Erasure Time Research Articles

INFLUENCE OF POST-TREATMENT ON OPTICAL PROPERTIES OF Sc:Ce:Cu:LiNbO3 CRYSTALS

The congruent Sc(3 mol%):Ce:Cu:LiNbO 3 single crystals were grown by the Czochralski method and three kinds of different samples were prepared by proper reduction or oxidation post-treatment processes. The extrinsic defect structures of samples were determined by infrared transmittance spectra. Two-wave coupling and light induced scattering experiments were used to measure the photorefractive properties. It is found that the reduction treatment made erasure time and diffraction efficiency decrease, but light-induced scattering resistance increase; the inverse case occurred with oxidation treatment. Analysis indicated that photoconductivity change was responsible for photorefractive properties.

Optical Erasure Characteristics of Holograms in BatchThermal-Fixing

The optical erasure dynamics in a batch-thermal fixing scheme ofholographic storage in photorefractive crystals is investigatedtheoretically and experimentally. The inter-batch optical erasure timeconstant τF is introduced to specify the optical erasure tocompensated gratings, and measured in a sophisticated experiment. Theexperimental result shows that τF is much longer than theintra-batch optical erasure time constant τE. The differencebetween τF and τE is fundamental for enhancingnonvolatile storage density.

Growth and photorefractive properties of Mg:Ce:Cu:LiNbO3 crystals grown by Czochralski method

AbstractIn this paper, photorefractive properties of Mg:Ce:Cu:LiNbO3 crystals were studied. The crystals doped with different concentration of Mg ions have been grown by the Czochralski method. Mg concentrations in grown crystals were analyzed by an inductively coupled plasma optical emission spectrometry (ICP‐OE/MS). The crystal structures were analyzed by the X‐ray powder diffraction (XRD), ultraviolet‐visible (UV‐Vis) absorption spectra and infrared (IR) transmitatance spectra. The photorefractive properties of crystals were experimentally studied by using two‐beam coupling. In this experiment we determined the writing time, maximum diffraction efficiency and the erasure time of crystals samples with He‐Ne laser. The results showed that the dynamic range (M/#), sensitivity (S) and diffraction efficiency (η) were dependent on the Mg doping concentration, and the Mg(4.58mol%):Ce:Cu:LiNbO3 crystal was the most proper holographic recording media material among the six crystals studied in the paper. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electron-Beam Detection of Bits Reversibly Recorded on Epitaxial InSe/GaSe/Si Phase-Change Diodes

We demonstrate a data read-back scheme based on electron-beam induced current in a data storage device that utilizes thermal recording onto a phase-change medium. The phase-change medium is part of a heterojunction diode whose local charge-collection efficiency depends on the crystalline or amorphous state of a bit. Current gains up to 65 at 2 keV electron beam energy have been demonstrated using InSe/GaSe/Si epitaxial diodes. Fifteen write–erase cycles are obtained without loss of signal contrast by using a protective cap layer and short write pulses. 100 write–erase cycles have been achieved with some loss of contrast. Erasure times for the bits are longer than in similar polycrystalline In–Se media films. Possible reasons for the long erasure times are discussed in terms of a nucleation- or growth-dominated recrystallization. Prospects for extension to smaller bit sizes using electron-beam writing are considered.

Influence of post‐treatment conditions on photoreactive effect of Zn:Fe:LiNbO3 crystals

AbstractThree kinds of different Zn:Fe:LiNbO3 wafers are prepared by proper reduction or oxidation post‐treatment processes. The optical‐damage‐resistance abilities and photorefractive properties are studied using the optical compensator technique and two‐wave coupling measurement, respectively. The holographic storage properties, that is, diffraction efficiency, writing time, erasure time, photorefractive sensitivity, and dynamic range, are also measured or calculated. The analyses indicate that the sample disposed by reduction is the most proper media for holographic storage application. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 986–988, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21542

Role of absorption in grating erasure

In this paper, we have investigated the grating erasure of a reduced LiNbO 3:Fe crystal with different erasing wavelengths. The overall hologram evolution in the process of grating erasure is nonexponential due to strong absorption which is contrary to the mono-exponential law. The hologram in the rear part of the crystal can persist for a long time in the grating erasure due to weak erasing light intensity by strong absorption, which can enlarge the erasure time constant. From the erasure experiments, the global absorption α d ≈ 5 can be taken as the optimum absorption to acquire a good trade-off between the sensitivity and hologram strength in the crystal.

