Papers by Keyword: Birefringence

Abstract: Refractive indices measurements are carried out in four alkoxy benzylidene anilines viz., N-(p-n-methoxy and ethoxy benzaldehyde)-p-n-dodecyl and tetra decyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. First three compounds exhibit monovariant nematic phase while the last compound exhibits nematic and SmA phases with variable thermal ranges. The molecular polarizabilities are calculated from the refractive indices and the density using the well known internal field models by Vuks and Neugebauer. The molecular polarizability anisotropy is estimated from the Lippincott δ-function model as well as molecular vibrational methods. The order parameter is estimated using a) from the Haller’s extrapolation from molecular polarizabilities, b) from the scaling factors obtained from the equations by Vuks and Neugbeaur and c) directly from the birefringence - a method developed by Kuczynski et al without considering any internal field model to the liquid crystal molecule. The results evaluated from these methods are compared from one another and the limitations of the methods used are discussed.

Abstract: The mixtures of nematic [4-Hexyloxy-4-Biphenyl carbonitrile] and cholesteryl propionate were investigated at various temperatures. Measurements of refractive index and transition temperatures were noted by using an Abbe refractometer with a heating arrangement. Ordinary and extraordinary refractive indices were obtained which helped us in calculating the order parameter and its variation with temperature. We also carried out Fabry-Perot Scattering Studies (FPSS) on our samples to confirm the various transition temperatures. Photographs of liquid crystal mixture samples placed between crossed nicols are taken at various temperatures to observe the phase transition.

Abstract: We have prepared an anisotropic hydrogel with birefringence by means of dialysis method and analyzed the dynamics of the gel-forming process using purified chitosan with the degree of deacetylation at 100%. The dynamics was expressed well by a theory based on “moving boundary picture”(Nobe, Dobashi and Yamamoto, Langmuir 2005).

Abstract: Photonic crystal fiber (PCFs) offer new possibilities of realizing highly birefringence fibers due to a higher intrinsic index contrast compared to conventional fibers. Here, based on general section structure of PCFs, we take some mend in the core configuration, and achieve highly birefringence effect. A elliptic air hole and its inscribed circular high refractive material form the core of PCFs together. Especially to mention, they are being tangent at two points. By optimally selecting parameters, the effective refractive index difference between two orthogonal directions neff can reach the magnitude of 10-2. After numerical calculation, we find that increase the size of circular solid core, or long axe size of elliptic air hole, birefringence parameter of modal field can become more highly. Moreover, by matching structure parameters appropriately, the modal field diameters can be equivalent in the two orthogonal directions. A Gaussian modal field with highly birefringence character can be acquired.

Abstract: The effects of ionic conductivity on the electro-optical properties of a chiral banana-shaped liquid crystal 1,3-phenylene bis{4-[3-chloro-4-(3,7-dimethyloctyloxyl)] phenyliminomethyl} benzoate were investigated with the techniques of polarizing optical microscopy and dielectric spectroscopy. When the banana-shaped liquid crystal was experienced a low-frequency (1 Hz) triangular waveform electric field, its polarizing optical microscopic textures were first turned into gray and then into black at about 95oC, a few degrees lower than the clearing temperature of the banana-shaped liquid crystal. Detailed dielectric spectroscopic characterizations showed that ionic conductivity increased exponentially as the temperature increased from 72 to 110oC. Our results suggested that dominant ionic conductivity near its clearing temperature is responsible for the electric-field induced loss in the birefringence of the banana-shaped liquid crystal.

Abstract: Magnetic birefringence in kerosene based magnetic fluid in variable and pulsing field is investigated. It is shown, that the size of aggregates of defining effect is about 70 nanometers. The absence of spontaneous magnetisation at such aggregates is installed. The value of the parameter connecting the permanent and induced magnetic moments of the aggregate of nanoparticles is experimentally defined.

Abstract: The dislocation-induced birefringence of Silicon Carbide (SiC) is analytically and quantitatively modelled by using the adequate SiC data. A good agreement can be obtained between theory and experiment, provided that a background residual (uniaxial) stress is added to the local dislocation-induced stress. Observations are compatible with or predictable from the Burgers vector values, so that birefringence reveals an interesting tool for probing the nature of the dislocations associated, e.g., to micropipes, also faster than and complementary to the more involved transmission electron microscopy (TEM) technique.

Abstract: We have investigated through birefringence microscopy, a set of 3C-SiC crystals grown with the CF-PVT process, starting from different seeds and under different growth conditions. Through self nucleation experiments, the stable growth of very high quality 3C-SiC crystals at high temperature (2100°C) and at high rate (roughly 0.2 mm/h) is demonstrated. The possibility to develop bulk growth of 3C-SiC crystals is discussed.

Abstract: An investigation into three dimensional fluid flow has been conducted which combines the use of Computational Fluid Dynamics (CFD) simulations with the experimental phenomenon of Streaming Birefringence. A versatile flow channel was designed and built for use in conjunction with a circular polariscope. The experimental liquid used was an aqueous solution of a dye, commercially known as Milling Yellow NGS with the addition of Sodium Chloride. To extract the flow fields, six image phase stepping photoelasticity was used over backward and forward steps, and flows around a cylinder, and full-field fringe data were obtained. This method needs laminar flow regimes and the Reynolds number of the flow was around 10. To allow direct comparisons of the CFD solutions with the optical results, a macro (UDF) was written to interpret the flow field results from a (FLUENT6) CFD simulation. This integrated the shear stresses across the flow field and banded the results into fringes. A good correlation between the simulated fringes and the shearstrain rate was obtained from these observations.

Abstract: We demonstrate a method of displacement measurement based on Nd:YAG laser with birefringence external cavity. The measurement system is composed of Nd:YAG laser, a wave plate with phase retardation of 450 and an external feedback mirror. Due to the birefringence effect, the external cavity modulates the laser output intensities in the two orthogonal directions with a phase difference of 900, which is two times to that of the wave plate. Both the in-quadrature laser intensities vary one period, when the external cavity length changes λ/2. These two channel laser intensities with phase difference of 900 can be subdivided to λ/8 after 4-fold evaluation. The movement direction of external mirror can be distinguished by the lead or lag between these two channel signals. Our method can improve the resolution of displacement measurement 4 times that of conventional optical feedback, and reach 133nm for a laser wavelength of 1.064µm.