光谱色散后的相位调制光束衍射特性研究

用数值方法研究了激光驱动器系统中使用光谱色散平滑单元后光束的衍射特性、模拟结果表明，光谱色散会使光束衍射光斑变大，近场空间强度均匀性改善，而远场光斑内部存在光强接近于均匀分布的区域．进一步分析了光谱色散平滑单元中相位调制器的调制深度、调制频率及光栅色散系数等主要元件参数对光束传输特性的影响，发现在一定情况下光斑内部会出现较强的强度调制。

高功率双包层光纤放大器

高功率双包层光纤放大器在光纤传感、光纤通讯、光谱测量和惯性约束聚变等领域有广泛应用。介绍了两种获得放大激光输出的高功率双包层光纤放大器：单频双包层光纤放大器和脉冲双包层光纤放大器。分析了它们的工作原理及关键技术，并对国内外近期进展作了综述。

Photonic nanowires directly drawn from bulk glasses

High-uniform nanowires with diameters down to 50 nm are directly taper-drawn from bulk glasses. Typical loss of these wires goes down to 0.1 dB/mm for single-mode operation. Favorable photonic properties such as high index for tight optical confinement in tellurite glass nanowires and photoluminescence for active devices in doped fluoride and phosphate glass nanowires are observed. Supporting high-index tellurite nanowires with solid substrates (such as silica glass and MgF2 crystal) and assembling low-loss microcoupler with these wires are also demonstrated. Photonic nanowires demonstrated in this work may open up vast opportunities for making versatile building blocks for future micro- and nanoscale photonic circuits and components. (c) 2006 Optical Society of America.

Sol-gel combustion synthesis and luminescent properties of nanocrystalline YAG : Eu3+ phosphors

EU3+ -doped Y3Al5O12 (YAG:Eu3+) phosphors were synthesized by a facile sol-gel combustion method. In this process, citric acid traps the constituent cations and reduces the diffusion length of the precursors. YAG phase is obtained through sintering at 900 degrees C for 2h. There were no intermediate phases such as YAlO3 (YAP) and Y4Al2O9 (YAM) observed. The charge transfer band of nanocrystalline phosphors shows a shift toward the high-energy side, compared with that of amorphous ones due to lower covalency of Eu-O bond for nanocrystalline phosphors. The higher concentration quenching in YAG:EU3+ nanophosphors may be caused by the confinement effect on resonant energy transfer of nanocrystalline. It also indicates that the sol-gel combustion synthesis method provides a good distribution of Eu3+ activators in YAG host. (c) 2005 Elsevier B.V. All rights reserved.

Solution combustion synthesis, structure and luminescence of Y3Al5O12 : Tb3+ phosphors

The synthesis and optical properties of Y3Al5O12:Tb3+ phosphors are reported in this paper. Y3Al5O12:Tb3+ phosphors were synthesized by a facile solution combustion method. Citric acid traps the constituent cations and also acts as a fuel. Y3Al5O12 (YAG) phase can crystallize through sintering at 900 degrees C for 2 h, and there were no intermediate phases such as YAlO3 (YAP) and Y4Al2O9 (YAM) in the sintering process. The excitation spectra of crystalline Y3Al5O12:Tb3+ are different from that of amorphous one due to the crystal field effect. The emission spectra mainly show D-5(4) -> F-7(6) transition under UV excitation. The higher concentration quenching in Y3Al5O12:Tb3+ nanophosphors may be due to the confinement effect on resonant energy transfer of nanocrystalline. It is also indicated that the solution combustion synthesis method provides a good distribution of Tb3+ activators in Y3Al5O12 host. (c) 2005 Published by Elsevier B.V.

Enhancement of near-band-edge photoluminescence of ZnO thin films in sandwich configuration at room temperature

ZnO/ITO/ZnO sandwich structure films were fabricated. The effects of buffer layer on the structure and optical properties of ZnO films were investigated by x-ray diffraction (XRD), photoluminescence, optical transmittance, and absorption measurements. XRD spectra indicate that a buffer layer has the effects of lowering the grain orientation of ZnO films and increasing the residual stresses in the films. The near-band-edge emissions of ZnO films deposited on both single indium tin oxide (ITO) buffer and ITO/ZnO double buffers are significantly enhanced compared with that deposited on a bare substrate due to the quantum confinement effect. (C) 2006 American Institute of Physics.

