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Prescription for optimizing holograms in LiNbO(3):Fe:Mn 总被引:4,自引:0,他引:4
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Lifetimes of thermally fixed holograms in LiNbO(3):Fe crystals 总被引:1,自引:0,他引:1
The thermal erasure decay at different temperatures of holographic gratings thermally fixed in iron-doped lithium niobate has been exhaustively studied. An activation energy of 0.94 eV was found to be independent of the grating fringe spacing. At a given temperature the decay time is strongly dependent on the grating spacing. This dependence is well fitted to a square fringe spacing law, as predicted theoretically. From the experimental data the room-temperature hologram lifetime under illumination is extrapolated, giving as a result t(years)=(5.2+/-0.2)?(2) , with the grating spacing ? in micrometers. 相似文献
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P. M. Garcia A. A. Freschi J. Frejlich E. Krätzig 《Applied physics. B, Lasers and optics》1996,63(2):207-208
We show that self-stabilized recording in photo-voltaic LiNbO3 crystals produces highly diffractive holograms with a 3- to 4-fold light scattering reduction. Low scattering is probably due to the nonstationary mechanism involved in self-stabilized recording that may not allow parasitic scattering patterns in the crystal to be efficiently recorded. 相似文献
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R. A. Rupp R. Sommerfeldt K. H. Ringhofer E. Krätzig 《Applied physics. B, Lasers and optics》1990,51(5):364-370
We use holographic techniques for the investigation of strongly oxidized LiNbO3:Fe crystals with small Fe2+ concentrations and compare the results with theoretical predictions. Experimental evidence is presented for enhanced phase shifts between light intensity pattern and refractive index grating and for limitations of optically induced space charge fields in photovoltaic crystals due to the low concentration of filled traps. Our findings do not support the model of a nonlocal photovoltaic effect in LiNbO3. 相似文献
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The diffraction efficiency of M holograms superimposed in the volume of the recording medium is proportional to 1/M(2). We present a method, based on nondestructive localized holograms in a doubly doped LiNbO(3) crystal, that allows us to also record M holograms in the same volume without an exposure schedule or a diffraction efficiency that has 1/M dependence. We compare experimentally the final diffraction efficiency obtained with the localized and distributed recording methods. 相似文献
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利用基于密度泛函理论的第一性原理,研究了Cu:Fe:Mg:LiNbO3晶体及对比组的电子结构和光学特性.研究显示,单掺铜或铁铌酸锂晶体的杂质能级分别由Cu 3d轨道或Fe 3d轨道贡献,禁带宽度分别为3.45和3.42 eV;铜、铁共掺铌酸锂晶体杂质能级由Cu和Fe的3d轨道共同贡献,禁带宽度为3.24 eV,吸收峰分别在3.01,2.53和1.36 eV处;Cu:Fe:Mg:LiNbO3晶体中Mg^2+浓度低于阈值或高于阈值(阈值约为6.0 mol%)的禁带宽度分别为2.89 eV或3.30 eV,吸收峰分别位于2.45 eV,1.89 eV或2.89 eV,2.59 eV,2.24 eV.Mg^2+浓度高于阈值,会使吸收边较低于阈值情况红移;并使得部分Fe^3+占Nb位,引起晶体场改变,从而改变吸收峰位置和强度.双光存储应用中可选取2.9 eV作为擦除光,2.5 eV作为读取和写入光,选取Mg^2+浓度达到阈值的三掺晶体在增加动态范围和灵敏度等参量以及优化再现图像的质量等方面更具优势. 相似文献
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The LiNbO3 crystal co-doped with ZrO4 and Fe2O3 has been grown with [Li]/[Nb]=0.85 and 1.20, respectively, by the Czochralski method in air atmosphere. The incident exposure energy flux threshold for the light-induced scattering was characterized to investigate the scattering properties of the crystals. Applying the results of the incident exposure energy flux threshold effect, the photorefractive properties at different laser wavelengths (473 nm and 532 nm) were also measured by using the typical two-wave coupling experiments. The results show that Zr:Fe:LiNbO3 crystal has a larger refractive index change, higher recording sensitivity and larger two-wave coupling gain coefficient at 473 nm wavelength than those obtained at 532 nm wavelength under the same experimental conditions. Moreover, the photorefractive properties decrease with the increasing [Li]/[Nb] ratios. The material of Zr:Fe:LiNbO3 crystal is a promising candidate for blue photorefractive holographic recording. 相似文献
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A series of Zr:Fe:LiNbO3 crystals with various levels of ZrO2 doping were grown by Czochraski technique. The optical damage resistance and photorefractive properties were deeply explored. The results showed that the ability optical damage resistance increased remarkably when the concentration of ZrO2 is over threshold concentration, but which is lower than that of traditional damage resistant additive MgO. While, the holographic storage properties can be greatly enhanced by proper level of ZrO2 doping in Fe:LiNbO3. In terms of ions' site occupation model, the photo-damage resistant ability enhancement and the change of the photorefractive properties were discussed. 相似文献
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建立了包括扩散、漂移和光伏打效应三种输运机制,小信号光强、小调制度近似下描述双掺杂LiNbO3:Fe:Mn晶体用双色光进行全息存储的动力学的耦合微分方程组,数值求解并解释了晶体光存储的时间动态发展过程.在此基础上,分析了晶体的氧化还原程度对全息存储过程的影响,只有在晶体总的受主数密度Na(即Fe3+和Mn3+的数密度之和)大于铁离子数密度N2的条件下,双掺杂LiNbO3:Fe:Mn晶体全息存储才能达到非破坏性存储的目的.经过光固定的光栅的衍射效率随氧化增大,光折变灵敏度随氧化而减小,要获得高衍射效率就必须以降低光折变灵敏度为代价.在掺铁浓度一定的情况下,掺锰浓度越高,能实现信息长期存储对应的氧化还原状态的有效动态范围越大. 相似文献
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从光折变效应的单中心模型和载流子的光伏迁移机理出发给出了高斯片光在LiNbO3:Fe晶 体中导致的折射率变化分布的解析表达式.利用片光以“三明治”辐照方式在LiNbO3:Fe晶 体中写入了平面光波导结构.用切片干涉法测量了波导区的折射率分布,并对波导进行了简 单的导光测试.根据射线方程以及波导的折射率分布对光写入波导的导光特性进行了模拟计 算分析.研究结果表明,在LiNbO3:Fe晶体中光写入光波导是可行的.
