摘要:

The electrical switching characteristics of reflection gratings formed using polymer-dispersed liquid crystals are explored. First, an explanation for the lack of switching in previously formed gratings formed using E7 as the liquid crystal is proposed based on experiments on slightly slanted gratings. These confirm that the LC director orientation within the anisotropically-shaped LC domains is parallel to the grating vector(and applied electric field direction). Slight modification of the syrup leads to transmission gratings with different polarization dependencies and reflection gratings (non-slanted) that switch completely with a modest electric field. These differences are attributed to a 90° rotation in the preferred LC director orientation within the LC domains. This change in orientation results in strong coupling of the electric field with the LC dipoles in a reflection geometry thereby leading to easier switching. The microstructure of these grating structures are explored using low-voltage scanning electron microscopy and bright-field transmission electron microscopy.

ISSN:1058-725X    

DOI:10.1080/10587259808024389

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Film morphology and electro-optical behaviour of Polymer Dispersed Liquid Crystals (PDLC) made by the standard mixture NOA 65/E7 have been studied for different exposure times and intensities of UV curing light. Special attention has been devoted to the study of the effects of curing parameters on film morphology, which were analysed by means of scanning electron microscopy (SEM). UV intensity has been proved to play an important role in the phase separation process. It affects not only liquid crystal droplets size, but also the morphological uniformity of PDLC samples and the extent to which phase separation is complete. A simple interpretation based on the temperature dependence of the free energies involved in the curing process is proposed. As we expected electro-optical responses show to be strictly related to film morphology.

ISSN:1058-725X    

DOI:10.1080/10587259808024390

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Interaction of intense laser light with chiral nematic structure was examined by use of a reflected-probe-beam experimental technique. The technique is sensitive to structural changes in periodic media and appears to be as valuable for chiral nematics investigation as rentgenografic diffraction for crystal lattices. The paper presents partial results of experiment which is just now continued. They suggest optical nonlinearity in chiral nematics of the collective nature rather than of thermal or photochemical origin. The experimental data obtained up to now are discussed in details, although at present some essential questions remain not clear and therefore no theoretical analysis is given.

ISSN:1058-725X    

DOI:10.1080/10587259808024391

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Nonlinear self-focusing of the laser beam in waveguide with nematic homeotropically aligned liquid crystalline layer is analysed theoretically and observed experimentally. The nonlinearity is caused by the reorientational effect and the stable self-trapped beams are created by the spatially periodic reorientation in the liquid crystalline layer.

ISSN:1058-725X    

DOI:10.1080/10587259808024392

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Interest in materials for optical storage effect has been intense in the last years. In this paper we report the observation of permanent gratings in a new liquid crystalline side-chain polymer containing a mononuclear cyclopalladated azobenzene complex. Two-beam coupling experiments indicate photorefractive properties. A gain of 900 cm−1, without applied electric field, was determined by two beam coupling measurements. A significant feature of this high gain material is that this effect occurs in an easily processable pure compound.

ISSN:1058-725X    

DOI:10.1080/10587259808024393

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We present the results of photon correlation spectroscopy investigations of the influence of the confinement and interfaces on the behavior of nematic liquid crystals (NLC) filled with aerosil particles as well as dispersed in porous matrices of different pore geometry and size. The experiments show significant changes in physical properties of LC in such confinements and suggest that there is some evidence for glass-like dynamical behavior, although bulk LC do not have glassy properties. In NLC with nanoparticle network, at least two well identified decays were observed. We attribute the first decay to the director fluctuations of the bulk NLC. The second, glass-like decay, could be related to director dynamics in surface layers at aerosil - LC interface. The mode corresponding to motions of individual aerosil nanoparticles was not detected. This confirms that the aerosil particles form a network in the LC.

ISSN:1058-725X    

DOI:10.1080/10587259808024394

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In the Janossy effect, the threshold intensity for the optical Freedericksz transition in nematic liquid crystals is dramatically reduced by the addition of a small amount of dichroic dye to the sample. We examine the source of torques in the system and the balance of angular momentum. We show that, due to the presence of the dye, the system is an optically pumped orientational ratchet.

ISSN:1058-725X    

DOI:10.1080/10587259808024395

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We investigated the behavior of a beam experiencing the Optical Fréedericksz effect while traveling through a nematic liquid crystal confined in a capillary and doped with a dye. The source is a specially tapered fiber that delivers a narrow and well collimated beam. We present the results we obtained with two different nematics, having different birefringence and aligned in two different ways along with the capillary wall. In the case of an alignment normal to the wall (radial escaped structure), we observed an optically induced displacement of the homeotropic central part of the structure and even a splitting of it. In the case of a planar alignment (fully axial structure), we observed a self focusing and a « selfwaveguiding » behavior, different from the usual filaments. We also give an experimental evidence of the difference between the Fréedericksz threshold and self trapping threshold. In both cases, the light acts on a larger volume than the so far reported non linear optics experiments, therefrom the title. Our results are compared with those obtained in a similar geometry and a pure nematic by other authors. Finally, the non linear behavior of the liquid crystal is discussed.

ISSN:1058-725X    

DOI:10.1080/10587259808024396

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effect of surface-induced (dis)order on collective orientational fluctuations in nematic liquid crystals is studied within Landau-de Gennes theory. Close to the nematic-isotropic phase transition the corresponding spectra are characterized by soft modes, which are associated with fluctuations of the thickness of the (dis)ordered wetting layer. In this range the dynamical part of the evanescent light scattering is dominated by the soft modes.

ISSN:1058-725X    

DOI:10.1080/10587259808024397

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The photoinduced trans-cis equilibrium in nematic liquid crystals is discussed. It is suggested that photoisomerisation leads to an anomalous angular dependence of the dye-induced optical torque.

ISSN:1058-725X    

DOI:10.1080/10587259808024398

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor