This article examines the transmission of light through an optically anisotropic layer of liquid crystal confined by dielectricwalls. The emphasis is on flat-parallel layers of ordered nematic liquid crystal. It discusses selected electro-optical effects (TN, ECB) andthe conditions necessary to maximise light transmission while minimising reflection. Different optical stack configurations are analysed.The paper also addresses the optimisation of optical parameters for high-transmission transducers for various applications.

In the paper, the viscosity and the electric, magnetic and acoustic properties of liquid crystals, especially nematics, are discussed.All these properties are very important for applications of liquid crystals, and all of them are anisotropic. In the last part of the paper, essentialinformation regarding the behaviour of mesogen mixtures is presented, with the emphasis on phenomena important for fundamentalstudies and applications. The paper is intended for students, PhD students and engineers interested in properties of liquid crystals.

The paper presents the basic optical properties of liquid crystals. It focuses in particular on nematic and cholesteric liquidcrystals, which exhibit particularly interesting and practical optical properties. The article also briefly covers the optical properties offerroelectric smectics and liquid crystal composites, as well as the nonlinear optical properties of liquid crystals.

In the paper, dielectric properties of liquid crystals, especially the nematic phase, arediscussed. An outline of the development of theories describing these properties is presented. Thestatic theory of dielectric permittivity of anisotropic nematic liquid crystals on Onsager, Maier andMeier approach is discussed in details. In this view, anisotropic properties of dielectric permittivityof nematics as well parameters describing these properties are presented.Keywords: material science, liquid crystals, nematics, dielectric permittivity, electron polarisability,constant and induced dipole moment of molecule, vectors of electric field intensity, induction andpolarisation in nematic phase.

The paper presents elastic properties of liquid crystals, especially their nematic phase. Anoutline of a development of theories describing these properties is given. The model describing liquidcrystal as continuous medium is formulated. The curvature theory of elasticity of nematic liquidcrystals based on Zocher – Oseen – Frank’s approach is discussed in details. In this way, essentialelastic properties of nematics as well their relative material parameters are described.Keywords: liquid crystals, nematics, elastic properties, deformations, continuous medium

Theories of a mean molecular field developed for nematic liquid crystals are discussed. Their advantages and disadvantages are highlighted. The role of the order parameter in the description of a liquid crystalline phase is shown. The role of molecular dipole moments is underlined. Keywords: liquid crystals, order parameter, molecular theories, molecular dipole moment

The paper presents basic types of liquid-crystalline phases obtained in different ways and supermolecular arrangement in those phases. Characteristic features of molecular structure of mesogens are discussed, moreover their influence on liquid-crystalline properties are described too. Examples of the effect of intermolecular interactions on the phase situation of a liquid crystal are given. Keywords: liquid crystals, mesophases, polymorphism, mesogens, molecular structure

A historical view of studies on liquid crystals is presented. Application of those materials are also taken into account. Special attention is paid to the studies conducted at Polish scientific centres since the thirties of the last century till now. Keywords: liquid crystals, physical properties, material science, liquid crystal displays

The aim of the presented research was an assessment of an effect of chiral dopants on the physical and electro-optical properties of a ferroelectric smectic mixture which is a key factor of elaboration of working ferroelectric liquid crystal (FLC) mixtures of tailored properties, especially with the tilt angle value near 22.5 degrees in a broad temperature range. Testing FLC mixtures were prepared using the common pyrimidine-based parent mixture F4 doped with three different chiral dopants. The thermal characteristic of the optical tilt angle , tilt angle calculated by means of X-ray diffraction method , spontaneous polarisation and layer spacing of obtained FLC mixtures were studied. Based on the above measurements and computer calculations, the relationship between spontaneous polarisation and tilt angle was discussed. Electro-optical performance of the Surface Stabilised Ferroelectric Liquid Crystal (SSFLC) structures was observed. The relation between the molecular properties of chiral dopants and the electro-optical and physical properties of obtained FLC mixtures is considered in frames of the extended microscopic model of the spontaneous polarisation in FLCs. [GRAPHICS] .

