Features of light attenuation in crystals under violation of the Bouguer law

A computer simulation and measurements of the light transmittance of germanium and paratellurite crystals of different thickness were used to show that, at scattering probabilities of photons comparable to their absorption probabilities, the standard methods for calculating light extinction coefficients on the basis of the Bouguer law lead to rough errors in estimation of the optical quality of a material.     

Optical properties of non‐centrosymmetric mixed crystals K2(La1‐x Cex)(NO3)5 · 2 H2O (x = 0.0 – 1.0)

Large single crystals of optical quality of the non‐centrosymmetric orthorhombic potassium rare earth nitrate mixed crystals K₂(La_1–x Ce_x)(NO₃)₅ · 2 H₂O were grown at 38 °C from diluted HNO₃. For crystals with x = 0.0, 0.19, 0.38 and 0.66 refractive indices and their dispersion were determined with an error less than 1 · 10^–4 in the wavelength range 0.404 – 1.083 μm by the prism method. Phase matching conditions for collinear SHG frequency conversion were analysed in detail, including calculation of the effective nonlinear optical susceptibility. By an appropriate choice of the fraction x of cerium the mixed crystals K₂(La_1–x Ce_x)(NO₃)₅ · 2 H₂O allow an adjustment of non‐critical type I phase matching conditions to a desired wavelength of the fundamental wave within the range 1.055(4) – 1.107(6) μm. Non‐critical type II phase matching can be tuned in the wavelength range 0.949(2) – 0.931(2) μm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of photorefractive Bi12TiO20 single crystals

Photorefractive Bi₁₂TiO₂₀ single crystals of high optical quality were grown in a resistive heating furnace from high temperature nonstoichiometric (10:1) solutions of Bi₂O₃ and TiO₂ at pulling rates 0.3–0.8 mm/h at rotation 20–30 rpm along the <001> and <011> axis. Powder X-ray analysis, Laue method, and electron-probe microanalysis were used for characterization. BTO crystals have the bcc structure of sillenite type with a₀ = 10.178(8) Å. The chemical composition of the crystals can be written down as Bi_{12.1 ± 0.2}Tio_{0.96 ± 0.09}O_20.1. Natural optical activity ρ of BTO crystals is 6.3 ± 0.2 deg/mm at λ = 0.633 μm and 11.9 ± 0.2 deg/mm at λ = 0.5145 μm, optical absorption coefficient α = 0.42 ± 0.04 cm⁻¹ at λ = 0.633 μm and linear electro-optic coefficient r₄₁ = r₅₂ = r₆₃ = 5.3 pm/V. Fanning effect in the “fiber-like” BTO sample was studied and double phase conjugation with conversion efficiency up to 8% was observed in a wide range of incidence angles of the pump at λ = 0.633 μm for 2 × 3 mW input light power.     

Observation of strong virtual scattering under three-beam (220, 371) X-ray diffraction in TeO<Subscript>2</Subscript> single crystal

A strong effect of virtual scattering has been experimentally observed when studying the nearly coplanar three-beam (220, 371) X-ray diffraction in a paratellurite single crystal under high-resolution double-crystal X-ray diffraction using MoK _α1 radiation. One characteristic feature of this effect is that the angular dependence of the first (strong) reflection intensity and its shape barely change in the three-beam range of parameters, whereas very strong changes are observed for the second (weak) reflection not only in the three-beam range but also far beyond it, which is related to the variation in the two-beam diffraction parameter due to virtual scattering. The changes observed are asymmetric and make it possible to determine the triplet combination of structure-factor phases.     

