坩埚下降法生长的LiNbO_3,Fe∶LiNbO_3,Zn∶Fe∶LiNbO_3单晶的吸收光谱特性

用紫外可见光谱 (UV/VisibleSpectra)测试并研究了坩埚下降法生长的LiNbO3 、Fe∶LiNbO3 ,以及Zn∶Fe∶LiN bO3 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 35 0～ 4 5 0nm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Fe2 + 离子在 4 80nm附近的特征吸收峰 ,并发现沿生长方向 ,Fe2 + 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。Fe2 + 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 ,Fe2 + 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Zn2 + 抑制Fe2 + 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Fe2 + 离子在晶体中的浓度分布的影响作了分析     

Zn∶Mn∶Fe∶LiNbO3晶体位相共轭性能和全息关联存储

在同成分LiNbO3中,掺入ZnO的摩尔分数分别为1％、3％、5％、7％和9％,掺入(质量分数)0.03％ MnCO3和0.08％Fe2O3,采用提拉法生长了优质Zn∶Mn∶Fe∶LiNbO3晶体,测试Zn∶Mn∶Fe∶LiNbO3晶体的OH红外吸收光谱,抗光损伤能力和位相共轭性能.Zn离子浓度在7％和9％时,OH吸收...     

ICP与吸收光谱测定LiNbO3, Zn:LiNbO3晶体中Cr3+离子的分布及有效分凝系数

应用坩埚下降法生长了掺杂Cr与双掺杂Cr，Zn的LiNbO3晶体。测定了掺杂晶体不同部位的吸收系数。用电感耦合等离子体原子发射光谱(ICP)法测定了Cr离子在LN晶体中的浓度，并计算了Cr离子在LiNbO3晶体中的有效分凝系数。研究结果表明：在单掺杂Cr的LiNbO3晶体中，随着Cr^3 掺杂浓度从0．1增加到0．5mol％时，其有效分凝系数从3．75减少到2．49，Cr^3 离子在晶体中的浓度分布差异逐步减少；ZnO的掺入能有效地减少Cr^3 的分凝系数，然而ZnO掺杂浓度从3增加到6mol％时，其有效分凝系数且从1．85增加到2．25。可从ZnO组分对Cr离子的排斥作用及Zn离子在LN晶体中随掺杂数量变化的分凝现象解释了产生Cr离子浓度及有效分凝系数变化的原因。     

Zn∶Mn∶Fe∶LiNbO3晶体位相共轭性能和全息关联存储

在同成分LiNbO3中,掺入ZnO的摩尔分数分别为1%、3%、5%、7%和9%,掺入（质量分数）0.03% MnCO3和0.08%Fe2O3,采用提拉法生长了优质Zn∶Mn∶Fe∶LiNbO3晶体.测试Zn∶Mn∶Fe∶LiNbO3晶体的OH-红外吸收光谱,抗光损伤能力和位相共轭性能.Zn离子浓度在7%和9%时,OH-吸收峰移到3 528 cm－1,讨论OH-吸收峰移动机理.随着Zn离子浓度增加,抗光损伤能力增加.Zn离子浓度增加到7%,达到阈值.Zn∶Mn∶Fe∶LiNbO3晶体抗光损伤能力比LiNbO3晶体高二个数量级,研究高掺锌Mn∶Fe∶LiNbO3晶体抗光损伤增强机理.随着Zn离子浓度增加,Zn∶Mn∶Fe∶LiNbO3晶体位相共轭反射率降低,位相共轭响应速度增加.Zn∶Mn∶Fe∶LiNbO3晶体位相共轭镜消除了光波的位相畸变.以Zn∶Mn∶Fe∶LiNbO3晶体作存储介质进行全息关联存储实验.讨论全息关联存储的工作原理.以原图象的25%和50%进行寻址,在输出平面上接收到较完整的存储图象.     

