(Ce,Cu)∶LiNbO3晶体非挥发全息记录理论研究与优化

根据双中心带输运模型,对(Ce,Cu)∶LiNbO3晶体双中心非挥发全息记录进行了理论研究与优化。推导了(Ce,Cu)∶LiNbO3晶体的微观参量,采用数值方法通过严格求解模拟双中心带输运方程来模拟全息记录过程。分析了记录过程中,记录与敏化光强、Ce和Cu掺杂浓度以及晶体微观参量对(Ce,Cu)∶LiNbO3晶体双中心全息记录的影响。发现(Ce,Cu)∶LiNbO3晶体非挥发全息记录中实现高衍射效率与固定效率的主导因素是深中心Cu,在记录过程中,深中心Cu建立起了很强的空间电荷场。数值模拟的结果经过实验验证,最高饱和与固定衍射效率别为60.5%和53.8%。     

（Ce，Cu）：LiNbO3晶体非挥发全息记录理论研究与优化

根据双中心带输运模型，对（Ce，Cu）：LiNbO3晶体双中心非挥发全息记录进行了理论研究与优化。推导了（Ce，Cu）：LiNbO3晶体的微观参量，采用数值方法通过严格求解模拟双中心带输运方程来模拟全息记录过程。分析了记录过程中，记录与敏化光强、Ce和Cu掺杂浓度以及晶体微观参量对（Ce，Cu）：LiNbO3晶体双中心全息记录的影响。发现（Ce，Cu）：LiNbO3晶体非挥发全息记录中实现高衍射效率与固定效率的主导因素是深中心Cu，在记录过程中，深中心Cu建立起了很强的空间电荷场。数值模拟的结果经过实验验证，最高饱和与固定衍射效率别为60．5％和53．8％。     

掺杂KNSBN晶体各向异性自衍射的耦合波分析

在晶体光轴垂直于入射面的各向异性实验组态下,对掺杂KNSBN晶体的各向异性自衍射过程进行了理论分析和实验观测,给出了包含空间电荷场前两阶分量作用的各向异性自衍射的耦合波方程及其数值解。理论分析和实验结果都表明各向异性自衍射光来自于两束入射光的共同作用。     

Fe：LiNbO3晶体光折变全息热固定动力学特性分析

以Fe:uNbO3晶体为例,考虑了电子载流子热激发(强烈地依靠于温度),通过对以扩散和光伏特效应为主导输运机制的带输运方程和耦合波方程进行数值求解,分析了热固定过程初始光强入射比和固定温度对光栅空间电荷场的影响,指出记录固定过程中内电场极值的出现来源于质子电场对施主光栅电场的部分补偿,质子光栅电荷场可以导致晶体中记录光束之间能量耦合方向的变化,得出了理论上的加热固定时间。     

双中心全息记录的矢量分析与记录方向优化

对描述双掺杂晶体非挥发性全息记录动力学过程的Kukhtarev方程进行了矢量分析,分析中考虑了体光生伏特效应和外加电场的作用。在小信号近似的基础上给出了双中心全息记录中记录与固定阶段空间电荷场的矢量解析解。在综合考虑空间电荷场的各向异性以及晶体有效电光系数的各向异性后,给出了双中心全息记录的优化记录方向。结果表明,对(Fe,Mn)∶LiNbO3晶体633nm寻常光记录,优化记录方向主要由有效电光系数决定,光栅波矢与光轴夹角为22°,方位角为30°;对(Fe,Mn)∶LiNbO3晶体633nm非寻常光记录,优化记录方向主要由固定空间电荷场决定,光栅波矢与光轴夹角为44°,方位角为90°。     

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N_a(即Fe³⁺和Mn³⁺的数密度之和)大于铁离子数密度N_{2的条件下,双掺杂LiNbO3:Fe:Mn晶体全 关键词：}     