Lattice Parameter Local Determination for Trigonal,Hexagonal, and Tetragonal Crystal Systems Using Several Coplanar X-Ray Reflections

The method for determining the local lattice parameters using quasi-multiple X-ray diffraction (which was proposed and used only for crystals of the cubic system) has been expanded to measure the local crystal lattice parameters for the trigonal, hexagonal, and tetragonal systems. Local variations in the lattice parameters in the tetragonal paratellurite (TeO₂) and trigonal lanthanum-gallium tantalate (La₃Ga_5.5Ta_0.5O₁₄) crystals have been investigated. Reflections necessary for implementing the quasi-multiple X-ray diffraction scheme are found for these crystals. The pairs of reflections that were found were used to complete quasi-multiple X-ray diffraction schemes on a laboratory X-ray source and determine the variation in the lattice parameter a along the surface of these crystals. The relative measurement error was 4 x 10^-6 at a spatial resolution of 140 μm. The accuracy of the method and the parameters determining this characteristic were analyzed based on the results. The locality of the method and the limits of the spatial resolution of an X-ray diffraction measurement of lattice parameters are estimated.     

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.     

Bidomain structures formed in lithium niobate and lithium tantalate single crystals by light annealing

The bidomain structures produced by light external heating in z-cut lithium niobate and lithium tantalate single crystals are formed and studied. Interdomain regions about 200 and 40 μm wide in, respectively, LiNbO₃ and LiTaO₃ bidomain crystals are visualized and studied by optical microscopy and piezoresponse force microscopy. Extended chains and lines of domains in the form of thin layers with a width less than 10 μm in volume, which penetrate the interdomain region and spread over distances of up to 1 mm, are found.     

Study on K(DxH1‐x)2PO4 Crystals: Growth Habit,Optical Properties and their Improvement by Thermal‐Conditioning

Phosphite, which often exists in growth solutions obtained directly from commercial P₂O₅ , was found to have significant inhibiting effects on the growth of pyramidal face of KDP crystals. K(D_xH_1‐x)₂PO₄ (referred to as DKDP) crystals with different deuterium fraction x were grown and the optical performances were investigated. The absorption coefficients at 1.05 μm decreases monotonically with the increase of x. The transmission threshold shift from 1.65μm at x=0 to 2.10 μm at x=0.96. The high temperature phase transition temperature and latent heat were measured using the method of differential scanning calorimetry (DSC). Thermal conditioning experiments were carried out at 180°C and 140°C for KDP and DKDP, respectively. After conditioning, a different degree of improvement was observed in the optical homogeneity of the samples, while the laser damage threshold and light absorption coefficient showed no significant change.     

A new optical medium—Cd<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>F<Subscript>2</Subscript> single crystals

For the first time, single crystals of the Cd_0.75Sr_0.25F₂ solid solution with the fluorite structure are grown from melt by the Bridgman-Stockbarger method. The composition of these single crystals corresponds to the composition congruently melting at the minimum point on the phase diagram. The maximum diameter of the crystal is 50 mm; the maximum height is 30 mm. The vickers microhardness of the semitransparent crystals equals 191 ± 43 kg/mm². The transmission cutoff in the IR range is ～10 μm.     

The growth and mechanical properties of paratellurite single crystals at high temperatures

α-TeO₂ single crystals have been grown by the Czochralski method on specially developed systems with automatic growth control. The mechanical properties of crystals under compression in the [100], [110], and [221] directions at a constant strain rate of about 10⁻⁴ s⁻¹ in the temperature range T = 733−993 K have been investigated. The distribution of plastic shear strain in deformed samples is has been experimentally studied. Manifestations of localized strain in covalent paratellurite crystals at T > 900 K are revealed for the first time. The active slip systems along which localized shear band are oriented are determined. The temperature dependence of the critical stress of transition to localized flow is investigated.     

