The photorefractive BGO crystal shows rapid respond (second level) when applied by external electric field, but it has weak photorefractive effect. CeO2 and CuO co-doped BGO (Bi12GeO20) crystal has been grown by Czochralski method for the first time. The diffraction efficiency and respond time of Ce:Cu:BGO and BGO crystals are determined with two-wave-coupling technology. The phase conjugate reflectivity and respond time are also determined in four-wave-fixing optical path. The results indicate that diffraction efficiency and phase conjugate reflectivity of Ce:Cu:BGO is 30% higher than those of non-doped BGO and the response time exhibits in second level with 6kv/cm2 external electric field. The improvement mechanism of photorefractive effect of Ce:Cu:BGO crystal is investigated systematically.
Doped 0.5mol% Er2O3 and (2,4,5,6)mol% MgO in LiNbO3 crystal, Mg:Er:LiNbO3 crystals were grown by Czochralski technique. The IR transmission spectra of those crystals were measured. The OH- absorption peak of Mg(2mol%):Er:LiNbO3 and Mg(4mol%):Er:LiNbO3 at about 3486 cm-1,while that of Mg(5mol%):Er:LiNbO3 and Mg(6mol%):Er:LiNbO3 at about 3535 cm-1. The shifting mechanism of OH- absorption peak was discussed based on the Li-site vacancy model. Using m-line method tested the photodamage of Mg:Er:LiNbO3 waveguide substrate. The photodamage resistant ability of Mg:Er:LiNbO3 is higher than that of Er:LiNbO3. The photodamage resistant ability of Mg(5mol%):Er:LiNbO3 waveguide substrate improves two orders than that of Er:LiNbO3.
Ce:Mn:LiNbO3 crystals with different Li/Nb mole ratios in the melts (Li/Nb = 0.94, 1.05, 1.20, 1.38) have been grown for the first time. The growing conditions varied greatly on the Li/Nb ratio. With the increase of Li/Nb ratio in crystals, the Curie temperature raises while the melting point drops. The infrared spectra of crystals were measured. The exponential gain coefficient, response time and diffraction efficiency were measured by two wave coupling experiments with He-Ne laser (632.8nm). The near-stoichiometric Ce:Mn:LiNbO3 crystal grown from the melt with Li/Nb ratio 1.38 exhibits the largest exponential gain coefficient (33cm-1) and shortest response time (19s), which is attributed to its larger photoconduction. Combined with spectrum analysis we deduced that the increase of photoconduction may be due to the decrease of anti-site (NbLi)4+in crystals.
Mn:Fe:LiNbO3 crystals were grown using the conventional Czochalski method. The phase conjugate reflectivity and response time were measured by four-wave fixing method with Ar+ laser (488nm) as light source. Non-degenerate phase conjugate wave varying frequency was obtained in Mn:Fe:LiNbO3 and Fe:LiNbO3 crystals with Ar+ laser (488nm) and He-Ne laser (632.8 nm) as light source. The maximum of phase conjugate reflectivity varying frequency of Mn:Fe:LiNbO3 crystal was up to 920%, three orders of magnitude than that of Fe:LiNbO3 crystal. Based on Li vacancy model, we discussed the photorefractive improving mechanism of Mn:Fe:LiNbO3 crystal.
Potassium lithium niobate doped with CeO2 and CuO, Ce:Cu:KLN crystals were grown by Czchralski method for the first time. The exponential gain coefficient of KLN and Ce:Cu:KLN crystals were measured. Effective charge densities of those crystals were computed. The exponential gain coefficient of KLN and Ce:Cu:KLN crystals are 7.4cm-1 and 4.1cm-1. The effective charge density exponential gain coefficient of KLN and Ce:Cu:KLN crystals are 3.2×1022/m3 and 4.2×1022/m3. The IR transmission spectra of KLN and Ce:Cu:KLN crystals were measured. OH- absorption peak of Ce:Cu:KLN shift red compare to that of KLN. The Raman spectra of those crystals were measured. The Raman spectra of KLN and Ce:Cu:KLN crystals were basically alike, which justified the fact that the ions of impurities entered into the lattice by replacement of original ions of KLN crystals.
The congruent tri-doped Mg:Mn:Fe:LiNbO3 crystals have been grown by Czochralski method in air atmosphere. The crystal samples are reduced in Li2CO3 powder at 500°C for 24 hours or oxidized for 10 hours at 1100°C in Nb2O5 powder. Compared with as-grown Mg:Mn:Fe:LiNbO3, the absorption edge in UV-Vis. absorption spectrum of the oxidized sample or the reduced shifts to the red. The post-disposal, oxidation or reduction disposing has no effect on O-H vibration absorption peak in infrared region. In two coupling experiments we determine the writing time, maximum diffraction efficiency and the erasure time of crystal samples in the same conditions. The results indicate that oxidation and reduction disposing has great effect on the holographic recording properties of these crystals. The reduced crystal exhibits the fastest response time 145s and the biggest diffraction efficiency 67% among the crystal series. The mechanism of post-disposing effect on the holographic recording properties of Mg:Mn:Fe:LiNbO3 crystals has been investigated.
