Optical Properties of TGS Crystal with <Emphasis Type="Italic">L</Emphasis>-Valine Admixture

The thermal expansion and temperature and the spectral dependences of the refractive indices and birefringence of triglycine sulphate (TGS) crystals with a 5% L-valine admixture have been investigated. It is established that the introduction of L-valine weakens the temperature dependence of the refractive indices and the birefringence and thermal expansion of TGS crystals. The parameters of the Sellmeier formula, refractions, and electronic polarizabilities are calculated. The changes observed may be related to the increase in hardness of admixture-containing crystals, the decrease in the spontaneous polarization, the replacement of the refraction components of the valine bond, or the spontaneous electro-optic effect.     

On the spontaneous electro-optic effect in triglycine sulphate crystals with L-threonine admixture

The temperature and spectral dependences of the coefficients R _i2* of the quadratic electro-optic effect (EOE) in triglycine sulphate crystals with 5% L-threonine admixture have been calculated using the temperature and spectral dependences of the refractive indices n _i . It is established that the coefficients R _i2* of the admixture-containing triglycine sulphate crystals exhibit weak spectral and temperature dependences. In the polar direction, R _i2* are substantially different from the coefficients of admixture-free triglycine sulphate crystals. This indicates the occurrence of a bias field, the predominant orientation of the dipole moment of the polar defect, and a decrease in the spontaneous polarization in admixture-containing crystals.     

Water-soluble ferroelectric crystals with inhomogeneous impurity distribution

Stabilization of the unipolar state via the formation of inhomogeneous impurity distribution in crystal bulk is considered. Possible growth of crystals with stable characteristics is demonstrated on triglycine sulfate (TGS) crystals with a regular inhomogeneous impurity distribution. The properties of TGS crystals with an inhomogeneous distribution of chromium ions grown above and below the Curie temperature T_C are studied. Inhomogeneous TGS crystals of three types are obtained: type-I crystals with a smooth variation of the concentration gradient along the growth direction, type-II crystals with a periodic layer variation of the impurity concentration, and type-III crystals with a sawtooth-like variation of the impurity concentration along the sample length. The TGS crystals with the regular inhomogeneous impurity distribution in the ferroelectric phase are characterized by higher values of the internal bias field E _b , unipolarity coefficient k, and pyroelectric coefficient γ than the inhomogeneous crystals in the paraelectric phase and the crystals with the statistic impurity distribution grown by the conventional method.     

Optical and nonlinear laser properties of the χ<Superscript>(3)</Superscript>-active monoclinic α-KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystals

Monoclinic α-KRE(WO₄)₂ crystals are grown. Their structure is described in two crystallographic settings. The principal refractive indices are determined and the coefficients and characteristic wavelengths are used for calculating refractive indices by the Selmeyer formulas. The data on the anisotropic parametric Raman generation in these crystals under the picosecond pumping are discussed.     

含孤立MO3平面基团晶体折射率计算

本文建立了一种计算含孤立MO3 (M=B,C)平面基团晶体折射率简单可行的方法,选择部分已知折射率的含孤立MO3平面基团的晶体,采用最小二乘拟合法,定出基团各向异性极化率和其晶体环境参数,并据此计算其它晶体的折射率.对30余种晶体折射率的计算结果表明,该方法所得结果与实测值之间相差不大于3.5;.同时计算了YCa4O(BO3)3,LaCa4O(BO3)3,Ca5(BO3)3F三种单斜晶体的折射率主轴方向,其中对LaCa4O(BO3)3和YCa4O(BO3)3两种晶体,计算结果与实验值符合很好,将为该晶体未来定向提供参考.     

Growth and some properties of cerium sulphate enneahydrate single crystals

Colorless single crystals of cerium sulphate enneahydrate were grown from aqueous solutions under carefully controlled conditions of temperature and supersaturation. Polarized Raman spectra and vibrational assignments of oriented single crystals are reported. Several physical properties (density, refractive indices, dielectric constants, coefficient of linear expansion, specific heat, microhardness) are also listed.     

