双掺杂LiNbO3晶体中光栅均匀性的优化研究

研究了非挥发全息记录中南于紫外光的强吸收而引起的光栅非均匀性，分析了这种非均匀性对光栅衍射效率的影响。结果显示，非均匀性致使光折变光栅的平均强度减弱，衍射效率降低。提出了采用两束等光强的敏化紫外光由晶体两侧入射的优化方案以改善光栅的均匀性，提高光栅的衍射效率。通过联立两中心带输运物质方程和双光束耦合波方程，进行了相应的理论模拟，并给出实验验证。结果表明双侧紫外光照射能够实现均匀性较好的光栅，是提高衍射效率的有效途径之一。

LiNbO3：Fe晶体光栅擦除特性

在光折变过程中，光波对掺杂中心的激发系数S是一个重要的物理量。为了求出光激发系数S对波长A的依赖，研究了在不同的擦除波长条件下，记录在光折变晶体LiNbO3：Fe中的光栅衰减特性。实验结果表明lnP（P为光擦除灵敏度）与擦除波长λ呈线性关系，即波长越短，光栅擦除越快，光擦除灵敏度越高。在单中心电子带传输模型的基础上，理论计算也证实了实验结果。利用带传输模型，给出了理论上光激发系数S对波长的指数依赖关系。同时微观量φμγ（φ为量子效率）也可由光栅擦除实验求出。

Scalable Methods for Deterministic Integration of Quantum Emitters in Photonic Crystal Cavities

We investigated four unique methods for achieving scalable, deterministic integration of quantum emitters into ultra-high Q{V photonic crystal cavities, including selective area heteroepitaxy, engineered photoemission from silicon nanostructures, wafer bonding and dimensional reduction of III-V quantum wells, and cavity-enhanced optical trapping. In these areas, we were able to demonstrate site-selective heteroepitaxy, size-tunable photoluminescence from silicon nanostructures, Purcell modification of QW emission spectra, and limits of cavity-enhanced optical trapping designs which exceed any reports in the literature and suggest the feasibility of capturing- and detecting nanostructures with dimensions below 10 nm. In addition to process scalability and the requirement for achieving accurate spectral- and spatial overlap between the emitter and cavity, these techniques paid specific attention to the ability to separate the cavity and emitter material systems in order to allow optimal selection of these independently, and eventually enable monolithic integration with other photonic and electronic circuitry.

We also developed an analytic photonic crystal design process yielding optimized cavity tapers with minimal computational effort, and reported on a general cavity modification which exhibits improved fabrication tolerance by relying exclusively on positional- rather than dimensional tapering. We compared several experimental coupling techniques for device characterization. Significant efforts were devoted to optimizing cavity fabrication, including the use of atomic layer deposition to improve surface quality, exploration into factors affecting the design fracturing, and automated analysis of SEM images. Using optimized fabrication procedures, we experimentally demonstrated 1D photonic crystal nanobeam cavities exhibiting the highest Q/V reported on substrate. Finally, we analyzed the bistable behavior of the devices to quantify the nonlinear optical response of our cavities.

Ce：Mn：LiNbO3晶体紫外记录研究

采用紫外光作记录光在Ce：Mn：LiNbO3晶体中实现非挥发全息记录，灵敏度可达0．0803cm／J，衍射效率（固定）为5．07％，比采用红光为记录光，紫外光为敏化光的非挥发双中心记录方案均提高了50多倍。分析表明，采用紫外光作为记录光，深能级电子被激发比例极大提高，参与光折变过程的电子平均运动周期变短．提高了衍射效率和灵敏度；深浅能级电子光栅的同相位，使得固定空间电荷场变强。文中还研究了退火对记录性能的影响。

组合外加电场提高Fe：LiNbO3中90°记录体全息的衍射效率

针对90°全息记录结构的特殊性，在记录和读出阶段分别施加不同极性的外加电场，实现了Fe：LiNbO3晶体中高衍射效率的全息记录和读出。在库赫塔列夫（Kukhtarev）方程基础上引人两维耦合波理论，对组合外加电场提高掺铁铌酸锂晶体光折变特性的机理进行了探讨。实验和理论计算结果都表明这种分别在记录和读出过程施加不同极性组合的外加电场是在Fe：LiNbO3中实现高衍射效率90°记录结构体全息的有效技术方案。

LiNbO3：Ru晶体的光折变特性研究

采用丘克拉斯基法生长了单掺杂的LiNbO3：Ru晶体，并对其作氧化处理。实验研究了LiNbO3：Ru晶体二波混频条件下光栅记录特性和波长的依赖关系；并且研究了氧化处理对其透射谱和光栅记录特性的影响。研究结果表明，LiNbO3：Ru晶体的最佳记录波长为458nm；氧化处理会增加LiNbO3：Ru晶体对光的吸收，同时提高光栅记录的灵敏度和饱和衍射效率，表现了不同于LiNbO3：Fe晶体的氧化态依赖特性。分析认为，LiNbO3：Ru晶体的反常氧化态依赖特性可能是由于出现了电子通道效应的暗衰减机制，以及Ru存在多

双掺杂LiNbO3：Fe：Ru晶体的全息读出特性

为了解决读出过程中全息数据的擦除问题，研究了新型双掺杂LiNbOa：Fe：Ru晶体的全息读出特性。分析了双中心和单中心记录方案光栅的读出特性，并联立双中心物质方程和耦合波方程进行了模拟计算。结果表明，双中心记录所得到的饱和全息的读出时间常数远低于LiNbO2：Fe：Mn晶体的读出时间常数；单色光记录可以实现有效的全息，且其读出时间常数远大于记录时间常数，表现为准态非挥发读出。分析表明，这可能由于Ru的能级比Mn更靠近Fe，更易被红光激发，从而使得双中心记录所得饱和光栅的存贮持久性降低；单色光记录中红光能够