ZnO对EU:LiNbO3晶体的性能及光谱性质影响

应用坩埚下降法技术，以同成份化学摩尔分数[x（Li2O）=48．6％,x（Nb2O3）=51．4％]为原料，生长出了以不同Zn，Eu双掺杂的LiNbO3晶体。测定了晶体下部与上部的X射线衍射图（XRD）、激发光谱、荧光光谱以及声子边带谱。Zn的掺杂量对Eu^3＋离子在晶体中的分布产生很大的影响。Zn掺杂摩尔分数为3％时．Eu^3＋离子在进入品格时受到有效的压制。随着Zn掺杂摩尔分数提高，达到6％时，压制作用减弱。从Zn^2＋离子在LiNbO3中随浓度变化的分凝情况以及对Eu^3＋离子的排斥作用解释了Eu^3＋离子分布的原因。同时测定了Zn掺杂样品的声子边带谱。     

掺杂光折变LiNbO3晶体光伏效应特性

用前向二波耦合实验方法，对几种掺杂的LiNbO3晶体的光折变性质中出现的光伏现象进行了研究。在双掺杂的Ce：Fe：LiNbO3晶体中得到强纵向光伏效应，该效应可以对衍射效率产生59．7％的调制；在单掺杂的Ce：LiNbO3和Zn：LiNbO3等晶体中，得到由横向光伏效应产生的偏振态记录光栅。     

Zn:Fe:LiNbO3晶体全息存储性能研究

以提拉法生长Zn(1mol%):Fe:LiNbO3, Zn(4mol%):Fe:LiNbO3,Zn(7mol%):Fe:LiNbO3晶体.Zn:Fe:LiNbO3晶体随着Zn2+浓度的增加,抗光致散射能力增加,Zn(7mol%):Fe:LiNbO3晶体抗光致散射能力比Fe:LiNbO3晶体提高两个数量级以上.测试了Zn:Fe:LiNbO3晶体衍射效率、响应时间.以Zn(7mol%):Fe:LiNbO3晶体作为存储元件,Zn(4mol%):Fe:LiNbO3晶体作为位相共轭镜,进行全息关联存储试验.试验结果显示出成像质量好、图像清晰完整、噪音小等优点.研究了Zn:Fe:LiNbO3晶体全息存储性能增强的机理.Zn(4mol%):Fe:LiNbO3晶体具有全息存储性能最佳的综合指标.     

ZnO对Eu∶LiNbO3晶体的性能及光谱性质影响

应用坩埚下降法技术,以同成份化学摩尔分数[x(Li2O)=48.6%,x(Nb2O5)=51.4%]为原料,生长出了以不同Zn,Eu双掺杂的LiNbO3晶体。测定了晶体下部与上部的X射线衍射图(XRD)、激发光谱、荧光光谱以及声子边带谱。Zn的掺杂量对Eu3+离子在晶体中的分布产生很大的影响。Zn掺杂摩尔分数为3%时,Eu3+离子在进入晶格时受到有效的压制。随着Zn掺杂摩尔分数提高,达到6%时,压制作用减弱。从Zn2+离子在LiNbO3中随浓度变化的分凝情况以及对Eu3+离子的排斥作用解释了Eu3+离子分布的原因。同时测定了Zn掺杂样品的声子边带谱。     

Zn∶Fe∶LiNbO_3晶体全息存储性能研究

以提拉法生长Zn(1mol% )∶Fe∶LiNbO3,Zn(4mol % )∶Fe∶LiNbO3,Zn(7mol% )∶Fe∶LiNbO3晶体 Zn∶Fe∶LiNbO3晶体随着Zn2 + 浓度的增加 ,抗光致散射能力增加 ,Zn(7mol% )∶Fe∶LiNbO3晶体抗光致散射能力比Fe∶LiNbO3晶体提高两个数量级以上 测试了Zn∶Fe∶LiNbO3晶体衍射效率、响应时间 以Zn(7mol % )∶Fe∶LiNbO3晶体作为存储元件 ,Zn(4mol% )∶Fe∶LiNbO3晶体作为位相共轭镜 ,进行全息关联存储试验 试验结果显示出成像质量好、图像清晰完整、噪音小等优点 研究了Zn∶Fe∶LiNbO3晶体全息存储性能增强的机理 Zn(4mol% )∶Fe∶LiNbO3晶体具有全息存储性能最佳的综合指标     

双掺杂LiNbO3:Fe:Mn全息存储动力学

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.     