Nonlinear optical properties of composites based on conductive metal-alkanoate liquid crystals

AbstractThe dynamic holography in new composite materials based on a novel class of metal-alkanoate ionic liquid crystals (ILCs) is studied experimentally and theoretically. The composites are formed as a dielectric dye film covered by lyotropic metal-alkanoate ILC and ionic smectic glasses with doped dye molecules. The dynamic gratings are created by nanosecond pulses of double frequency Nd:YAP laser, the recording demonstrates fast erasure time of residual thermal gratings. The nonlinear optical properties are determined by the resonance nonlinearity in photosensitive centres of ILC. Note, that permanent relief gratings will be formed on a dielectric dye film only as well as in composite cells either with nematic LC or with polymers under action of pulsed laser radiation. Lyotropic ILC layer applied over the dye film provides the dynamic regime of grating recording in composite cells. We found a secondary thermal grating is much smaller, the conductive ILC matrix provides effective heat dissipation and erasure of this thermal grating. A theory of Raman-Nath self-diffraction holography on thin films followed from the wave equation and the nonlinear mechanism of absorption saturation is developed to explain experimental results.

Identification of Ag37Sn33Te30 Phase-Change Filmsfor Optical Data Storage

The Ag37Sn33Te30 film has been investigated todetermine its suitability as phase change optical recording alloy basedon static tester and atomic force microscopy measurements. Switchingproperties and the recording bit topography of the film are studied.With a writing pulse of power 2.5 mW, width 10 μs, and an erasure pulseof power 0.25 mW, width 10 μs, optical contrast of 31.8% is obtained.Re-crystallization experiments identify the Ag37Sn33Te30film as a suitable phase change material for optical data storage with acomplete erasure time of 1.1 μs at low erasure power.

The influences of ZnO doping concentration on structure and photorefractive properties of Zn:Fe:LiNbO3 crystals grown by TSSG method

In this paper, LiNbO3 crystals doped with same concentration of Fe2O3 and with different concentration of ZnO have been grown by the top-seeded-solution-growth (TSSG) method. Their IR transmittance spectra, UV–vis absorption spectra, lattice constants, and Curie temperature were measured. In two-wave coupling experiments, writing and erasure time constants, and maximum diffraction efficiency of the crystals were measured and compared with those of congruent LiNbO3 (CLN) crystals doped with same ions. The crystals grown by TSSG method show shorter writing time, erasure time, and lower diffraction efficiency than the CLN crystals. The influences of ZnO doping concentration on photorefractive properties are studied.

Photorefractive properties of MnO and Fe 2O 3 co-doped near stoichiometric LiNbO 3 crystals

In this paper, photorefractive properties of MnO and Fe 2O 3 co-doped near stoichiometric LiNbO 3 (SLN) crystals are studied. The SLN crystals were co-doped with 0.005 wt.% Fe 2O 3 and MnO at the concentration of 0, 0.003, 0.005, and 0.01 wt.%, respectively. The crystals have been grown by the top seeded solution growth (TSSG) method by adding K 2O flux to Li 2O–Nb 2O 5 melt. Their structures are analyzed by the UV–vis spectra and IR spectra. The recording and erasure curves were measured by the two-wave coupling experiments with He–Ne laser. From the recording and erasure curves at the incident angle of 25° in the air, diffraction efficiency, writing time, erasure time, the dynamic range ( M/#), and sensitivity ( S) of the crystals were measured and calculated.