Growth,structural and optical properties of 12%‐deuterated KDP crystals

K(D_0.12H_0.88)₂PO₄ crystals were chosen to be used for quadratic nonlinear medium of wideband frequency doubling at 1 μm. A key limitation on this application is that little information can be found in the previous reports. In this work, growth as well as structural and optical properties of this crystal were investigated in detail. Experimental results in comparison with KDP indicate that lattice parameter along a‐axis changes much more than lattice parameter c and infra‐red absorption edge shift by 0.08 μm accompanied with increasing of transmittance in the whole region. With the introduction of deuterium atom, peak of ν₁(PO4) shifts to lower wave number and transverse stimulated Raman scattering was effectively suppressed. Extra‐ordinary and ordinary indices were also measured as function of wavelength. Good crystalline perfection and great performance of damage threshold also indicate that 12%‐DKDP is an appropriate choice in the application of wideband frequency doubling at 1 μm.     

Optical Properties of MnIn2S2Se2 Single Crystals

Optical transmittance and reflectance spectra of MnIn₂S₂Se₂ single crystals are measured in the wavelength range from 0.5 to 30 μm. The interference method is used to determine the refractive index of the compound for wavelengths between 0.8 and 12 μm. From an analysis of the absorption spectrum it follows that the fundamental edge is due to forbidden indirect transitions between parabolic bands for the polarization E ⊥ c with a gap energy of 1.50 eV at room temperature.     

Defect structure and light‐induced scattering of Zr‐doped near‐stoichiometric Mn:Fe:LiNbO3 crystals grown by TSSG method

Near‐stoichiometric Mn:Fe:LiNbO₃ crystals doped with various concentration of ZrO₂ were grown by top seed solution growth (TSSG) method in the air atmosphere. The Zr concentration in the crystal was determined by inductively coupled plasma optical emission spectrometer. The defect structures were analyzed by means of ultraviolet‐visible and infrared transmittance spectra. The appearance of vibration peak at 3466 cm^‐1 in infrared spectra manifested that Li/Nb ratio in crystals approached to stoichiometric proportion. The fundamental absorption edge represented continuous red‐shift which was discrepancy with congruent doped LiNbO₃ crystals showed that doping ions possessed different location mechanism. The light‐induced scattering of the doped stoichiometric LiNbO₃crystals were quantitatively scaled via incident exposure energy. The results demonstrated that Zr(2 mol%):Mn:Fe:LiNbO₃ crystal had the weakest light‐induced scattering and the mechanism related to their defect structures was discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comments on the properties of an NH4OH-H2O2 etch on epitaxial GaAs

The etching rate of the NH₄OH : H₂O₂ : H₂O = 1:4:20 etch was determined on epitaxial GaAs films and bulk GaAs monocrystals. The etching process has a rather large scattering at the start of the process depending on the origin and properties of films. The etching rate of epitaxial layers approaches the value of 2 μm/min, characteristic of bulk crystals. Surfaces treated with the 1:4:20 etch are applicable to ohmic contacts of Gunn diodes.     

The Crystallisation of Aluminium Trihydroxide (Gibbsite) from Sodium Hydroxide Solution Onto Fine Seeds: Physico-chemical Studies on the Internal Structure and Agglomeration of Different Crystal Fractions

A batch of Bayer gibbsite crystals (particle size range 3 to 70 μm) was prepared by crystal growth onto fine seeds (1 to 3 μm) from sodium hydroxoaluminate/sodium hydroxid-solution. The internal structures and seed agglomeration of different fractions were examined by optical microscopy, infra-red spectrophotometry, thermal analysis and chemical dissolution analysis. These physico-chemical studies confirmed that crystal growth occurs with some seed agglomeration in the early stages, followed by growth onto the ‘agglomerates’. The agglomerated seeds contents (X) were as follows: for fraction DiD (l₀ = 6.3 μm), X = 0.44; for fraction Gi C (l₀ = 20 μm), X = 0.41; for fraction Gi B (l₀ = 38 μm), X = 0.31 and for fraction Gi A (l₀ = 55 μm), X = 0.24.     

