Light-induced periodic lattice of defects in smectic A and C liquid crystals: Structural and dynamical aspects

Structural and dynamical studies of optically-induced effects in SmA and SmC* liquid crystals are presented. The smectic materials are doped with photosensitive molecules capable of trans-cis isomerization under light illumination. Laser irradiation leads to the formation of strongly scattering textures with periodical array of parabolic focal conic domains (PFCD's). What is most surprising is that the effect is caused by a low-power (< 10 mW) He-Ne laser beam; its efficiency is highest in the visible part of the spectrum. The written information can be erased by another beam with shorter wavelength, such as from an Ar laser 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 of the molecules.