In pursuance of an accurate reality description, more and more physical theories and models are being developed. MRI techniques have superiority in terms of sensitivity to the specific tissue features and their variations. Thus, very precise determination of relaxation and diffusive properties in biological systems may enhance the cellular-level mapping. In this work we present new anisotropic phantoms with layered and capillary geometries, which can contribute to the characterization of biological samples far below the voxel size. Highly advanced manufacturing technique allowed us to obtain well-defined, stable structures, which is undisputable advantage of these models. The phantoms were tested in terms of relaxation and diffusion behavior of water in 50 mT and 0.6 T magnetic field strength. 1D and 2D relaxation experiments revealed many relaxation mechanisms. Diffusion Weighted Imaging confirmed speculations about heterogeneous diffusion coefficient, despite application of the recently proposed BSD-DTI method.

Physical and Technical Aspects of Measurements of Ordinary and Extraordinary Refraction Indices and Birefringence of Nematic Liquid Crystals J. Kędzierski, M.A. Kojdeckib,∗, K. Kowiorski, Z. Raszewski and E. Miszczyk Institute of Applied Physics, Military University of Technology, Warsaw, Poland Institute of Mathematics and Cryptology, Military University of Technology, Warsaw, Poland Institute of Electronic Materials Technology, Department of Chemical Technologies, Warsaw, Poland Institute of Physics, University of Technology and Humanities, Radom, Poland

There exists a problem in advanced numerically controlled automatic laser metrology. Reported study is related to minimising the system generating three or more coherent laser measuring beams. These rays, generated in a proper rangefinder, are necessary to determine the spatial coordinates and spatial orientation of the measured details. The simplest solution is to generate laser coherent light beams of wavelength =0.6328 mu m with a given light polarisation plane and then to direct them along three or more independent optical paths. To form these optical paths, a special refractive index matched liquid crystal cell (MLCC) might be applied. To ensure a stable laser operation during the measurement process, the back reflection of the laser beam from MLCC should not exceed 0.7%. The main task of this work is developing such a MLCC transducer. To reach the critical back reflection low enough, the MLCC is constructed as multilayer structure. MLCC operates in positive twisted nematic (TN) mode. Owing to the high-birefringence nematic liquid crystal mixture used and rather big cell gap, the elaborated low reflective MLCC (with R<0.7%) works at TN mode above the sixth interference maximum of transmitting linearly polarised light. [GRAPHICS] .

Methods of 3D imaging present on the market can be divided into two basic groups: autostereoscopic and stereoscopic. At the stereoscopic methods of 3D imaging it is necessary to use special glasses for separation of images constituting stereo-pair. The most commonly used active glasses consist of two electro-optical transducers based on twisted nematic or other electro-optical effects. Here the evaluation of liquid crystal mixtures is designed intentionally for 3D active glasses in order to eliminate drawbacks of active glasses available on the contemporary market. Material parameters of new designed liquid crystal mixtures such as: elastic constants, viscosity, refractive indices, dielectric and spectral properties as well as response times have been determined. In addition to the symmetrisation of the switching times of 3D active glasses, a dual frequency nematic liquid crystal has been proposed.[GRAPHICS].

We developed an interference method for determination refractive indices of nematic liquid crystals in a broad electromagnetic spectrum. Values of ordinary and extraordinary refractive indices were measured in VIS (from 0.4 to 0.8m), NIR (from 0.8 to 1.4m), SWIR (from 1.4 to 3.0m) and at an edge of MWIR (from 3.0 to 4.2m) regions. The main task of this work was to develop the efficient and accurate interference method. The absolute error of these measurements is not higher than 0.02. The method was tested on two newly designed mixtures. The first one was a high birefringence liquid crystal mixture for the laser rangefinder, while the second one is intentionally prepared for breathalyser application. The mixture does not possess high absorption bands at 3.4m. To measure a dispersion of the refractive indices cells with various thicknesses and dielectric mirrors were prepared. The paper presents a theoretical discussion and experimental results. [GRAPHICS] .

There exists a problem with an in situ diagnostics of contamination of ethyl alcohol in a human being exhaled air. When ethyl alcohol in a mouth blowing (in a gaseous state) exists, the characteristic CH stretch absorption bands in CH3 and CH2 functional groups in ethanol (CH3CH2OH) appear at a wavelength of λ=3.42μm. To investigate the presence of ethyl alcohol in exhaled human air, the light beam of λ=3.42μm is passing through an air sample. If one alternately measures the intensity of the investigated beam and the reference, a percentage of ethanol in the air sample can be estimated using a sensitive nondispersive infrared (NDIR) system with a stable operating flow mass detector. To eliminate a mechanical chopper and noise generating stepper motors, a photonic chopper as a liquid crystal shutter for λ=3.42μm has been designed. For this purpose, an innovative infrared nematic liquid crystal mixture was intentionally prepared. The working mixture was obtained by a selective removal of CH bonds and its exchange by heavier polar substituents, what ensures a lack of absorption band of CH bonds. The paper presents theory, concept and final experimental results of the infrared nematic liquid crystals mixture and the liquid crystal shutter for breathalyzer applications.