Measurement of the Refractive Index and Estimate of the Order Parameter in Oriented Liquid Crystals

The refractive indices of a cholesteric liquid crystal, cholesteryl dodecyl carbonate (CDC), and a smectic liquid crystal, p-n-octoxybenzilidene-p-n-butylaniline (OOBBA), have been measured as a function of temperature in the transition temperature regions. The measurements were made on oriented liquid crystals with an Abbe refractometer. By combining the data on ordinary and extraordinary refractive indices, the relative order parameter, α_aS/α, is plotted as a function of temperature. The behavior of the order parameter near the cholesteric to isotropic transition of CDC is similar to a nematic liquid crystal, whereas, the order parameter in OOBBA shows only a slight temperature variation like many solids.     

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)     

Dependence of refractive indexes dispersion for LiNbO3 on impurity

The effect of the impurities of the transition metals Co, Mn, Cr, Fe, Ni, Cu on the dispersion of the refractive indexes of LiNbO₃ is studied. The dispersion curves for LiNbO₃ are compared to those for the pure crystals. The relation between the difference of the refractive indexes of the pure and doped LiNbO₃ and the ionic radius of the impurity is established.     

An analysis of the phenomenon of thermostimulated long-term memory of LiNbO<Subscript>3</Subscript> crystals

The way that the difference in the refractive indices of lithium niobate crystals changes upon the rapid heating of a sample with electroconductive masks deposited on its surface has been studied. It is shown that the phenomena observed are fully described by the pyroelectric effect in the presence of temperature gradient on polar surfaces of the sample.     

Linear optical properties and Raman spectroscopy of natural fluorapatite

Precision refractive indices and their dispersion in the visible and near IR range (430 – 2400 nm) and thermal expansion (including its anisotropy and temperature dependence between 144 K and 673 K) were determined for gem‐quality crystals of fluorapatite from Durango, Mexico. In addition, results of a polarized Raman spectroscopy study on these crystals are given. Fluorapatite crystals show moderate values of thermal expansion with small anisotropy. The linear optical properties of the crystals allow no phase matching for third harmonic generation, but signalize, together with the Raman characteristics, a potential suitability of fluorapatite as nonlinear optical material for χ⁽³⁾‐based stimulated Raman scattering.     

Thermal conductivity and refractive indices of Nd:GdVO4 crystals

The thermal conductivities of Nd:YAG, M(Y,Gd)VO₄ crystals were measured at 298 K. The value of Nd:GdVO₄ crystal along <001> direction was 11.4 W/mK, which was higher than that of YAG crystal measured to be 10.7 W/mK. The principal refractive indices of Nd:GdVO₄ crystal in the temperature range from 20 °C to 170 °C were determined by auto‐collimation method. Based on the measured values of refractive indices, the Sellmeier equation and expression of temperature dependence of refractive indices have been obtained. The measured results show that the birefringence Δn is 0.22007 at 20 °C and temperature coefficient of birefringence is 4.33 × 10⁻⁶/°C for 1.064 μm. These results prove that the GdVO₄ crystal is a laser crystal with excellent thermal and birefringence properties. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of lanthanum-gallium tantalate at different growth and post-growth treatment conditions

Optical properties of lanthanum-gallium tantalate crystals grown in different atmospheres (argon, argon-oxygen mixture, air) have been investigated. Optical transmission spectra in the ranges 0.185–0.800 and 2.0–10.0 μm have been recorded. The range of lanthanum gallium tantalate transparency is established to be 0.26–7.6 μm. The main refractive indices n _o and n _e have been measured and their inhomogeneity and dispersion have been investigated in the range 0.40–0.70 μm. It is shown that the growth atmosphere significantly affects the optical properties of the crystals studied.     

The distribution of impurities in lysozyme crystals

The effective distribution coefficient, K_Ieff, of turkey egg white lysozyme into host hen egg white lysozyme crystals was measured for varying levels of relative supersaturation, impurity concentrations and temperatures. Turkey egg white lysozyme served as a test impurity of high homology to hen egg white lysozyme. K_Ieff increased with increasing host protein concentration and temperature, consistent with a kinetically controlled incorporation process. The principles of slow crystal growth rate to limit impurity incorporation were applied to a commercial source of lysozyme with concomitant improvement in purity of re-crystallized protein.     

