Piezo-optic properties of TGS crystals doped with <Emphasis Type="Italic">D</Emphasis>-serine

The effect of uniaxial mechanical pressure along the main crystallophysical axes on the principal values of birefringence Δn _i in TGS crystals doped with 5% D-serine is investigated. It is ascertained that the values of Δn _i are rather sensitive to the action of uniaxial stresses. The temperature shift coefficients ?T _c /?σ_m are determined for the phase-transition points. The temperature and spectral dependences of the combined piezo-optic constants π _im ⁰ are calculated. The contribution of the secondary electro-optic effect to the changes in the birefringence and the piezo-optic constants of doped crystals is determined. It is found that the piezooptic constants π ₂₃ ⁰ and π ₁₂ ⁰ have the same values, which indicates a decrease in the anisotropy of the optical indicatrix of doped crystals under the action of uniaxial stress. The optical and deformation contributions to the relaxation effect of piezo-optical birefringence in doped TGS crystals are found.     

Absolute piezo-optic constants of Rochelle salt crystals

The effect of uniaxial mechanical pressures applied along the main crystallophysical axes and the corresponding bisector directions on the birefringence of Rochelle salt crystals has been studied. The temperature (77–300 K) and spectral (300–700 nm) curves of the combined, π _im ⁰ and absolute, π_im, piezo-optic constants of crystals are calculated. It is found that the disperse π_im curves are intersected in the vicinity of the inversion of the birefringence sign, which indicates a higher symmetry of the piezo-optic constant tensor. The temperature dependences of the absolute piezo-optic constants show no clearly pronounced anomalies in the vicinity of the phase transitions in the Rochelle salt crystals.     

Isogyre equation for uniaxial and biaxial crystals

The isogyre equation determining the functional dependence between the coordinates of optical axes and isogyre points, valid for any cross sections in uniaxial and biaxial crystals, has been derived. It is used for plotting an isogyre and solving the inverse problem of determining the angle between the optical axes and the elements of orientation of a crystal’s optical indicatrix.     

Static photoelasticity of gallium phosphide crystals

The piezo-optic effect (POE) in cubic GaP crystals (symmetry class [`4]\bar 43m) is studied in detail by interferometry. The relations for determining the absolute piezo-optic coefficients (POCs) π _im or their combinations on a sample of X/45° cut at all allowable geometries of the experiment are recorded. The determination of a specific coefficient π _im at different experimental geometries on samples of right cuts and a X/45° cut made it possible to find the π _im values with a high accuracy and reliability.     

Temperature dependence of the crystal-optics characteristics of [N(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>]<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript>:Ni<Superscript>2+</Superscript> crystals with correlated motion of tetrahedral groups

The optical birefringence, optical indicatrix rotation, and residual intensity have been experimentally investigated in the parent and incommensurate phases of [N(CH₃)₄]₂ZnCl₄ crystals doped with Ni²⁺. The temperature dependences obtained are nonlinear in a wide temperature range (T _i − 360 K). It is shown that the nature of this nonlinearity is related to the presence of local spatial regions of the correlated motion of tetrahedral groups. It is established that the deformation of tetrahedral groups increases the temperature range of existence of these regions.     

Effect of optical basicity on Er3+ up-conversion luminescence in GeO2–R2O glasses

The effect of optical basicity on Er³⁺ up-conversion luminescence in germanate glasses is investigated under 980 nm excitation. The intensity of green and red up-conversion luminescence decreased with the increase in radius of alkali ion or Li₂O content, implying that up-conversion luminescence strongly relates to the optical basicity of glass host. On the other hand, as increasing the optical basicity, the red emission intensity decreased significantly, while the green emission intensity decreased slightly. It has been proposed that the up-conversion luminescence intensity was dominated by the optical basicity, which theoretically estimated from glass composition. The interaction mechanism between up-conversion process and optical basicity was proposed.     

A Direct Method for the Determination of Orientation Relationships Using TEM

A new method for the determination of orientation relationships has been developed. The method is based on a recently proposed direct method for orientation determination using a transmission electron microscope (TEM). The determination of the orientation relationship can be done by two different but generally applicable approaches. The first approach is especially applicable for crystals with orthogonal base vectors, the second approach is especially applicable for crystals with non-orthogonal base vectors and the general bicrystal.     

