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1
Content available Właściwości i zastosowania nematycznych ciekłych kryształów w technologii terahercowej
Chodorow U., Parka J.
Biuletyn Wojskowej Akademii Technicznej
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2013
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Vol. 62, nr 1
13-30
PL
Prace nad technologią terahercową (THz) prowadzone są już od przeszło trzech dekad, podczas gdy badania nad wykorzystaniem ciekłych kryształów (CK) w zakresie THz trwają dopiero od dekady. W artykule przedstawione zostały wyniki pomiarów spektralnych CK w obszarze Thz. Opisano wybrane właściwości komercyjnie dostępnego związku CK o symbolu 5CB oraz dwóch mieszanin CK o nazwach 1832B i 1825. Korzystając z dostępnej literatury, zostało wybranych i omówionych kilka urządzeń modulujących promieniowanie THz, w których jako elementy przestrajalne wykorzystane zostały ciekłe kryształy.
EN
Works on terahertz (THz) technology have been conducted for over three decades while research on the use of liquid crystals in the THz range lasted only a decade. In the paper, the results of spectral measurements of LC in the THz range are presented. Selected properties of a commercially available LC compound with the symbol 5CB and two LC mixtures called 1832B and 1825 are described. Using available literature, several devices, which modulate the THz radiation, were selected and discussed. In these devices, liquid crystals were used as tunable elements.
2
Content available remote Investigations of twist elastic constant K₂₂ of new nematic liquid crystal materials using threshold IPS method
Parka J., Dąbrowski M., Kowerdziej R.
Opto-Electronics Review
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2011
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Vol. 19, No. 1
114-118
EN
The liquid crystal technology is one of the most popular at the present time. To the most important parameters of liquid crystals belong optical anisotropy, viscosity, and twist elastic constants. One of the most difficult and problematic to measure parameters is a twist elastic constant K₂₂. For new liquid crystalline materials, we have to characterize their physical properties, also a twist elastic constant K₂₂. As a final result of this work, a twist elastic constant of new nematic liquid crystal materials was investigated. In this paper, a transmission-voltage characteristic of the in-plane switching cell was observed to find Freedericksz threshold, and then twist elastic constants could have been calculated. The method was checked on well-characterized materials E7 and 6-CHBT and its accuracy was better than 20%. In addition, the temperature dependence of K₂₂ was determined for all materials.
3
Content available remote Polarization difference image analysis with LC filter
Sutkowski M., Garbat P., Nowinowski-Kruszelnicki E., Walczak A., Parka J., Woźnicki J.
Opto-Electronics Review
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2009
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Vol. 17, No. 1
53-58
EN
Image analysis using polarizing methods allows removing the polarized light component from recorded images. This is known as polarization difference imaging (PDI). The use of liquid crystals (LC) in PDI was proposed in 2002. Modified LC unit with a properly oriented LC layer was proposed by the authors. The main parameters which characterize an imaging system, employing a circular LC filter, were determined and presented in previous papers. In this work, the basics of the circular LC filter construction and theory are presented. Two application configurations of PDI imaging systems are shown. Experimental results of image processing based on object's polarization properties are discussed.
4
Content available remote Mesomorphic and dielectric properties of esters useful for formulation of nematic mixtures for dual frequency addressing system
Ziobro D., Kula P., Dziaduszek J., Filipowicz M., Dąbrowski R., Parka J., Czub J., Urban S. S., Wu S. T.
Opto-Electronics Review
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2009
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Vol. 17, No. 1
16-19
EN
Mesomorphic and dielectric properties of three homologous series of two and three ring fluorosubstituted esters are described. They are 4-cyano-3-fluorophenyl 4-alkyloxy-2-fluorobenzoates, 4-cyano-3-fluorophenyl 4-(4-alkylbenzoyloxy)-2-fluorobenzoates and 3-fluoro-4-cyanophenyl, or 3-fluoro-4-isothiocyanatophenyl or 3,4-difluorophenyl 4'-alkyl-2,3-difluoro-biphenyl-4-carboxylates. The compounds exhibit the nematic mesophase accompanied by the smectic A or smectic C mesophase in some cases. Most of them show strong dependence of the dielectric anisotropy Δ ε upon frequency, at low frequencies Δ ε reaches a value ∼ 200, while at high frequencies a small negative dielectric anisotropy appears.
5
Content available remote Light-controlled helical pitch and dynamic gratings
Boychuk V. N., Gerus I. I., Iljin A. G., Parka J.
