Effect of speckle pattern on laser Doppler velocimeters

The effect of speckle pattern on laser Doppler velocimeters is studied theoretically and experimentally. We have found that dynamic speckle patterns can cause error in velocity measurement. Increasing sampling time and using proper signal processing circuits can eliminate this bad effect caused by speckle pattern. The accuracy of velocity measurement is better than 2.1% in a wide velocity range (4.66-468.86 mm/s) when speckle effects are taken into account.     

Bulk-Quantity Synthesis and Conductive Properties of Comb-Like Dendritic ZnO Nanostructures

Adopting a simple low-temperature (-500℃) vapour process, we have synthesized bulk quantity comb-like dendritic ZnO nanostructures in large area. An atomic force microscope equipped with Au-coated probes was employed to elucidate the current-voltage characteristic of the individual ZnO nanocomb. The connection electrodes were defined by depositing Pt wires using focused ion beam (FIB). A rectification effect was observed,while it was slightly suppressed compared with that of the previous reports. The good conductive properties of the sample can be attributed to the Ga ions implantation through the FIB process of electrode definition. We suggest that the material and the FIB method can be developed to fabricate novel nanosized devices.     

Study on incident laser modulation using surface micro-defects on KH2PO4 crystal

KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries （e.g., width, morphology, and depth of defects） are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 p-m. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μm for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.     

聚丙烯分子量对热致相分离制备微孔膜的影响

通过对等规聚丙烯与邻苯二甲酸二戊酯体系的相分离过程进行研究,绘制了3种分子量等规聚丙烯与邻苯二甲酸二戊酯体系的相图.研究结果表明,聚丙烯分子量的增大导致聚合物单个分子占据的晶格数Np增加,总分子数减少,使混合熵对混合自由能的贡献降低,因此浊点曲线向高温方向移动,而结晶曲线基本不变.聚丙烯分子量的增大延长了聚合物贫相分散液滴的生长时间、增加了聚合物富相黏度和过冷度.聚丙烯分子量变化不仅改变了微孔尺寸,而且改变了微孔结构.在相同淬冷条件下,微孔平均尺寸的变化趋势是贫相分散液滴的生长时间、聚合物富相黏度和过冷度3种因素共同作用的结果.     

Defect-Related Photoresponse and Polarization-Sensitive Photodetection of Single ZnO Nanowires

Defect-related photoconductivity of single ZnO nanowires is investigated. The photoconductivity shows powerlaw dependence with incident green laser intensity due to the defect mechanisms including both recombination centres and traps. The device based on single ZnO nanowire shows a sensitive photoresponse to green light with significant on/off ratios. In addition, the photocurrent ＆ highly sensitive to the polarization of the incident illumination. Therefore, the nanowire may act as a polarized photodetector.     

玫瑰扫描亚成像系统的性能分析

利用调制传递函数(MTF)法,分析了玫瑰扫描制导系统的光学系统模块和探测器模块的参量对系统性能的影响,重点分析了探测器模块的影响,并给出仿真计算结果,由结果分析指出系统设计时选择参量的一种新思路.     

3-连通(X,Y)-free图的Hamiltonian-连通性

一个图G称为(X,Y)-free图,如果G不含同构于子图X和Y的导出子图.本文证明了X=K_(1,3)、Y∈{D,W,B}的3-连通(X,Y)-free图是Hamiltonian-连通的.     

Ultra-Thin Silicon Carbon Nitride Film: a Promising Protective Coating for Read/Write Heads in Magnetic Storage Devices

Ultra-thin amorphous Si C-N films, down to 2nm, have been synthesized by MW-ECR plasma enhanced unbalanced magnetron sputtering. The friction coefficient of the film is only 0.11, determined in dry friction tests against the GCr15 ball at a load of 400mN for 20min. The films exhibit good protection against corrosion when they are immersed in a more severe corrosion environment of 0. 1 mol/L oxalic acid for 12 h compared to the usual conditions （0.05 mol/L, 4min） used in current computer industries. These good properties can be attributed to the smooth, dense and pore free structure of the film. These indicate that the Si-C-N film synthesized by the present technique may be a promising protective coating for read/write heads and other magnetic storage devices.     

封离式He-N$lt;sub$gt;2$lt;/sub$gt;-CO$lt;sub$gt;2$lt;/sub$gt;激光器横模特性的测量与分析

利用激光光束分析仪,实时在线测量了一根He-N₂-CO₂封离式激光管的横模分布特性,得到了激光模式随放电电流的变化关系.实验表明该激光器在最佳工作电流时,容易形成低阶模运转,但很难获得基模运转,通过改善对称性以及加快冷却水流速可以获得基模运转.通过激光动力学过程分析了模式变化的形成原因,为大功率激光器模式控制与改善提供了一定的理论和实验借鉴. 关键词： 2激光')" href="#">CO₂激光 横模 激光模式分析 光束质量