There exists a need in a quality and accuracy of a three-dimensional laser metrology operating in numerically controlled automatic machines. For this purpose, one sends three laser beams mutually perpendicular. These three beams of the wavelength lambda = 0.6328 mu m are generated by the same laser and are directed along three independent, orthogonal, mutually perpendicular, optical paths with a given light polarization plain. Using these beams, constituting the frame of coordinates, three independent laser rangefinders are able to determine spatial coordinates of a working tool or a workpiece. To form these optical pulses, a special refractive index matched Half-Wave Plate with nematic Liquid Crystal (LCHWP) was applied. The presented half-wave plate is based on a single Twisted Nematic (TN) cell (with the twist angle Phi = pi/2) of a rather high cell gap d similar to 15 mu m filled with a newly developed High-Birefringence Nematic Liquid Crystal Mixture (HBLCM) of optical anisotropy as high as Delta n similar to 0.40 at lambda = 0.6328 mu m, where the Mauguin limit above 5.00 similar to Delta nd >> lambda/2 = 0.32 is fulfilled.

Wedge cells of small apex angle, filled with liquid crystals, were used to determining optical characteristics as functions of temperature for three liquid crystalline mixtures recently produced and a reference nematic. The interference fringes appearing in polarised monochromatic light (of sodium yellow line) normally incident on the cell were exploited to measure the ordinary and extraordinary refractive indices in the reflection mode and birefringence in the transmission mode. The measurements were repeated using Abbe's refractometer for 6CHBT as the reference to verifying the precision. Additionally the order parameter was computed from birefringence as a function of temperature. The results confirm the usefulness of the method and provide the properties of two nematic liquid crystals of small and large birefringence and one smectic liquid crystal of medium birefringence, recently produced. The experimental systems served also to investigating phase transition between the liquid crystals and the isotropic liquid at near-clearing temperature.

Even though Magnetic Resonance Imaging (MRI) gives possibility to obtain qualitatively very good images, most quantitative results obtained by means of MRI are biased with high dependence on particular hardware parameters, imaging sequence used, and properties of analysed sample. Thus to enable comparison between results obtained on different scanners a calibration is needed. In one of the approaches to Diffusion Tensor Imaging (DTI), a B-matrix Spatial Distribution DTI (BSD-DTI) anisotropic phantoms are crucial in precise determination of the diffusion tensor. Anisotropic phantoms can be also useful as a porosity models or rock models in geology. The paper focuses on characterization of several anisotropic phantoms and describes their applications in DTI, and other domains related to MRI.

We outline the development and application of the Autonomous Fibre-Optic Rotational Seismograph (AFORS), which utilizes the Sagnac effect for a direct measurement of seismic rotation. The main advantage of AFORS is it complete insensitivity to linear motions as well as a direct measurement of rotational components emitted during seismic events. The presented system contains a special autonomous signal processing unit which optimizes its operation for the measurement of rotation motions, whereas applied telemetric system based on the Internet allows for a remote AFORS control. The laboratory investigation of the two such devices indicated they keep accuracy no less than 5.1·10-9to 5.5·10-8rad/s in the frequency bandpass from 0.83 Hz to 106.15 Hz with protect linear changes of sensitivity in above bandpass. The experimental results of AFORS-1 application for continuous monitoring the rotational events in the Książ (Poland) seismological observatory are also presented.

There exists the problem in diagnostics of dense plasma (so-called Thomson diagnostics). For this purpose the plasma is illuminated by series of high energy laser pulses. The energy of each separate pulse is as large as 3 J, so it is impossible to generate a burst of such pulses by a single laser. In this situation, the pulses are generated by several independent lasers operating sequentially, and these pulses are to be directed along the same optical path. To form an optical path with λ = 1.064 μm and absolute value of the laser pulse energy of 3 J, a special refractive index matched twisted Nematic Liquid Crystal Cell of type LCNP3, with switching on time τ ON smaller than 3 μs was applied.