LIGHT-INDUCED PERIODIC LATTICE OF DEFECTS IN SMECTIC-A AND SMECTIC-C LIQUID-CRYSTALS - STRUCTURAL AND DYNAMICAL ASPECTS

Structural and dynamical studies of optically-induced effects in SmA a nd SmC liquid crystals are presented. The smectic materials are doped with photosensitive molecules capable of trans-cis isomerization unde r light illumination. Laser irradiation leads to the formation of stro ngly scattering textures with periodical array of parabolic focal coni c domains (PFCD's). What is most surprising is that the effect is caus ed by a low-power (< 10 mW) He-Ne laser beam; its efficiency is highes t in the visible part of the spectrum. The written information can be erased by another beam with shorter wavelength, such as from an Ar las er or a UV source. The PFCD's lattice can be stabilized by a polymeric network. The most plausible mechanism of the light-induced effect is compression/dilation of smectic layers caused by phototransformation o f the molecules.