Photorefractive properties of MnO-doped near stoichiometric LiNbO 3 crystals

In this paper, photorefractive properties of MnO-doped near stoichiometric LiNbO 3 (SLN) were studied. The SLN crystals doped with different concentration of Mn ions have been grown by the top-seeded-solution-growth method by adding K 2O flux to Li 2O–Nb 2O 5 melt. The crystal structures were analyzed by the UV–vis spectra and IR spectra. The photorefractive properties of SLN were experimentally studied by using two-beam coupling. The results of the two-wave coupling experiments showed that, with a He–Ne laser of 632.8 nm wavelength, the MnO-doped SLN crystals had long writing time and long erasure time constants, and the dynamic range ( M/#), sensitivity ( S), and diffraction efficiency were dependent on the doping concentration.

Effect of UV light on multiplexing holograms in near-stoichiometric LiNbO3:Ce:Fe

We performed recording–readout and bleaching experiment in lightly reduced near-stoichiometric LiNbO3:Ce:Fe with 532 nm recording beams after UV pre-exposure to get the information of the effect of the UV light on erasure. 100 holograms of nearly equivalent strength were angle multiplexed in the crystal with the erasure time constant after UV pre-exposure. With multiplexing 100 holograms, an M/# of 1.85 was obtained in a 3.5 mm thickness crystal.

Influence of post-growth treatment on the holographic storage properties of In:Fe:LiNbO 3

Summary The congruent In (3 mol%):Fe (0.03 wt%): LiNbO3 crystal has been grown by Czochralski method in air. Some crystal samples were reduced in Li2CO3 powder, and others were oxidized in Nb2O5 powder. The defects and ions location in crystal were investigated by infrared (IR) transmission spectrum. The photorefractive properties were measured by two-wave coupling and light-induced scattering resistance experiments. In the oxidized sample, the photovoltaic effect was the dominant process during recording. However, for the as-grown sample as well as the reduced, the photorefractive effect was governed by the diffuse field and the photovoltaic field, together. In addition, the reduction treatment made the photoconductivity increase, which resulted in shorter erasure time and lower diffraction efficiency, but higher light-induced scattering resistance ability. The oxidation treatment caused the inverse effect.

Photorefractive Effect of Fe:KLN Crystal

We have grown KLN and Fe:KLN crystals using the TSSG method. The crystal lattice constants are measured by the X-ray diffraction technique and the crystal optical absorption edges are characterized by an ultraviolet-visible absorption spectrum measurement. The results show that the absorption edge of the Fe:KLN crystal shifts to the longer wavelengths compared with that of the KLN crystal. The exponential gain coefficient and erasure time are examined by two-beam coupling experiment. The results indicate that the exponential gain coefficient of Fe:KLN crystal is twice as large as that of the KLN crystal, and the photoconductivity of the Fe:KLN is three orders of magnitude higher than that of KLN. The enhancement of photorefractive properties of Fe:KLN crystal is also discussed.

The correlation of doping ions to holographic storage properties of Mg:Mn:Fe:LiNbO 3 crystals

The congruent Mn(0.1 wt%):Fe(0.03 wt%):LiNbO 3 crystals doped with different concentration of MgO(0,1,3,6 mol%) have been grown by Czochralski method in air atmosphere. Some crystal samples were reduced in Li 2CO 3 powder. The defects and doping ions location in crystals were investigated by UV–Vis. absorption spectrum as well as infrared transmittance spectrum analysis. In two wave coupling experiments we determined the writing time, maximum diffraction efficiency and the erasure time of four crystal samples with He–Ne laser at 633 nm. The results indicated that Mg(3 mol%):Fe:Mn:LiNbO 3 was the most proper holographic recording media material among four crystals in the paper.

