Fixed Diffraction Efficiency Research Articles

Nonvolatile photorefractive properties of triply doped stoichiometric lithium tantalate single crystals

Triply doped Mg:Fe:Mn:LiTaO3 crystals with near stoichiometry were grown by the top seeded solution growth technique. Defect structure was investigated by infrared absorption spectra and Curie temperature. Using blue laser as light source, excellent photorefractive properties were obtained. Nonvolatile holographic storage properties were investigated by dual wavelength technique. High fixed diffraction efficiency and sensitivity were acquired. The energy of blue light is high enough to excite holes of deep (Mn) and shallow (Fe) trap centers, which enhance dramatically blue photorefractive properties and nonvolatile holographic storage. Mg2+ ion is no longer damage resistant under blue laser, but enhances photorefractive characteristics. Using 476 nm laser to record grating, 633 nm laser as reading light, the fixed diffraction efficiency of 62.5% was obtained in 2 mol% Mg2+ doped crystal, the sensitivity of nonvolatile holographic storage was improved to 0.335 cm/J.

OH− absorption and one-color holographic recording in Ru:Fe:LiNbO3 crystals varied co-doped with HfO2

A series of Ru:Fe:LiNbO3 crystals with various doping concentrations of HfO2 were grown by the Czochralski technique. Their defect structures were analyzed by the infrared absorption spectra and the Lorentzian fitting. The one-color holographic storage characteristics of these crystals were investigated by means of two-wavelength technology. The experimental results showed that fast response time of 12.7s and high one-color holographic recording sensitivity of 0.53cm/J were obtained in Hf(5mol%):Ru:Fe:LiNbO3 crystal, meanwhile the fixed diffraction efficiency was as high as 44.3%. These results indicated Hf, Ru and Fe co-doped LiNbO3 crystals were outstanding media for holographic storage applications.

Nonvolatile photorefractive properties in triply doped stoichiometric Mg:Fe:Mn:LiTaO3 crystals

We have grown triply doped Mg:Fe:Mn:LiTaO3 crystals with near stoichiometry using the top seeded solution growth technique. The defect structure was investigated by infrared absorption spectra and Curie temperature. Using a blue laser as the source, excellent photorefractive properties were obtained. Nonvolatile holographic storage properties were investigated using the dual wavelength technique. We got a very high fixed diffraction efficiency and nonvolatile holographic storage sensitivity. The blue light has more than enough energy to excite holes of deep (Mn) and shallow (Fe) trap centers with the same phase, which enhance dramatically the blue photorefractive properties and the nonvolatile holographic storage. Mg2+ ion is no longer damage resistant at blue laser, but enhances photorefractive characteristics.

IMPROVEMENT OF NONVOLATILE BLUE PHOTOREFRACTIVE PROPERTIES IN In:Ce:Cu:LiNbO3 CRYSTALS

The In : Ce : Cu : LiNbO 3 crystals used in this work were grown by Czchralski method. The key parameters: the exponential gain coefficient Γ, the diffraction efficiency ηS, the response time τw, the dynamic range M/#, the sensitivity S and the maximal refractive index change Δn max were measured with conventional two beam coupling. The optimal values of Γ, ηS, M/#, S and Δn max achieved are 44.7, 68.6%, 6.02, 0.471 cm/J and 5.37 × 10-5, respectively. It was found that the blue light photorefractive properties of Γ, ηS, M/#, S and Δn max increased with increasing In 3+ ions concentration, while the red light photorefractive properties of Γ, ηS, Δn max decreased with increasing In 3+ ions concentration. The nonvolatile holographic storage properties were measured by both the dual wavelength and two color techniques. The maximal diffraction efficiency and fixing diffraction efficiency using the dual wavelength technique were doubled compared to those obtained in using the two color technique. The sensitivity and nonvolatile sensitivity were one order of magnitude higher than those by the two color technique. The photorefractive property enhancement by the dual wavelength technique was investigated.

Improved nonvolatile holographic storage properties in Zr:Ru:Fe:LiNbO 3 crystal by blue light recording

Lithium niobate crystal triply doped with zirconium, ruthenium and iron was grown by conventional Czochralski method and its nonvolatile storage characteristics were investigated by means of two-wavelength technology, where blue and red beam were used as recording and readout light, respectively. In oxidized Zr:Ru:Fe:liNbO 3 crystal, short response time of 9.1 s and high recording sensitivity of 0.92 cm/J were demonstrated, together with high fixed diffraction efficiency of 44.9% maintained. These excellent properties were attributed to the elimination of intrinsic defects by ZrO 2 doping and effective excitation of electrons by blue light. Our experimental results indicated this doped LiNbO 3 crystal was an outstanding medium for holographic storage applications.