Effect of microstructure of TiO2 thin films on optical band gap energy

TiO2 coatings are prepared on fused silica with conventional electron beam evaporation deposition. After annealed at different temperatures for four hours, the spectra and XRD patterns of TiO2 thin film are obtained. XRD patterns reveal that only anatase phase can be observed in TiO2 coatings regardless of the different annealing temperatures, and with the increasing annealing temperature, the grain size gradually increases. The relationship between the energy gap and microstructure of anatase is determined and discussed. The quantum confinement effect is observed that with the increasing grain size of TiO2 thin film, the band gap energy shifts from 3.4 eV to 3.21 eV. Moreover, other possible influence of the TiO2 thin-film microstructure, such as surface roughness and thin film absorption, on band gap energy is also expected.

Influence of buffer layer thickness on the structure and optical properties of ZnO thin films

A series of ZnO thin films were deposited on ZnO buffer layers by DC reactive magnetron sputtering. The buffer layer thickness determination of microstructure and optical properties of ZnO films was investigated by X-ray diffraction (XRD), photoluminescence (PL), optical transmittance and absorption measurements. XRD results revealed that the stress of ZnO thin films varied with the buffer layer thickness. With the increase of buffer layer thickness, the band gap edge shifted toward longer wavelength. The near-band-edge (NBE) emission intensity of ZnO films deposited on ZnO buffer layer also varied with the increase of thickness due to the spatial confinement increasing the Coulomb interaction between electrons and holes. The PL measurement showed that the optimum thickness of the ZnO buffer layer was around 12 nm. (c) 2005 Elsevier B.V. All rights reserved.

全电介质脉宽压缩光栅的研究进展

超短脉冲超高能量激光器作为研究光和物质相互作用以及惯性约束聚变的手段而得到了广泛的应用。综述了应用于啁啾脉冲放大(CPA)系统的脉冲压缩光栅(PCG)的发展概况；分析和评述了脉宽压缩光栅的设计原理和制作工艺，并给出了脉宽压缩光栅的发展展望。实践和理论证明采用多层膜介质衍射光栅是实现高性能脉宽压缩光栅的一种优良的设计方案。

Structure and UV emission of nanocrystal ZnO films by thermal oxidation of ZnS films

ZnO films prepared by the thermal oxidation of the ZnS films through thermal evaporation are reported. The as-deposited ZnS films have transformed to ZnO films completely at 400 degrees C. The 400-700 degrees C annealed films with a preferential c-axis (002) orientation have a hexagonal wurtzite structure. The band gap of ZnO films shifts towards longer wavelength with the increase of the annealing temperature. The relationship between the band gap energy of ZnO films and the grain size is discussed. The shift of the band gap energy can be ascribed to the quantum confinement effect in nanocrystal ZnO films. The photoluminescence spectra of ZnO films show a dominant ultraviolet emission and no deep level or trap state defect emission in the green region. It confirms the absence of interstitial zinc or oxygen vacancies in ZnO films. These results indicate that ZnO film prepared by this simple thermal oxidation method is a promising candidate for optoelectronic devices and UV laser. (c) 2005 Elsevier BN. All rights reserved.

光学薄膜元件的激光预处理技术

激光预处理技术作为一种提高激光约束核聚变装置中光学元件损伤阈值的有效方法，有重要的使用价值和学术价值。介绍了激光预处理的研究现状，重点介绍了小光斑光栅扫描预处理的方法及其应用，以及应注意的问题。讨论了几种被广泛认可的预处理增强机理，并对激光预处理技术进行了展望。

