Conditions for obtaining backward collinear isotropic acousto-optic interaction in germanium and iodic acid crystals

The possibility of experimentally obtaining backward collinear isotropic acousto-optic interaction based on bulk ultrasonic waves and terahertz electromagnetic waves is considered. The magnitudes of the acousto-optic figure of merit and the corresponding acoustic frequencies are calculated for the basic crystallographic axes in germanium and iodic acid crystals. The acousto-optic parameters of both crystals are compared.     

Determination of the dislocation structure in paratellurite single crystals using the piezo-optic effect

It is shown theoretically and experimentally that dislocations in paratellurite single crystals can be revealed using the piezo-optic effect. The mechanical-stress distribution near dislocations is calculated. Dislocations in the samples are observed using the photoelastic method and chemical etching. Data on the spatial distribution of dislocations in Czochralski-grown paratellurite crystals are reported.     

Evolution of X-ray rocking curves for paratellurite and lithium fluoride crystals under intense ultrasound

Local deformations of the crystal lattice under ultrasonic loading over a wide range of amplitudes have been investigated by means of recording the X-ray rocking curves for paratellurite and lithium fluoride single crystals.     

Thermal characteristics of paratellurite single crystals by the rectangular thermal wave method

The study of the thermal characteristics of bulk nonferroelectric materials with low heat conductivity coefficient by the pyroelectrical rectangular thermal wave is shown to need the solution of the problem of the thermal conductivity for a three-layer system. The thermal characteristics of a paratellurite crystal with various crystallographic directions were studied. The heat conductivity coefficient is found to depend on the crystallographic direction.     

Diffraction of light by ultrasound in paratellurite crystals under Fresnel reflection conditions

We show that layers of acousto-optic gyrotropic paratellurite crystals perturbed by ultrasound can be used as efficient light modulators in transmission and reflection mode. We have established that the relative intensities of the diffracted waves are determined by the ratio of the refractive indices of the bounding media, the intensity of the ultrasound, and the thickness of the modulated layer. We show that for an asymmetric diffraction structure, efficient acousto-optic conversion is possible in reflection mode, and the weak effect of the gyrotropy is due to its suppression by Fresnel reflection at the boundaries of the layer. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 819–823, November–December, 2006.     

New form for the Coulomb potential in crystals

The Poisson equation is solved by the Green's function method. A nonstandard approach is used in the calculation of the potential of the electron cloud. It is shown that the lattice contribution to the electron density is given by a universal function of distance. The potential is determined in the whole unit cell and has an expression convenient for practical realization. The corresponding formulas are easily generalized to complex crystals.Altai State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 35–39, May, 1995.     

Structural characterization of opal-based photonic crystals in the visible range

For structural characterization of periodic three-dimensional systems with submicron-scale lattice parameters (optical photonic crystals), is analogous to the use of visible light of x-rays. It is shown that specular reflectance and transmittance spectra of opal do indeed yield information on the lattice period and structural perfection of photonic crystals. Fiz. Tverd. Tela (St. Petersburg) 40, 648–650 (April 1998)     

Propagation characteristics of two-dimensional photonic crystals in the terahertz range

Based on the plane wave expansion method, the complete band gaps of two-dimensional terahertz photonic crystals with typical structures are optimized through varying structural parameters. During our calculation, two kinds of lattice structures that are very promising for the materials of terahertz components are found and some interesting phenomena that were not reported in the former papers are also presented. Using the finite difference time domain method, we simulated the electromagnetic field distribution of THz waves in a PC splitter. And by the plane wave expansion method, we achieved the dispersion relation and defect modes in a rotated PC waveguide. These results provide a useful guide and a theoretical basis for the developments of THz functional components. PACS 42.72.Ai; 42.70.Qs     

Photonic crystals for the visible range fabricated by autocloning technique and their application

We fabricate photonic crystals for the visible range by the autocloning technique, in which multilayers are stacked by an appropriate combination of sputter deposition and sputter etching. TiO₂/SiO₂ and Ta₂O₅/SiO₂ are chosen as materials since they are transparent in the range and give a high contrast of refractive indices. The fabrication technique has flexibility regarding materials and size and is very reliable and reproducible even if the pitch is less than 0.2 m. We also study the application of photonic crystals to birefringent elements such as waveplates and polarization selective gratings and experimentally verify that they are useful for optical pick-up systems.     