Effect of axial vibration on Bi12SiO20 crystal growth by vertical Bridgman technique

Bi₁₂SiO₂₀ single crystals have been grown successfully by vertical Bridgman technique. During the crystal growth process, different axial vibration amplitudes of 50 μm, 70 μm and 100 μm were applied with the same vibration frequency of 50 Hz. The effect of different axial vibration amplitudes on quality of the as‐grown Bi₁₂SiO₂₀ single crystals was discussed. The crystals have been characterized by X‐ray rocking curve optical and absorption spectrum. The experimental results reveal that the axial vibration amplitude has a pronounced effect on quality of the as‐grown Bi₁₂SiO₂₀ single crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects in B–doped KDP crystals irradiated with neutrons of large spectra energy

The results obtained for the r₆₃ electro‐optic coefficient of B‐doped and undoped KDP (KH₂PO₄) crystals irradiated with neutrons (including thermalized neutrons) produced by scattering of 30 Mev cyclotron protons on a target of Ta²⁰¹, are presented and compared to those obtained for non‐irradiated doped and undoped crystals. The B‐doped (H₃BO₃, Na₂B₄O₇ and Li₂B₄O₇) crystals were obtained by the conventional growth method by temperature decrease with 1 wt % dopant concentration in solution. The thermal neutron flux was around ϕ = 1. 10¹⁰ n/cm² s. Pulses of ∼15 μs long, in damped oscillatory mode (V= 8 kV, τ=1.95 μs) were used for the electro‐optic measurements. A Pockels cell, a photomultiplier, a He‐Ne laser (λ=632.8 nm, 5 mW, linearly polarized) and a Tk 720 A oscilloscope complete the experimental setup. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photorefractive Properties of Stoichiometric Lithium Niobate Single Crystals

The specific features of photorefractive light scattering in nominally pure stoichiometric (Li/Nb = 1) sin- gle crystals grown from a melt with 58.6 mol % Li₂O (LiNbO₃st) and in the stoichiometric single crystals grown from a melt of congruent composition in the presence of K₂O flux (LiNbO₃stK₂O) have been investi- gated. At an excitation power of 30 mW, LiNbO₃stK₂O single crystals are found to exhibit a stronger photo- refractive effect than LiNbO₃st single crystals.     

Precipitation of nesquehonite from homogeneous supersaturated solutions

The homogeneous (unseeded) precipitation of nesquehonite (MgCO₃·3H₂O) was studied over the temperature range of 10‐40 °C. Precipitation was triggered by the supersaturation created by mixing MgCl₂ solution (0.5‐1.5 M) with Na₂CO₃ solution in the same concentration range. The Meissner's method was adopted in the calculation of supersaturations during the MgCl₂‐Na₂CO₃ reaction to monitor the precipitation. Solids were identified using X‐ray diffraction (XRD) analysis and scanning electron microscope (SEM) images. In the temperature range of 10‐40 °C, MgCO₃·3H₂O with needle‐like or gel‐like morphology was precipitated. It was seen that the length, width and surface smoothness of the particles changed with reaction temperature and supersaturation. The supersaturation (S) was in the range of 1.09‐58.68 during titration of Na₂CO₃ solution. The dimension of the crystals increased with longer addition time (or lower initial concentration of reactant) at the same temperature. Slower addition via titration of 2 h followed by 2 h of equilibration at 40 °C proved successful in producing well developed needle‐like MgCO₃·3H₂O crystals of 30‐50 μm long and 3‐6 μm wide. MgCO₃·3H₂O obtained were calcined to produce highly pure magnesium oxide (MgO) at 800 °C. The morphology of MgO was similar to that of their corresponding precursors. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of dislocations in a LiNbO3 single crystal grown by micro pulling down method

LiNbO₃ single crystals grown by the micro pulling down (μ-PD) method have been revealed to be as free of dislocations and subgrain boundaries up to 500 μm in diameter. On the other hand, μ-PD LiNbO₃ single crystals grown along the x-axis in diameter of 800 μm were observed to be dislocated due to the size effect of crystal. The Burgers vectors of dislocations were determined to be [22 01], [101 1], and [01 11] by X-ray topography.