Light-Induced Ring Pattern in a Dye-Doped Nematic Liquid Crystal

The use of dye-doped liquid crystals allows the amplification of the coupling of light and liquid crystals. Light can induce the self-organization of the molecular order. The appearance of ring patterns has been observed, which has been associated with phase modulation. However, the morphology and dynamics of the ring patterns are not consistent with self-modulation. Based on an experimental setup with two parallel coherence beams orthogonal to a liquid crystal cell, one of which induces photo-isomerization and the other causes illumination, the formation of ring patterns is studied. To use these two coherent beams, we synthesize methylred methyl ester as a dye-dopant, which is photosensitive only to one of the light beams, and a commercial E7 liquid crystal as a matrix. Based on a mathematical model that accounts for the coupling between the concentration of the cis-state and the order parameter, we elucidate the emergence of the rings as forming patterns in an inhomogeneous medium. The bifurcation diagram is analytically characterized. The emergence, propagation of the rings, and the establishment of the ring patterns are in fair agreement with the experimental observations.

Efficiency of diffraction gratings based on liquid crystals

Wehave recorded geometric-phase diffraction gratingusing the method of holography on a thin layer of dichroic dye. A transmission liquid crystal cell hasbeen assembled inorder to obtain electrically-controlled diffraction in visible range. Also, using software for electrooptical effects modeling wehavecalculated the diffraction efficiency (DE) of the LC-based phase grating as a function of the voltage amplitude at the electrodes,es-timatedtheDEvariation as a function of LCcell thickness, LC materialbirefringenceand the radiation wavelength. The experimental data qualitatively matched with calcu-lation results. 1-st order DE of16% (at 532 nm) has been obtainedforsingle-sided phase grating LC. Furthermore, we have observed the decrease ofDEwith the increase of radiation wavelength.