Characterization of the diffraction efficiency of new holographic gratings with a nematic film-polymer-slice sequence structure

We have performed a first characterization of the diffraction efficiency of gratings written in liquid-crystalline composite materials by the interference pattern of two curing beams. The grating fringes consist of polymer slices separated by films of continuous nematic phase. The dependence of the diffraction efficiency on temperature reveals a nonmonotonic behavior, with several maxima and minima. The shapes of curves are dependent on slight changes in the initial concentration of the nematic component of the mixture: the number of extrema increases with an increase of this concentration. The dependence of the diffraction efficiency on an applied external voltage also appears to be nonmonotonic: The shape depends on the sample's temperature. Both switch-on and switch-off responses have been observed. The behavior of our gratings can be explained in the framework of the conventional Kogelnik theory for the diffraction efficiency of Bragg gratings.