. Such in-situ quantitative analysis of the domain nucleation process is a key to optimizing domain structure fabrication. 相似文献
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A.S. Andrushchak B.G. Mytsyk N.M. Demyanyshyn M.V. Kaidan O.V. Yurkevych I.M. Solskii A.V. Kityk W. Schranz 《Optics and Lasers in Engineering》2009,47(1):31-38
The paper presents a technique suitable for the determination of linear electro-optic effect (LEOE) tensor components in crystal materials of any symmetry. The method is based on the Michelson interferometer, where the sample being studied is set into one of its arms to measure the electro-induced changes of the optical path. We describe in detail the sample geometries that are needed to determine a complete set of the LEOE tensor components and derive the corresponding equations. The experimental technique has been tested and verified on lithium niobate crystals as well as applied to MgO-doped LiNbO3 crystals to study their electro-optic properties. The developed method can be useful for optical engineering, which deals with new materials being used in design or production of devices, such as, e.g., modulators or deflectors. 相似文献
13.
An efficient method to model guided and leaky modes of anisotropic dielectric waveguides with arbitratry dielectric tensor ¯¯ is presented. This method takes advantage of a particular -formulation approach of the finite element method (FEM), leading to an optimized use of the computational resources. 相似文献
14.
《Current Applied Physics》2002,2(6):483-487
The crystalline and electronic structures of the α-phase BEDT-TTF organic superconductors were controlled by the uniaxial compression along the selected crystalline axes. We found the bandwidth to be increased by the compression parallel to the a-axis while the c-axis compression reduced the bandwidth. Similar controls were possible also in the θ-phase compounds. The a-axis compression made the material metallic although the c-axis one insulating. It is possible to systematically explain these changes in electronic properties under the uniaxial compression in terms of the changes in the electronic band structure in the conducting layer. 相似文献
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Modulated UV light is used to increase the sensitivity of the two-centre holographic recording. Inherent mechanisms of nonvolatile holographic recording in oxidized and reduced crystals are numerically analysed based on solving the two-centre material equations modified for UV-light recording. Experiments verification is performed with an oxidized crystal and a reduced crystal, and the role of UV intensity on the sensitivity is presented. 相似文献
18.
The effect of repeated cycles of water adsorption/desorption on the structural stability of ordered mesoporous silica SBA-15 is studied by small-angle x-ray scattering (SAXS). In?situ sorption measurements are conducted using a custom-built sorption apparatus in connection with a laboratory SAXS setup. Two striking irreversible changes are observed in the sorption isotherms as derived from the integrated SAXS intensity. First, the capillary condensation pressure shifts progressively to lower relative pressure values with increasing number of sorption cycles. This effect is attributed to chemisorption of water at the silica walls, resulting in a change of the fluid-wall interaction. Second, the sorption cycles do not close completely at vanishing vapour pressure, suggesting that progressively more water remains trapped within the porous material after each cycle. This effect is interpreted to be the result of an irreversible collapse of parts of mesopores, originating from pore wall deformation due to the large Laplace pressure of water acting on the pore walls at capillary condensation and capillary evaporation. 相似文献
19.
Compton mechanism of γ-quanta emission in the extremely inelastic scattering of electrons by hadrons
M. P. Rekalo 《Russian Physics Journal》1982,25(1):7-11
The Compton mechanism at the emission of -quanta, in the extremely inelastic scattering of charged leptons by hadrons is investigated using the quark-parton model. The cross section of the e– + qe– + q + (q-quark) process, in which two particles are recorded in the final state corresponding to the Compton mechanism, is calculated. The structural functions of the extremely inelastic scattering of electrons by nucleons are obtained for this mechanism. A violation of the gauge invariance of extremely inelastic scattering due to consideration of the radiational corrections is pointed out.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 9–13, January, 1982. 相似文献
20.
《Surface science》1990,231(3):L196-L200
β-SiC surfaces have been investigated in terms of surface composition and reconstruction by medium energy ion scattering (MEIS), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). A (3 × 2) phase is produced by evaporating Si on a β-SiC surface. Heat treatment at 1065°C causes consecutive transformation into (5 × 2), c(4 × 2), (2 × 1), (1 × 1) and c(2 × 2) phases. Quantitative analysis of MEIS spectra shows that the c(4 × 2) surface has a full silicon topmost layer, whereas the c(2 × 2) surface has a full carbon topmost layer. The (3 × 2) and (5 × 2) phases are believed to originate from additional Si dimer rows on top of a Si terminated crystal. 相似文献