ELECTRIC-FIELD CONTROLLED DYNAMIC HOLOGRAMS ON POLARIZATION GRATINGS IN A FERROELECTRIC LIQUID-CRYSTAL

The irradiation at 514.5 nm of a ferroelectric liquid crystal (FLC) fi lm doped with a photochromic chiral thioindigo dye causes a change in the birefringence of the FLC film under a constant de voltage. This bi refringence photomodulation is used to create electric field controlle d dynamic holograms. The diffraction efficiency of the hologram is fou nd to depend resonantly on the applied de voltage. The unwinding of th e FLC helical structure into a planar alignment as a result of a photo induced increase of the spontaneous polarization (P-s) and of the corr esponding dielectric torque is thought to be at the origin of the obse rved birefringence photomodulation. (C) 1998 American Institute of Phy sics.