光生伏打-光折变介质中光学涡旋孤子

简化了描述光生伏打光折变效应的模型方程.给出了光生伏打空间电荷场的形式解.讨论了单光束在光生伏打、自散焦光折变介质(LiNbO3∶Fe晶体)中的三维传播行为.指出在适当近似条件下,光生伏打光折变非线性可以维持圆对称的涡旋孤子. 关键词：     

自散焦向自聚焦转换中背景光作用的理论分析

理论分析了背景光辐照在光折变晶体中从自散焦向自聚焦特性转化过程中的作用,得到了R>1是不同类型（Δn<0和Δn>0）晶体中这种转变的条件.实验观察到了铌酸锂晶体中这种转变的现象.并依据Glass常量的光伏打效应表征意义,提出了光伏孤子形成过程中载流子的竞争效应模型.基于此,分析了折射率变化为负的光生伏打晶体在背景光和信号光Glass常量比大于1条件下的载流子竞争效应,得到了与实验现象和已知理论分析相一致的结论.研究表明,背景光引起的载流子竞争效应是影响晶体自散焦向自聚焦特性转换的内在物理本质.     

Y向切割掺杂铌酸锂晶体中的光耦合

实验研究了y向切割掺杂铌酸锂晶体中入射光和反射光之间的光耦合.当异常光分别沿+y和-y轴方向入射时，二者的透射率和反射率的时间行为基本一致.而寻常光分别沿+y和-y轴方向入射时，二者的透射率和反射率的时间行为明显不同.初步探讨了该现象的物理机理. 关键词： 反射光栅 光耦合 光生伏打效应 扩散机理     

光折变晶体在全息干涉实验中的应用

文章介绍了光折变晶体的物理特性，综述了用铌酸锂晶体作为记录介质的各种全息干涉实验     

LiNbO2∶Fe晶体中的涡旋孤子及由它们写入波导的研究

在LiNbO3∶Fe晶体中观察到由光生伏打效应实现的涡旋孤子对和涡旋孤子阵列并成功地由它们写入了圆形和椭圆形波导.研究了涡旋孤子之间的相互作用,影响涡旋孤子形状的因素和实现稳定孤子的条件. 关键词： 涡旋孤子 波导 光生伏打效应     

掺Ce,Fe系列LiNbO3晶体光折变效应光存储特性

研究了系列Ce：Fe掺杂以及不同后处理态(生长态、还原态和氧化态)铌酸锂晶体的透过率光谱和光折变全息存储特性。实验结果表明单掺Ce铌酸锂晶体具有较好的图像存储质量和较宽的透过率光谱范围,二波耦合增益相对较低;高掺杂铌酸锂样品的透过率光谱范围较窄,光折变二波耦合增益较低。晶体的后处理对铌酸锂样品的光折变特性影响明显,双掺Ce:Fe还原态铌酸锂晶体具有较高的二波耦合增益;氧化态样品具有较大的透过率光谱范围;还原态样品具有较大的光折变二波耦合增益特性。实验结果还表明在同种样品中难于同时获得大的二波耦合增益和图像存储质量。     

静电染色法在铌酸锂晶体铁电性显示中的应用

我们应用静电复印油墨将铌酸锂铁电畴染色(静电染色法)显示,并扩展到铌酸锂晶体光铁电性的显示,包括单畴铌酸锂光折变区电场电荷分布、单畴掺铁铌酸锂晶体表面电击穿效应和单畴掺铁铌酸锂晶体存储的全息衍射光栅图象的显示等. 上述光铁电性显示图象,与使用其他实验手段所得到的     

诱导光偏振态对激光诱导掺杂铌酸锂晶体畴反转的影响

研究了诱导光的偏振态对激光诱导原子数分数为3%掺镁同成分铌酸锂晶体和原子数分数为3%掺铪同成分铌酸锂晶体畴反转的影响.用数字全息干涉测量的方法再现了激光诱导畴反转过程中的相位分布.通过对比线偏振、圆偏振和椭圆偏振不同偏振态诱导光形成的成核场,认为诱导过程中出现的沿z方向的空间电荷场对激光诱导优先畴成核有着非常重要的影响...     