Pr:LiNbO3 crystal can be used in two-color gated storage process for its special energy-level structure. Compared with other crystals used as volume holographic storage media, it has a great merit that an image recording does not erase the recorded one in multiplex storage process. But its photorefractive effect appears weaker than other crystals in the same conditions. We doped photorefractive sensitizing element Ce into Pr:LibNO3 to get Ce:Pr:LiNbO3 crystal with Czochralski method. The structure of crystals has been determined by X-ray powder diffraction method. The results indicate Pr:LiNbO3 and Ce:Pr:LiNbO3 keep the same structural characteristics as pure lithium niobate. In the absorption spectra of Pr:LiNbO3 and Ce:Pr:LiNbO3 samples with non-polarized light in wavelength of 300 - 900 nm, the absorption edge of Ce:Pr:LiNbO3 shifts to the red compared with that of Pr:LiNbO3. The diffraction efficiency, writing time and especially erasing time of Ce:Pr:LiNbO3 have been measured. We find that maximum diffraction efficiency of Ce:Pr:LiNbO3 has increased without at cost of decreasing the erasing time. The effect of doping ions on the optical properties of Ce:Pr:LiNbO3 crystal as holographic recording media has been studied systematically.
Pr:LiNbO3 crystal can be used in two-color gated storage process for its special energy-level structure. Compared with other crystals used as volume holographic storage media, it has a great merit that an image recording does not erase the recorded one in multiplex storage process. But its photorefractive effect appears weaker than other crystals in the same conditions. We doped photorefractive sensitizing element Ce into Pr:LibNO3 to get Ce:Pr:LiNbO3 crystal with Czochralski method. The structure of crystals has been determined by X-ray powder diffraction method. The results indicate Pr:LiNbO3 and Ce:Pr:LiNbO3 keep the same structural characteristics as pure lithium niobate. In the absorption spectra of Pr:LiNbO3 and Ce:Pr:LiNbO3 samples with non-polarized light in wavelength of 300 - 900 nm, the absorption edge of Ce:Pr:LiNbO3 shifts to the red compared with that of Pr:LiNbO3. The diffraction efficiency, writing time and especially erasing time of Ce:Pr:LiNbO3 have been measured. We find that maximum diffraction efficiency of Ce:Pr:LiNbO3 has increased without at cost of decreasing the erasing time. The effect of doping ions on the optical properties of Ce:Pr:LiNbO3 crystal as holographic recording media has been studied systematically.
The congruent tri-doped Mg:Mn:Fe:LiNbO3 crystals have been grown by Czochralski method in air atmosphere. The crystal samples are reduced in Li2CO3 powder at 500°C for 24 hours or oxidized for 10 hours at 1100°C in Nb2O5 powder. Compared with as-grown Mg:Mn:Fe:LiNbO3, the absorption edge in UV-Vis. absorption spectrum of the oxidized sample or the reduced shifts to the red. The post-disposal, oxidation or reduction disposing has no effect on O-H vibration absorption peak in infrared region. In two coupling experiments we determine the writing time, maximum diffraction efficiency and the erasure time of crystal samples in the same conditions. The results indicate that oxidation and reduction disposing has great effect on the holographic recording properties of these crystals. The reduced crystal exhibits the fastest response time 145s and the biggest diffraction efficiency 67% among the crystal series. The mechanism of post-disposing effect on the holographic recording properties of Mg:Mn:Fe:LiNbO3 crystals has been investigated.
Ce:Co:SBN, Ce:SBN and Co:SBN crystals have been grown by Czochralski method with CeO2 and Co3O4 as dopants in air atmosphere. With these crystals as holographic storage media, the diffraction efficiency, response time and phase conjugate reflectivity are measured. The Ce:Co:SBN crystal exhibits better properties than SBN crystal and especially its diffraction efficiency is up to 70%. The Ce:Co:SBN crystal is used as holographic storage media to realize highly effective association storage in four-wave-mixing-frequency path with Zn:Fe:LiNbO3 crystal as feedback threshold element.
The pure congruent LiNbO3, Er:LiNbO3 and Zn,Er- codoped Li-rich LiNbO3 crystals were grown by Czochralski method. In order to analyze their structure, the X-ray diffraction method, ultraviolet-visible absorption spectra and infrared absorption spectra of the crystals were investigated. The photo damage resistance ability of the crystals was measured. The Zn,Er-codoped Li-rich lithium niobate crystals showed a decrease in lattice constant values, a shift in absorption edge of ultraviolet-visible absorption spectra towards shorter wavelength, and increase in OH- absorption peak of infrared absorption spectra towards longer wavelength, and three orders of magnitude increase in phtorefractive damage resistance compared to congruent LiNbO3 crystal.
Nondoped, Fe2O3 and Eu2O3-codoped near stoichiometric LiNbO3(Eu:Fe:LiNbO3) single crystals were grown by the top-seeded solution method. The solution with [Li]/[Nb] ratio of 1 contained K2O component of 10.6mol%(7.0wt%). The ultraviolet-visible absorption spectra, infrared absorption spectra of the crystals were measured in order to analyze their structure. The photorefractive properties of stoichiometric LiNbO3 crystals were investigated and compared with congruent LiNbO3 crystal. Two-wave-coupling experiments shown that doped stoichiometric LiNbO3 crystals exhibited much larger photorefractive gain and faster response speed than congruent ones.
Ca4YO(BO3)3 crystal doped with Nd3+ has been grown by the Czochralski method under air atmosphere. The growth conditions were studied in the paper. X-ray powder diffractogram, the absorption spectra and infrared spectra have been measured. The effects of ions in the crystal on the absorption peak of OH- have been also discussed. The second harmonic generation (SHG) and self- frequency-doubling (SFD) experiments were carried out on the sample with the dimension of 4x4x8mm3.
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