Calculation of Optical Parameters of Liquid Crystals (original) (raw)
Related papers
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.
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 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.
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.
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.
Self-consistency of Vuks equations for liquid-crystal refractive indices
Journal of Applied Physics, 2004
Vuks equations correlate the microscopic molecular polarizabilities to the macroscopic refractive indices of anisotropic crystalline materials. For anisotropic liquid crystals, the molecular polarizabilities are difficult to measure directly due to the short-and long-range interactions. We have converted Vuks equations into different forms. By measuring the refractive indices at different temperatures and wavelengths, the Vuks equations can be validated. Five liquid-crystal materials with refractive index ranging from ϳ1.46 to ϳ1.86 are used to validate the modified Vuks equations. The experimental results agree with the theory very well. Based on the Vuks equations, the molecular polarizabilities of 4-cyano-4-n-pentylbiphenyl are calculated.
Refractive indices of liquid crystals E7 and K15 in the mid- and near-IR regions
Journal of Optical Technology, 2006
This paper presents the results of refractive-index measurements of the extraordinary and ordinary rays in nematic liquid crystals (NLCs) using a refractometric technique in the mid-IR (lambda=10.6 µm) and near-IR (lambda=1550 nm) regions for NLC E7 and at lambda=1550 nm for NLC K15. The optical anisotropy of NLC E7 at 10.6 µm is determined independently by means of the interferometric method in order to compare it with the results obtained by the refractometric technique.
High temperature-gradient refractive index liquid crystals
Optics Express, 2004
We have analyzed the physical origins of the temperature gradient of the ordinary refractive index ( dT dn o / ) of liquid crystals. To achieve a large dT dn o / , high birefringence and low clearing temperature play crucial roles. Based on these simple guidelines, we formulated two exemplary liquid crystal mixtures, designated as UCF-1 and UCF-2, and compared their physical properties with a commonly used commercial liquid crystal compound 5CB. The dT dn o / of UCF-1 is ~4X higher than that of 5CB at room temperature.
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.