Optical Measurements of Thermotropic Liquid Crystals (original) (raw)
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Temperature effect on nonlinear refractive indices of liquid crystals in visible and NIR
Optics Communications, 2016
The effect of temperature variation on nonlinear refractive indices of several types of liquid crystals (LCs) compound has been reported. Birefringence and the temperature gradients of refractive indices of the LCs are determined. Five samples have been investigated; two of them are E7 and MLC 6241-000. The other three have been obtained by mixing the previous two LCs in different proportions. The measurements performed at 632 nm and 1550 nm wavelengths using wedged cell refractometer method. The variation in refractive indices and birefringence were fitted theoretically using the modified Vuks equation. Excellent agreement between the fitted values and experimentally is obtained.
Birefringence measurements of liquid crystals
Applied Optics, 1984
A convenient and accurate technique for measuring the birefringence of liquid crystals at discrete wavelengths or as a continuous function of wavelength in the ultraviolet, visible, or infrared spectral regions is described. The method is based on determination of the phase differences which occur when monochromatic polarized light propagates through a medium with an anisotropic refractive index. Birefringence measurements at 0.6328 Am for two liquid crystal materials, BDH-E7 and ZLI-1132, and a continuous birefringence spectrum of ZLI-1132 from 2 to 16 Am are reported. Additionally, a liquid crystal based phase retardation plate which can be voltage tuned and calibrated to provide any degree of phase shift from 0 to 27r over a wide wavelength range (0.4-16 Am) is discussed.
Journal of Molecular Liquids, 2014
We report new high-resolution experimental data for the optical birefringence over the temperature range spanning the nematic (N) and smectic A (Sm A) phases of various liquid crystals (LCs) by means of a rotating-analyzer method. In this work we proposed a simple procedure to determine high-accuracy extraordinary (n e) and ordinary (n o) refractive indices of LCs both in the N and Sm A phases based on the birefringence measurements. We then show that, apart from the birefringence data, the procedure needs only a single value for the refractive index which is the value of that in the isotropic (I) phase just above the N-I transition temperature. The consistency of our approximation has been checked under the framework of the Vuks model using the criteria found in the literature. We then conclude that our proposal is self-consistent for obtaining the extraordinary and ordinary refractive indices of LCs with high accuracy and seems to be readily applied as compared to the other methods reported to date and also that temperature variation of n e and n o refractive indices is well portrayed by the fit expression presented here for the first time contrary to the Haller extrapolation method. Furthermore, we then show that, without addressing density measurements, the proposed method allows one to obtain the temperature dependence of normalized molecular polarizabilities for extraordinary and ordinary rays, and the effective geometry parameter α eg. It has been observed that α eg changes linearly with the order parameter and the same slope value has been obtained for all investigated samples, which can be ascribed to the global behavior of the nematic phase, which has been reported most recently.
Bulletin of the American Physical Society, 2015
e) and ordinary refractive indices (n o) of LCs both in the N and Sm A phases based on the high-accuracy birefringence measurements. We show that, apart from the birefringence data, the procedure needs only a single value for the refractive index which is the value of that in the isotropic (I) phase just above the N-I transition temperature. By checking the consistency of our approximation model using the criteria found in the literature, we then conclude that our proposal is self-consistent. Additionally, we show that the temperature variation of refractive indices is well portrayed by the fit expression presented here for the first time contrary to the Haller extrapolation method. Furthermore, we then show that, without addressing density measurements, the proposed method allows one to obtain the temperature dependence of normalized molecular polarizabilities for extraordinary and ordinary rays, and the effective geometry parameter.
Acta Physica Polonica A, 2012
The variation of refractive indices with temperature of three pure nematogenic compounds 5OCB, CPHB and 6CHBT were studied experimentally using thin prism technique. The refractive indices no and ne were measured using 633 nm lines from a HeNe laser. A modied four-parameter model was taken which is based on the Vuks equation describing the eect of temperature on the refractive indices of liquid crystals. In this paper we report the variation of refractive indices of these three liquid crystals with temperature, using the thin prism method. The variation in birefringence was determined experimentally. The variation in refractive indices and birefringence were also tted theoretically using the modied Vuks equation. On comparison, the theoretically tted values show close agreement with the experimental values.
Calculation of Optical Parameters of Liquid Crystals
Acta Physica Polonica A
Validation of a modified four-parameter model describing temperature effect on liquid crystal refractive indices is being reported in the present article. This model is based upon the Vuks equation. Experimental data of ordinary and extraordinary refractive indices for two liquid crystal samples MLC-9200-000 and MLC-6608 are used to validate the above-mentioned theoretical model. Using these experimental data, birefringence, order parameter, normalized polarizabilities, and the temperature gradient of refractive indices are determined. Two methods: directly using birefringence measurements and using Haller's extrapolation procedure are adopted for the determination of order parameter. Both approches of order parameter calculation are compared. The temperature dependences of all these parameters are discussed. A close agreement between theory and experiment is obtained.
Temperature effect on refractive indices and order parameter for mixture liquid crystal (UCF)
2015
Liquid crystals are state of substance possesses characteristics between traditional liquid and crystallization. For instance, perhaps liquid crystal away similar to the crystals. There are different types of crystal in the liquid phase .In this research has been the use of high refractive birefringence as well as (UCF), the study of the influence of temperature on the refractive indices at wavelength (623.8 nm), and room temperature. In addition, we used the fourparameters model to study this case, and compared between the experimental results with theoretical. This study is showed, when the temperature increases the ordinary refractive indices (no) increases. And both the extraordinary refractive indices (ne), optical anisotropy (birefringence Δ n) are decreases, also we find the order parameter (S) decreased as the temperature is increased.
Temperature effect on liquid crystal refractive indices
Journal of Applied Physics, 2004
A model describing the temperature effect of liquid crystal ͑LC͒ refractive indices is derived and confirmed by experiment. Two single LC compounds ͑5CB, 5PCH͒ and two mixtures ͑MLC-6241-000 and UCF-35͒ with different birefringence values were used to validate the model. This model fits all the experimental data well. For a low-birefringence LC mixture, if the operating temperature is far below its clearing point, the temperature-dependent refractive indices can be approximated as a parabolic form. This prediction is also experimentally validated. In addition, a linear relationship between ͗n 2 ͘ and temperature is found.
Thermally induced nonlinear optical effects in an isotropic liquid crystal at 10.6 μm
2002
We investigate thermally induced nonlinear optical effects on a CO 2 laser beam that passes through an isotropic liquid crystal film. We evaluate the thermal nonlinear coefficient of the refractive index at a wavelength of 10.6 m by means of a thermographic technique combined with an optical method based upon the measurement of the self-defocusing effect caused by the heating of the liquid crystal induced by the laser beam. The novelty of our work is the application of thermography in order to measure the temperature field on the liquid crystal film caused by the partial absorption of the laser radiation by the liquid crystal. These measurements provide a precise evaluation of the thermal diffusion length of the liquid crystal under investigation. Moreover, thermography results in a straightforward experimental technique that can be used to investigate the thermal properties of a wide class of other fluids.