Growth and nonvolatile holographic storage properties of Hf:Ce:Cu:LiNbO3 crystals

The congruent Ce(0.1%):Cu(0.2%):LN crystals doped with different concentrations of 0, 2.0 and 4.0mol% HfO2 were grown by the Czochralski method. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) and the infrared (IR) spectrum were measured and are discussed in terms of the spectroscopic characterization. The nonvolatile holographic storage properties of Hf:Ce:Cu:LN crystals were experimentally studied using the two-color holographic recording method. The results indicated that the codoping with Hf eliminated undesirable intrinsic traps, which strongly enhanced the charge transition speed. As the doping concentration of Hf increased, the fixed diffraction efficiency decreased, but the holographic response time and photorefractive sensitivity improved.

Defect structure and optical fixing holographic storage of Mg:Mn:Fe:LiNbO3 crystals

AbstractMg:Mn:Fe:LiNbO3 crystals were grown by the Czochralski method. The defect structure was analyzed by UV‐vis spectra and IR spectra. The holographic storage of Mg:Mn:Fe:LiNbO3 crystals was measured by the two color fixed method. The results show that with the increase of MgO doping concentration, the writing time becomes shorter, the dynamic range decreases, photorefractive sensitivity increases and fixing diffraction efficiency decreases. When the MgO doping concentration exceeds 4.5 mol%, the fixing diffraction efficiency approaches zero. The effect of doping Mg ions on the holographic storage properties of Mn:Fe:LiNbO3 crystals is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Nonvolatile two-color holographic recording in Tm-doped near-stoichiometric LiNbO3

We have observed ultraviolet-induced visible absorption and performed two-color holographic recording at green, red, and near-infrared light in thulium doped near-stoichiometric LiNbO3 crystal. The diffraction efficiency and sensitivity of the recording process at all wavelengths are increased by ultraviolet gating light. Characteristics of recording in the visible are explained by a two-center model. Two-color recording in the near-infrared exhibits significant improvements of the fixed diffraction efficiency and the role of small polarons is discussed in the visible and near-infrared recording with ultraviolet sensitizing light.

Effect of dopant composition ratio on nonvolatile holographic recording in LiNbO3:Cu:Ce crystals.

The effect of dopant composition ratio on nonvolatile holographic recording in LiNbO3:Cu:Ce crystals is investigated experimentally. The results show that the dopant composition ratio affects the recording sensitivity and fixed diffraction efficiency by altering the UV light absorption characteristics of the crystals during nonvolatile, holographic recording. Increasing the dopant composition ratio of Cu and Ce leads to an increase in the absorption of UV light and further to an increase in the recording sensitivity and fixed diffraction efficiency. The UV light absorption characteristics of LiNbO3:Cu:Ce crystals and their roles in nonvolatile holographic recording are theoretically analyzed. The theoretical results are consistent with those of the experiments.

Recording and fixing dynamics of nonvolatile photorefractive holograms in LiNbO_3 :Fe:Mn crystals

A theoretical explanation of nonvolatile holographic recording in LiNbO3:Fe:Mn crystals is given based on jointly solving the two-center material equations and the coupled-wave equations. The nonuniformity of the dynamics of the photorefractive grating can be effectively described and analyzed by using this method. The time–space evolution, including the space-charge field, the diffraction efficiency, the light modulation depth, the phases of the space-charge field and the interference field, as well as the relative spatial phase shift between them, is studied for both oxidized and reduced crystals. The optimal conditions for material prescriptions and oxidation–reduction processing are discussed in detail. The bending isophase of the fringe pattern and the redistributed intensities of the two-coupled beams inside the crystal are presented. The theoretical results can confirm and predict experimental results. Some new effects are also discovered, such as: The fixed diffraction efficiency can exceed the saturation diffraction efficiency for strongly recorded gratings; the energy transfer direction between two-coupled beams can be reversed with crystal thickness; and the holographic readout in reduced crystal is always accompanied by fast phase changes, which results in the slow deterioration of the recorded holograms as a result of the production of homogeneous distributions of electrons.

Experimental study of accumulative recording during nonvolatile holographic storage in LiNbO3:Fe:Mn crystals

AbstractAn accumulative recording scheme capable of enhancing diffraction efficiency effectively during nonvolatile holographic storage in LiNbO3:Fe:Mn crystals is proposed and experimentally demonstrated in this paper. The main idea of this new holographic recording schedule is that, during every red‐beam recording interval, an ultraviolet light is used to excise more electrons to a shallower center for the next faster and higher recording. After sufficient accumulation of the space‐charge fields developed in a deeper center, it is possible to gain a high diffraction efficiency of the finally fixed hologram. The experimental results demonstrate that the finally fixed diffraction efficiency is enhanced by about 31% compared to the conventional recording schedule. No additional equipment is needed in this method, and it has potentials for applications. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 32: 423–425, 2002.

Thermal fixing of holographic gratings in BaTiO_3

Fixing of a holographic grating in a single BaTiO(3) crystal is studied in detail by means of a thermal process. Above T = 78 °C, oscillations of the diffracted intensity of the sample appear, which are related to the fixing process. Different methods to perform and optimize the fixing process are described. A fixed diffraction efficiency of ~25% was obtained. Self-enhanced as well as self-depleted diffraction from the fixed photorefractive gratings was observed.