LiNbO3:Fe晶体二波耦合弱光放大的物理机理

对LiNbO₃: Fe晶体中二波耦合过程进行了动态观测.进一步探讨了LiNbO ₃:Fe晶 体中弱光放大的物理机理.发现LiNbO₃ : Fe晶体中二波耦合过程的弱光放大 对c轴指 向有明显的依赖关系，虽然光生伏打效应对光生载流子的迁移有主要贡献，但扩散机理的贡 献仍不可忽略.弱光最终得到放大是瞬态能量转移与扩散机理引起的能量转移的共同贡献.弱 光放大达到准稳态之后的下降过程为瞬态能量转移的时间指数衰减过程与光散射引起的能量 耗散的共同贡献. 关键词： 光折变效应 光放大 掺杂铌酸锂     

Fe:LiNbO_3晶体光折变性能分析计算

掺铁铌酸锂晶体的光折变性能 ,一方面取决于晶体材料制备时的工艺条件和参数 ,另一方面和记录光路布置及晶体光轴的选取密切相关。给出了常用的 90°记录光路中光折变晶体折射率调制度的计算方法和公式 ,并分析了写入光的偏振方向、晶体光轴 (C轴 )方向及全息图折射率调制度之间的关系。     

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.     

Study of near-infrared nonvolatile two-center holographic recording in LiNbO3:Fe:Rh crystal

The near-infrared nonvolatile holographic recording has been realized in a doubly doped LiNbO₃:Fe:Rh crystal by the traditional two-center holographic recording scheme, for the first time. The recording performance of this crystal has been investigated by recording with 633 nm red light, 752 nm red light and 799 nm near-infrared light and sensitizing with 405 nm purple light. The experimental results show that, co-doped with Fe and Rh, the near-infrared absorption and the photovoltaic coefficient of shallow trap Fe are enhanced in this LiNbO₃:Fe:Rh crystal, compared with other doubly doped LiNbO₃ crystals such as LiNbO₃:Fe:Mn. It is also found that the sensitizing light intensity affects the near-infrared recording sensitivity in a different way than two-center holographic recording with shorter wavelength, and the origin of experimental results is analyzed.     

Forced oscillator model of dynamic spatial charge field in the reduced Zn:Fe:LiNbO3 crystal

Holographic data storage is promised to be the next-generation optical storage technology for many years. The Zn:Fe:LiNbO₃ crystal is studied widely because of its promising holographic storage properties. The forced oscillator model is used to explain the self-erasing phenomenon in the reduced Zn:Fe:LiNbO₃ crystals. It is showed that the total spatial charge field is dominated by two kinds of carrier with different respond time, which are electron and hole, respectively. The cooperative action of two kinds carrier induces that the total charge field non-monotonically varies with the recording time. The same diffraction efficiency of hologram with equal exposure energy is realized by the self-erasing property. The precision of the optical correlation recognition based on holographic storage will be improved.     

Enhanced nonvolatile holographic properties in Zn,Ru and Fe co-doped LiNbO3 crystals

A series of LiNbO₃ crystals doped with various concentrations of ZnO and fixed concentrations of RuO₂ and Fe₂O₃ have been grown by the Czochralski method from the congruent melts. The type of charge carriers was determined by Kr⁺ laser (476 nm) and He–Ne laser (633 nm). The results revealed that the holes were the dominant charge carriers at blue light irradiation. Dual-wavelength and two-color techniques were employed to investigate the nonvolatile holographic storage properties of Ru:Fe:LiNbO₃ and Zn doped Ru:Fe:LiNbO₃ crystals. The essential parameters of blue nonvolatile holographic storage in Zn:Ru:Fe:LiNbO₃ crystals were enhanced greatly with the increase of Zn concentration. This indicates that the damage resistant dopants Zn²⁺ ions enhance the photorefractive properties at 476 nm wavelength instead of suppressing the photorefraction. The different mechanisms of blue photorefractive and nonvolatile holographic storage properties by dual wavelength recording in Zn:Ru:Fe:LiNbO₃ crystals were discussed.     

Formation dynamics of nonvolatile crossed-beam photorefractive gratings in doubly doped LiNbO3 crystals: Theoretical investigation

The formation dynamics of crossed-beam photorefractive gratings formed by the method of two-center holographic recording in doubly doped LiNbO₃ crystals is investigated in this paper based on the theoretical model combining the two-center band transport model with the two-dimensional coupled-wave theory. The numerical simulations are presented for two-center holographic recording crossed-beam photorefractive gratings in LiNbO₃:Fe:Mn crystals. The temporal and spatial evolutions of the refractive index modulation and the diffraction efficiency are shown. The spatial variation of the wave intensity is also presented.     