Opto-Electronics Review
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2009
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Vol. 17, No. 4
287-292
EN
A chiral nematic liquid crystal (LC) with a photo-sensitive chiral agent is employed for a light-controlled modulation of optical activity and used as a model substance for a dynamic diffraction grating recording. The described liquid crystalline system has shown a strong nonlinear response with effective parameter of cubic nonlinearity being much greater of that characteristic of the orientational nonlinearity of LC. A simple mathematical model of light diffraction on the grating of modulated optical activity was developed. Calculated values of intensities and polarisation states of diffracting beams have shown very good agreement with the experimental data. LC systems with light-controlled chirality could be promising media for nonlinear optical applications or all-optical switching devices.
6
Content available remote Investigations of dynamic photorefractivity regime by optical polarizing microscopy
Agashkov A. V., Kovalev A. A., Parka J.
Opto-Electronics Review
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2009
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Vol. 17, No. 2
99-104
EN
We present a technique, based on optical polarizing microscopy, and results of direct observation of the optical interference field effect on the transient domains excited by ac electric field in a nematic planar cell with photosensitive aligning layers. The light source used in a microscope operated in DC mode as well as in triggered pulse one. Obtained microscopic snapshots of transient domain structure confirmed our assumption of the transient domains reordering (trapping) by the low intensity optical interference field.
7
Content available Glass cockpits : advantages and problems
Kłosowicz S. J., Zieliński J., Parka J., Olifierczuk M.
Biuletyn Wojskowej Akademii Technicznej
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2009
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Vol. 58, nr 1
69-85
EN
New trends of construction of information displays used in cockpits of different modern aircrafts are presented. The main attention is paid to the liquid crystal displays as the most commonly used nowadays and still of interest in the future. Other technologies of flat information panels interesting for the future applications are discussed. The results of theoretical works performed at the Institute of Applied Physics MUT and an example of integrated display for gliders designed there are also given.
PL
Przedstawiono nowe kierunki konstrukcji wyświetlaczy informacyjnych do kokpitów współczesnych samolotów. Główny nacisk położono na wyświetlacze ciekłokrystaliczne jako najbardziej obecnie rozpowszechnione i perspektywiczne. Przedyskutowano inne technologie płaskich ekranów, interesujące z punktu widzenia przyszłych zastosowań. Przedstawiono również wyniki prac teoretycznych oraz przykład zintegrowanego wyświetlacza dla szybowca skonstruowanego w Instytucie Fizyki Technicznej WAT.
8
Content available remote Optical data storage in LC cells
Sutkowski M., Grudniewski T., Zmijan R., Parka J., Nowinowski-Kruszelnicki E.
Opto-Electronics Review
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2006
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Vol. 14, No. 4
335-337
EN
Liquid crystal devices as a medium for holograms storage have been investigated. Long term memory effects in LC cells have been observed. Experiments proved that certain combination of insulating alignment layers has a major influence on the long term memory effect. Optimal liquid crystal cell construction allows us to achieve sufficient diffraction efficiency to record holographic patterns and to develop a re-writable holographic medium. The configuration of PVK and polyimide layers in LC cell construction with specific LC mixture was tested. The method of permanent and re-writable recording of optical data (holographic pattern) onto LC cells was achieved. However, the method of erasing recorded data was realized but mechanisms of this phenomenon are not clearly understood yet.
9
Content available remote One dimensional model of dye-doped nematic layer for holography
Derfel G., Buczkowska M., Parka J.
Opto-Electronics Review
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2006
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Vol. 14, No. 2
149-154
EN
The layer of electrically conducting nematic liquid crystal doped with photosensitive dye and confined between polyimide coated electrodes can serve as a diffraction grating. In this paper, the deformations of the nematic director field induced in such a system by external voltage were studied numerically by means of one-dimensional model. The dissociation and recombination of ions were taken into account according to weak electrolyte model. The director orientation in the deformed layers and the distributions of the electric field and of the ion concentrations were calculated for blocking and for conducting electrodes. The effective extraordinary refractive index was also determined as a function of average ion concentration.
10
Content available remote Optically addressed holographic gratings in LC cells with different layers and high optical anisotropy liquid crystals
Parka J., Grudniewski T., Kurioz Y., Dąbrowski R.