Piezo-optic properties of K2SO4 crystals

The effect of uniaxial stresses applied along the principal crystallographic directions on the dispersion and temperature dependences of birefringence of K₂SO₄ crystals is studied. The birefringence is found to be sensitive to uniaxial stresses. The spectral and temperature dependences of the combined and absolute piezo-optic coefficients of these crystals are investigated. Their significant anomalies are observed at the ferroelectric phase transition. They are caused by the change in the induced birefringence due to the occurrence of spontaneous deformation. The contributions of the electro-optic and elasto-optic effects to the spontaneous variations in the piezo-optic constants are separated.     

Piezo-optic properties of incommensurately modulated K<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> crystals

The effect that uniaxial pressures along the principal crystallophysical directions have on the dispersion and temperature dependences of the birefringence in incommensurate K₂ZnCl₄ crystals has been investigated in a wide temperature range. This parameter has been established to be fairly sensitive to uniaxial pressures. The spectral and temperature dependences of combined piezo-optic coefficients are analyzed. Significant anomalies of these coefficients are found at the incommensurate-commensurate phase transition. They are due to the change in the induced birefringence that results from spontaneous polarization and to the significant effect of uniaxial stress on the soliton structure of the crystal. The contributions that the electrooptic effect, the elasto-optic effect, and the order parameter make to the spontaneous changes in the piezooptic coefficients are separated.     

Thermal stresses in a cylinder: Application to optical waveguide blanks

An analysis is presented for the calculation of thermal stresses in a hollow cylinder with free ends, in which the elastic and thermal properties are all functions of radius, r. When Young's modulus and Poisson's ratio vary with r, the solution is obtained by the method of successive approximations, but the first approximation is sufficiently accurate for most purposes. For the particular case of optical waveguide blanks, it is shown that the variation in set point with radius can have a significant effect on the calculated stresses. When variations in all properties are considered, the calculated axial stress is in good agreement with a measured value.     

Athermal Directions in KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> Crystal

All orientations of the phase normal, at which the phase of a light wave propagating through a crystal is independent of its temperature (athermal phase directions), have been numerically found for a KGd(WO₄)₂ crystal. There are two sets of such directions for each isonormal wave. Their intersection with the main planes of the optical indicatrix of the crystal yields four athermal directions in the planes orthogonal to the axes with the minimum and intermediate refractive indices and two directions in the plane orthogonal to the axis with the maximum refractive index.     

Investigation of the concave spherical surface quality by a sliding X-ray beam

A new approach to the investigation of the quality of concave spherical surfaces has been proposed and experimentally implemented for the first time. This approach is based on the whispering gallery effect in the X-ray wavelength range. One distinctive feature of the technique proposed is the application of algorithms of computed tomography for locating surface defects and describing their shape. It is noteworthy that the sizes of surfaces and their radius of curvature are not restrictive factors for this analysis.     

Optical properties of KGd(WO4)2 single crystals studied by Brillouin spectroscopy

The results of a study of KGd(WO₄)₂ single crystals by Brillouin scattering method are presented. The Brillouin spectra for the acoustic phonons propagating in the [100], [010], [001], [110] and [101] directions, taken in 90° and 180° scattering geometry at room temperature have been recorded. Using the Brillouin spectroscopy the refractive indices for some directions of KGd(WO₄)₂ crystals were determined. The refractive indices were also calculated for the same directions by the rotation transformation of the principal optical axes of the optical indicatrix to the crystallographic directions of KGd(WO₄)₂ crystals. Moreover, some anomalies of the acoustic phonons propagating connected with birefringence of KGd(WO₄)₂ crystals were discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The stress birefringence images of low angle grain boundaries in 6H‐SiC single crystals

Low angle grain boundaries, also referred to as domain walls, is one of the major structural defects in c‐axis physical vapor transport (PVT) grown hexagonal Silicon Carbide. To investigate the nature of the low angle boundaries, polarized optical microscope was used. The low angle boundary gives bright stress birefringence images under polarizing optical microscope. Periodic extinction of the stress birefringence images occurs when the (0001)‐face SiC is rotated under polarizing optical microscope. The micro‐structure of the low angle boundary is proposed. Using dislocation elastic theory, it is theoretically confirmed that the domains consist of uniform pure edge dislocations with Burgers vectors perpendicular to the dislocation arrays. The simulation results coincide with the experimental observations.     