关键词:
LiNbO3:Fe晶体
光辐照法
平面光波导
导光特性
高斯片光 相似文献
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用紫外可见光谱(UV/Visible Spectra)测试并研究了坩埚下降法生长的LiNbO3、Fe:LiNbO3,以及Zn:Fe:LiNbO3晶体的吸收特性。分析了产生这些吸收特性的原因以及与工艺生长方法的内在联系。研究结果表明:LiNbO3单晶沿晶体生长方向,其紫外吸收边向长波方向移动,且在350—450nm波段的吸收也逐渐增大,这是由于Li的分凝与挥发,逐渐产生缺锂所造成的;在Fe:LiNbO3单晶中观察到Fe^2 离子在480nm附近的特征吸收峰,并发现沿生长方向,Fe^2 离子的浓度逐渐增加,这与提拉法生长得到的晶体不同;在Fe:LiNbO3单晶中掺入质量分数为1.7%ZnO后,吸收边位置发生蓝移,而掺杂质量分数达到3.4%时,观察到有红移现象。Fe^2 离子在Zn:Fe:LiNbO3单晶中的浓度与ZnO掺杂量有密切关系。在掺杂质量分数1.7%ZnO的Fe:LiNbO3单晶中,Fe^2 离子从底部到顶部的浓度变化比在掺杂质量分数3.4%ZnO晶体中大,这是由于Zn^2 抑制Fe^2 离子进入Li位的能力随掺杂量的增加而逐渐减弱造成的。就该下降法工艺技术对Fe^2 离子在晶体中的浓度分布的影响作了分析。 相似文献
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Holographic gratings were thermally fixed in iron-doped photorefractive LiNbO(3) crystals and developed with frequency-doubled Q -switched pulses of a Nd:YAG laser (light wavelength, 532 nm; pulse duration, 3 ns). The saturation values of the diffraction efficiency increased with increasing pulse light intensity. Compared with development with cw light, high-intensity laser pulse development resulted in an enlargement of the diffraction efficiency of a factor of ~2 . A contribution of the intrinsic defect Nb on Li site to the charge transport is most probably the origin of this effect. The results are useful, e.g., for improvements of volume holographic memories and wavelength filters. 相似文献
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Huixian Feng Jinke Wen Hong Wang Huafu Wang 《Applied Physics A: Materials Science & Processing》1990,51(5):394-397
The absorption spectra, photoconductivities and photovoltaic currents of LiNbO3:Fe crystals with different Mg doping levels and Li/Nb ratios in the oxidized state have been investigated at room temperature. The Fe2+ ions in LiNbO3:Mg:Fe with Mg content above a critical value are more easily oxidized than in crystals with Mg content below a critical value. The photoconductivity of LiNbO3:Mg:Fe crystals with Mg content above a critical value is one order of magnitude higher than those with Mg content below a critical value, however, the photovoltaic current of the former is one order of magnitude lower than the latter. The differences are postulated to be due to different sites of Fe in these two classes of crystals. 相似文献
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Holographic gratings are recorded in LiNbO3: Fe using frequency-doubled pulses of aQ-switched Nd : YAG laser (light wavelength = 532 nm, pulse durationt
p = 20ns). We monitor diffraction efficiencies of the holograms during and several milliseconds after exposure. Variations of Fe2+ concentration, light intensity, and fringe spacing show that different types of gratings are involved: photochromic, thermooptic, pyroelectric, and space-charge gratings. The influence of the internal pyroelectric field on the light-induced charge transport is discussed in terms of a two-center model. Pyroelectric and bulk photovoltaic effect are shown to partially compensate each other. In LiNbO3: Fe, the photovoltaic effect is the dominant charge-driving force for our recording conditions. 相似文献
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I. F. Kanaev V. K. Malinovskii A. V. Novomlintsev A. M. Pugachev 《Physics of the Solid State》1997,39(9):1459-1465
This paper attempts to explain the experimental facts that the resolution of LiNbO3 crystals in writing holograms is poor, and that large discrepancies exist between the measured characteristics of diffraction
efficiency and predictions based on current and widely used models. A new model for charge transport is proposed that takes
into account macro-and mesoscopic nonuniformities. It is shown that the electric fields arising from modulation of the spontaneous
polarization by defects lead to asymmetric diffusion of photoexcited electrons, which makes it highly unlikely that the writing
of shifted components of holograms is via a diffusion mechanism. Possible characteristics of shifted and non-shifted holograms
written via photogalvanic currents are discussed.
Fiz. Tverd. Tela (St. Petersburg) 39, 1636–1642 (September 1997) 相似文献