Wyniki wyszukiwania - Biblioteka Nauki

1

Possible limitations of the classical model of orientational optical nonlinearity in nematics

100%

Sierakowski M. , Teterycz M.

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tom 6

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nr 3

575-581

EN

Orientational nonlinearity is the major mechanism of nonlinear optical phenomena observed in liquidcrystalline phase while it does not appear to such extent in any other materials. It is caused by distortion of initial molecular arrangement of an anisotropic medium induced by optical field. Deformation of the anisotropic structure means spatial changes of refractive index of the medium. This effect has been studied in earnest since the 1980s as its application became more apparent. In this paper, some results of experimental examination of molecular reorientation in nematics by optical field are presented, which are not explained in frame of existing Oseen-Frank model and Erickson-Leslie continuous theory. Possible reasons of this discordance are considered and a way of explanation is suggested.

2

Investigations of the diffraction efficiency in dye-doped LC cells under low frequency AC voltage

100%

Grudniewski T. , Parka J. , Dąbrowski R. , Januszko A. , Miniewicz A.

Opto-Electronics Review

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2002

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tom 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.

3

Bistability and dual-frequency nematic liquid crystals

100%

Palto S. P. , Barnik M. I.

Opto-Electronics Review

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2007

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tom Vol. 15, No. 1

52-59

EN

Different modes of bistable switching in liquid crystals with frequency inversion of the dielectric anisotropy sign are discussed. The study is performed by numerical simulation and experimentally. It is shown that dual frequency driving can be effectively used to control switching between topologically equivalent and non-equivalent director field distributions. The experimental results on temperature performance of the dual-frequency switching and possible driving methods for energy consumption and expanding the temperature range are presented.

4

Preparation of Polythiophene Films Showing Optical Activity by Electrochemical Polymerisation in Cholesteric Liquid Crystal Containing Coumarine

80%

Hayashi H. , Goto H.

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tom Vol. 46

42--47

EN

We carried out electrochemical polymerisation in a cholesteric liquid crystal electrolyte solution. The polymer film prepared in the cholesteric liquid crystal showed chiropticality even though its monomer is an achiral. The surface morphology of the polymer was observed with polarising optical microscopy. Optical and electric properties were examined by UV-vis optical absorption, circular dichroism spectroscopy, and cyclic voltammetry.

5

Transparent laser damage resistant nematic liquid crystal cell “LCNP3”

80%

Raszewski Z. , Piecek W. , Jaroszewicz L. , Dąbrowski R. , Nowinowski-Kruszelnicki E. , Soms L. , Olifierczuk M. , Kędzierski J. , Morawiak P. , Mazur R. , Miszczyk E. , Mrukiewicz M. , Kowiorski K.

Opto-Electronics Review

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2014

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tom Vol. 22, No. 3

196-200

EN

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 ʎ = 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 ƮON smaller than 3 μs was applied.

6

Synthesis and Characterization of Self-Organized Discotic Porphyrin Liquid Crystals

80%

Liu W. , Shi T.

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2006

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tom Vol. 80, nr 5

767-772

EN

The synthesis and characterization of 5,10,15,20-tetrakis(4-myristyloxyphenyl) porphyrin and [5,10,15,20-tetrakis(4-myristyloxyphenyl)porphyrin]zinc(II) with long ester chains are reported. The domains of stability and the structure of the liquid crystalline phaseswere determined by optical microscopy and differential scanning calorimetry (DSC). According to theDSC thermogram of the Zn complex, this compound exhibits a phase transition at -7.45 graduate C, lower than that of the ligand and a wide mesophase range at 77graduate C.

7

Electrode polarization and interface effects in liquid crystal systems with mobile ions: development of a model of bipolar diffusion

80%

Ganea C.

Open Physics

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2013

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tom 11

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nr 4

497-511

EN

The influence of mobile ions on the results of impedance spectroscopy (dielectric spectroscopy) measurements performed on a liquid crystal cell using the new mathematical model recently described was investigated. This mathematical model reformulates the fundamental equation system of continuity for mobile charge carriers and the Poisson equation using new variables. One makes the following assumptions: ions have different mobilities and diffusion coefficients, there is no generation-recombination process, the equilibrium carrier concentrations are uniform and equal each other, the electrodes are either completely blocking or blocked with adsorption-desorption processes. The final result is the analytical expression of the equivalent admittance for the system, allowing to have a clearer picture of the mobile ions and of the processes that occur at the electrode interface influencing the dielectric behavior.

8

Identifying of thermotropic liquid crystal phase and its influence on lubricity of ionic liquids

80%

Kałdoński T. J. , Piecek W. , Kałdoński T. , Pawlak Z.

Journal of KONES

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2015

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tom Vol. 22, No. 1

143--156

EN

In this article there is discussed a possibility of forming the liquid crystal structure in ionic liquids and its influence on performance characteristics, especially tribological, of these liquids. Formation of such thermal phase might influence on, among other things, easier creation of the boundary lubricating film, which is characterized by high viscous anisotropy. The results of tribological tests showed better lubricity of selected ionic liquids than modern PFPE oils. Identification of mesophase in ionic liquids was necessary. This method is described in the paper. Biolar PL polarizing interference microscope with thermal stabilizing table, with birefraction system, and Brüker Discover 8 powder diffraction instrument with a Cu lamp and monochromator were used. There was being searched the state characterized simultaneously by optical anisotropy properties and liquid state of aggregation. For identification of phase transition temperature, the additional calorimetric tests were carried out during the cycle of heating and cooling. These researches were carried out within the framework of the development and research project no. PBR 15-249/2007/WAT-OR0002904, financed by Ministry of Science and Higher Education during 2007-2011.

9

Progress of Understanding Liquid Crystsls Made of Bent-Shaped Molecules

80%

Mieczkowski J. , Matraszek J.

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2005

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tom Vol. 79 / nr 2

179-209

EN

Many strongly bent, so-called banana mesogenes have been synthesized and examined. These liquid crystalline materials are very attracted due to their unique properties and possible applications. In this paper we gathered information about bent-core mesogenes reported in the literature and described connections between molecular structure and polymorphism.

10

Tunable properties of light propagation in photonic liquid crystal fibers

80%

Szaniawska K. , Nasilowski T. , Woliński T. R. , Thienpont H.

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tom Vol. 14, No. 4

339-343

EN

Tunable properties of light propagation in photonic crystal fibers filled with liquid crystals, called photonic liquid crystal fibers (PLCFs) are presented. The propagation properties of PLCFs strongly depend on contrast between refractive indices of the solid core (pure silica glass) and liquid crystals (LCs) filing the holes of the fiber. Due to relatively strong thermo-optical effect, we can change the refractive index of the LC by changing its temperature. Numerical analysis of light propagation in PLCF, based on two simulation methods, such as finite difference (FD) and multipole method (MM) is presented. The numerical results obtained are in good agreement with our earlier experimental results presented elsewhere [1].

11

Tunable topographical cellulose for electro-optical liquid crystal cells

80%

Costa I. , Almeida P. L. , Filip D. , Figueirinhas J. L. , Godinho M. H.

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tom Vol. 14, No. 4

299-303

EN

In this work we have used acetoxypropylcellulose (APC) to produce free standing solid films (~60 µm) that were used for assembling electro-optical devices. Thin films were obtained from concentrated lyotropic solutions of cellulose derivatives. Induced by the cast and shearing preparation conditions wrinkles and band textures can be observed in their free-surface plane. In order to eliminate and control these textures we used a process similar to that introduced in literature [1] which consists of storing the films in the same solvent-vapour atmosphere as the solution system. Lyotropic APC liquid crystalline solutions in dymethylacetamide (DMA) with crosslinker were prepared, thin films were obtained by using a shear/casting technique and stored in the solvent-vapour atmosphere until a planar structure was achieved. The dried crosslinked films were analyzed by optical polarised microscopy (POM) and scanning electron microscopy (SEM). The films with different topographies were used to produce optical cells composed by the cellulose derivative film covered on both free surfaces by a layer of the nematic liquid crystal E7 and placed between two transparent conducting substrates. The electro-optical properties of these cells were obtained.

12

Design and simulation of single-electrode liquid crystal phased arrays

80%

Bellini B. , Geday M. A. , Bennis N. , Spadło A. , Quintana X. , Otón J. M. , Dąbrowski R.

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tom Vol. 14, No. 4

269-273

EN

Liquid crystal (LC) phased arrays and gratings have been employed in optical switching and routing [1]. These diffractive optic elements are of great interest because they can be scaled up to a large number of elements and their optical properties can be electrically addressed with a low driving voltage. LC phase gratings have been achieved either by periodic addressing of pixels or by using periodically-modified structures. The latter approach leads to less reconfigurable devices but the addressing is simpler. In this paper we focus on optical phased arrays where the phase is varied either continuously or discretely and where the periodicity is induced by electrode configuration. We first describe a possible structure based on a conductive silicon wafer. We argue that this structure can induce either continuously or discretely varying arrays while applying single voltage to the array. In the second part we simulate the behaviour of such arrays. We base the simulation on a LC synthesized at the Military University of Technology, this high-birefringence nematic LC shows in a 4-µm thick cell a linear phase shift range of more than 3600 between 1.2 V and 1.8 V. We calculate the distribution of the LC molecule director and assess the performance of the array with respect to the applied voltage. Finally, the relevance of such technology for switchable phased arrays is discussed.

13

Photonic liquid crystal fibers : a new challenge for fiber optics and liquid crystals photonics

80%

Woliński T. R. , Ertman S. , Lesiak P. , Domański A. W. , Czapla A. , Dąbrowski R. , Nowinowski-Kruszelnicki E. , Wójcik J.

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tom Vol. 14, No. 4

329-334

EN

The paper reviews and discusses the latest developments in the field of the photonic liquid crystal fibers that have occurred for the last three years in view of new challenges for both fiber optics and liquid crystal photonics. In particular, we present the latest experimental results on electrically induced birefringence in photonic liquid crystal fibers and discuss possibilities and directions of future developments.

14

Depolarization of partially coherent light in liquid crystals

80%

Domański A. W. , Budaszewski D. , Sierakowski M. , Woliński T. R.

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tom Vol. 14, No. 4

305-310

EN

In the paper we present results of analysis of partially coherent light depolarization in two types of liquid crystals possessing linear birefringence controlled by temperature and external electric field changes. Some experimental results of degree of polarization measurements for different light sources as a superluminescent diode and a laser diode are also presented.

15

General properties of lasing effect in chiral liquid crystals

80%

Palto S. P. , Shtykov N. M. , Umansky B. A. , Barnik M. I. , Blinov L. M.

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tom Vol. 14, No. 4

323-328

EN

Numerical simulations and experimental studies of the lasing effect in chiral liquid crystals are presented. It is shown that ring-like light emission, which is often observed experimentally, is a true lasing effect. Lasing condition and different modes in thin liquid crystal layers are discussed.

16

Observation of out-coupling of a nematicon

80%

Beeckman J. , Neyts K. , Hutsebaut X. , Haelterman M.

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tom Vol. 14, No. 4

263-267

EN

In this work we present the observation of spatial optical solitons in liquid crystal cells by recording the diffraction pattern of the out-coupled beam on a distant screen. Simultaneously, the light propagation is observed via scattering measurements. The most important observation is displacement of the beam on the screen due to the transverse undulation inside the cell. This undulation is caused by the anisotropic walk-off of the beam. The displacement is in good agreement with the values of the undulation earlier reported.

17

Reconfigurable optical multiplexer based on liquid crystals for polymer optical fiber networks

80%

Lallana P. C. , Vázquez C. , Pena J. M. S. , Vergaz R.

