Refractive indices of liquid crystals E7 and K15 in the mid- and near-IR regions (original) (raw)
Related papers
2012
A conoscopic method to determine the main refractive indices of a uniaxial anisotropic substance (anisotropic plate or liquid crystalline layer) with its optical axis parallel to the cutting surface is developed in this paper. The values of the birefringence for blue radiation emitted by a Hg light source are determined here for a lyotropic liquid crystal layer in planar orientation. To check the validity of the proposed method, the results obtained are compared with those obtained by supplementary measurements at a Rayleigh interferometer and from the channeled spectra.
Measurement of the refractive index of nematic liquid crystals 5CB by means of x-ray interferometry
Advances in X-Ray/EUV Optics and Components IX
In the present work the X-ray optical anisotropy of 5CB type liquid crystals has been investigated based on the method of X-ray interferometry. In this way Moire fringes have been obtained both in the absence and presence of specimens with different orientations of optical axes. The relative displacement of Moire fringes enabled us to observe and immediately ascertain the presence of X-ray optical anisotropy, to measure the values of refractive indices n o and n e for this specimen (n o is the refractive index for radiation with polarization normal to the principal plain, n e is that for radiation with polarization in the principal plain parallel to the optical axis). X-ray optical anisotropy of 5CB type liquid crystal was observed using the proposed method and values of refractive indices n o and n e for this specimen were measured. It was found out that 5CB type nematic liquid crystal was X-ray anisotropic optically positive medium.
Opto-Electronics Review, 2010
A new accurate and fast interference method for determining ordinary and extraordinary refractive indices of nematic liquid crystals is presented and discussed. The method relies on microscopic measurements of distances between interference fringes appearing in polarised parallel coherent monochromatic light beam transmitted normally to the surfaces through a wedge cell filled with a nematic. Both glass plates confining the cell are coated with a partly transparent thin film of metal which is deposited by evaporation in vacuum. Owing to the multiple reflections between the surfaces and a small edge angle, the interference fringes observed near the wedge apex edge are sharp and equidistant. To apply this method one needs only small amount of an investigated liquid crystal. Basic mathematical formulae and results of an experiment are briefly discussed.
Acta Physica Polonica A, 2006
Measurements of ordinary refractive index, birefringence, density, and order parameter were made on a technologically important nematogen and the data obtained for its nematic and isotropic phase were reported. A modified wedge method was used for the measurement of the birefringence (δn). The nematic-isotropic phase transition temperature matches very well as is exhibited from the value of refractive indices and densities obtained using different techniques. The optical anisotropy and density data were used to determine the order parameter and principal polarizability of the nematic mixture using the Vuks approach and their temperature dependence was discussed. The macroscopic order parameter was obtained and compared with microscopic order parameter. These two values agree very well.
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.
Infrared refractive indices of liquid crystals
Journal of Applied Physics, 2005
The refractive indices of E7 liquid-crystal mixture were measured at six visible and two infrared ͑ = 1.55 and 10.6 m͒ wavelengths at different temperatures, using Abbe and wedged cell refractometer methods, respectively. The experimental data of the visible wavelengths fit the extended Cauchy equations well. Using the extended Cauchy equations, we can extrapolate the refractive indices of E7 to IR. The extrapolated results almost strike through the measured data. Thus, the extended Cauchy equations can be used to link the visible refractive indices to infrared, where the refractive index measurements are more difficult.
Acta Physica Polonica A, 2013
Wedge cell lled with a homogeneously oriented nematic liquid crystal was exploited as an interference wedge to measuring indices of refraction. Interference fringes from the wedge were observed in polarised light in reection or transmission mode of a polarisation microscope to determining ordinary and extraordinary indices of refraction or birefringence (i.e. anisotropy of both indices). The interference fringes close to wedge apex were uniform and could be well described in two-beam interference approximation. The refractive indices were computed with using simple formulae involving only distances between subsequent fringes in a cell lled with the liquid crystal and an empty reference cell. Several new highly-birefringent nematic mixtures produced in the Military University of Technology were investigated. The 6CHBT nematic was used as the reference material.
Soviet physics, JETP, 1984
A model approach for the Mueller matrix (MM) of the twisted nematic liquid crystal spatial light modulator (TNLC-SLM) was proposed. In the first part of the study, the MM of the TNLC cell in the absence of applied voltage was investigated both theoretically and experimentally. In the second part, the model approach was improved by considering the reorientation of both tilt and azimuth angles of the liquid crystal (LC) molecules in the presence of applied voltage. Comparison of the theoretical MM elements with the experimental ones from the literature showed that, instead of decaying exponentially, the azimuth angle rotates with respect to the cell walls in a critical voltage range before the molecules are completely untwisted. It also pointed out that the effect of the tilt and the azimuth angles of the molecules on the optical properties of the light travelling in the LC cell could change depending on the polarization state of the input light and the voltage applied to the cell.
Refractive indices and order parameters of some tolane-based nematic liquid crystals
Four tolane-based liquid crystals, 4′-pentyl-, 4′-hexyl-, and 4′-heptyl-3-fluoro-4-isothiocyanatotolane and 4′-hexyloxy-3′-fluoro-4-isothiocyanatotolane have been investigated throughout the nematic and isotropic phase in order to determine their refractive indices and order parameters using the Vuks method. These factors characterize anisotropic behaviors of selected liquid crystals that are essential for their applications and improvement. The temperature dependence of refractive indices, birefringence and order parameters in anisotropic nematic phase, have been investigated for these four nematic liquid crystals. All the compounds have positive and large optical anisotropies that increase with decreasing temperature.