我国严重威胁性外来入侵植物入侵与扩散历史过程重建及其潜在分布区的预测

外来生物入侵已经在世界范围内造成严重的危害，它不仅导致生物多样性的减少和丧失而且威胁着全球的生态环境和经济发展。入侵种在入侵区域的种群扩散是入侵种带来风险的最根本问题，也是其造成危害的重要原因。研究入侵物种的扩散规律可以了解其在入侵地的入侵状况和扩散趋势，这对制定合理的控制措施具有重要意义。本研究选取14种在我国具有较强威胁性的外来入侵植物，通过对其入侵历史动态的分析，判断其在我国的入侵与扩散阶段，进而预测其在我国的潜在分布区。这14种外来植物为紫茎泽兰（Ageratina adenophora）、土荆芥 （Chenopodium ambrosioides.）、喜旱莲子草（Alternanthera philoxeroides）、反枝苋（Amaranthus retroflexus）、刺苋（Amaranthus spinosus）、皱果苋（Amaranthus viridis）、北美独行菜（Lepidium virginicum）、藿香蓟（Ageratum conyzoides）、钻形紫菀（Aster subulatus）、小蓬草（Conyza canadensis）、一年蓬（Erigeron annuus）、牛膝菊（Galinsoga paviflora）、飞机草（Eupatorium odorata）和北美商陆（Phytolacca americana）。 　　紫茎泽兰最早于20世纪40年代入侵我国，经过1940—1960年长达20年的时滞期，紫茎泽兰开始在云南及其临近的省份如四川、贵州和广西迅速扩散。其中，紫茎泽兰在南亚热带和中亚热带气候条件下的扩散速度为20公里/年，而在垂直地带性北亚热带地区的扩散速度为6.8公里/年。紫茎泽兰仍没有入侵到垂直地带性暖温带地区。尽管1990年后，紫茎泽兰在云南基本停止扩散，但其在邻近省（市）的快速传播表明紫茎泽兰在我国仍处在扩散阶段，还没有达到饱和阶段。生态位模型预测结果和紫茎泽兰在已经入侵地区扩散的地理生态式样基本相符。我国南部及中南部地区的气候条件十分适合紫茎泽兰生长。而在华中地区，由于环境条件不太适宜，其扩散速度会相对较慢。我国北部和西北部的气候条件完全不适合紫茎泽兰生存。因此，我国南部和中南部广大未入侵地区将会受到紫茎泽兰入侵和快速扩散的严重威胁，对此应该立即采取紧急措施。 　　自从紫茎泽兰于1978年首次入侵四川省以来，已经在四川、重庆和湖北大面积扩散。紫茎泽兰在此新近入侵区域主要沿河流、公路、铁路扩散。其中沿安宁河、108国道和成昆铁路向北扩散的平均速度为19公里/年，而沿金沙江－长江向东北扩散的平均速度为33公里/年。特别是2000年以后，紫茎泽兰沿金沙江－长江的扩散速度达到了88公里/年。紫茎泽兰得以如此迅速扩散是其本身生物学特性和当地地理生态特点多种因素之间一系列耦合关系共同作用的结果。人类活动和1998年金沙江－长江特大洪水也促进了紫茎泽兰在该地区的扩散。另一方面，紫茎泽兰在新近入侵地区的垂直分布范围说明随海拔高度上升所引起的垂直地带性气候变冷是紫茎泽兰入侵和扩散的自然限制条件。 　　此外，通过对其余13种外来入侵植物入侵历史过程重建发现，除了牛膝菊、反枝苋和皱果苋最早入侵地位于内陆地区以外，其余10种外来入侵植物的最早入侵地都位于我国的东部、南部沿海和西南边境地区。这13种外来植物通常不是通过单一途径传入，而是通过两种或多种途径传入不同的地点。相应地，入侵后也呈现不同的扩散模式。这13种外来植物在我国大体上包括5种入侵和扩散式样即1）从南部沿海和西南边境分别向内陆扩散，如霍香蓟、飞机草，北美商陆;2）从东部沿海向内陆扩散，例如钻形紫菀，小蓬草、北美独行菜和喜旱莲子草;3）从东部沿海、南部沿海和西南边境分别向内陆扩散，如刺苋;4）从南部沿海向内陆扩散，如土荆芥;5）从最早入侵的内陆地区向周边地区扩散，如反枝苋、牛膝菊和皱果苋。分布区动态分析显示当前这13种外来入侵植物在我国都还处在扩散阶段，而且有些外来植物还处在快速扩散阶段，如飞机草。 　　在上述研究基础上，我们对这13种外来入侵植物开展了生态位模型适生区预测和比较分析。并且结合其扩散动态和当前分布现状，我们对其潜在的分布区及扩散趋势进行了系统分析和预测。飞机草、土荆芥、霍香蓟、牛膝菊和北美商陆，这5种外来植物的现有分布区明显小于其在我国的适生区，因此它们在我国的潜在分布区很广，应给予足够的重视。喜旱莲子草、反枝苋、皱果苋、北美独行菜、一年蓬、钻行紫菀和北美商陆在我国的入侵范围与其适生区域之间基本重合，但在其入侵范围内仍存在大面积的未入侵区域。这些未入侵地区通常被已入侵区域所包围，因此也应当给予足够的重视。刺苋和小蓬草在我国的潜在的分布区相对较小，这些植物已经基本上完全入侵了其适生区。因此，这些植物在我国向临近区域继续扩散的可能性不大。 　　

