M. P. Smayev

Orientational optical nonlinearity induced by comb-shaped polymers in a nematic liquid crystal

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.

Orientational optical nonlinearity of nematic liquid crystals induced by high-molecular-mass azo-containing compounds

Processes of light-induced reorientation of nematic liquid-crystalline molecules induced by the addition of low concentrations (0.1–2.0 wt %) of comb-shaped polymers and carbosilane dendrimers containing azobenzene fragments are studied. When the molecular structure of the above compounds becomes more complicated, the induced orientational nonlinearity increases. The introduction of 2G and 3G dendrimers into a nematic has for the first time made it possible to visualize and study a purely optical first-order Freedericksz transition in the field of a linearly polarized wave.

Orienting effect of light on dye-doped liquid-crystal polymer

Light-induced reorientation of the dye-doped liquid-crystal polymer director is found and studied. The director rotates from the light field direction, which corresponds to the negative optical nonlinearity. The nonlinearity coefficient is several times larger than that of a low-molecular liquid crystal doped with the same dye.

Generation of spiral dislocation of wave front in absorbing nematic liquid crystal

It is demonstrated that an optical beam acquires a component with spiral dislocation of wave front (optical vortex) due to passage through a layer of homeotropically aligned nematic liquid crystal with light-absorbing admixture. The vortex is formed owing to the heating of liquid crystal and transition to isotropic phase in the irradiated region, which leads to the generation of axisymmetric field distribution of director at the interface of the isotropic channel and nematic liquid crystal.

Formation of the light beam with wavefront screw dislocation at the photorefractive effect in nematic liquid crystal

A light beam with wavefront screw dislocation is generated using a nematic liquid crystal under a dc electric field. Axisymmetric deformation of the director field required for the formation of such a beam appears due to light-induced removal of dc field screening by surface electric charges.

Light-induced orientation of the molecules of nematic liquid crystals doped with comb-shaped polymers with different spatial distributions of chromophores

The orienting effect of light on nematic liquid crystals (NLCs) doped with comb-shaped polymers with different spatial distributions of side absorbing azobenzene fragments, i.e., a homopolymer (containing only azofragments), a block copolymer (containing additionally a block of non-absorbing fragments), and a statistical copolymer (containing randomly arranged absorbing and non-absorbing fragments) is experimentally studied. The light-induced Freedericksz transition threshold for the block copolymer is two times lower than that for the homopolymer. For NLC with statistical copolymer dopant, the first-order orientation transition with an extremely wide optical bistability region is observed.

Self-action of a light beam in nematic liquid crystals in the presence of a DC electric field

The results of experimental study of the light beam self-action in a nematic liquid crystal placed in a dc electric field are presented, and a theory of this effect is developed. This self-action of a light beam is shown to cause a hyperbolic umbilic caustic. The intensity distribution and caustics calculated in the far diffraction zone of the light beam agree well with the experimental data.

Image processing by means of orientational self-action of light in nematic liqud crystal

The Zernike method using a nematic liquid crystal (NLC) filter with orientational optical nonlinearity was applied to visualize phase objects. It was shown that the contrast sign of the image switches by means of varying the incidence angle of a light beam on liquid crystal cell. The comparison of a contrast sign change of opaque object in the schemes based on NLC-filter and on liquid filter with thermal optical nonlinearity was performed.

Optical vortex generation using photoinduced orientational defects in nematic liquid crystals

Optical vortices were generated by means of photoinduced point defects in orientation of the nematic liquid crystal (NLC). The axisymmetric distribution of NLC director field was produced due to photorefractive effect in NLC or due to isotropic channel formation in light absorbing NLC.

Zernike filter based on orientational optical nonlinearity of liquid crystalline systems

Visualization of the phase object with the use of a phase-contrast scheme incorporating a nonlinear Zernike filter was carried out. A liquid crystal or liquid crystalline polymer doped with azobenzene dye inducing orientational optical nonlinearity was used as the filter. Inversion of the image contrast depending on the angle of incidence of the light beam on a nematic liquid crystal cell was implemented.