摘要:

Smectic A films with a positive dielectric anisotropy can be switched to homeotropic textures by application of sufficiently high AC electric fields. They can relax to a light scattering state when the field is removed. The transition between the homeotropic and the light scattering focal conic texture is attractive for display applications, but Le Berre and Hareng found with 4–4′-cyano-octyl biphenyl (8CB), that the relaxation was slow and limited to a range of 3° C at the SA-N phase transition. We found that the relaxation can be enhanced by suitable surface treatments. With conventional polyimide coatings the relaxation to the scattering state occurs through the entire SArange (12° C). Observations on samples with differently treated polyimide coated surfaces indicate that the surface roughnes facilitates the relaxations. The relaxation time depends strongly on the temperature. It increases from 50ms near the N-SAtransition to 0.3s at the SA-solid crystal transition. In the range of 5 to 50μm, the contrast and the relaxation time are nearly independent of the sample thickness. The drive voltage is temperature and thickness dependent. For a 5μm film it was below 20V over the whole temperature range. Comparing a smectic A shutter with a typical PDLC device we found that the contrast ratio is smaller, but the non scattering state is completely haze free.

ISSN:1058-725X    

DOI:10.1080/15421409208048685

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The field correlation function of light scattered from the evanescent wave at a solid-nematic interface is deduced. Its perpendicular part has a nonexponential tail falling off ast−3/2and depends on the anchoring energy. Different possible orientations at the surface are discussed.

ISSN:1058-725X    

DOI:10.1080/15421409208048686

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The goggles based on LC spatial light modulator for protection observers' eyes from blinding objects are discussed.

ISSN:1058-725X    

DOI:10.1080/15421409208048687

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Various types of organic polymer photoconductors have been successfully used in optically addressed liquid crystal (LC) light valves based on the electrically controlled birefringence, optical activity, cholesteric-nematic phase transition, dynamic scattering, and polymer dispersed LC. Record regime optimization in projection or holographic manner is necessary to obtain the best device characteristics. The highest parameters obtained in the pulse holographic regime were diffraction efficiency of 36%, limiting resolutions of 1500 mm−1, and spectral sensitivity of 10−8J/cm2%. Photoconductive polymers themselves may be used for LC alignment simplifying the light valve construction. High aperture devices were realized side by side with the small ones. Polymer dispersed LC's connected with the photoconductive polymers allow for the realization of entirely solid state valves. High resolution, mechanical and elecrical stability, and the possibility for sensitization make the use of the polymer photoconductors in spatial light valves very perspective. Such valves can be used as phase reversible medium in various optoelectronic devices and processes.

ISSN:1058-725X    

DOI:10.1080/15421409208048688

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper presents the results of investigations of light scattering and transmission in porous glass-liquid crystal (LC) and polymer systems. It was shown that for cholesteric LC in macropores (unlike the nonmesogenic system isotropic liquid-porous matrix) polarized component of scattered light intensity cannot be described by the sum of intensities caused by: doublescattering, scattering by the matrix, scattering due to the refractive index mismatch between LC and the glass, scattering by the density and the order parameter fluctuations. The existence of essential surplus light scattering, its dependence on the wave number and results of temperature measurements are explained with the only assumption that LC in pores at temperatures above the critical one is pseudotwo phase system with anisotropic interphase layer on pore walls arrising as result of orientational wetting. The interpretation of the results of optical investigations of comblike polyalkylmethacrylates in macroporous glasses is based on the suggestion of the existence of orientational order in the arrangement of relatively long side radicals, which is induced by the pore surface.

ISSN:1058-725X    

DOI:10.1080/15421409208048689

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A new method of experimental determination of the local-field parameters of the light wave in uniaxial molecular media from spectral data has been suggested and realized for several tens of doped liquid crystalline and anisotropic polymeric systems. Anisotropy of the effective local-field tensor for the solute molecules has been found to be determined mainly by the matrix's anisotropic optical properties and also to depend on the specific features of the solute molecules' electronic structure but not to depend on the shape and character of the orientational order of the solute molecules.

ISSN:1058-725X    

DOI:10.1080/15421409208048690

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Accurate measurements near the threshold for the Optical Fréedericksz Transition were made using a heterodyne interferometer-polárimeter. Evidence of multistability and Optical Phase Locking to odd multiple of π was obtained. A physical explanation of these phenomena based on total angular momentum conservation was also proposed.

ISSN:1058-725X    

DOI:10.1080/15421409208048691

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A ferroelectric liquid crystal light valve (FLCLV) for laser pulse recording is studied. We have fabricated a FLCLV that is equipped with a SiO obliquely evaporated film as a liquid crystal alignment layer and a metal-insulator-semiconductor (MIS) photodiode as a photoconductive layer. When the cell gap is about 3um, the liquid crystal alignment shows scale like defects. When the cell gap is reduced to 2um, that scale like defects disappear. High resolution capability of 50 lp/mm is obtained using diode laser, the power of which is merely 20pJ, in this cell.

ISSN:1058-725X    

DOI:10.1080/15421409208048692

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

There is considerable interest in the dynamics of topological defects formed during a symmetry breaking phase transition in fields as diverse as condensed matter physics, particle physics and cosmology. Liquid crystals, with their many symmetry breaking phase transitions are ideal materials for such studies. Here we report on light transmission studies of the coarsening of three-dimensional defect tangles in uniaxial nematic liquid crystals subjected to a sudden pressure jump from the isotropic phase to the nematic phase. We have verified that the type 1/2 disclination line density, as a function of time, scales ast−vwithv= 1.0 ± 0.1 over four decades in time. The transmitted light intensity exhibits two distinct scaling regimes depending on whether propagation without scattering or diffusive propagation with multiple scattering dominates the light reaching the detector.

ISSN:1058-725X    

DOI:10.1080/15421409208048693

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We report measurements of the heat capacity at the N-I transition for 5CB confined in submicron size cavities. A radically different behavior is observed depending on the orientation of the liquid crystal molecules within the cavities. A comparison with bulk measurements is also made.

ISSN:1058-725X    

DOI:10.1080/15421409208048694

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor