Photoassisted alignment and formation of polarization gratings in a ferroelectric liquid crystal

The photoinduced isomerization of a guest chiral thioindigo dye causes an i ncrease in the spontaneous polarization of a ferroelectric liquid crystal ( FLC) host, which is used to control the dielectric torque exerted on the FL C dim by a de electric field. The resulting reorientation of the FLC direct or and modification of domain walls lead to a significant change of the ave rage birefringence of the film. This birefringence photomodulation is used to create electric-field controlled dynamic holograms. The diffraction effi ciency of holograms is found to depend resonantly on the applied de voltage . Non-monotone dynamics of reorientation is observed for step-like voltage changes under continuous light illumination. Dynamic holography, resonant p hotoexcitation, light scattering, polarized microscopy and polarization tec hniques are used to study these phenomena. (C) 1999 Elsevier Science B.V. A ll rights reserved.