Nonvolatile Two-color Holographic Recording Research Articles

Comparison of two-color holography among different doped LiNbO3 crystals at low intensities

The effects of material and experimental parameters on the nonvolatile two-color holographic recording space charge field and sensitivity for different doped LiNbO3:Fe crystals have been studied theoretically based on a two-center model. When the direct electron transfer between the deep-trap centers and the shallow-trap centers was considered, the near-stoichiometric LiNbO3:Fe is confirmed theoretically to be of bigger space charge field and higher recording sensitivity than the LiNbO3:Fe:Mn and LiNbO3:Cu:Ce in the low intensity region. A further improvement of the recording sensitivity can be achieved by doping concentration, thermal reduction treatment of Fe, appropriate gating and recording wavelengths with large photo-excitation cross sections.

Defect structure and nonvolatile hologram storage properties in Hf:Fe:Mn:LiNbO 3 crystals

A series of Hf:Fe:Mn:LiNbO 3 crystals with various levels of HfO 2 doping were grown by Czochralski technique. The infrared spectra and ultraviolet spectra were measured and discussed to investigate their structure and defects. The optical damage resistance was characterized by the transmitted beam pattern distortion method. The nonvolatile two-color holographic recording experimental results showed that the recording speed was faster with the increase of HfO 2 doping concentration and at the same time little loss of nonvolatile diffraction efficiencies could be achieved.

近化学计量比铌酸锂晶体在非相干紫外光敏化下的双色全息存储

Nonvolatile two-color holographic recording gated by incoherent ultraviolet (UV) light centered at 365 nm is investigated in near-stoichiometric lithium niobate crystals. The influence of thermal treatment on the two-color recording is studied. The results show that thermal reduction tends to improve the two-color recording performance, whereas thermal oxidation degrades the two-color recording. With an incoherent 0.2-W/cm2 UV gating light and a 0.25-W/cm2 semiconductor recording laser at 780 nm, a two-color recording sensitivity of 4\times10^{-3} cm/J and a recording dynamic range characterized by M/# of 0.12 are achieved in a 2.2-mm thermally reduced near-stoichiometric lithium niobate crystal. We attribute the improvement to the prolonged lifetime of small polarons and the increased absorption at the gating wavelength due to thermal reduction.

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.

Nonvolatile two-color holographic recording in nondoped near-stoichiometric lithium tantalate crystals with continuous-wave lasers

Nonvolatile holograms have been recorded in nondoped near-stoichiometric LiTaO3 crystals by use of a near infrared (IR) laser for writing and a ultraviolet beam as a gating source. This material exhibits good overall two-color holographic recording characteristics including a high sensitivity of 0.086 cm/J with a gating intensity of 1 W/cm2 at 350 nm, a large refractive index change of as much as 1×10−4, a high resistance to IR erasure, and a long hologram lifetime of five years. The sensitivity can be further enhanced using writing and gating beams of a shorter wavelength without sacrificing readout nonvolatility.

Optimization of Non-Volatile Two-Color Holographic Recording in Near-Stoichiometric LiNbO 3

We investigate two-color holography using Tb doped near-stoichiometric LiNbO 3 . We present the measurements of the hologram strength and sensitivity dependences on the wavelength and intensity of the writing near-IR laser light and on the gating UV light intensity. The diffraction efficiency of the holograms is satisfactory when the writing light wavelength is below 800 nm. The rapidly changing sensitivity around the photon energy of 1.6 eV is an indication that small polarons are involved in the recording mechanism. The recording speed mainly depends on the gating beam intensity, while the hologram strength is much more affected by the writing beam properties, both the intensity and wavelength. We show how to choose appropriate intensities to optimize the desired two-color performance that can be also applied to other two-color schemes.

Optimization of Non-Volatile Two-Color Holographic Recording in Near-Stoichiometric LiNbO3

We investigate two-color holography using Tb doped near-stoichiometric LiNbO3. We present the measurements of the hologram strength and sensitivity dependences on the wavelength and intensity of the writing near-IR laser light and on the gating UV light intensity. The diffraction efficiency of the holograms is satisfactory when the writing light wavelength is below 800 nm. The rapidly changing sensitivity around the photon energy of 1.6 eV is an indication that small polarons are involved in the recording mechanism. The recording speed mainly depends on the gating beam intensity, while the hologram strength is much more affected by the writing beam properties, both the intensity and wavelength. We show how to choose appropriate intensities to optimize the desired two-color performance that can be also applied to other two-color schemes.

Nonvolatile and quasi-nonvolatile holographic recording in near-stoichiometric lithium niobate doubly doped with Tb and Fe

We have observed that newly developed near-stoichiometric LiNbO 3 crystals doubly doped with Tb and Fe have three different types of energy levels: ultraviolet (UV) absorption centers just above the valence band, metastable shallow electron traps slightly below the conduction band, and deep traps located about 1.9 eV below the conduction band. Irradiation with UV light induced a stable absorption band extending from λ ≈650 nm to the absorption edge, which is caused by the photoinduced charge transfer from UV-sensitive absorption centers to deep traps (Fe 3+ ) via the conduction band. The electron lifetimes at shallow and deep traps could be controlled by doping concentrations. Based on these favorable energy states, nonvolatile two-color holographic recording has been demonstrated by use of 852 nm recording beams and UV gating light. Quasi-nonvolatile one-color recording at 532 nm has also been demonstrated in these codoped crystals. Hologram recording from the UV-exposed, colored state revealed a much improved sensitivity in comparison to that from the uncolored state. The obtained M/# was 1.73 for a 3.3 mm-thick crystal.

Photochromic effect in near-stoichiometric LiNbO3 and two-color holographic recording

We have observed that newly developed near-stoichiometric LiNbO3 crystals have three different types of energy levels: ultraviolet (UV) absorption centers just above the valence band, metastable shallow electron traps slightly below the conduction band, and deep traps located about 1.9 eV below the conduction band. Irradiation with UV light induced a stable absorption band extending from λ ≈650 nm to the absorption edge, which is caused by the photoinduced charge transfer from UV-sensitive absorption centers to deep traps via the conduction band. The electron lifetimes at shallow and deep traps could be controlled by doping elements and concentrations. Based on these favorable energy states, nonvolatile two-color holographic recording has been carried out by use of 852 nm recording beams and UV gating light. Nonvolatile readout by a single 852 nm beam was demonstrated for several hours. It was found that two-color recording from the pre-exposed, colored state can also be an attractive way of achieving nonvolatile readout. In this article, we investigate the photochromic effect observed in near-stoichiometric LiNbO3 and its use in two-color holographic recording.

Nonvolatile two-color holographic recording in Tb-doped LiNbO3

We have found that Tb-doped near-stoichiometric LiNbO3 crystals have three different types of energy levels: ultraviolet (UV) absorption centers just above the valence band, shallow electron traps slightly below the conduction band, and deep traps located about 1.9 eV (λ≈650 nm) below it. Using this shallow trap as an intermediate energy state, two-color holographic recording has been carried out at λ=852 nm with a UV gating light at 313 nm. A few % of diffraction efficiency was achieved, and the measured two-color sensitivity was 0.01–0.02 cm/J. No reduction of diffraction efficiency was observed during 4 h continuous readout, and the bit-error-rate of constructed digital hologram was less than 10−5.