Effect of wavelength of sensitizing light on holographic storage properties in LiNbO3:Fe:Ni crystal

By sensitizing with 514 nm green light, 488 nm blue light and 390 nm ultraviolet light, respectively, recording with 633 nm red light, effect of wavelength of sensitizing light on holographic storage properties in LiNbO₃:Fe:Ni crystal is investigated in detail. It is shown that by shortening the wavelength of sensitizing light gradually, nonvolatile holographic recording properties of oxidized LiNbO₃:Fe:Ni crystal is optimized gradually, 390 nm ultraviolet light is the best as the sensitizing light. Considering the absorption of sensitizing light, to obtain the best performance in two-center holographic recording we must choose a sensitizing wavelength that is long enough to prevent unwanted absorptions (band-to-band, etc.) and short enough to result in efficient sensitization from the deep traps. So in practice a trade-off is always needed. Explanation is presented theoretically.     

Preparation and holographic storage properties of tri-doped Mg:Mn:Fe:LiNbO3 crystals

Doping MgO, MnO and Fe₂O₃ in LiNbO₃ crystals, tri-doped Mg:Mn:Fe:LiNbO₃ single crystals were prepared by the conventional Czochralski method. The UV-vis absorption spectra were measured and the shift mechanism of absorption edge was also investigated in this paper. In Mg:Mn:Fe:LiNbO₃ crystal, Mn and Fe locate at the deep level and the shallow level, respectively. The two-photon holographic storage is realized in Mg:Mn:Fe:LiNbO₃ crystals by using He-Ne laser as the light source and ultraviolet as the gating light. The results indicated that the recording time can be significantly reduced for introducing Mg²⁺ in the Mg:Mn:Fe:LiNbO₃ crystal.     

Nonvolatile holographic storage in triply doped LiNbO3: Hf, Fe, Mn crystals

It has been suggested to use LiNbO3:Fe,Mn crystal for solving the problem of information volatility during the read-out process with all-optical facilities,but the minute order response time is far from the requirements for the real-time information processing.We present the nonvolatile holographic storage properties of LiNbO3:Hf,Fe,Mn.The response time is shortened to 5.0 s,and the sensitivity S is enhanced to 0.22 cm/J in this triply doped crystal.The experimental results show that the HfO2 doping threshold is 5.0 mol.%.Thus it seems that we have found a useful tetravalent dopant for LiNbO3:Fe,Mn that can obviously improve the nonvolatile holographic recording sensitivity.     

Growth and photorefractive properties of near-stoichiometric In:Fe:Cu:LiNbO3 crystals

The near-stoichiometric LiNbO₃ crystal co-doped with In₂O₃, Fe₂O₃, and CuO has been grown from a Li-rich melt (Li/Nb = 1.38, atomic ratio) by the Czochralski method in air atmosphere for the first time. The OH⁻ absorption spectra were characterized to investigate the structure defects of the crystals. The appearance of the 3506 cm⁻¹ absorption peak manifests that the composition of the grown crystal is close to the stoichiometric ratio. The photorefractive properties were also measured by the two-wave coupling experiments. The results show that the near-stoichiometric In:Fe:Cu:LiNbO₃ crystal has a larger refractive index change, higher recording sensitivity and larger two-wave coupling gain coefficient than those obtained in the congruent In:Fe:Cu:LiNbO₃ crystal under the same experimental conditions. The material of near-stoichiometric In:Fe:Cu:LiNbO₃ crystal is a promising candidate for blue photorefractive holographic recording.     

Enhancement of blue holographic properties in Zr4+-doped near stoichiometric Fe:LiNbO3 crystals

The near stoichiometric LiNbO₃ crystals co-doped with ZrO₂ and Fe₂O₃ have been grown from a Li-rich melt (Li/Nb=1.38, atomic ratio) by the Czochralski method in air atmosphere at the first time. The OH^? absorption and UV–vis absorption spectra were characterized to investigate the defect structure of the crystals. The appearances of the 3479 cm^?1 absorption peak and 358 nm absorption edge manifest that the composition of the grown crystal is close to the stoichiometric ratio. The blue holographic properties were also measured by the two-wave coupling experiments. As a result, in the near stoichiometric Zr:Fe:LiNbO₃ crystals, photorefractive response speed, recording sensitivity, and two-wave coupling gain coefficient are significantly enhanced. Meanwhile, the high saturation diffraction efficiency is still maintained. These findings prove that the material of near stoichiometric Zr:Fe:LiNbO₃ crystals are a promising candidate for blue photorefractive holographic recording.