A method for magnetoptic studies on crystals in the temperature range of helium superfluidity

Test results are given on a method for magnetoptic studies on crystals down to temperatures of about 1.2°K.We are indebted to A. B. Fradkov for valuable assistance.     

Artificial ultrasound anisotropy of crystals in the range of X-ray frequencies

Phenomenon of artificial ultrasound anisotropy is revealed in crystals in the range of X-ray frequencies and an attempt is made to explain this effect theoretically for the case of the Bragg-Laue diffraction. It is established that an isotropic crystal becomes, under action of ultrasound, optically anisotropic like a uniaxial crystal with the optical axis along the direction of the external action; this axis is the symmetry axis and causes birefringence.     

Non-scalar contribution of potential in crystals

Ewald-parameter dependence of Coulomb interaction in ionic crystals was studied using a point-charge model. In the presence of the long-range interaction, the ion configuration breaks spherical symmetry of local potential and charge at each ion site, and gives non-scalar contributions to them. This non-scalar potential has similar effects to Heisenberg interaction, while is intrinsically distinct from conventional multipole expansions of the scalar potential. Symmetry and magnitude of the scalar and non-scalar potentials are similar for most materials despite the different definitions, but one exception can be seen in parent materials of hole-doped high-_Tc$T_{\mathrm{c}}$ cuprates.     

小波变换在太赫兹时域光谱分析中的应用

随着超快激光技术的发展及其人们对太赫兹(THz)电磁波波段与脉冲光源认识的进一步深入,太赫兹时域光谱(THz-TDS)技术作为一种新的、快速发展的光谱分析方法在许多领域备受关注。利用太赫兹时域光谱技术在空气环境下测量样品时,样品的太赫兹光谱会因空气中水蒸气的影响而出现振荡现象。文章利用太赫兹时域光谱分析技术分别在氮气和空气环境下测量了七种样品在0.2～1.9太赫兹波段的光谱,并以氮气环境下的太赫兹光谱为参考,利用小波变换对空气环境下测量的数据进行了处理,消除了太赫兹光谱中水蒸气吸收造成的影响,实验结果证明了该方法的可行性,在此基础上,还对其中四种样品做了成像和识别,并得到了较好的结果。     

Interatomic potential for uranium in a wide range of pressures and temperatures

Using the force-matching method we develop an interatomic potential that allows us to study the structure and properties of α-U, γ-U and liquid uranium. The potential is fitted to the forces, energies and stresses obtained from ab initio calculations. The model gives a good comparison with the experimental and ab initio data for the lattice constants of α-U and γ-U, the elastic constants, the room-temperature isotherm, the normal density isochore, the bond-angle distribution functions and the vacancy formation energies. The calculated melting line of uranium at pressures up to 80 GPa and the temperature of the α-γ transition at 3 GPa agree well with the experimental phase diagram of uranium.     

太赫兹技术在医学检测和诊断中的应用研究

近年来太赫兹科学技术日益受到科学界和工业界的重视并得到了较大的发展,太赫兹技术在医学领域上的应用已成为人们关注的重要方面之一。介绍了太赫兹波的特点、太赫兹光谱和成像技术;重点讨论了近年来太赫兹光谱和成像技术在医学检测和诊断领域中的应用和研究进展;并探讨了太赫兹光谱和成像技术发展中需要解决的问题以及今后发展的方向。     

Magnetic and structural correlations in EuMnO and BiMnO crystals in the paramagnetic temperature range

The magnetic and dielectric properties of EuMn₂O₅ and BiMn₂O₅ crystals are investigated over a wide range of temperatures 4.2–250 K, including the range T≫T _N ≃40 K. Significant departures from the Curie-Weiss law are observed in both crystals for the magnetic susceptibility in the paramagnetic range; they are attributed to the presence of correlated domains of magnetic order over a wide range of temperatures. Anomalies in the dielectric properties of the crystals are observed in the same temperature range T>T _N and, as in the case T<T _N , are correlated with the magnetic properties. Zh. éksp. Teor. Fiz. 112, 284–295 (July 1997)