Number of optical axes in absorbing triclinic crystals

The possible numbers of optical axes in absorbing triclinic crystals have been considered. Most of these crystals possess four circular optical axes; however, there may be crystals having one isotropic optical axis, two or three circular optical axes, or simultaneously one isotropic and one or two circular optical axes. It is shown that particular cases significantly differ from the general case of crystal with four circular axes. The dependence of the form of the complex permittivity tensor on the number of optical axes is presented. The ellipticities of eigenwaves and the transmitted-light ellipticity in the case of normal incidence of a wave with a right- or left-hand circular polarization are calculated for these crystals.     

Ordinary electromagnetic waves in absorptive crystals

It is shown that “switching-on” of absorption in a continuum of the directions of propagation of ordinary electromagnetic waves in transparent triclinic crystals results in the “survival” of only a discrete number of these directions. The relationships for the angular coordinates of these directions are obtained in terms of the components of a complex permittivity tensor.     

Optical axes in various absorbing crystals

Analytical expressions have been derived for the components of the complex permittivity tensor as a function of the number of optical axes existing in an absorbing monoclinic crystal. Some specific features of the orientation of these axes are considered. The ellipticities of natural waves are calculated for these crystals, as well as the ellipticities of transmitted light for right- or left-hand circularly polarized waves normally incident on a crystal. A significant difference of particular cases of absorbing monoclinic crystals from the general case of crystal with four circular axes is demonstrated.     

Topological approach to investigation of acoustic axes in crystals

The concept of topological degree of a map is generalized to the case of discontinuous maps. The numerical value of such a degree may be a rational number. The representations developed are used for topological interpretation of the characteristics of special directions of propagation of acoustic waves in crystals (specifically, acoustic axes). The Euler theorem is generalized to the case of singularities with rational indices, and this result is applied to the set of acoustic axes in crystals.     

Orientation dependence of electrical and optical properties of ZnSiP2 crystals grown from melt

Undoped and Ga-doped ZnSiP₂ crystals grown by spontaneous crystallization from nonstoichiometric melt show a pronounced dependence of electrical properties (conductivity, carrier concentration) and cathodoluminescence on the orientation of various crystal faces. Breakdown voltage measurements and Hall measurements yielded that the (112)B face is always low-resistivity n-type and the (112)A face is always semi-insulating. The spectral position of the broad luminescence band observed at 80 K differs in a characteristical manner for the various crystal faces. The luminescence behaviour correlates partly with the electrical properties. The results are explained by an orientation dependence of the impurity incorporation which is reflected also in the bulk properties of the crystals.     

Anisotropic optical properties of crystals with the Ca-gallogermanate structure

The optical properties of inactivated and activated crystals with the structure of Ca-gallogermanate have been studied. The components of the gyration pseudotensor for Sr₃Ga₂Ge₄O₁₄ crystals are determined. In the ultraviolet range of the spectra of all the crystals studied, the bands of circular and linear dichroism and the anomalous behavior of the linear birefringence are observed irrespective of the activating dopant. The formation of these bands is not associated with the electron transitions of doping ions and can be caused by structural defects formed in the growth process.     

Orientation of protein crystals grown in a magnetic field

Three crystal forms of hen egg-white lysozyme, and ribonuclease A and met-myoglobin crystals exhibited orientation in a magnetic field of <1 T. Magnetic field application is thus shown to be a possible means to orient protein crystals. The conditions for the orientation to occur and some of its applications are discussed.     

Orientation changes during recovery of compressed Mo crystals

The type of the recovery variety which is accompanied by changes in texture is studied. Reorientation of the surface of compressed Mo crystal was observed during its annealing before recrystallization. As a result, new macroscopic {100} orientation areas appear on the contact crystalline surface of {111} orientation. Turned areas have a more perfect inner structure and correspondingly lesser density of deformation defects. As a result of rotation a high-angle boundary interface occurs as a “broken boundary”. The transition layer considered is highly stressed and contains microcracks. The boundary interface is shown to be the intensive recrystallization source, where the recrystallization grains are nucleated at the expence of interface dislocation bulgings. The driving forces of the rotation observed and a scheme of a residual stress distribution in the compressed crystal are analysed. According to the scheme a deformed crystalline surface is affected by the compressive stresses and the inner layers are affected by the tensile ones. A relaxation of the internal stresses results from plastic rotations. A rotation moment arising between the surfaces and internal layers of the crystal leads to reorientation.     

Anisotropy of optical absorption in layered single crystals

The optical energy gap of Re doped MoSe₂ single crystal Mo_0.995Re_0.005Se₂ has been measured at room temperature near the fundamental absorption edge. The incident light was kept normal to the basal plane i.e. along the c‐axis of the grown crystals. Results have been given on the basis of two and three dimensional models. Both direct and indirect transitions are involved in the absorption process. The indirect transition was found to be allowed with two phonons involved in the process. The three dimensional model and not the two dimensional could be used to describe the optical properties of Re doped MoSe₂ single crystal. Also, the optical energy gaps depend upon the amount of the intercalating Re material. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth conditions and electrical properties of KDP crystals: II. Dielectric permittivity measurements

The dielectric properties of potassium dihydrophosphate single crystals, which were grown from crystallization solutions at different pH, have been studied. The dielectric response of the single crystals is shown to vary substantially depending on the growth conditions and can be significantly different for samples from different growth sectors of the same single crystals and even within one sector. The results of this study are useful for optimizing the growth conditions of these single crystals.     