不同电极对α-LiIO3离子输运特征的影响的光学显微观测

介绍了用偏光显微镜对α-LiIO₃特性的观察.研究了五种不同电极界面状态的八块晶体样品在c向静电场作用下晶体的电导、空间电荷的沉积和分布.观察到由于α-LiIO₃的空间电荷的输运形成的彩色准直条纹.此彩色条纹与光折变型光栅的衍射带之间有对应关系.而不同的电极界面状态对α-LiIO₃晶体的电导和离子输运有明显的影响. 关键词：     

Fe：LiNbO3晶体光折变全息热固定动务学特性分析

以Fe:LiNbO3晶体为例,考虑了电子载流子热激发（强烈地依靠于温度）,通过对以扩散和光伏特效应为主导输运机制的带输运议程和耦合波方程进行数值求解,分析了热固定过程初始光强入射比和固定温度对光栅空间电荷场的影响,指出记录固定过程中内电场极值的出现为源于质子电场对施主光栅电场的部分补偿,质子光栅电荷场可以导致晶体中记录光束之间能量耦合方向的变化,得出了理论上的加热固定时间。     

连续光条件下对LiNbO3∶Fe∶Mn晶体全息存储性能的理论研究

以双中心模型为基础,在低光强连续光条件下研究了LiNbO3∶Fe∶Mn晶体在稳态情况下的非挥发双光双步全息存储性能。采用数值方法,通过比较双中心模型中深(Mn2+/Mn3+)、浅(Fe2+/Fe3+)能级之间所有可能的电子交换过程,发现由隧穿效应引起的深浅能级之间直接电子交换过程对LiNbO3∶Fe∶Mn晶体总的空间电荷场大小起着决定性的作用。同时,这一电子交换过程对晶体非挥发全息存储性能也起着至关重要的作用。此外,通过相同实验条件下LiNbO3∶Fe∶Mn晶体与近化学比LiNbO3∶Fe晶体总的空间电荷场的比较,显示LiNbO3∶Fe∶Mn晶体在低抽运光和高记录光光强条件下有着比近化学比LiNbO3∶Fe晶体更佳的全息存储性能。     

连续光条件下对LiNbO3:Fe:Mn晶体全息存储性能的理论研究

以双中心模型为基础,在低光强连续光条件下研究了LiNbO3:Fe:Mn晶体在稳态情况下的非挥发双光双步全息存储性能.采用数值方法.通过比较双中心模型中深(Mn2 /Mn3 )、浅(Fe2 /Fe2 )能级之间所有可能的电子交换过程,发现由隧穿效应引起的深浅能级之间直接电子交换过程对LiNbO3:Fe:Mn晶体总的空间电荷场大小起着决定性的作用.同时.这一电子交换过程对晶体非挥发全息存储性能也起着至关重要的作用.此外.通过相同实验条件下LiNbO3:Fe:Mn晶体与近化学比LiNbO3:Fe晶体总的空间电荷场的比较,显示LiNbO3:Fe:Mn晶体在低抽运光和高记录光光强条件下有着比近化学比LiNbO3:Fe晶体更佳的伞息存储性能.     

光折变聚合物中载流子特性对空间电荷场的影响

根据适用于光折变聚合物系统的空间电荷场形成的动力学微分方程,将陷阱情况分为四类,分别讨论了光折变聚合物中光生载流子的量子产生效率及其迁移率对空间电荷场的稳态和动态特性的影响.结果发现空间电荷场的稳态特性相对于光生载流子的量子产生效率的变化比较敏感,而空间电荷场的动态特性则易受到载流子的迁移变化的影响.     

Crystallographic fringe orientation diffraction efficiency in bismuth silicon oxide

We report the first experimental measurement of fringe-angle applied electric field scaling of space charge growth and of crystallographic orientation effects in the initial development of the diffraction efficiency of thick holograms produced by the photorefractive effect in a bismuth silicon oxide (BSO) crystal. Diffraction efficiencies of holograms made by interfering two plane waves on the [¯110] face are measured as a function of the angle between the fringe pattern and the applied electric field. As the crystal is rotated relative to the interference fringes, the applied field may be scaled to yield identical space charge growth. Polarization-dependent diffraction measurements agree with the theory of a birefringent grating when optical activity is included as a separate, serial effect. Both the rotation-scaled applied electric fields and the crystallographic variations in the birefringent diffraction grating are consistent with charge transport processes in which the initial space charge fields are perpendicular to the interference fringes over growth times extending nearly into the steady state regime.     

