Improvement of the diffraction efficiency of isotropic and anisotropic gratings in Fulgide film by auxiliary light

No matter during the ordinary holograph recording process in photochromic media, or during the polarization holograph recording process in photoinduced anisotropy media, there exits an overshooting peak in the diffraction efficiency, which then decays to a lower permanent level or also to zero, because of the diminishing of fringe contrast caused by a photochemically active readout beam, unequal intensities of object and reference waves and the nonlinear saturation effects of photoisomerization process and photoinduced anisotropy process. It is known that in ordinary holograph recording, this decreasing process can be eliminated by illuminating the hologram with a uniform control beam that has the effect of molecular back-conversion photo chrome. It was found that in polarization holograph recording, this method also can be used. Experiments done with an ordinary hologram and a polarization hologram recorded in a bistable state photochromic 3-indoly-benzylfulgimide/PMMA film at 633 nm have shown that a control beam at 405 nm can increase the stable-state diffraction efficiency, thus, allowing to decrease the rigorous requirements on the recording time, the object reference ratio and the reading beam intensity in the holographic recording. And the theoretical qualitative analyses are also given.