LiNbO3：Ru：Fe晶体畴反转过程中的电色效应

观察到了双掺杂LiNbO3：Ru：Fe晶体中电色效应伴随畴反转而发生，且与畴反转一样也具有可逆性，两者相辅相成，畴反转导致了晶体变色，电色效应促进了畴反转，系统的实验结果证明了两者的相辅相成性．基于铌酸锂铁电微结构模型，简要解释了其机理．而且发现在极化过程中电色效应促使了畴核的形成，使之不同于非掺杂同成分比铌酸锂晶体的矫顽场大于击穿电场，用恒定直流电场代替脉冲电场也能实现畴反转，这将为周期性极化铌酸锂的制备提供一种新的技术改进．

Studies of the representation of interatomic distances in molecules and crystal as sum of atomic radii

The electron diffraction investigation of the following compounds has been carried out: sulfur, sulfur nitride, realgar, arsenic trisulfide, spiropentane, dimethyltrisulfide, cis and trans lewisite, methylal, and ethylene glycol.

The crystal structures of the following salts have been determined by x-ray diffraction: silver molybdateand hydrazinium dichloride.

Suggested revisions of the covalent radii for B, Si, P, Ge, As, Sn, Sb, and Pb have been made, and values for the covalent radii of Al, Ga, In, Ti, and Bi have been proposed.

The Schomaker-Stevenson revision of the additivity rule for single covalent bond distances has been used in conjunction with the revised radii. Agreement with experiment is in general better with the revised radii than with the former radii and additivity.

The principle of ionic bond character in addition to that present in a normal covalent bond has been applied to the observed structures of numerous molecules. It leads to a method of interpretation which is at least as consistent as the theory of multiple bond formation.

The revision of the additivity rule has been extended to double bonds. An encouraging beginning along these lines has been made, but additional experimental data are needed for clarification.

Characteristics of recording and thermal fixing in lithium niobate

We present a theoretical model in which the band-transport equations and the coupled-wave equations are considered to study the two thermal-fixing methods (simultaneous fixing and postfixing) in Fe:LiNbO3. We found that, in simultaneous fixing, the existing ionic-grating affects the writing of the electronic grating by reduction of the coupling gain, and the grating envelope of the fixed-index grating is quite uniform inside the photorefractive crystal in comparison with the method of postfixing. The resulting diffraction efficiency of the fixed-volume grating is dependent mainly on the initial intensity modulation of the two writing beams. A set of experiments is also presented. (C) 1998 Optical Society of America.

Nonvolatile holograms in LiNbO3 : Fe : Cu by use of the bleaching effect

We report our observation of a bleaching effect under an ultraviolet exposure in LiNbO3:Fe:Cu crystals. Two three-step recording-transferring-fixing schemes are proposed to record nonvolatile photorefractive holograms in such crystals. In the schemes two red laser beams and an ultraviolet illumination are used selectively to write the charge grating in the shallow-level Fe centers, to develop the charge grating in the deep-level Cu centers by transferring the charge grating in the Fe centers, and to fix only the charge grating in the Cu centers for unerasable read-out. Experimental results, verifications, and an optimal recording scheme are given. A comparison of the lithium niobate crystals of the same double-doping system of Fe:Mn, Ce:Mn, Ce:Cu, and Fe:Cu is outlined. (C) 2002 Optical Society of America.

Nonvolatile photorefractive holograms in LiNbO3 : Cu : Ce crystals

We report experimental and theoretical studies of nonvolatile photorefractive holographic recording in LiNbO3:Cu:Ce crystals with two illumination schemes: (1) UV light for sensitization and a red interfering pattern for recording and (2) blue light for sensitization and a red pattern for recording. The results show that the oxidized LiNbO3:Cu:Ce crystals can provide high, persistent refractive-index modulation with weak lightinduced scattering. The optimal working conditions and the prescription for doping and oxidation-reduction processing that yields the maximum refractive-index modulation are discussed. (C) 2000 Optical Society of America OCIS codes: 050.7330, 190.5330, 090.2900.

Electrochromic effect in domain-inversion process LiNbO3 : Ru : Fe crystals

A reversible electrochromic effect accompanying domain-inversion during the electrical poling process in LiNbO3: Ru: Fe crystals at room temperature has been observed. In electrode area, both electrochromism and domain-inversion occur alternately, and electrochromism is also reversible during back-switch poling, which is experimentally verified and whose mechanism is briefly explained using a microstructure ferroelectric model. In addition, because of the enhancing elcctrochromic effect, different from the undoped LiNbO3 crystals, the coercive riled (21.0 kV/mm or so) measured in LiNbO3: Ru: Fe is lower than its breakdown field, thus providing a possible new technique for realizing the domain-inversion by constant electric field rather than a pulsed one.

Reversible electrochromic effect accompanying domain-inversion in LiNbO3 : Ru : Fe crystals

A reversible electrochromic effect during the electrical poling process in LiNbO3:Ru:Fe crystals at room temperature is observed. In electrode area, both electrochromism and domain-inversion occur mutually and electrochromism is reversible during back-switch poling, which are experimentally verified, and a microstructure model to explain the mechanism is proposed. In addition, different from the undoped LiNbO3 crystals, the breakdown field (> 25.0 kV/mm) is higher than the coercive (21.0 kV/mm) measured in LiNbO3:Ru:Fe, which proves a possible new technique to realize domain-inversion by constant electric field rather than pulsed one. (c) 2005 American Institute of Physics.