Quantum dynamics of a driven correlated system coupled to phonons

Nonequilibrium interplay between charge, spin, and lattice degrees of freedom on a square lattice is studied for a single charge carrier doped in the t-J-Holstein model. In the presence of a static electric field we calculate the quasistationary state. With increasing electron-phonon (e-ph) coupling the carrier mobility decreases; however, we find increased steady state current due to e-ph coupling in the regime of negative differential resistance. We explore the distribution of absorbed energy between the spin and the phonon subsystem. For model parameters as relevant for cuprates, the majority of the gained energy flows into the spin subsystem.     

Pressure effect on the space charge in low density polyethylene (LDPE)

Abstract

Electrical conductivity of LDPE films was studied with pressure P (1 to 1500 bar). An anomalous discharge current (ADC) was observed in the transient state following a d.c field application. This anomalous current, depending on these parameters, and the steady state current were attributed to the existence of a space charge in polymer. The space charge phenomena and the conduction mechanisms could be given from experimental results and theoretical calculations.     

The role of Jahn–Teller ions in the creation of domain structures in lithium niobate

Using tightly focused laser beams, features of space charge fields (～107 V/m) are studied through the photoionization of doped Jahn–Teller Fe²⁺ ions in LiNbO₃ single crystals. These fields can be used for selective formation of the inverse domain state following the additional application of a field with a strength below the coercive field. The characteristics of laser-induced domains and periodic domain structures are studied by laser-acoustic means.     

Anisotropic Carrier Transport in n-Doped 6H-SiC

Physics of the Solid State - In this paper, a study is presented on the charge transport in n-type doped semiconductor 6H-SiC (in both transient and steady state) using a nonequilibrium quantum...     

Time-domain investigation of the tunneling modes in photonic heterostructure containing single-negative materials

We present a theoretical investigation into the energy transport and transient wave propagation in metamaterial tunneling structures consisting of ??-negative (ENG) and ??-negative (MNG) materials. It is proved that a conjugated matched ENG/MNG bilayer and a (zero-index-material doped) photonic crystal heterostructure can work as a sub-wavelength resonator at tunneling frequency. The tunneling modes need a certain time to achieve the steady state and the charge up characteristic time increases (nearly) exponentially with the thickness of the structures. Under the steady state, the wave in the single-negative-material structures is not evanescent, but a hybrid of a traveling wave and a reactive standing wave. The phase difference between the electric field and the magnetic field varies with the position and time. The investigation of transient wave propagation in the metamaterial tunneling structures will help us to understand the interaction process between wave and metamaterial and to design special functional apparatus.     

Steady-State Spatial Solitons in Low-Amplitude Regime in Biased Photorefractive-Photovoltaic Crystals

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Simulation of unipolar space charge controlled electric fields

A model is discussed, which allows in an easy way to perform electric field simulations in unipolar space charge controlled dielectric media with the finite element method. The approach is appropriate for a variety of different devices in electrical engineering, containing solid, liquid, or gaseous insulators. The main issue concerns the boundary condition at the charge injecting contacts, including ohmic contacts (leading to space charge limited currents) as well as contacts with a finite threshold field for injection (e.g., by Corona onset in gas). The model naturally contains the high-current limit, where the current is injection dominated, i.e., given by the saturation current of the contact, and the capacitive field is restored.Results for a few examples are presented, in order to validate the method by comparison with analytical results, and in order to illustrate its usefulness for applications. In particular, for gaseous insulation various steady state and transient field distributions are calculated. With this approach it is easily possible to investigate the effect of convective currents as well as the charging of dielectrics surfaces.