Upon massive generation of anisotropic grains of azo dye methyl orange in a gelatin film exposed to active polarized light, a cluster of micro crystals with optical axes of similar orientations has been produced. The anisotropy observed has been found to disappear under exposure to active natural light.

Two-color holographic recording was performed in near-stoichiometric LiNbO3 crystals doped with 50-ppm Mn, where the crystals were thermally annealed in different oxidation/reduction atmospheres. Two-color recording properties including sensitivity, dynamic range, activity energy, and dark decay time were measured and compared, and the results were explained reasonably by measuring some characteristic material parameters.

Amorphous bulk composites were prepared by doping azo-dye disperse red 1 (DR1) in poly(methyl methacrylate) (PMMA) matrices. Photoinduced anisotropy of such kind of bulk polymer material was investigated experimentally by measuring the dichroism when irradiating with linearly polarized green light with different polarization direction. With the interaction of bi-photonic beams at 514 and 632.8 nm, transient gratings in the bulk composites could be established, which was a kind of population gratings of trans and cis DR1 isomers and was attributed to the weak absorption of cis isomers at 632.8 nm and the positive dichroism of trans isomers at 514 nm. Furthermore, the all-optical switching behavior of the transient holographic gratings was observed repeatedly by turning on and off the writing beams and a response time of ten milliseconds order could be obtained.

Nonvolatile holographic recording is performed with green light in LiNbO3:Ce:Cu crystals. The refractive-index change and the recording sensitivity are times better than those obtained by recording with red light, and higher optical fixing efficiency is obtained. Correspondingly, theoretical investigations are given.

A novel wideband sensitive dry holographic photopolymer sensitized by rose bengal (RB) and methylene blue (MB) is fabricated, the holographic storage characteristics of which are investigated under different exposure wavelengths. The result shows that the sensitive spectral band exceeds 200 nm in visible light range, the maximum diffraction efficiency under different exposure wavelengths is more than 40% and decreases with the decrease of exposure wavelength, the exposure sensitivity is not change with the exposure wavelength. This photopolymer is appropriate for wavelength multiplexing or multi-wavelength recording in digital holographic storage.

Scattering noises in four kinds of lithium niobate crystals with the same double doping system, which are LiNbO3:Fe:Mn, LiNbO3:Ce:Mn, LiNbO3:Ce:Cu, and LiNbO3:Fe:Cu, are observed and compared experimentally. The results show that nonvolatile holographic recording can effectively suppress scattering noise, which mainly depends on recombination coefficients of both the shallower centers and the deeper centers. The small recombination coefficients of the shallower centers and the large recombination coefficients of the deeper centers benefit the amplification of the signal gratings and the suppression of the noise gratings. In addition, the initial seed scattering also impacts the recorded scattering noise, and the little seed scattering results in low scattering noise. The theoretical simulations are performed for confirmation. Among the four kinds of doubly doped crystals, in LiNbO3:Ce:Cu the performances of nonvolatile recording are the best with low scattering noise and high diffraction efficiency.

The changes of holographic characteristics of photopolymer induced by temperature are studied experimentally. The results show that the exposure sensitivity increases with the increase of temperature. The maximum diffraction efficiency and the final maximum diffraction efficiency increase with the increase of temperature when the temperature is lower than Tg (glass transition temperature), while they decrease with the increase of temperature when the temperature is higher than Tg. The effect of the change of temperature on the saturation refractive index modulation is very weak.