Erasure Behavior of Isothermal Physical Aging Effect below Glass Transition Temperature in a Fully Cured Epoxy Resin. Differential Scanning Calorimetry Measurement

A mixture of diglycidyl ether of bisphenol A (DGEBA) epoxy resin and amine curing agent with a stoichiometric ratio was fully cured at 220°C for 30h (T goo = 179°C ). The fully cured specimen was isothermally aged at various aging temperatures (T a = 90-150°C) for aging time (t a ) of 1000 min, and effect of the isothermal physical aging was investigated by differential scanning calorimetry (DSC). The effect of the physical aging appeared as a sharp endothermic peak in the glass transition temperature (T g ) region at higher aging temperatures but a small broad peak below T g at lower aging temperatures. In this work, erasure below Tg of the isothermal physical aging effect was examined for a specimen aged at T a = 150°C by heating to different erasure temperatures (T er = 155-170°C) above the aging temperature but below the glass transition temperature for different erasure times (t er = 10-60 min). Enthalpy relaxation was obtained from area difference of DSC thermograms between aged and de-aged specimen, and used to investigate the effect of heating to T er . It was found that the heating to T er affects differently to the previous aging at T a = 150°C. When the aged specimen was heated at T er = 155 °C near Ta, the heating leads to additional aging to the previous aging. However, the previous aging effect was partially erased with residual aging during heating at higher erasure temperatures. Amount and rate of the erasure became larger with increasing T er . After the erasure, a small amount of further aging occurred with erasure time. This result indicates that there is competition between aging and de-aging at an aging temperature between aging temperature and glass transition temperature.

Photorefractive properties of potassium lithium niobate doped with copper

Summary Potassium lithium niobate doped with copper (Cu:KLN) were grown by the Czochralski method for the first time. The structure of Cu:KLN was measured by the x-ray powder diffraction method, and its lattice constants were obtained. The position of copper ions in KLN crystal was determined. The exponential gain coefficient, response time and erasure time were measured. It was found that the exponential gain coefficient of Cu:KLN is 10.5 cm−1, as two times high as that of KLN, and its response time of 1.53 s is one order of magnitude shorter than that of Cu:LiNbO3. The type of light exciting carriers in Cu:KLN has been investigated. The result showed that the electron acts the main role in Cu:KLN.

Realization of fast photorefractive response speed in near-stoichiometric LiNbO3 crystals

Nominally pure near-stoichiometric LiNbO3 crystals are grown by Czochralski method from the congruent melt with addition of 11 mol% K2O. The photorefractive properties of strongly reduced near-stoichiometric LiNbO3 crystals are studied, and fast photorefractive buildup time (191 ms) and erasure time (78 ms) are observed at an intensity of 1.3 W/cm2. As we known, so fast response speed is firstly observed in nominally pure LiNbO3 crystals.

A Study on Batch Method of Thermal Fixing for Multiplexed Holographic Recordings

ABSTRACTWe have investigated the batch method of thermal fixing for multiplexed holograms. The batch fixing process is pictured and analyzed, for the first time to our knowledge. The batch procedure of thermal fixing includes optical erasure of electronic gratings by subsequent recordings both in the same batch and in different batches, ionic compensation during thermal fixing in one batch, smoothing of ionic gratings during thermal fixing of subsequent batches, and revealing of ionic gratings. The inter-batch optical erasure time constants of LiNbO3:Fe:Ce crystals are measured in experiment.

Photorefractive trapping and the correlation between recording and erasure dynamics in a polymer composite

The fast time constants of holographic contrast growth and erasure for various photorefractive polymer composites were measured under a wide range of experimental conditions. Either of two sensitizers, 2,4,7-trinitro-9-fluorenone (TNF) or (2,4,7-trinitro-9-fluorenylidene)malonodinitrile (TNFDM), were used in a degenerate four-wave mixing experiment under varying conditions of field, wavelength and intensity. Collected together, the fast growth and erasure time constants were found to be correlated with a coefficient of 0.96. From this correlation we conclude that the charge generation process during holographic recording and the optical de-trapping process during hologram erasure are indistinguishable. Hence in accordance with the photorefractive crystal model, hole recombination with the sensitizer anions forms the primary charge trapping mechanism in the majority of photorefractive polymer composites.