寄生植物在入侵植物防治中的作用——以两种菟丝子为例

生物入侵在全世界广泛发生，目前已经受到全球关注。入侵生物对群落生物多样性和生态系统功能造成严重威胁，导致严重的环境问题和惨重的经济损失。薇甘菊(Mikania micrantha)、五爪金龙(Ipomoea cairica)和南美蟛蜞菊(Wedelia trilobata)是我国华南地区危害最严重的三种外来入侵种，其中以薇甘菊危害最严重，是世界十大有害杂草之一。从20世纪80年代发生以来，薇甘菊已在我国广东农林区域造成严重危害。 机械防治、化学防治和传统的生物防治等治理措施，未能有效治理外来入侵种的危害，直到使用本地种菟丝子(Cuscuta spp)的防治策略。与从原产地引进有害生物天敌的传统生物防治方法不同，本地种由于适应当地气候且与其他物种协同进化，因此，对生态环境潜在的负作用小。从2000年，被发现寄生和抑制薇甘菊之后，菟丝子被认为是防治薇甘菊的有效措施。 为了探讨菟丝子寄生对外来入侵种的治理，及对入侵群落的恢复，本研究在内伶仃岛的林地(入侵种群落被引入菟丝子寄生1-4年)，以及东莞、深圳和海丰的干扰样地(入侵种群落被菟丝子自然寄生5年以上)开展野外调查。在每个样地分别设立外来种入侵亚群和菟丝子治理亚群，通过测定群落结构与组成、土壤性质与养分含量，以及外来种和菟丝子的生长与养分含量等参数之后，本研究得出以下主要结论。 (1) 虽然，被寄生的外来入侵种薇甘菊、五爪金龙和南美蟛蜞菊通过调节资源分配以抵御南方菟丝子(Cuscuta australis)的寄生影响，但是，菟丝子寄生导致外来入侵种生物量降低、繁殖能力下降、养分含量降低。虽然，很多寄生植物都是广谱寄生，能同时寄生多种寄主植物，但是，在本研究的被入侵的群落中，菟丝子主要寄生外来入侵植物。尤其是寄生于南美蟛蜞菊和薇甘菊的菟丝子，生长旺盛、繁殖能力强，表现出高度的适应性。因此，菟丝子对外来入侵种(南美蟛蜞菊和薇甘菊)有寄生偏好性，并对本地种的负面影响小。 (2) 通过吸收寄主的养分，田野菟丝子(Cuscuta campestris)有效地抑制了薇甘菊的危害。由于入侵种的凋落物养分含量高且分解效率高，而且，菟丝子能够促进其它凋落物的分解，并使难以被植物吸收的养分转化成易于被吸收利用的状态。因此，菟丝子与薇甘菊的寄生作用导致土壤养分含量的升高。在薇甘菊被抑制之后，本地种利用丰富的土壤养分资源，提高生长适应性，增强抵抗入侵的能力，甚至抵制薇甘菊的再生。 (3) 菟丝子的寄生作用改变了外来寄主与本地非寄主的竞争平衡，促进本地植物的生长与重建。在外来种被抑制之后，本地种的丰度和群落的物种多样性逐渐增加。本地种如：野葛(Pueraria lobata)和芦苇(Phragmites australis)，取代了入侵群落中的入侵种，成了群落的优势种。而其它原先被薇甘菊抑制的本地草本、藤本和灌木，在引入菟丝子防治之后长势较好。群落稳定性与物种多样性密切相关，被治理群落本地种的增加有利于群落的演替与稳定。 (4) 被干扰的生态系统往往更容易被外来种入侵，而外来入侵种又常导致人工干扰生境的严重退化。在人工干扰样地的菟丝子对薇甘菊的抑制效果与在林地的效果一致，导致被寄生的薇甘菊生长衰退、养分竞争能力下降、入侵危害能力降低。而在薇甘菊被菟丝子治理之后，土壤养分资源增加，入侵群落的物种丰度和生物多样性提高。本 地种的重建与本地群落的恢复密切相关，利于本地被治理群落的稳定，促进被干扰植被的恢复。 菟丝子是一种治理外来入侵种危害的有效措施，适用于破碎的生境和被干扰的生态系统，尤其是在采用目前防治措施难以治理的情况下。本研究为本地种防治外来入侵种提供科学依据，且表明以入侵地的本地种治理外来入侵种有可能成为有效且可持续发展的生物防治策略。

Threat and management strategies of potentially invasive insects in China

The Global Invasive Species Database, GISD, comprises 27 species of the most significant invasive alien insects in the world (through November, 2005), 6 of which are originally native to China, 11 are established in China, and 10 have a potential invasion

Codoping of magnesium with oxygen in gallium nitride nanowires

Codoping of p-type GaN nanowires with Mg and oxygen was investigated using first-principles calculations. The Mg becomes a deep acceptor in GaN nanowires with high ionization energy due to the quantum confinement. The ionization energy of Mg doped GaN nanowires containing passivated Mg-O complex decreases with increasing the diameter, and reduces to 300 meV as the diameter of the GaN nanowire is larger than 2.01 nm, which indicates that Mg-O codoping is suitable for achieving p-type GaN nanowires with larger diameters. The codoping method to reduce the ionization energy can be effectively used in other semiconductor nanostructures. (C) 2010 American Institute of Physics.