Temperature-dependent behavior of birefringence and rotation of the optical indicatrix in crystals of deuterated triglycinesulfate

On the basis of a complex null-polarimetric method, the natural birefringence and the rotation of the optical indicatrix in crystals of deuterated triglycinesulfate are measured in the temperature range of 300–340 K. The temperature-dependent behavior of the optical parameters is shown to be close to that observed previously in triglycinesulfate crystals. Changes in them upon the ferroelectric phase transition can be accounted for by the spontaneous quadratic electro-optic effect, with the values of the electro-optic coefficients being larger by a factor of 1.4 than in triglycinesulfate crystals.     

Investigations of crystalline and optical perfection of SHG oriented KDP crystals

Potassium dihydrogen phosphate (KDP) crystals grown along the type-II phase-matching direction were investigated for crystalline and optical perfection. High-resolution X-ray diffraction (HRXRD) technique was used for investigating crystalline perfection. UV–VIS transmission, Mach–Zehnder interferometry, birefringence interferometry and conoscopy were performed for optical characterization. HRXRD results show that the grown crystals have good structural perfection. A uniform transmittance of 92% was observed in the visible region of the spectrum. Straight and parallel fringes were observed in Mach–Zehnder interferometric studies. A symmetrical fringe pattern was obtained in conoscopy images. These interferometric results suggest that the optical homogeneity of the grown crystal was good and not influenced by the growth technique.     

Effect of Mn(II) doping on crystalline perfection, nonlinear, optical and mechanical properties of KDP single crystals

The effect on crystalline perfection, second harmonic generation (SHG) efficiency, optical transparency and mechanical properties due to Mn(II) doping in KDP single crystals grown by slow evaporation solution technique by adding different quantities of MnCl₂ in the solution has been investigated. The actual incorporated quantity of Mn(II) in the crystals was evaluated by atomic absorption spectroscopy. Powder XRD study confirms the crystal system of KDP and found no additional phases at all doping levels (1 to 5 mol%). The influence of Mn(II) doping on the crystalline perfection has been assessed by high-resolution XRD and these studies revealed that the grown crystals could accommodate Mn(II) in the interstitial positions of the crystalline matrix of KDP only up to some critical concentration, above which the crystal developed structural grain boundaries. The relative SHG efficiency of the crystals was found to be increased sharply at low concentrations (1 mol%), and above this value it was decreased as the concentration increases though it is still higher than that of pure KDP. UV-Vis studies also revealed the same behavior with a significant enhancement at 1 mol% concentration and later gradually decreased. Good increment in the hardness values has been observed by increasing the doping concentrations.     

The parameter of the optical indicatrix of guanidinium aluminum-sulfate hexahydrate crystals

The absorption coefficient (220–1200 nm) and refractive index (800–450 nm) spectra of a strongly anisotropic guanidinium aluminum-sulfate hexahydrate (GASH) crystals are measured. It is shown that the optical anisotropy of GASH crystals in the visible spectral region is significant, while the crystal in the polar direction becomes isotropic. The contribution of IR oscillators to the electronic polarizability of GASH is sharply anisotropic. It is found that the constants of the Sellmeier dispersion formula qualitatively agree with the vacuum ultraviolet spectra calculated from first principles. The experimental refractive indices coincide with the calculated values with an accuracy of 0.10 (n _e ) and 0.1% (n _o ). It is proposed to use the GASH crystal for development of optical phase difference compensators.     

Negative optical refraction in crystals with strong birefringence

The possibility of negative optical refraction of the extraordinary ray in crystals with strong birefringence is demonstrated.     

Influence of l-alanine doping on crystalline perfection, SHG efficiency, optical and mechanical properties of KDP single crystals

Pure and l-alanine (LA) doped single crystals of potassium dihydrogen orthophosphate (KDP) were grown by slow evaporation solution technique (SEST) in aqueous solution at ambient temperature. Powder X-ray diffraction study was done to confirm the crystal system and lattice parameters of KDP. No additional phases were observed at all doping concentrations (1-7.5 mol%), which was further confirmed by FT-Raman spectroscopy analysis. The influence of LA doping on the crystalline perfection was assessed by high-resolution X-ray diffractometry (HRXRD) analysis. HRXRD studies revealed that the grown crystals could accommodate LA at the interstitial positions in the crystalline matrix of KDP up to some critical concentration without any deterioration in the crystalline perfection. Above this concentration, very low angle structural grain boundaries were developed and it seems that the excess LA above the critical concentration was segregated along the grain boundaries. The SHG efficiency was measured using the Kurtz powder technique. The relative SHG efficiency of the crystals was found to be increased with doping concentration up to 5 mol% and above this it decreases. Optical transmission study also revealed the same behavior with enhancement up to 5 mol% concentration and later decreased. The hardness values were found to be increased by increasing the doping concentration.     

Growth, thermal, optical and birefringence studies of semiorganic nonlinear optical thiosemicarbazide cadmium chloride monohydrate (TCCM) single crystals

A semiorganic nonlinear optical material (thiosemicarbazide cadmium chloride monohydrate) (TCCM) was synthesized and single crystals was grown from aqueous solution by slow evaporation method at ambient temperature. Crystal of average size up to 5×4×3 mm³ were harvested and characterized by powder X-ray diffractometry (XRD) and Fourier transfer infrared (FTIR) technique to confirm the identity of the compound formed. The thermal stability was analyzed by TG/DTA. The birefringence values (Δ_n) were determined in the wavelength region 540-6500 Å. The second harmonic generation (SHG) from the materials was confirmed using Nd:YAG laser.     

Anisotropy of laser emission in monoclinic Nd:ScYSiO_5 crystals cut along the optical indicatrix axes

In this Letter,we demonstrate the anisotropy of laser emission in disordered Nd:ScYSiO_5(Nd:SYSO) crystals cut along the optical indicatrix axes.High-powered lasers with different oscillation wavelengths and polarizations are realized by using different oriented crystals as gain media.For Y-cut crystals,the dual-wavelength laser vibration direction is found to be along the X axis and a maximum output power of 9.43 Wis obtained,giving an optical-to-optical conversion efficiency of 48.8% and a slope efficiency of 51.3%.For X-and Z-cut crystals,1075 and 1078 nm lasers operating orthogonally polarize oscillate with total output powers of 7.07 and 8.43 W,respectively.The experimental results reveal that the intrinsic anisotropy for the monoclinic disordered laser crystals could make laser design flexible and controllable.     

Effects of the induced birefringence in photorefractive crystals on speckle optical vortices

In this work, we show that it is possible to change the properties of an optical vortex formed in a speckle pattern by the control of an external electric field applied to a sillenite-type photorefractive material in a non-holographic configuration. To show it, a scheme that allows the recovering of both, the polarization state and the phase distribution of an optical field was implemented. Changes in the polarization state of the light in the neighborhood of the vortex were observed with the application of an external electric field. Likewise, changes in the phase structure around the vortex and displacements of the vortices themselves were measured. These displacements have a fairly linear dependence on the applied field to the photorefractive crystal. Experimental results are qualitatively explained with the theoretical treatment of non-holographic recording in photorefractive crystals.     

Calculation of geometrical birefringence from two-dimensional refractive-index profile in single-mode fibres

We present two numerical approaches to calculate the geometrical birefringence from two-dimenslonal refractive-index profile in single-mode fibres. One is the improved perturbation model theory, the other is based on the general solution of noncircular uniform optical waveguide in an arbitrary coordinate system. Using these methods, we can obtain not only the magnitude of geometrical birefringence, but also the orientation of birefrlngent axes. We report the calculation results of geometrical birefringence in a real single-mode fibre.     

Low viscosity, high birefringence liquid crystalline compounds and mixtures

Two types of fast switching mixtures with high positive dielectric anisotropy were described. The first type, with a birefringence below 0.3, was designed for devices operating at room or lower temperatures and the second one, with a birefringence higher than 0.3 for devices operating at elevated temperatures.     

Determination of birefringence dispersion in nematic liquid crystals by using an S-transform

An analysis of the transmittance signal of the 5CB-coded nematic liquid crystal by using an S-transform is presented. The transmittance spectrum of this liquid crystal is acquired in the 1.26-2.22 microm(-1) region at room temperature. The dispersion curve of birefringence is obtained for 5CB by this analysis, and data are fitted to the Cauchy formula, whereby the dispersion parameters are extracted. The result is found to be in favorable accordance with the Merck catalog value.     

Effect of xylenol orange on the crystalline perfection,optical, piezoelectric and NLO behavior of unidirectionally grown imidazolium L-Tartrate single crystal

Pure and 0.1 mol% Xylenol orange (XO) doped Imidazolium L-tartrate (IMLT) nonlinear optical (NLO) single crystals were grown using Sankaranarayanan–Ramasamy (SR) method of uniaxial solution crystallization technique. The pure IMLT crystal is 100 mm in length and 15 mm in diameter. The doped IMLT crystal is 25 mm in length and 10 mm in diameter. UV–Vis-NIR spectrum shows that the pure and XO doped IMLT crystals' cut off wavelength is 235 nm. High-resolution X-ray diffraction (HRXRD) measurement and birefringence interferometry confirm that the SR method grown crystal has good crystalline perfection and optical homogeneity. The wavelength dependent refractive index and piezoelectric d₃₃ coefficient were measured. The difference refractive index (Δn) of (100) plane in parallel and perpendicular directions shows a strong dependence on wavelength. The dielectric constant, hardness and SHG conversion efficiency were also increased as a result of XO dye doping in IMLT crystal.     

