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Lifetimes of two-color nonvolatile holograms recorded in undoped or in slightly doped near-stoichiometric lithium niobate and tantalate crystals were measured and compared by extrapolation of the high-temperature data. A proton-compensation mechanism dominated the dark decay and yielded similar activation energies, of 1.05 and 1.10 eV, for near-stoichiometric lithium niobate and tantalate crystals, respectively. The lifetime of holograms in lithium tantalate was 1 order of magnitude longer than that in lithium niobate with the same proton concentration, which was consistent with our theoretical estimation. The projected lifetime of two-color holograms in lithium tantalate without observable OH-absorption is longer than 50 years. OCIS codes: 160.5320, 090.2900, 210.2860.

The two-color photorefractive response of near stoichiometric lithium niobate (SLN) doped with Mg above a critical threshold has been investigated. Striking differences as compared with non Mg-doped material were observed: The intermediate level in the two-color writing process has approximately a two orders of magnitude longer lifetime in SLN:Mg than in nominally undoped SLN, the grating is written in a shallower level but can be fixed via a simple thermal process and complementary electron-hole gratings are formed. It is proposed that the Fe impurity level moves from below the small-polaron level in nonMgO-doped material to above it, resulting in the increased lifetime of the small polaron. These changes are associated with a shift of the Fe from a Li site to a Nb site. The two-color sensitivity is higher than in the absence of MgO but the dynamic range is much lower. OCIS codes: 160.5320, 160.3730, 210.2860.

Research describing the photochromic effects of LiNbO3 is presented. In particular analysis by electron paramagnetic resonance and holographic storage utilization is investigated.

Near-stoichiometric LiNbO3 shows a strong an stable photoinduced absorption band when illuminated with ultraviolet light.

A study was done on the relationship between the optical damage resistance and LiNbO3 stochiometry as well as the effects of x-ray rocking curve peak width on the optical damage resistance. Calculations of photoinduced birefringence change showed an increase with increasing Li content of lithium niobate crystals and is subsequently reduced by the presence of niobium (Nb). These findings suggest that Nb enhances the optical damage resistance of undoped LiNbO3 and that optical damage resistance is not affected by crystal quality.

The two-color photorefractive properties in undoped as-grown near-stoichiometric lithium tantalate crystals were investigated, where a near-infrared laser and a cw ultraviolet beam were used for writing and gating, respectively. The key parameters in characterizing two-color photorefractive effect, light-induced absorption change, two-color sensitivity, refractive index change, readout characteristics, and dark decay were measured by changing intensities of gating and writing beams, wavelengths of gating and writing beams for the crystals with different near-stoichiometric crystal compositions, and proton concentrations. The results showed that there exists an optimal crystal composition of around 49.65% for both sensitivity and refractive index change together with moderate lifetime of small polarons. The achieved refractive index change was on the order of 10-4, and the obtained maximum sensitivity was 0.18 cm/J. The extrapolated lifetime of holograms at room temperature in the crystals without observable OH- absorption was longer than 50 yr. The measurements of UV-induced absorption change at room temperature and low temperature of 77.3 K suggested that the unintentional impurity of Fe and intrinsic defects were responsible for two-color photorefractive effect. The excellent two-color photorefractive properties of undoped as-grown near-stoichiometric lithium tantalate crystals were discussed based on this mechanism and the physical properties of lithium tantalate. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Near-stoichiometric LiNbO[sub 3] (LiNbO[sub 3], LiNbO[sub 3]:Tb, and LiNbO[sub 3]:Tb,Fe) crystals have exhibited a reversible photochromic effect at room temperature. Irradiation by UV light induced a visible absorption band extending from λapprox. 650 nm to the absorption edge, which could be bleached by subsequent illumination with visible light. Electron paramagnetic resonance (EPR) analysis at 15 K revealed an EPR signal of gapprox. 2.0 appearing after UV irradiation with a simultaneous decrease in the Fe[sup 3+] signal intensity. This implies that the Fe[sup 3+] ions (natural impurities or dopants) act as electron traps and the induced absorption band is caused by the charge transfer from UV-sensitive absorption centers to Fe[sup 3+] ions via the conduction band. Using the induced absorption band, a high-sensitive holographic recording has been achieved with a continuous-wave green laser at λapprox. 532 nm. In addition, the fast response to UV light made it possible to quickly erase the stored information by UV illumination. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses the exhibition of a photochromic effect of near-stoichiometric LiNbO[sub 3] when exposed to ultraviolet (UV) light near 313 nanometer. Presence of three different types of energy levels of the crystals; Occurrence of UV-sensitive absorption centers just above the valence; Observation of a metastable shallow electron traps slightly below the conduction band.

Discusses the crystal-growth conditions and the damage resistant properties of MgO-doped LiNbO[sub3] against Q-switched pulse. Bulk damage threshold, optical transmission spectra and magnesium distribution in the crystal; Relation between the bulk damage threshold and the optical quality of the crystals; Damage traces observed in the crystals irradiated by laser.