Solidification behaviour of organic nonlinear optical crystals

A representative rather than exhaustive review has been given on the solidification behaviour of organic nonlinear optical crystals. Many of the developments reported here represent quick experimental responses to the rapid theoretical advances made in the field of nonlinear optics. The article is divided into four parts. The first part deals with the characteristics of the organic nonlinear materials and need for large single crystals. The second and third parts are devoted to the thermophysical properties and experimental studies on crystallization processes. Here, recent work by authors is reviewed on the purification of source material, solidification behaviour and crystal growth. Various interactions between morphology, microsegregation, defects, growth velocity and temperature gradient are discussed. Specific examples of substituted anilines are presented. In the fourth section a stronger interaction is suggested between optical physicists and crystal growers to understand the problems of inhomogeneity, stress, damage threshold and doping in the organic crystals.     

Specific features of optical activity in various uniaxial crystals

The influence of the antisymmetric part of the gyration pseudotensor on the characteristics of reflected and transmitted light has been considered for crystals of classes 3, 4, and 6. The results are compared with the corresponding data for crystals of classes 32, 422, and 622 with a symmetric gyration pseudotensor. Specific features of the optical activity in crystals of classes 3m, 4mm, and 6mm with an antisymmetric gyration pseudotensor have been studied. Crystals of classes \(\bar 42m\) and \(\bar 4\) with the symmetric gyration pseudotensor of an unusual form have been considered. The polarization azimuth and ellipticity of the reflected and transmitted light are calculated for these crystals at different angles of incidence.     

Observation of optical inhomogeneities in flux grown KTP crystals

Optical inhomogeneities in potassium titanyl phosphate crystals grown from different fluxes have been investigated. In the crystals grown from a flux which contains tungsten, striations parallel to the {011} faces were observed. The main reason for forming striations is the change in tungsten concentration with change in growth rate. In the case of a potassium phosphate flux, no striations were observed in the crystal which was grown at almost the same temperature and stirring conditions as for the tungstate flux. We can conclude that the phosphate flux is more suitable for the growth of optically good crystals for KTP as laser harmonic converters.     

Doping of KDP single crystals with cerium: Growth and optical properties

The features of doping of KDP crystals with cerium ions and organocerium complexes with alizarin complexon and arsenazo III have been investigated. It is established that “direct” doping by introducing cerium salts into the initial solution cannot be implemented. The effect of organometallic complexes of cerium on the crystal growth has been studied. Organocerium complexes predominantly enter the prismatic or pyramidal growth sectors. It is shown that the complex arsenazo III + Ce blocks the growth of the prismatic sector. Cerium-doped KDP crystals exhibit a photoluminescence band peaking at the wavelength λ_max= 350 nm.     

Optical activity along the optical axis of crystals with ordered langasite structure

Optical activity along the optical axis of four piezoelectric crystals Sr₃TaGa₃Si₂O₁₄ (STGS), Sr₃NbGa₃Si₂O₁₄ (SNGS), Ca₃TaGa₃Si₂O₁₄ (CTGS) and Ca₃NbGa₃Si₂O₁₄ (CNGS) with ordered langasite structure were studied via a convenient method. All the crystals investigated show unusually large values of the specific rotation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Manifestation of optical activity in crystals of different symmetry classes

Specific features of manifestation of optical activity in cubic, uniaxial, and biaxial crystals are described. The effect of optical activity on characteristics of transmitted light is considered as a function of the wavelength of incident light, temperature, and the orientation the optical axis. The results of the investigation of crystals of different symmetry classes are reported.     

Acoustically induced optical second harmonic generation in InAs crystals

Acoustically induced optical second harmonic generation (AIOSHG) in InAs single crystals was investigated. With increasing acoustical power, the AIOSHG for fundamental CO laser light (λ = 7.1 μm) increases and achieves its maximum value at acoustical power density about 1.70 W/cm². The value of the AIOSHG for InAs was substantially higher than for key inorganic photo‐refractive and ferroelectrics materials. With decreasing temperature, the AIOSHG signal strongly increases below 42 K. The AIOSHG maxima were observed at acoustical frequencies ranged at 7‐11 kHz. Comparing the obtained results with the acoustically induced IR spectra at low temperature, one can conclude that the observed effect is associated with acoustically‐induced phase transformations. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Pinacoidal growth and optical properties of calcite crystals

Optical quality calcite single crystals, CaCO₃, have been grown under hydrothermal conditions in the of CaCO₃ - NH₄Br - H₂O system doped with Li ions. 24- liter autoclaves including titanium inserts were used in these experiments. Optical properties of calcite crystals were studied. The light absorption index of the crystals grown is similar to rhombohedron materials, but pinacoidai calcite have no V-shaped defects.     

Special features of optical strength change in melt-grown NaCl crystals

The variation of the CO₂-laser pulse induced breakdown threshold has been studied experimentally in melt-grown NaCl crystals. An increase of the optical strength (up to two order of magnitude) is observed from the „top”︁ towards „bottom”︁ of the large diameter crystal boules, i.e. in the direction in which the impurities are driven away. The dependence of the threshold with the Ca²⁺ concentration demonstrates a complicated character of the effect of the impurity content on the optical strength of sodium chloride.