We observed the photorefractive spatial dark-soliton stripes in LiNbO3:Fe crystal, and demonstrate the planar waveguide property of refractive index profile induced by these spatial dark-soliton stripes. We suggest a new toothed to form the planar waveguide utilizing the grating fixing technique.

Based on a multi-three-wave mixing model, we theoretically study the resistance against light-induced scattering in LiNbO3: M sM-Mg21, Zn21, In31, Sc31d crystals. We have simulated the intensity angular distribution of light-induced scatterings. We have also shown that the total light-induced scattering will be much less than 1% of the incident light intensity when the photovoltaic field Eph is less than 4.03 106 Vym. Phase gratings and signal beams can still be formed and amplified effectively in LiNbO3: Mcrystals, with Eph less than 4.03 106 Vym.

Based on a multiwave mixing model, we explain the symmetrical and broad light-induced scattering effect in LiNbO3: Fe crystal sheets. Analytical results are given in the undepleted-pumps approximation. The competition between forward small-angle scattering and climbing lights and its relation to the ratio of the size of the incident-light spot to the crystal thickness are discussed. The intensity angle distribution of the forward small-angle light-induced scattering is studied theoretically and experimentally. We suggest that the selfdefocusing effect of the LiNbO3: Fe crystal plays an important role in the formation of the fanning intensity angle distribution.

On the basis of the idea that signal gratings have a faster formation rate than noise gratings and signal gratings have a slower erasure rate than noise gratings under the same erasing beam, we report a new technique to suppress or eliminate the noise in image processing in photorefractive crystals. A general theoretical analysis and experimental results in LiNbO3:Fe crystals are given.

We analyze the valence and electronic shell configuration characters of all damage-resistant dopants found in LiNbO3 crystals up to now. We show that all damage-resistant dopants have only one valence state. We also show that the electronic shell configurations of these damage-resistant ions are filled fully, as are the cases of the inert elements. From this point of view, we conclude that the anti-site NhLi should be involved in the charge transport process, while the Li vacancy VLI is not involved in the charge transport process. It also can give us some insights about how to select a damage-resistant dopant for LiNbO3 crystal.

Based on the two-center model and the multi-three-wave mixing model, we theoretically study the possible origins of the threshold effect of the incident light intensity for the photorefractive light-induced scattering in LiNbO3: Fe,M, (M5Mg21, Zn21, In31) crystals. Our results show that the value of the threshold intensity of incident light is strongly dependent on the dark conductivity of the crystal, and the maximum total fanning noise is dependent on the concentration of Fe ion on the Li site. These two factors together determine the threshold behavior of incident light intensity for the photorefractive light-induced scattering in LiNbO3:Fe,M crystals when the incident light intensity is in moderate range.

Based on a multi-three-wave interaction model, we theoretically analyze the intense amplification competition between fanning noise and the signal beam in doped lithium niobate crystals. Our results show that the signal beam can be most effectively amplified for a specific value of the photovoltaic field because of the amplification competition between fanning noise and the signal beam. When the threshold effect of incident-light intensity for photorefractive light-induced scattering is taken into account in LiNbO3: Fe, M (M 5 Mg21, Zn21, In31, Sc31) crystals, the signal beam can be most effectively amplified for a specific pump intensity.

Light-induced space-charge fields and the related orientational photorefractive effects in nematic liquid crystal cells are studied both theoretically and experimentally. Analytical solutions for the refractive index change distribution are obtained under the single-elastic-constant approximation with various configurations of externally applied electric and magnetic fields and of the nematic liquid crystal director. The effects of the rigid boundary condition are investigated in detail. The grating spacing for which the refractive index change is maximized depends on the strength of external electric and magnetic fields. The responses of parallel cells differ from those of homeotropic cells, both upon the dependencies on the grating spacing and on the external fields. Under the same conditions, the orientational photorefractive effects are stronger in parallel cells than in homeotropic ones. It is also shown that the investigated effects will be greatly enhanced near the Free

We demonstrate nonvolatile two-color holography in an as-grown congruent LiNbO3: In crystal of 2.2 mm thickness. We show that the nonvolatile two-color holographic performance of the crystal is significantly improved as compared with that of other congruent LiNbO3 crystals reported so far. The figure of merit M/# and the two-color recording sensitivity S are measured to be; 0.04 and; 3.531024 cm/J, respectively, with a writing intensity of 4 W/cm 2 at 780 nm and a gating intensity of 1.15 W/cm 2 at 488 nm. These values are comparable to those of unreduced near-stoichiometric LiNbO3 crystals under similar recording conditions.

We observe ultraviolet-light-induced absorption changes in spectral regions from the near-ultraviolet to the near-infrared in as-grown LiNbO3: Mg. Such a broad light-induced absorption band is unstable at room temperature and decays nonmonoexponentially in the dark with a time constant on the order of tens of seconds.We attribute the appearance of the broadband light-induced absorption to the creation of the intermediate state O2 in which holes excited from deep defect centers are trapped at O22 sites near cation vacancies. It is also found that near-infrared photorefractive sensitivities increase by several orders of magnitude by pre-exposing the crystal to incoherent ultraviolet light. These properties may be useful for an application of LiNbO3: Mg to nonvolatile two-color holography.