The results of the studies of the orientational optical nonlinearity of a nematic host doped with high-molar-mass compounds of different molecular architecture such as a comb-like polymer and a dendrimer containing azobenzene chromophores are presented. The nonlinearity induced by these compounds was found to be higher than that induced by the low-molar-mass dyes similar in structure to the light-absorbing constituents of the polymer and dendrimer. Possible reasons for the nonlinearity enhancement for macromolecular dopants are discussed.

Interaction of light and ac electric fields with a nematic liquid crystal (NLC) doped with nanosized second-generation carbosilane codendrimers containing terminal azobenzene fragments has been studied. A first-order Freedericksz transition in the linearly polarized light, accompanied by an intrinsic bistability in a wide region, was observed. An additional ac electric field decreases the light-induced Freedericksz transition threshold and narrows the bistability region. Light illumination transforms the second-order electric-field-induced Freedericksz transition to a first-order one. The width of the bistability region increases with the light wave intensity. The theory of the interaction of light and ac electric fields with the dendrimer-doped NLCs is developed taking into account an additional (with respect to the undoped nematic host) dependence of the optical torque on the angle between the director and the light field.

The interaction of light with a nematic liquid crystal (NLC) doped with dendrimers containing terminal light-absorbing azobenzene fragments and a low-molar-mass dye identical to the fragments was studied in detail. Both the dendrimers and the dye induce orientational nonlinearity in a transparent nematic host. For the fifth-generation dendrimer, the nonlinearity is negative (director is rotated away from the light field direction). For the first-generation dendrimer and the dye, the nonlinearity sign depends on the light propagation direction with respect to the NLC director, light polarisation and external electric field. The results obtained show that complication of the molecular structure of the dopant, i.e. passing from the ‘free’ dye molecule to the first- and fifth-generation dendrimers, results in an increase of the efficiency of the orienting effect of the light.

Light diffraction was found and studied on “Channels” i.e. cylindrical regions of isotropic liquid in the nematic phase of a liquid crystal, created along the path of a laser beam by heating. Reorientation of the director is shown to take place at the boundary of these channels.

The generation of optical vortices in nematic liquid crystals (NLCs) due to the photorefractive effect has been studied. The vortices can appear in the NLCs with both positive and negative dielectric anisotropy. The efficiency of the Gaussian beam (TEM₀₀) to vortex conversion approached about 30%.