Rafał Mazur

Nematic liquid crystal mixtures for 3D active glasses application

ABSTRACT 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. GRAPHICAL ABSTRACT

Transparent laser damage resistant nematic liquid crystal cell “LCNP3”

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 τON smaller than 3 μs was applied.

A direct assessment of refractive indices of nematic liquid crystals at broad VIS - MWIR range

ABSTRACT 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 0.8 μm), NIR (from 0.8 to 1.4 μm), SWIR (from 1.4 to 3.0 μm) and at an edge of MWIR (from 3.0 to 4.2 μm) 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 3.4 μm. 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. Graphical Abstract

Refractive index matched half-wave plate with a nematic liquid crystal for three-dimensional laser metrology applications

Abstract 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 λ = 0.6328 μm 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 Φ = π/2) of a rather high cell gap d ~15 μm filled with a newly developed High-Birefringence Nematic Liquid Crystal Mixture (HBLCM) of optical anisotropy as high as Δn ~0.40 at λ = 0.6328 μm, where the Mauguin limit above 5.00 ~ Δnd >> λ/2 = 0.32 is fulfilled.

High Birefringence Liquid Crystals Mixtures and their Selected Applications

High-Birefringence Nematic Liquid Crystals Mixtures (HBNLCM) recently developed in the Military University of Technology (Poland) are presented in this paper. Dielectric, refractometric, viscosimetric and elastomeric characteristic were determined. The properties are discussed in terms of their applicability to electro-optical devices. Applying HBNLCM of LCM to space mission (Phobos Ground) applications for a space-borne laser rangefinder was developed, manufactured and tested under cooperation between Military University of Technology (MUT) in Poland and Vavilov State Optical Institute (Vavilov SOI) in Russia. Transmission T of Liquid Crystal Cell (LCC) at λ=1.064 μm was not smaller than 95% at the aperture diameter not less than 15 mm. Switching on and switching off times in 2.5 μm thick LCC driven by voltage 10 V were not larger than 0.7 ms. Applying HBNLCM of LCM3 to refractive index matched twisted Nematic Liquid Crystal Cell of type LCNP4 for Thomson diagnostics of dense plasma was developed, manufactured and tested under cooperation between MUT in Poland and the National Research University of Information Technologies, Mechanics and Optics in Russia. Transmission T of LCNP4 at λ=1.064 μm was not smaller than 97% at the aperture diameter not less than 30 mm. Switching on time in 2.5 μm thick LCNP4 driven by voltage 200 V was not larger than 3 μs. LCNP4 can easily tolerate 0.42 J/cm2.

Liquid Crystal Aligning Ability of Photosensitive Polymer Material

In the present work the usefulness of photoalignment as a nematic liquid crystal aligning technique has been evaluated. A photocrosslinking mechanism of photosensitive polymer material has been used to cause anisotropy in the layer. The influence of the UV dose on the LC alignment of liquid crystal material in the TN-type cell has been examined.

Refractive index matched liquid crystal cell for laser metrology application

ABSTRACT 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 λ = 0.6328 µm 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. Graphical Abstract

Liquid crystal phase shifter for THz radiation with cholesteric liquid crystal

ABSTRACT In this work we present phase shifters with cholesteric liquid crystal (ChLC) for the terahertz (THz) range with fast modulation. The phase shift of presented phase shifters is equal ∼π at 2.5 THz. The characterization of the phase shifters was done by using terahertz time-domain spectroscopy from 0.3 THz up to 3 THz. Also electro-optical measurements were made to obtain response times of ChLC.

Modulators for MWIR detectors with liquid crystals

In this paper a two liquid crystal (LC) modulators for mid-wave infrared radiation (MWIR) are presented. A two electrooptical effects (EOE) in liquid crystalline structures have been utilized for MWIR modulation: electric field induced cholesteric - nematic (Ch-N*) phase transition (ChN mode) and switching of the twisted-nematic (TN) structure (TN mode). At the Ch-N* mode an intensity modulation depth was of order of 15% but there wasn’t a dark state. In case of the modulation induced at TN mode was near full. These modulators are quite slow, switching times are order of a few hundreds of milliseconds for Ch-N* mode electrooptical effect and dozens of minutes in case of TN mode.