LD相对于铯原子超精细跃迁线的偏频锁定

Holographic storage properties of iron-doped and cerium/iron-doped LiNbO3 with different doping concentrations and treatment conditions have been measured for different recording wavelengths. The results show that at recording wavelengths of 532 nm and 633 nm the holographic storage properties of Ce:Fe:LiNbO3 are generally better than those of Fe:LiNbO3.     

Light-induced thermal gratings in LiNbO3: Fe

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.     

Intrinsic photorefractive centers in LiNbO3:Fe

In LiNbO₃:Fe,Me crystals (Me = K, Mg, Zn) elementary holograms are recorded and erased with frequency-doubled, ordinarily polarized pulses of a Q-switched Nd:YAG laser. At high light intensities (I > 10⁹ Wm^–2) holographic sensitivities and saturation values of refractive index changes grow with increasing intensity and a contribution to photo-conductivity appears increasing quadratically withI. The intensity-dependent parts of the holographic quantities are diminished by increasing the lithium content of the samples or by doping the crystals with magnesium or zinc. Experimental results can be described by a two-center charge transport model, which is the Fe^2+/3+ model supplemented by shallow traps, namely niobium ions occupying lithium sites.     

Angle-multiplexed hologram storage in LiNbO(3):Tb, Fe

We have performed hologram multiplexing with a cw laser at lambda=532 nm in a near-stoichiometric LiNbO(3) :Tb, Fe crystal that exhibits a visible absorption band induced by UV light. When 50 plane-wave holograms were angle multiplexed from the UV preexposed state, the recording sensitivity gradually decreased, owing to bleaching of the induced absorption. However, a conventional recording schedule of multiplexing many holograms of equal diffraction efficiency can be used in this photochromic material. The gradual decrease in recording sensitivity throughout multiplexing can be compensated for by the increased erasure-time constants of later-written holograms. An M/# of 1.73 was obtained in a crystal of 3.3-mm thickness.     

在LiNbO_3:Fe晶体中写入Y结孤子的实验研究

采用振幅掩模穿过部分空间非相干光的方法产生一暗迹,将暗迹成像在晶体前表面,得到入射暗迹半高宽为16.75μm,入射光功率为400μW.基于LiNbO3:Fe晶体的强光伏效应,在无背景光辐照时,在晶体内写入一对部分空间非相干Y结暗光伏孤子.实验结果表明:在无背景光辐射时可以在LiNbO3:Fe晶体内写入部分空间非相干Y结孤子.     

Multiplexing holograms in LiNbO3:Fe:Mn crystals

Persistent holograms are recorded with red light in lithium niobate crystals doped with manganese and iron. Different erasure mechanisms are investigated, and a recording schedule for multiplexing holograms with equal diffraction efficiencies is proposed. To test the recording schedule experimentally, we multiplex 50 plane-wave holograms with the proposed recording schedule.     

Fe∶LiNbO3和(Fe,Tb)∶LiNbO3晶体中入射光强对光折变性质的影响

用一种新的测量方法在不同入射光强下同时观测了Fe∶LiNbO3 和 (Fe,Tb)∶LiNbO3 晶体中光致折射率变化Δns、吸收系数α和光电导σph与入射光强I的依赖关系 ,并从理论上对观测结果给予了初步解释     

Mössbauer study of proton-exchanged LiNbO3:Fe

Topotactic proton exchange (Li against H) can be achieved by treating LiBnO₃ with appropriate acids. In order to investigate the effect of proton exchange on Fe-impurities we studied LiNbO₃:Fe powder material treated in sulphuric acid and LiNbO₃:Fe single crystals treated in benzoic acid by Mössbauer spectroscopy. During the topotactic ion exchange only the Li-ions are exchanged for protons, whereas the Fe-impurities are retained in the material.     

Seeded and spontaneous light hexagons in LiNbO3:Fe

The first observation of optical hexagons in a medium with dominating photovoltaic charge transport – in LiNbO₃:Fe – is reported. The optimum conditions for hexagon observation are revealed and discussed. The dynamics of hexagon formation are also studied. Received: 9 February 2000 / Published online: 8 March 2000