Opto-Electronics Review
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2004
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Vol. 12, No. 3
317-320
EN
Dynamic optical data storage and other applications in the field of optical data processing would be possible due to development of suitable nonlinear optical materials. In this paper, we present experimental investigations of an orientation photorefractive effect in nematic liquid crystal mixtures with different optical anisotropy and various layers of cell.
11
Content available remote Dynamic photorefractivity in nematic loquid crystal panels with photoconducting polymeric layers
Agashkov A., Kovalev A., Parka J.
Opto-Electronics Review
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2004
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Vol. 12, No. 3
271-275
EN
A novel mechanism of photorefractivity in nematic liquid crystal (LC) cells is presented. Dynamic photorefractivity is based on temporal quasiperiodic modules excitation in the liquid crystal layer by applied external alternating electric field and their reorientation due to the charges induced by interference optical field on a surface of photoconducting orienting layer.
12
Content available remote Properties of different LC cells with high optical anisotropy as a dynamic holographic media
Grudniewski T., Parka J.
Opto-Electronics Review
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2003
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Vol. 11, No. 3
243-245
EN
Dynamic optical data storage and other applications in the field of optical data processing would be possible due to development of suitalbe nonlinear optical materials. The experimental investigations of the orientation photorefractive effect in nematic liquid crystals have been presented. The investigations showed that the orientational optical sensitivity of liquid crystals can be greatly enhanced by an external electric and optical applied field. The photorefractive volume space charge field in the LC cell is the result of charge generation in the bright regions of interference pattern and charge transportation.
13
Content available remote Photorefractivity of dye-doped NLC layers and possibility of their application
Parka J.
Opto-Electronics Review
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2002
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Vol. 10, No. 1
83-87
EN
Photorefractive properties and possibility of guest-host effect application for real time holography have been described. Isothiocyanate nematic liquid mixtures with positive dielectric anisotropy as hosts while antraquinone dyes as guests were used. In dye-doped nematic liquid crystals high diffraction efficiency approaching 20% were obtained. Fast optical grating formation with thee time constant of a few ms have been observed. The dependence of grating formation on strength of applied dc and low frequency of ac electric field, configuration of light polarisation and nematic director orientation were reported.
14
Content available remote Investigations of the diffraction efficiency in dye-doped LC cells under low frequency AC voltage
Grudniewski T., Parka J., Dąbrowski R., Januszko A., Miniewicz A.
Opto-Electronics Review
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2002
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Vol. 10, No. 1
11-15
EN
In this paper, relation between the diffraction efficiency in LC dye doped cell in two wave mixing system and the applied voltage parameters had been described. The goal of this work was increase in diffraction efficiency using low frequency AC voltage. The LC cells used in the experiments were filled with pure and dye-doped liquid crystal mixtures. In this system, we obtained diffraction efficiency increasing about five to eight times.
15
Content available remote The digital holograms projected onto LC cells
Grudniewski T., Parka J., Sutkowski M., Miniewicz A.
Biuletyn Wojskowej Akademii Technicznej
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2002
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Vol. 51, nr 1
121-131
PL
W pracy przedstawiono rozważania dotyczące zapisu hologramów generowanych cyfrowo i projektowanych na przetworniki ciekłokrystaliczne. Na podstawie zaproponowanego modelu oraz danych doświadczalnych prześledzono wpływ konstrukcji przetwornika ciekłokrystalicznego, parametrów mieszaniny ciekłokrystalicznej oraz parametrów zapisu i odczytu hologramów.
EN
Holographic gratings formed by interfered He-Ne laser beams in cells with pure liquid crystal and dye-doped liquid crystal were described. The possibility of diffraction pattern generation in LC cells as a media was proven. Newly developed projection method of optoelectronic reconstruction of holograms expands possible applications of liquid crystals in holography. The presented works goal is to check the physical and optical parameters of liquid crystals mixtures in reference to set-up mentioned above. The relations between experimental results and theoretical needs of holographic reconstruction are discussed. Sample reconstructions of synthetic holograms are shown.
16
Investigation of electrooptical properties of supertwisted nematic efect for multibottle liquid crystal mixture system
Parka J., Żmija J., Dąbrowski R.
Journal of Technical Physics
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1998
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Vol. 39, no 2
205-211
EN
Electrooptical properties of supertwised nematic effect depend on material constants of liquid crystal technical parameters of display construction. Optimisation of these parameters for isothiocyanate and esters liquid crystals mixtures has been carried out. Some experimental results have been presented.
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