Influence of far-red light coherence on the functional state of plants.

The influence of the coherence of far-red (730 nm) light on the functional activity of plants was studied. Blackberry explants cultivated in vitro on an artificial nutrient medium served as a biological model. The explants were irradiated with light beams with different spatial and temporal coherence. The average cell size D was taken as the discrimination threshold for the coherence length L_{coh} and the correlation radius r_{cor}. The results of irradiation were judged by the length and number of shoots formed on each explant. The greatest photoinduced effect was observed when the conditions L_{coh}, r_{cor}>D were fulfilled, i.e., when the cell fit completely in the coherence volume of the light wave field. Significant differences in growth parameters were also observed in the variants of the experiment with a constant frequency spectrum of radiation (fixed L_{coh}), but different r_{cor}. It is concluded that the correlation properties of radiation affect photoregulatory processes.

Highly efficient optical director reorientation of liquid-crystalline polymer induced by dye additives.

Light-induced director orientation of polymeric liquid-crystalline systems was investigated. The materials under study were composed of a nematic liquid-crystalline polymer (NLCP) and a small amount (0.05-0.5 wt.%) of conformationally active (azobenzene) or stable (anthraquinone) dye impurity. Light action on the homogeneously aligned polymer films above glass transition temperature leads to the director reorientation and, consequently, to a change in the extraordinary refractive index. The effect is associated with the dye molecule excitation and related change of intermolecular forces. In the case of NLCP with conformationally active dye dopant, an extremely high orientational optical response was detected (nonlinear coefficient is n_{2}∼0.1cm^{2}/W). In contrast, the efficiency of orientational light action on NLCP with conformationally stable dye dopant is of the same order of magnitude as that of dye-doped low-molar-mass liquid crystals. At the normal light incidence on the NLCP doped with azo-dye, the threshold director orientation is observed which is similar to the Fréedericksz transition under the action of magnetic and electric fields. The obtained high-orientational optical response of NLCP caused by azo-dye dopant in combination with the possibility of the recording of deformed structure in the glassy state, typical for polymer compounds, reveals new opportunities in photonics applications.

Effect of spatial coherence of light on the photoregulation processes in cells.

The effect of the statistical properties of light on the value of the photoinduced reaction of the biological objects, which differ in the morphological and physiological characteristics, the optical properties, and the size of cells, was studied. The fruit of apple trees, the pollen of cherries, the microcuttings of blackberries in vitro, and the spores and the mycelium of fungi were irradiated by quasimonochromatic light fluxes with identical energy parameters but different values of coherence length and radius of correlation. In all cases, the greatest stimulation effect occurred when the cells completely fit in the volume of the coherence of the field, while both temporal and spatial coherence have a significant and mathematically certain impact on the physiological activity of cells. It was concluded that not only the spectral, but also the statistical (coherent) properties of the acting light play an important role in the photoregulation process.

Light- and electric-field-induced first-order orientation transitions in a dendrimer-doped nematic liquid crystal.

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.