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1
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Influence of External Electric Field on Time of Nonlinear Optical Reorientational Effect in Nematics

100%
Bajdecki W., Karpierz M.
Acta Physica Polonica A
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2003
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vol. 103
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issue 2-3
187-193
EN
Nonlinear reorientation phenomena in nematic liquid crystals cause extremely large refractive index changes. However, this effect is relatively slow and the determination of the time necessary to appearing or disappearing of the nonlinear effect is an important issue. In this work we present measurements of the time of increasing the nematics reorientation induced by the light beam passing through the liquid crystalline layer. The influence of external low-frequency electric field suppressing reorientation is also reported. The obtained results describing relations between time and optical power of light as well as between time and external electric field intensity are in good agreement with theory.
2
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Reorientational Nonlinear Phenomena in Thin Nematic Liquid Crystals Layer

100%
Brzdąkiewicz K., Bajdecki W., Kozanecka A., Karpierz M.
Acta Physica Polonica A
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2001
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vol. 99
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issue 1
183-192
EN
In this paper the detailed study of the self-diffraction phenomena due to reorientational optical nonlinearity in nematic liquid crystalline cell is presented. The optical nonlinear effect is additionally modified by external low-frequency electric field. The dependence of nonlinear response on light polarization is also analyzed. The theoretical investigations are compared with experimental results and the theoretical predictions are in excellent agreement with experimental data.
3
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Nonlinear Properties of Waveguides with Twisted Nematic Liquid Crystal

100%
Karpierz M.
Acta Physica Polonica A
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2001
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vol. 99
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issue 1
161-173
EN
Optical reorientational nonlinearity in twisted nematic liquid crystalline planar waveguide is analyzed theoretically. It is shown that optical nonlinearity for guided modes in analyzed waveguides can be approximated by saturation nonlinearity. Predicted nonlinearity is large enough to observe effects like spatial solitons formation with milliwatts of light power.
4
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Hyper-Solitons in Nematic Liquid Crystals

100%
Strinic A., Petrović M., Belić M.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
510-512
EN
We study laser light propagation in a cell containing a liquid crystal in the nematic phase. We launch hyper-Gaussian beams and follow their behavior within the cell, in time and in three spatial dimensions, utilizing an appropriately developed theoretical model and a numerical procedure based on the fast Fourier transform. We demonstrate the formation of stable "hyper-soliton" breathers in a narrow region of beam intensities, for fixed other parameters. Hyper-solitons are similar in appearance and behavior to the usual solitons, formed by launching the usual Gaussian beams; however noticeable differences persist.
5
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Modeling of Spatial Solitons in Twisted Nematics Waveguides

100%
Karpierz M., Brzdąkiewicz K., Nguyen Q.
Acta Physica Polonica A
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2003
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vol. 103
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issue 2-3
169-175
EN
Theoretical analysis of light beam propagation in twisted nematic liquid crystalline waveguides is presented. Due to the optical reorientation nonlinearity, the light beam changes the direction of propagation and optical spatial soliton is formed. Modeling of such behavior is presented by using (2+1)-dimensional vector beam propagation method as well as simplified (1+1)-dimensional method. Although both approaches give similar results, the differences are discussed in detail.
6
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Dynamical Electro-Optical Characterization of Policryps Gratings

100%
Abbate G., Marino A., Vita F.
Acta Physica Polonica A
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2003
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vol. 103
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issue 2-3
177-186
EN
We have studied the dynamical response at 633 and 1550 nm of a new polymer-liquid crystal composite, realized in a form of a thick grating. This composite is known as Policryps, an acronym that stands for "Polymer Liquid Crystals Polymer Slides", because it shows a sequence of polymeric sheets alternated by layers containing only liquid crystal. Policryps gratings can be electrically switched between diffracting and non-diffracting states with a good diffraction efficiency in the visible region. After optimization of their performances, including response time, in the near infrared region, they can be conveniently proposed as a key component in photonic devices for telecom applications. Our results show very interesting response times ranging from 1 to 3 ms (switching on) and from 0.1 to 0.4 ms (switching off). Furthermore, switching ON times appear to be ruled by two different physical mechanisms with characteristic times differing by one order of magnitude. A deeper insight of these mechanisms might lead to response times, all in the submillisecond range.
7
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Spatial Optical Solitons in Bulk Nematic Liquid Crystals

100%
Assanto G., Peccianti M., Conti C.
Acta Physica Polonica A
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2003
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vol. 103
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issue 2-3
161-167
EN
We present an overview of our recent experimental results on two-dimensional optical spatial solitons in voltage biased planar cells with nematic liquid crystals. Excitation, induced waveguiding, and interactions are illustrated and interpreted in terms of the inherent re-orientational, non-resonant and nonlocal nonlinear response.
8
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Influence of Light Polarization on Reorientation Nonlinearity in Nematic Liquid Crystals

100%
Brzdąkiewicz K., Karpierz M.
Acta Physica Polonica A
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2003
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vol. 103
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issue 2-3
195-205
EN
Nematic liquid crystals are characterized by a giant optical nonlinearity which has its origin in the molecular reorientational phenomenon. Uniqueness of this nonlinear mechanism causes that response of the medium is dependent on many conditions. Among various circumstances, both an initial alignment of liquid crystal cell and geometry of the system are very important, but in this paper a significant role of light polarization in nonlinear effects observed in nematics is emphasized. Additionally, it is underlined that dependence on light polarization does not have only trivial aspect of initial conditions. More complex seems to be the fact that due to the high optical anisotropy of the medium the state of light polarization is changing on the way of beam propagation. As a consequence, the modifications of molecular orientation in the liquid crystal cell are strongly dependent upon light polarization.
9
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Optical Nonlinearity in Liquid Crystalline Optical Waveguides

100%
Karpierz M., Domański A., Sierakowski M., Swillo M., Woliński T.
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vol. 95
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issue 5
783-792
EN
The analysis of optical orientational nonlinearity in nematic liquid crystalline planar waveguides is presented. The analyzed nonlinearity leads to unique properties that are not observed in other types of nonlinear waveguides. Theoretical results are confirmed by experimental data obtained in liquid crystalline directional couplers and in the self-focusing effect observed in the planar liquid crystalline waveguides.
10
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Nonlinear Optical Measurements of Elastic Constants in Nematic Liquid Crystal

100%
Bajdecki W., Karpierz M.
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EN
A new method of measurements of elastic constants of nematic liquid crystals by applying the nonlinear optical effect is presented. This method bases on measurements of a value of the reorientation threshold in a liquid crystal layer while the reorientation is induced by the light beam passing through the layer. The obtained results are in a qualitative compatibility with the results obtained by classical methods.
11
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Refractive Indices, Order Parameter and Optical Transmittance Studies of a Nematic Liquid Crystal Mixture

100%
Singh A., Manohar R., Shukla J., Biradar A.
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EN
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 (δ n). 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.
12
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Molecular Dynamic of (4-(4'Octylobiphenyl)carboxylan) 4-(2-methylobuthyl) phenol Liquid Crystal Having Blue Phase Seen via the Dielectric Spectroscopy Method

80%
Otowski W., Lewińska G.
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vol. 125
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issue 5
1152-1158
EN
(4-(4'octylobiphenyl)carboxylan) 4-(2-methylobuthyl) phenol (CE8), the substance showing complex polymorphism, has been investigated using the dielectric spectroscopy method. This substance exhibited polymorphism during heating and cooling: a few smectic phases, a cholesteric phase, and a blue phase as well. Despite the fact that the substance polymorphism depends on the rate of heat flow existing of the blue phase has been confirmed by polarizing microscopic observations as well as dielectric spectroscopy investigations.
13
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Biomedical Optical Applications of Liquid Crystal Devices

80%
Abdulhalim I., Moses R., Sharon R.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
715-722
EN
Liquid crystals exhibit large electro-optic effects which make them useful for a variety of applications as fast, compact, and tunable spectral filters, phase modulators, polarization controllers, and optical shutters. They were largely developed for liquid crystal displays and in the last decade for optical telecommunications, however their application in the field of optical imaging just started to emerge. These devices can be miniaturized thus have a great potential useful in miniature optical imaging systems for biomedical applications. Using a collection of tunable phase retarders one can perform: 1. Stokes parameters imaging for skin and eye polarimetric imaging; 2. Tunable filtering to be used for hyperspectral imaging, fluorescence microscopy, and frequency domain optical coherence tomography; 3. Adaptive optical imaging and eye aberrations correction; 4. Phase shift interferometric imaging; 5. Variable frequency structured illumination microscopy. Basic optics of liquid crystals devices is reviewed and some novel designs are presented in more detail when combined to imaging systems for a number of applications in biomedical imaging and sensing.
14
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Comparison of Different Liquid Crystal Materials under Planar and Homeotropic Boundary Conditions in Capillaries

80%
Chychłowski M., Ertman S., Nowinowski-Kruszelnicki E., Dąbrowski R., Woliński T.
Acta Physica Polonica A
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2011
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vol. 120
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issue 4
582-584
EN
We present a thermally-induced liquid crystal orientation method by applying an extra orienting layer onto an inner capillary surface that can induce either planar or homeotropic liquid crystal boundary conditions. Experimental evidence of boundary-induced orientation in two types of liquid crystal (nematic, chiral nematic) in a capillary are shown.
15
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Phase States in Potassium Oleate+Water and Potassium Oleate+Water+Decanol Lyotropic Systems

80%
Nesrullajev A., Kazanci N., Yildiz T.
Acta Physica Polonica A
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1998
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vol. 94
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issue 1
25-32
EN
In this work the investigations of the characteristic textures and the dynamics of their concentration and temperature transformations in potassium oleate+water lyotropic system have been carried out. The effect of the decanol on lyotropic mesomorphism as well as on the character of typical textures and the concentration ranges of lyotropic liquid crystalline mesophases have also been studied. The phase states diagrams of the potassium oleate+water and potassium oleate+decanol+water lyotropic liquid crystalline systems are presented.
16
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Peculiarities of the Schlieren Textures in Lyotropic Nematic Mesophases

80%
Nesrullajev A., Kazanci N.
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vol. 95
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issue 6
931-937
EN
In the present paper the peculiarities of schlieren textures of lyotropic nematic mesophases have been investigated by polythermic polarization microscopy and capillary temperature wedge methods. The lyotropic nematiccalamitics (N_{c}) and lyotropic nematic-discotics (N_{d}) formed in binary and ternary systems on the base of tetradecyldimethyl amino bromide and tetradecyldimethyl amino oxide have been the subjects of our investigations. The dynamics of time and temperature transformations of schlieren textures have been studied. The comparative estimation of schlieren textures of N_{c} and N_{d} mesophases has been performed. The optical force and optical sign of the schlieren textures observed have been determined.
17
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Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

80%
Wolarz E., Bauman D., Jadżyn J., Dąbrowski R.
Acta Physica Polonica A
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2011
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vol. 120
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issue 3
447-454
EN
Dielectric relaxation study of nematogenic 4-n-alkyl-4'-cyanobiphenyls (nCB, n = 5, 6), 4-(trans-4'-n-alkylcyclohexyl)isothiocyanatobenzenes (nCHBT, n = 6, 8), 4-cyanophenyl-4'-n-alkylbenzoates (nCPB, n = 6, 8), 4-cyano-3-fluorophenyl-4'-n-octyloxybenzoate (8OCFPB), and 4-cyanophenyl-4'-n-octyloxy-3'-fluorobenzoate (8OCPFB) was performed in the frequency range from 50 kHz to 100 MHz in the nematic and isotropic phases. The static permittivity and the relaxation process related to the rotation of molecules around their short axis was analyzed. For some of these liquid crystals anomalous temperature dependence of static permittivity in the pretransitional region of the isotropic phase was observed. Based on the Meier-Saupe-Martin model of molecular diffusion in nematics, the orientational order parameter 〈P_2〉 was determined from dielectric relaxation times and retardation factor. The values of 〈P_2〉 calculated from the dielectric relaxation data were compared with the results obtained from measurements of polarized electronic absorption. Correlations between the magnitude of the dielectric pretransitional effect and the orientational order in the nematic phase were discussed.
18
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Determination of Orientational Order Parameters of Two Tri-Component Mixtures from Optical Birefringence and X-Ray Diffraction Measurements

80%
Basak S., Dasgupta P., Das B., Das M., Dabrowski R.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6
1037-1042
EN
Two tri-component mixtures as base mixtures for vertically aligned mode LCD's were prepared. The eutectic compositions were theoretically estimated and experimentally verified from differential scanning calorimetry studies. A room temperature nematic mixture with fairly broad operating range emerged from each of the tri-component mixtures. The optical birefringence of these mixtures at the eutectic composition was measured as a function of temperature. X-ray diffraction measurements were done on these mixtures to obtain the orientational order parameters as a function of temperature. The order parameter values were also determined from birefringence measurements and the results were compared with mean field theory. Structural parameters like intermolecular distance and apparent molecular length have also been determined.
19
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Photonic Liquid Crystal Fibers with Polymers

80%
Woliński T., Tefelska M., Mileńko K., Siarkowska A., Budaszewski D., Domański A., Ertman S., Orzechowski K., Rutkowska K., Sierakowski M., Nowinowski-Kruszelnicki E., Dąbrowski R., Mergo P.
Acta Physica Polonica A
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2013
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vol. 124
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issue 3
613-616
EN
Photonic liquid crystal fibers with polymers constitute a new solution based on liquid crystals and microstructured polymer optical fibers opening up new areas in innovative sensing and photonic devices applications. Compared with their silica-based microstructured fibers, it is easier to fabricate exotic microstructured polymer optical fibers by extrusion or drilling at low temperature; their nonlinearity is potentially stronger, the range of available polymers that may be drawn is more diverse and the biocompatibility of polymers is often better. Liquid crystals due to their attractive properties i.e., the high birefringence, high electro-optic and thermo-optic effects are a very good candidate for microstructured polymer optical fiber infiltration to obtain tunable all-in-fiber innovative photonic devices. The paper will discuss basic properties and possible applications of the polymer photonic liquid crystal fibers that will arise from their high optical tunability with external and internal factors. Current research effort is directed towards two main solutions: photonic crystal fibers and microstructured polymer optical fiber-based structures, both infiltrated with liquid crystals of tailored optical properties.
20
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Beam Propagation in Nematic Liquid Crystals

80%
Strinic A., Belic M.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
877-883
EN
We investigate the behavior of beams propagating in nematic liquid crystals. A spatiotemporal model for the beam propagation and the director reorientation in a nematic liquid crystal is treated numerically in three spatial dimensions and time. We demonstrate the formation of stable solitons in a narrow threshold region of beam intensities for a set of fixed parameters and display soliton breathing. Below the threshold region the beams diffract, above the region spatiotemporal instabilities are observed, as the input intensity and the optical and static permittivity anisotropies of the liquid crystal molecules are increased. We demonstrate the filamentation of solitons above the threshold with increasing input intensity.
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