Light scattering in langasite (La3Ga5SiO14) crystals

A way to plot the light-scattering indicatrix for crystals in the form of rectangular parallelepipeds of different crystallophysical orientations has been proposed. The experimental setup, which makes it possible to record the intensity of light scattered in these samples in the plane oriented perpendicular to the input face, has been designed. The light-scattering indicatrices for langasite crystals have been plotted in the XY and YZ planes. The reflectance and transmittance of the samples under the normal incidence of light have been estimated. The maximum angle at which the light scattered within the crystal bulk emerges from it without total internal reflection has been found. The angle by which langasite crystal should be rotated to record the scattered-light intensity by a photodetector has been experimentally determined.     

大尺寸高浓度掺杂Nd:GGG和Nd:YAG晶体的光谱性质

由于Nd3 离子半径0.112nm和Y3 离子半径0.101nm相差10.9%,使得Nd3 离子非常难于进入YAG晶体中。我们用温度梯度法生长了大尺寸高浓度(2.8 at%)的Nd:YAG晶体,同时与用提拉法Nd:GGG晶体进行了比较。分析了高浓度掺杂Nd:GGG和Nd:YAG晶体浓度猝灭问题。研究了不同浓度掺杂的猝灭效应。在同样的掺杂浓度下,我们发现它们的猝灭程度不同,其原因是两种晶体中ΔE(m is-)m和ΔE(m i s )m不同。     

Electro-optical effects in anisotropic crystals: I. The Pockels effect

The perturbation-theory method is proposed to calculate the induced anisotropy optical effects in crystals with different symmetries. On its basis, the influence of the Pockels effect on the light propagation in crystals with different symmetries is analyzed using Fedorov’s approach of invariant vector fields. This approach has many advantages over known methods in calculating different versions of Pockels effect application for different purposes. Calculation schemes are presented that make it possible to select longitudinal and transverse versions of electro-optical sensors and modulators, which can be used, in particular, to design optical measuring transformers and electric field sensors in high-voltage power lines.     

Capillary shaping of crystals pulled downward from a melt by the crucibleless AHP method

A model is proposed for capillary shaping of a crystal in the crucibleless variant of the AHP (axial heat flux close to the phase interface) method when the melt in the form of a film flowing over the AHP heater is fed to a meniscus. The meniscus and the film of the melt are described by the same equation with a discontinuous right-hand side. The dependences of the crystal radius and the thickness of the melt film on the parameters of the process are numerically investigated, and the capillary stability of the pulling process is analyzed. It is demonstrated that, in this method, the thickness of the melt layer between the crystal and the heater can be considerably larger than the capillary constant.     

Complex study of the structural and optical homogeneity of lithium niobate crystals

Methods of Raman spectroscopy, laser conoscopy, optical microscopy, and electron spin resonance have been used to study the photorefractive properties and structural and optical homogeneity of the following lithium niobate (LiNbO₃) crystals: nominally pure crystals of congruent composition (LiNbO_3con); LiNbO₃:Cu[0.015 wt %] crystals grown from a melt of congruent composition and nominally pure crystals of stoichiometric composition grown from a melt with 58.6 mol % Li₂O (LiNbO_3st). A small deformation of optical indicatrix and regular microdomain structures of fractal type are revealed for the LiNbO₃:Cu[0.015 wt %]; the microdomain structures may be due to the nonuniform impurity incorporation into the structure. It is shown that oxygen octahedra in the LiNbO₃:Cu[0.015 wt %] crystal are deformed in comparison with the octahedra in LiNbO_3st and LiNbO_3con crystals and that the main and impurity cations are clusterized along the polar axis. It is established that the LiNbO₃:Cu[0.015 wt %] crystal exhibits photorefractive properties not only due to the presence of intrinsic defects with localized electrons, as in the case of LiNbO_3st, but also due to the charge exchange in copper cations (Cu²⁺ → Cu⁺) under illumination.