POLARIZATION PROPERTIES AND DIFFRACTION EFFICIENCIES OF BINARY ANISOTROPIC GRATINGS - GENERAL STUDY AND EXPERIMENTS ON FERROELECTRIC LIQUID-CRYSTALS

Binary gratings recorded in anisotropic (birefringent or dichroic) med ia exhibit peculiar polarization properties and a method to calculate the polarization states and the irradiances of diffracted spots in the Fraunhofer diffraction pattern for an incident wave of arbitrary pola rization state is proposed. The gratings under consideration have peri ods made of domains of different widths in which the anisotropic mediu m can be in two states. Anisotropic modulation results in spatial modu lation of polarization with two possible states; for every spot in the diffraction pattern, the polarization state and the irradiance are de rived as functions of these two states and are shown to depend on the order of diffraction of the spot. More specific results are obtained f or phase shift, axis or mixed birefringence modulations and a comparis on between the relative irradiances obtained in each case is establish ed. The theory is illustrated by experimental results with ferroelectr ic liquid crystals. (C) 1998 Elsevier Science B.V. All rights reserved .