摘要:

A detailed study of the transmittance of dye-doped LC-film in dependence on the excitation laser radiation intensity in different LC-phases (nematic and chiral liquid crystals) is presented. It should be underlined that these compounds are based on the same molecular basis (cyanobiphenyls and their derivatives). Transmittance of the investigated systems appeared to be independent on the light intensity in a wide power region. The observed effect could be associated with the dye re-absorption to a higher electron level with the “left” absorption equaling the fundamental one.

ISSN:1058-725X    

DOI:10.1080/10587259508033457

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have studied the optical Fréedericks transition for normal incidence in chiral-nematic mixtures in cells coated for homeotropic alignment. In the case of linear polarization of the incident beam two optical thresholds were observed: the first one is second-order and the second one is first-order, accompanied by very large hysteresis loop. In the case of circular polarization, the double-threshold feature was noticed only when the light elicity was the same as the sample chirality. When the elicity is opposite to the chirality, only one second order reorientational transition is produced. The experimental results were found only in partial agreement with the predictions of a simple plane-wave model.

ISSN:1058-725X    

DOI:10.1080/10587259508033458

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We have calculated the scattering properties of a single droplet with uniform and radial structures in PDLCs in the absence of a voltage for a non-collimated system such as a real PDLC projector. In these calculations, we have developed Zumer's result for a collimated system based on the anomalous diffraction approach. The scattering properties of PDLCs depend not only on droplet properties, e. g. refractive indices, radius and director configuration, but also on the film thickness and the number density of droplets. Assuming a constant concentration, we have shown that the scattering properties of PDLCs can be discussed in terms of an efficiency factor, which removes the dependence on thickness and number density. The differences between collimated and non-collimated systems are discussed as well as the effects of refractive indices, droplet radius and angular dependence of the scattering.

ISSN:1058-725X    

DOI:10.1080/10587259508033459

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Optical vortices are found in the thermal Rayleigh scattering light field of a nematic liquid crystal film. The optical vortices change their positions on the wave front quickly, and at a certain point, the vortices with different topological charges appear in a random way.

ISSN:1058-725X    

DOI:10.1080/10587259508033460

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The influence of dipole phototransformed molecules on the orientational instability threshold of homeotropic NLC exposed to spatially modulated light is studied. The orientational spatial distribution of the director is calculated, in linear approximation, at the non threshold director reorientation. It is shown that the orientational instability threshold may significantly decrease (increase) and the optical nonlinearity constant may increase (decrease) by orders of magnitude as phototransformed molecules with typical value of permanent electric dipole appear in the nematics.

ISSN:1058-725X    

DOI:10.1080/10587259508033461

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effect of a light polarization plane rotation in a cell with weakly twisted nematic liquid crystal (LC) caused by phototransformation of chiral molecules has been found. Such a behavior was stimulated by trans-cis isomerization of twisting agent resulting in a strong decrease of its twisting power. Non-stimulated cholesteric spiral unwinding was observed after an exciting light had been switched off.

ISSN:1058-725X    

DOI:10.1080/10587259508033462

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The light scattering properties of spherical droplets of a nematic low molar mass liquid crystal dispersed either in a polymer matrix or in water have been investigated. The size of the droplets varied from 0.5μm to 100μm. Only a radial arrangement of the director in spherical droplets was considered. Up to ten orders HV scattering patterns were experimentally measured. Calculations have been conducted using the anomalous diffraction and Rayleigh-Gans-Debye theories. Particles larger then 2μm show an extremely good agreement with the anomalous diffraction theory. Particles smaller than 2μm show no agreement with either theory. This may be due to a more complex director arrangement than the radial distribution assumed here.

ISSN:1058-725X    

DOI:10.1080/10587259508033463

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The peak intensities of the diffraction grating obtained in a nematic liquid crystal cell above the critical point of the flexoelectrically induced Pikin transition have been measured as a function of the applied voltage. The obtained results have been analyzed in the framework of a non-linear theory of the transition.

ISSN:1058-725X    

DOI:10.1080/10587259508033464

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

It is described the “self - heterodyning” technique, based on the detection of the intensity oscillations which, in the far field zone, can be observed, in the initial transient, at the center of a beam which crosses a homeotropically aligned nematic liquid cristal. The simplicity and versatility of the technique is supported by the wide range of its applications.

ISSN:1058-725X    

DOI:10.1080/10587259508033465

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The director deformations induced by electric field in weakly anchored nematic and chiral nematic layers were studied numerically. The director distributions were calculated for various parameters of the system, by minimizing the free energy in the course of an iterative process. The earlier qualitative results were confirmed.

ISSN:1058-725X    

DOI:10.1080/10587259508033466

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor