共查询到20条相似文献,搜索用时 15 毫秒
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I. A. Budagovsky A. S. Zolot’ko V. N. Ochkin M. P. Smayev A. Yu. Bobrovsky V. P. Shibaev M. I. Barnik 《Journal of Experimental and Theoretical Physics》2008,106(1):172-181
The effect of optical orientation in nematic liquid crystals containing small additions of high-molecular compounds, i.e., comb-shaped polymers with light-absorbing azobenzene side fragments, was studied. The effects of light-induced reorientation of the director of nematic liquid crystals caused by light absorption of polymers and a low-molecular compound with a structure similar to side fragments of the polymers were compared in detail. An explanation was proposed for large values of the orientational nonlinearity induced by polymers. 相似文献
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J. Kobayashi 《Phase Transitions》2013,86(1-4):95-128
This article reviews at an introductory level the physics of optical activity and its recent applications to studies of phase transitions of ferroelectrics. Optical activity is a kind of internal perturbation of the refractive index, and accordingly induces a resonating effect on the eigenstates of the susceptibility. This is the reason why optical activity provides us with unreplaceable information concerning the chirality of the structure and specific bonding nature of constituent atoms. The principles of our high accuracy universal polarimeter (defined as HAUP) method are described, which realized for the first time simultaneous measurements of birefringence, optical activity, and rotation angles of the indicatrices of any crystals, even those belonging to monoclinic and triclinic systems. The utility of the HAUP method is exemplified by our recent experiments. The origin of the occurrence of incommensurate states in some A2BX4 crystals was theoretically explained from the fact that they showed optical activity. It is of particular interest that the origin is also resonance of eigenstates of the dynamical matrix. The merits of the HAUP method have been extended to the evaluation of the soliton density in the incommensurate phase, discrimination of the twin mechanism of the ferroelectric domains, and search for the origin of ferroelectricity of Rochelle salt. 相似文献
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In this work we demonstrate the properties of spatial solitary waves in chiral nematic liquid crystals with an external electric field. Such self-trapped beams, called nematicons, were created due to the optical reorientation nonlinearity for a light power of a few tens of milliwatts. We show that the direction of propagation of such nematicons can be changed by applying an external electric field. Additionally, this effect can be modified by changing the input polarization of the light beam. The experimental results were obtained in four independent guiding layers created by a chiral nematic structure. 相似文献
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K. A. Brzdąkiewicz U. A. Laudyn M. A. Karpierz T. R. Woliński J. Wójcik 《Opto-Electronics Review》2006,14(4):287-292
We investigate linear and nonlinear light propagation in the photonic crystal fibers infiltrated with nematic liquid crystals.
Such a photonic structure, with periodic modulation of refractive index, which could be additionally controlled by the temperature
and by the optical power, allows for the study of discrete optical phenomena. Our theoretical investigations, carried out
with the near infrared wavelength of 830 nm, for both focusing and defocusing Kerr-type nonlinearity, show the possibility
of the transverse light localization, which can result in the discrete soliton generation. In addition, we present the preliminary
experimental results on the linear light propagation in the photonic crystal fiber with the glycerin-water solution and 6CHBT
nematics, as the guest materials. 相似文献
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The nonlinear refractive index of some pure and dye-doped nematic liquid crystals was measured and compared using extraordinary polarized light. The optical torque of the nematic liquid crystals was strongly enhanced by a small amount of dye impurities (Sudan Black B). This observation is found to be in good agreement with the Janossy model. The dependence of the enhancement factor on the nematic host structure was investigated. The sign of all nonlinear refractive indices were determined by the Z-scan technique. 相似文献
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D. Budaszewski A. W. Domański A. Czapla S. Ertman T. R. Woliński T. Nasilowski H. Thienpont 《Opto-Electronics Review》2009,17(2):156-160
In the paper we analyze microstructured optical fibers filled with typical nematic liquid crystals, i.e., 5CB and 6CHBT under
influence of external electric field or temperature. We use the modified Mueller matrix method with an additional depolarization
matrix to calculate degree of polarization changes of the light propagating in the liquid-crystal infiltrated microstructured
optical fibers. Preliminary experimental results of light depolarization measurements during propagation in these microstructured
fibers are also presented. 相似文献
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Suleyman Yilmaz 《Journal of Quantitative Spectroscopy & Radiative Transfer》2007,104(3):305-309
New computer modelling of light scattering and its propagation through liquid crystal has been presented using T-matrix method in the structural phase transition regions. Numerical aspects of light scattering process, which are based on numerically solving Maxwell's equations, were calculated for some nematic liquid crystals. Firstly, we described in detail T-matrix method for computing light scattering from nematic liquid crystals and presented results of benchmark computations for the considered model. We reported results of extensive calculations for polydisperse, randomly oriented rod-like multilayered systems (nematic liquid crystals). Our results are associated with light scattering by ferroelectric and ferroelastic materials. 相似文献
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A. Piccardi M. Trotta M. Kwasny A. Alberucci R. Asquini M. Karpierz A. D’Alessandro G. Assanto 《Applied physics. B, Lasers and optics》2011,104(4):805-811
We investigate the propagation of nematicons in various nematic liquid crystals. Following some general considerations on
the role of material parameters in light self-trapping via a reorientational nonlinear response, we discuss numerical results
on light self-action and transverse localization. Finally, we validate our findings with experimental measurements in three
liquid crystalline mixtures featuring different amounts of birefringence. 相似文献
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K. Kowiorski J. Kędzierski Z. Raszewski O. Chojnowska K. Garbat 《Phase Transitions》2016,89(4):403-410
ABSTRACTWedge 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. 相似文献
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Urszula A. Laudyn Katarzyna A. Rutkowska Robert T. Rutkowski Mirosław A. Karpierz Tomasz R. Woliński Jan Wójcik 《Central European Journal of Physics》2008,6(3):612-618
We have investigated the nonlinear propagation of light in photonic crystal fibers filled with nematic liquid crystals. We
analyzed a configuration with a periodic modulation of the refractive index corresponding to a matrix of waveguides. Matrices
of coupled waveguides allow observing a variety of new phenomena both for low power light beam propagation and with an existence
of nonlinear effects. The opportunity for the creation of solitary waves caused by the interplay between diffraction and nonlinear
effects in these kinds of fibers is investigated. At low power the propagating light beam spreads as it couples to more and
more waveguides. When the intensity is increased the light modifies the refractive index distribution, inducing a defect in
the periodic structure. The creation of such a defect can lead to a situation in which the light becomes self-localized and
its diffractive broadening is eliminated. Eventually, in the case of positive Kerr-type nonlinearity, a discrete soliton can
be created. In the case of negative nonlinearity the refractive index decreases with the optical power and can lead to bandgap
shifting. The incident beam, with a frequency initially within the bandgap, is then turned outside the bandgap resulting in
the changing of the propagation effect for the discrete diffraction effect. As a consequence the delocalization of the light
can be observed.