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tom Vol. 14, No. 4

311-318

EN

In this work, different novel 3×1 multiplexer structures for being used in polymer optical fiber networks are proposed. Designs are compact, scalable, and of low consumption, capable of operating in a large wavelength range simultaneously 660, 850, and 1300 nm, due to the use of nematic liquid crystal cells. Light that comes from each input port is handled independently and eight operation modes are possible. Control electronics has been made using a programmable integrated circuit. Electronic system makes available the managing of the optical stage using a computer. An additional four optical sensors have been included for allowing the optical status checking. Finally, a polarization independent multiplexer has been implemented and tested. Insertion losses less than 4 dB and isolation better than 23 dB have been measured. In addition, 30-ms and 15-ms setup and rise times have been obtained. The proposed multiplexer can be used in any polymer optical fiber network, even in perfluorinated graded index one, and it can be specially useful in optical sensor networks, or in coarse wavelength division multiplexing networks.

18

Study of the effect of director fluctuations on liquid-crystalline molecular reorientation

80%

Sierakowski M. W.

Opto-Electronics Review

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2014

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tom Vol. 22, No. 2

109-112

EN

Initial phase of field-induced molecular reorientation in threshold geometry of a liquid-crystalline structure is essentially influenced by thermal orientational fluctuations. Still not quite clear is the way in which the reorientation starts and how it runs over an LC-structure in its initial phase. Fluctuations are stochastic events in time and also in space. This feature suggests, that the reorientation process may be induced by director fluctuations locally in a particular part of the LC-structure. In this work we have studied the impact of fluctuations on the molecular reorientation in nematics involving optical nonlinear interaction. The restricted area of a nematic layer was excited by light beam that amplified director fluctuations locally. By manipulation of optical excitation we were able to affect the dynamics of the effect. Since the threshold-type configuration of nematics is used in a number of optical devices, the obtained results may have practical aspect contributing to a new way of controlling the field-induced transition.

19

Propagation properties of photonic crystal fibers filled with nematic liquid crystals

80%

Woliński T. R. , Szaniawska K. , Bondarczuk K. , Lesiak P. , Domański A. W. , Dąbrowski R. , Nowinowski-Kruszelnicki E. , Wójcik J.

Opto-Electronics Review

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2005

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tom Vol. 13, No. 2

177-182

EN

The paper presents the latest experimental results on propagation properties of a photonic crystal fiber infilled with a nematic liquid crystal characterized by either extremely low (of the order of ~0.05) or relatively high (of the order of ~0.3) material birefringence. The nematic liquid crystal was introduced into the micro holes of the photonic crystal fiber by the capillary effect. Due to anisotropic properties of the obtained photonic liquid-crystal fiber, guiding mechanism that has to be attributed to the photonic band gap effect has been demonstrated.

20

Dye-enhanced nonlinearity threshold measurements in liquid crystals

80%

Sierakowski M. , Waga Ł.

Opto-Electronics Review

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2005

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tom Vol. 13, No. 2

151-155

EN

Since early eighties it is well known, that optical field can interact with liquid crystalline structures inducing molecular motion in similar way to quasi-electrostatic fields. This nonlinear optical effect (NOE) causes changes of refractive index distribution in the structure and in this way leads to several optical phenomena, like self-diffraction of the propagating beam, harmonic generation, four-wave mixing, nonlinear wave-guiding, etc. At first, NOE was observed in nematics for relatively high optical power densities. In the middle of nineties, Istvan Janossy discovered, that small addition of specific dopants to LC-material can significantly reduce the light power required for NOE. At present, NOE can be induced in certain LC-materials by sub-miliwatt laser beams. This achievement opened a way to many applications of the accompanied optical phenomena. Mechanism of the Janossy effect is still not quite clear. NOE is generally a threshold effect, which means that it starts after a certain threshold value of the optical power. In this work we examine the threshold of the self-diffraction of light in doped nematics in selected conditions, trying to understand its nature. Final goal of the work is examination of NOE in chiral liquidcrystal structures (cholesterics).