Refractometry of mechanically compressed RbKSO<Subscript>4</Subscript> crystals

The unit-cell parameters and the spatial symmetry of RbKSO₄ crystals are determined. The temperature and spectral dependences of the refractive indices and birefringence of these crystals are measured. Two first-order phase transitions are found to occur at 116 and 820 K, and the occurrence of isotropic points for three crystallophysical directions is established. The effect of uniaxial stresses on the optical properties of the crystal is studied. Both the birefringence and the birefringence-sign inversion points are found to be rather sensitive to the action of uniaxial mechanical stresses. The temperature-spectral and spectral-baric diagrams of the isotropic state of the RbKSO₄ crystal, as well as the baric shifts of the phase-transition temperatures, are determined.     

The distribution of Ga and Sb impurities in Ge-Si crystals grown by the Bridgman method using a feeding rod

Gallium- and antimony-doped Ge_{1 ? x} Si _x crystals (0 ≤ x ≤ 0.25) have been grown by the improved Bridgman method using a silicon seed and a macrohomogeneous feeding Ge-Si rod of the corresponding composition. The impurity concentration profiles along the grown crystals were determined from Hall measurements. The mathematical problem of impurity distribution along two-component mixed crystals grown from a melt with uniform and graded composition is solved in the Pfann approximation and within the virtual-crystal model for the solid solution. It is shown that the experimental impurity distributions in Ge_{1 ? x} Si _x crystals are described well by the data calculated on the assumption of linear change in the impurity segregation coefficient with the crystal composition.     

Refractive indices of LiNb1−yTayO3 single crystals

The refractive indices of LiNb_1?yTa_yO₃ single crystals grown by the Czochralski method were determined in the wavelength range 5893 to 10600 Å at 20 ± 0.5°C. The results indicate that a single crystal (0.95 < y < 0.96) has zero birefringence. Such composition is independent of the wavelength.     

Investigation of the optical properties of KGd(WO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Nd<Superscript>3+</Superscript> crystals with allowance for absorption

The optical properties of a biaxial absorbing KGd(WO₄)₂:Nd³⁺ crystal have been investigated. The main refractive indices were measured in the visible spectral range and the absorption and transmission spectra of samples of these crystals were studied. The changes in the refractive indices were in the region of the absorption bands with the use of the Kramers-Kronig relation. Conoscopic pictures of this crystal in the regions of transparency and absorption bands were calculated and are presented.     

A survey of research on KTP and its analogue crystals

This paper reviews the growth and properties of KTiOPOP₄ (KTP) and its analogue crystals including its isomorphous crystals and doped crystals. Based on the calculation of the refractive indices and phase matching of KTP crystals, it is shown that non-critical phase matching can be achieved theoretically. In a 4%Nb-doped KTP crystal, non-critical phase matching was obtained with a pulsed Nd:YAG laser in an efficiency of ca. 4%. Most of the isomorphous and doped KTP crystals possess similar physical, optical and nonlinear optical properties as those of KTP.RbTiOPO₄, KTiOASO₄ and RbTiOASO₄ crystals have better electrooptical figure of merit and RbTiOPO₄ crystals have a fast ion conductor character. Some doped KTP crystals have shown high second harmonic generation efficiencies and damage thresholds. But the homogeneity of KTP analogue crystals is poorer than that of KTP. On the base of damage threshold tests using a CW Argon laser, it is concluded that the best second harmonic generation crystal among all the KTP analogue crystals is still KTP itself. Special care must be taken to eliminate impurity centers to avoid the formation of gray track and photorefractive centers.     

On the coexistence of phases at the α–β transition in quartz

The character of the α–β transition in crystals of natural and synthetic quartz has been studied by measuring the refractive index. The coexistence of two different crystallographic modifications over some temperature range has been established. The α–β phase transition is supposed to be attributed to the near-critical phase transitions. In synthetic quartz with Al and Fe structural impurity the α–β transition consists of two successive transitions. First the transition from the α-phase to an intermediate one takes place, then the intermediate phase is transformed into the β-Phase. Within a certain temperature range there exists only the intermediate phase.