Presented at 9-th International Workshop on Nonlinear Optics Application, NOA 2007, May 17–20, 2007, Świnoujscie, Poland 相似文献
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E. V. Aksenova A. A. Karetnikov A. P. Kovshik E. V. Kryukov V. P. Romanov 《Optics and Spectroscopy》2008,104(6):909-919
The particular features of the propagation of light in uniaxial chiral liquid crystals with a large pitch of the spiral are considered. There exist forbidden zones in these systems for fairly large angles of incidence of an extraordinary ray. On the one hand, this results in an efficient reflection of the wave from the zone boundary, and, on the other hand, this causes the wave to decay inside the zone. A case of narrow forbidden zones is studied, and it is shown that optical effects that arise upon propagation of rays near turning points are equivalent to the tunnel and over-barrier reflection effects. The angular dependences of the intensities of rays that were refracted in a forbidden zone and transmitted through it are calculated. The percolation effect is experimentally studied in a mixture of a nematic liquid crystal with a chiral addition. The intensity of a transmitted extraordinary ray is studied as a function of the angle of incidence, which determines the width of the forbidden zone. Both the over-barrier reflection and the percolation effects are observed. The calculation results are shown to agree with experiment. 相似文献
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O. A. Kapustina 《Acoustical Physics》2004,50(4):427-433
The orientation behavior of homogeneous planar layers of nematic liquid crystals with open and closed ends in the field of compressional deformations caused by an acoustic effect is studied. The mechanisms determining the connection of the optical response of a nematic liquid crystal (the variable component of an optical signal and its spectrum) with the acoustic parameters (the oscillation amplitude and frequency, and the amplitude of sound pressure) and the layer thickness are revealed. The factors responsible for the mechanism and modes of acoustooptic conversion are considered. It is demonstrated that, by varying the layer thickness, it is possible to implement different modes of signal conversion. The possibility of designing a new modification of a sound receiver based on a nematic liquid crystal and the specific features of this design are discussed. Its advantages over conventional sound pressure receivers based on nematic liquid crystals are indicated, in particular, the absence of limitation of the frequency of the received signal in the low-frequency range. 相似文献
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Molecular orientations and photorefractive effects of C60-doped nematic liquid crystals were investigated with layer-structured liquid crystal cells where a nematic phase was injected.
Regardless of the surface treatments of the layers, liquid crystals injected with nematic phase showed a higher degree of
director orientation and photorefractivity than those injected with an isotropic phase. The nematic alignment of liquid crystals
in an untreated cell is generated by a capillary flow of liquid crystal during the nematic injection. However, it was observed
that the grating formation was delayed a little longer with injection of nematic phase than with injection of isotropic phase.
Received: 11 March 2002 / Revised version: 22 April 2002 / Published online: 12 July 2002 相似文献
15.
P. Kopperschmidt 《Applied physics. B, Lasers and optics》2001,73(7):717-720
Electrically induced birefringence is studied in photonic bi-oriented crystals in terms of molding lightflow in optical devices.
In photonic bi-oriented crystals, misorientation of dielectric anisotropic grains results in a dielectric contrast at the
grain boundaries. The translational periodicity of the optical constants depends upon a regular network of twisted dielectrics.
Due to the anisotropy of the bicrystalline structure the direction of light propagation determines the dielectric contrast
at the grain boundaries. In a specific crystallographic arrangement the optical properties of the bi-oriented crystal can
be tuned by the electro-optical effect: the periodic dielectric contrast is electrically induced and photonic bandgaps are
generated by applying external electric fields. The geometrical requirements for tunable photonic bicrystals are evaluated
based on materials employed for electro-optical applications. Tunable photonic bi-oriented crystals may be candidates for
fast optical switches, modulators and multiplexers in the optical communication network.
Received: 5 July 2001 / Revised version: 3 August 2001 / Published online: 15 October 2001 相似文献
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We investigate multiband optical breathers in a voltage-adjustable array of coupled waveguides in nematic liquid crystals. Symmetric breathers resulting from vector composition of modes from two bands are observed over large propagation distances and are described in terms of the Floquet-Bloch theory. 相似文献
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Molecular dynamics simulations of the Gay-Berne model have been undertaken and optical response properties calculated for the isotropic and nematic phases. The components of the optical response were calculated for the coordinate system with respect to the director. Furthermore, the response for the components was separated into the orientational and collision induced contributions in order to analyse the mechanism of the optical response. It was observed, in particular, that one of the depolarized components of the response function does not vanish after long times for the nematic phase, unlike in the isotropic phase. This means that the orientation of the director can be permanently changed by instant irradiation with polarized light. The results give a microscopic picture of the optical Kerr effect in nematic liquid crystals. 相似文献