Study of optical parameters of two fluorinated isothiocyanato nematic liquid crystals exhibiting high birefringence

Optical studies have been carried out on two fluorinated isothiocyanato nematic liquid crystal (LC) compounds 4′-butylcyclohexyl-3, 5-difluoro-4-isothiocyanatobiphenyl and 4′-pentylcyclohexyl-3, 5-difluoro-4-isothiocynatobiphenyl. Transition temperatures of the two samples were confirmed using a polarizing microscope. The two LC compounds were found to exhibit fairly high clearing temperatures. Measurements of refractive indices of the two compounds were done by using thin prism method with He-Ne laser beam of wavelength 630 nm. Birefringence of the two LC compounds was calculated from the measured refractive indices. Both the compounds are found to display fairly high values of birefringence. Validation of a modified four-parameter model, based on Vuks equation describing the temperature dependence of refractive indices of the two liquid crystals, is also presented in this paper. The model is validated by fitting the experimentally measured values of refractive indices, birefringence and average refractive indices of the two nematic LCs with the theoretical values. In this paper, the calculation of order parameters of the LCs is presented by using two methods: direct extrapolation method based solely on the birefringence data and by using modified Vuks method based on Haller’s extrapolation. As observed from the obtained results, this procedure of calculating order parameter gives very reasonable results.     

Investigation on the bulk crystal growth,crystalline perfection,refractive index and piezoelectric properties of borate single crystals for piezoelectric and electro-optic applications

Low solubility potassium pentaborate tetrahydrate (KB5), ammonium pentaborate tetrahydrate (AB5) and mixed (KAB5) single crystals have been grown by the Sankaranarayanan-Ramasamy (SR) method. The crystal structures and space groups have been confirmed by powder XRD analysis. The direction of the grown crystal was confirmed by the back reflection X-ray Laue pattern. The crystalline perfection (CP) of the crystals have been evaluated using HRXRD studies. The transmittance spectra of the grown crystals were recorded by UV–Vis-NIR transmission studies showing that all the crystals have 90% transmittance in the entire visible region and found that the crystals' cut off wavelengths were below 200 nm. The optical studies such as refractive index (RI) and birefringence interferometry (BI) were reported. The RI for five different wavelengths of KB5, AB5 and KAB5 crystals were analyzed using the prism coupling method (PCM). Electromechanical behavior of the grown crystals was observed using piezoelectric coefficient (d₃₃) measurement. Vickers Microhardness (VMH) measurement carried out at 30 °C shows increased hardness as the load increases.     

高质量胶体晶体薄膜的快速制备及表征

通过控制温度和湿度，用垂直沉积法（vertical deposition method）快速制备出了可精确控制样品的厚度、在较大范围呈现好的有序性的密排结构的聚苯乙烯（PS）胶体晶体 薄膜.利用透射电子显微镜直观准确地确定了样品为面心（fcc）密排结构.通过控制样品干燥速度和加温处理，胶体颗粒排列更加有序,并且克服了胶体晶体干燥后易碎和在水等溶 剂中容易再分散等缺点，为胶体晶体实际应用创造了条件. 关键词： 胶体晶体薄膜 垂直沉积法 面心密排结构 再分散     

Investigation of optical homogeneity and photorefractive properties of lithium-niobate single crystals by the Raman-spectroscopy and laser-conoscopy methods

Photorefractive properties and structural and optical homogeneity of (1) LiNbO₃:Cu crystals ([Cu] = 0.015 mas %) grown from a congruent melt, (2) nominally pure stoichiometric crystals grown from a melt with 58.6 mol % of Li₂O (LiNbO_3stoich), and (3) nominally pure congruent crystals (LiNbO_3congr) have been studied using the Raman-spectroscopy method with excitation in the UV, visible, and near-IR ranges; the laser-conoscopy method; and the electron paramagnetic resonance-spectroscopy method. In optically uniaxial LiNbO₃ crystals, a weak optical biaxiality has been revealed, which is attributed to an insignificant deformation of the optical indicatrix. This deformation can be caused both by the initial structural inhomogeneity of crystals and by the photorefractive effect. It has been shown that, under the action of light, charge exchange of copper cations Cu²⁺ → Cu⁺ takes place in the crystal LiNbO₃:Cu ([Cu] = 0.015 mas %). The LiNbO₃:Cu crystal exhibits photorefractive properties not only because of the occurrence of intrinsic defects with electrons localized at them, as is the case with the LiNbO_3stoich and LiNbO_3congr crystals, but also due to the charge exchange of copper cations under the action of the laser radiation.