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A liquid-crystal optical modulator working with acoustic signals is considered. It is shown that it can be operated also with white light up to frequencies of at least 1 MHz. 相似文献
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We study spontaneous pattern formation in a glass-forming nematic liquid crystal during the magnetically induced dynamic Fréedericksz
transition. Pattern growth rates and wavelengths as functions of the magnetic field are extracted from optical transmission
textures of thin planar cells. The characteristics of the observed stripe pattern can be related to viscoelastic parameters
of the nematic by means of a linear stability analysis of director fluctuation modes. The viscous properties of the material
allow to vary the time scales of the experiment with temperature by orders of magnitude, leaving the spatial structure of
the pattern essentially unchanged. We find that the ratios of shear and rotational viscosity coefficients relevant for the
pattern wavelength selection remain constant in the temperature range investigated, whereas their absolute values change by
almost two orders.
Received 23 November 2001 and Received in final form 19 April 2002 相似文献
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The effect of nanoobjects, molecular objects, and α particles introduced into a liquid-crystal matrix that is placed in a dc electric field is studied theoretically and experimentally. The introduced particles form a charged defect, the radius of which is much larger than the particle sizes, in the orientational structure of the liquid crystal. This defect is easily observed under an optical microscope, and its image agrees with calculated data. It is suggested that this effect be used for detection and diagnostics of small objects and for design of ionizing radiation detectors. The phenomena revealed in this work can help in producing new charged-defect-saturated liquid-crystal structures formed by introducing nanoparticles in a medium or by irradiating a medium by ionizing radiation. A nonmechanical principle of transport of nanoparticles and their regular incorporation into the lattice is implemented. The essence of this principle is control of molecular orientations in a liquid crystal by quasi-stationary electric fields. 相似文献
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M. I. Barnik A. S. Zolot’ko V. F. Kitaeva 《Journal of Experimental and Theoretical Physics》1997,84(6):1122-1130
The interaction of linearly and circularly polarized beams with a nematic liquid crystal doped with light-absorbing dyes has
been studied by light-diffraction and microprojection methods. It has been found that there is a threshold for the emergence
of light-induced anisotropic structures, which, depending on the type of dye, can be axisymmetric or extended in a direction
determined by the light field. Possible mechanisms leading to the formation of the anisotropic structures are discussed.
Zh. éksp. Teor. Fiz. 111, 2059–2073 (June 1997) 相似文献
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At a temperature lower than the melting point of pure pentyl-cyanobiphenyl liquid crystal (5CB) we studied the photorefractive effect of 5CB heavily doped with fullerene (C60) and obtained a diffraction efficiency of the photorefractive grating of more than 40%, which is more than twice as high as the best data reported to our knowledge. A quasi-permanent grating was observed with a diffraction efficiency of 11.2% after the grating was kept in the dark for a month. 相似文献
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The spectral characteristic of a nematic liquid crystal photonic crystal fiber is analyzed. The locations of the transmission minima in the transmission spectrum can be evaluated by examining the modal cutoffs of specific modes in the liquid crystal inclusion. The selection criteria for these specific modes are based on the fraction of power residing in the core. Explicit expressions for these modal cutoffs are also derived. 相似文献
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Light traveling through a liquid crystal with disclinations perceives a geometrical background which causes lensing effects
similar to the ones predicted for cosmic objects like global monopoles and cosmic strings. In this paper we explore the effective
geometry as perceived by light in such media. The comparison between both systems suggests that experiments can be done in
the laboratory to simulate optical properties, like gravitational lensing, of cosmic objects. 相似文献
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We report a biaxial nematic liquid crystal in a simple thermotropic system. 相似文献
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We have systematically analyzed the spatial dynamics of the polarization state of light in smoothly inhomogeneous anisotropic media. As a medium of this kind, we have considered a nematic liquid crystal with twist orientation. A system of coupled equations has been solved with respect to the Cartesian components of the electric-field component using a rotating coordinate system. We have shown that, upon propagation of light in this medium, the state of the polarization experiences oscillations the spatial frequency of which depends on the thickness of the specimen. Our analysis also has shown that, at an appropriate choice of the thickness, this twist cell behaves as a broadband half-wave plate. 相似文献
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We investigate the polarization structure of coherent light, produced by a convergent light beam transmitted through nematic liquid crystal (NLC) cells with different director configurations. Employing solutions to the transmission problem for the case when plane wave propagates through an anisotropic layer, we analyze the arrangement of the topological elements, such as polarization singularities (C points with circular polarization and L lines with linear polarization), saddle points and extrema of polarization azimuth. We observe transformations of the topological structure under the variation of the incident light ellipticity and represent it by corresponding trajectories of topological elements in three-dimensional space. For the cells with uniform and non-uniform director configuration we describe the processes of creation/annihilation of C point pairs, which can be controlled precisely in the case of the cell with non-uniform director. Our experimental measurements for the homeotropically oriented NLC cells are in good agreement with the theoretical predictions. 相似文献
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The system of equations describing the thermal orientation effect in nonchiral liquid crystals, which was observed earlier,
is proposed and substantiated. The effect of the director reorientation under the action of the temperature gradient is in
many ways analogous to the Freedericksz transition in electric or magnetic fields. The angle of deviation of the director
from the initial position is determined by the square of the temperature gradient. The effect is observed for a nematic liquid
crystal, initially uniformly oriented, and is not accompanied by macroscopic fluxes of the medium under stationary conditions. 相似文献
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Dominique Langevin 《Solid State Communications》1974,14(5):435-437
The absorption coefficient of a nematic liquid present an important anisotropy. The measurement of this coefficient in three simple geometries allows the determination of the three Frank elastic constants on the same sample. We give the results obtained for MBBA at room temperature. 相似文献
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Lin Ziyang Jue Shi Xiang Ying L. P. Shi Wang Jian Z. X. Liang Z. R. Qiu 《Physics letters. A》2000,270(6):207-330
We observed an azo-isomerization-induced Freedericksz transition of the 5CB liquid crystal doped with 1% double-azo. In experiment, we found that the Freedericksz transition threshold occurred at optical intensity level of 0.3 mW/mm2 for the 12.5 μm-thickness planar alignment doped 5CB, which is four orders of magnitude lower as that for the pure 5CB. Using optical phase retardation, we measured the relations between the Freedericksz transition threshold and the pump beam polarization. The maximum twist angle of liquid crystal molecules under different pump beam intensity is given. The experiment indicated that trans–cis isomerization plays an important role in the decrease of the Freedericksz transition threshold. 相似文献
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S. Lecommandoux F. Hardouin A.J. Dianoux 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):79-85
From quasi-elastic neutron scattering experiments performed in glassy, nematic and isotropic phases, the dynamics of oriented
samples of strong anisotropic side-on fixed liquid crystal polymers have been analysed. Using the selective deuteration method,
we are able to attribute motions to specific parts of the molecule in the parallel and perpendicular orientations. The motions
of the whole macromolecule decrease as soon as the temperature decreases below the isotropic-nematic transition. Nevertheless,
the motions of the polymer backbone, compared to the whole polymer dynamics, are systematically reduced, even in the isotropic
phase. Moreover, an anisotropy of the motions is revealed, with a reduction in the direction parallel to the orientation.
An harmonic character of the vibrational processes is also evidenced. We conclude that the anisotropy of the dynamic corroborates
the anisotropy of conformation of the macromolecule (so-called jacketed structure).
Received: 29 October 1997 / Revised: 22 January 1998/
Accepted: 11 May 1998 相似文献