一种新型的实验地震学光学模拟系统

介绍了一种新型的实验地震学光学模拟系统。它将实时全息技术与声发射源测定技术相结合应用于实验地震学研究 ,前者检测和记录试件内应力场及其变化 ,后者检测和记录微破裂所激发的超声波 ,借以确定试件内微破裂发生的时间、位置和强度。综合两种方法所获数据 ,从微破裂丛集成核过程与应力场之间的关系来寻求破裂形成、扩展的某些规律性。试验观察到一些极有研究价值的现象 ,特别是系统能将破裂的形成和扩展 ,从微破裂丛集成核直至整个试件碎裂的过程 ,以较高的分辨率记录下来 ,初步获得微破裂成核过程与应力场关系的某些规律性。     

实现CLOS变换网络与蝶形变换网络的光学方法

本文介绍了实现CLOS变换网络与蝶形变换网络的光学方法,它是通过利用计算全息原理制作的光学元件来完成的。给出了一维16个元素的CLOS变换和一维8个元素的蝶形变换的计算全息光学元件的制作方法,并给出了实验结果,整个实验光路简单,该方法亦可很方便地推广到其它光学互连网络。     

用频闪法对在同一平面内旋转的物体进行全息照相

阐述了用频闪法对在同一平面内旋转的物体进行全息照相的基本思路,并分析讨论了该方法的主要特点及改进措施。     

Electron holography and AFM studies on styrenic block copolymers and a high impact polystyrene

Many of the artifacts of conventional electron microscopy can be avoided if the unstained polymers are studied by electron holography and atomic force microscopy (AFM). Holograms of thin sections (50–70 nm) of organic block copolymers were recorded, and the corresponding phase images were reconstructed. In this way, typical structures such as lamellae and cylinders could be imaged without any staining. In addition, we successfully recorded holograms and performed Lorentz microscopy of an impact‐modified polystyrene (high‐impact polystyrene). The results were compared with the tapping mode AFM phase images. Electron holography and AFM have been demonstrated as suitable tools to image unstained heterogeneous polymers, leading to the understanding of their structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1573–1583, 2005     

Correlative High‐Resolution Mapping of Strain and Charge Density in a Strained Piezoelectric Multilayer

A key to strain engineering of piezoelectric semiconductor devices is the quantitative assessment of the strain‐charge relationship. This is particularly demanding in current InGaN/GaN‐based light‐emitting diode (LED) designs as piezoelectric effects are known to degrade the device performance. Using the state‐of‐the‐art inline electron holography, we have obtained fully quantitative maps of the two‐dimensional strain tensor and total charge density in conventional blue LEDs and correlated these with sub‐nanometer spatial resolution. We show that the In_0.15Ga_0.85N quantum wells are compressively strained and elongated along the polar growth direction, exerting compressive stress/strain on the GaN quantum barriers. Interface sheet charges arising from a polarization gradient are obtained directly from the strain data and compared with the total charge density map, quantitatively verifying only 60% of the polarization charges are screened by electrons, leaving a substantial piezoelectric field in each In_0.15Ga_0.85N quantum well. The demonstrated capability of inline electron holography provides a technical breakthrough for future strain engineering of piezoelectric optoelectronic devices.     

反射式离轴数字全息再现像中的噪声抑制

为了抑制反射式离轴数字全息再现像中的零级像和散斑噪声对再现像的影响,利用高斯核函数在空域对数字全息图进行低通滤波,再用原数字全息图减去滤波后的低频信息来抑制零级像,采用非局部均值滤波来抑制散斑噪声。实验结果表明空域高斯核函数处理法能有效地抑制零级像,非局部均值滤波可以抑制散斑噪声但对部分细节的保持能力不强,改进后的非局部均值滤波在抑制散斑噪声的同时能很好地保护细节信息,提高了离轴数字全息再现像的质量。     

Quantitative Imaging of the Magnetic Configuration of Modulated Nanostructures by Electron Holography

By means of off‐axis electron holography the local distribution of the magnetic induction within and around a poly‐crystalline Permalloy (Ni₈₁Fe₁₉) thin film is studied. In addition the stray field above the sample is measured by magnetic force microscopy on a larger area. The film is deposited on a periodically nanostructured (rippled) Si substrate, which was formed by Xe⁺ ion beam erosion. This introduces the periodical ripple shape to the Permalloy film. The created ripple morphology is expected to modify the magnetization distribution within the Permalloy and to induce dipolar stray fields. These stray fields play an important role in spinwave dynamics of periodic nanostructures like magnonic crystals. Micromagnetic simulations estimate those stray fields in the order of only 10 mT. Consequently, their experimental determination at nanometer spatial resolution is highly demanding and requires advanced acquisition and reconstruction techniques such as electron holography. The reconstructed magnetic phase images show the magnetized thin film, in which the magnetization direction follows mainly the given morphology. Furthermore, a closer look to the Permalloy/carbon interface reveals stray fields at the detection limit of the method in the order of 10 mT, which is in qualitative agreement with the micromagnetic simulations.     

中子全息术中孪生像消除模拟

在中子全息照相的记录过程中,参考波与物波近似沿同一方向传播至全息屏,并在重建时形成不可分离的原像和共轭像,在特定波长下,两者可能干涉相消,产生孪生像现象。受制于中子探测效率和单色器能量分辨率,目前中子全息成像中孪生像的消除技术尚未得到系统的理论和实验研究。本文采用数值方法对已成功应用于X射线全息孪生像消除的两种全息记录及重建技术展开模拟,讨论基于研究堆的中子全息成像技术实现孪生像消除的可行性,并从实验效率和重建质量出发,对单色器分辨率、波数记录间隔、波数记录范围等关键参数进行定量分析和优化选取。结果表明,在研究堆中子源相对较低的单色器分辨率和较窄的可选能区条件下,通过记录2~4个不同能点的全息图即可获取较理想的中子全息重建结果。     

压缩感知重建离轴菲涅耳全息图

针对基于传统数字全息重建算法对待测物体的不同纵向深度截面进行聚焦重构时,聚焦面物体会受到共轭像及背景离焦物体的干扰,本文提出基于压缩感知理论,构建单幅离轴菲涅耳数字全息图层析成像的算法框架。该方法通过自适应空间滤波技术对全息图进行处理,基于压缩感知理论重构不同纵向深度截面图像,并有效抑制背景离焦物体的干扰,最终达到层析成像的目标。计算机数值模拟以及三维待测物体实验结果表明该方法的有效性和可行性。     

全息方法制备嵌段式液晶弹性体

研究了热致收缩形变三嵌段式液晶(LC)弹性体薄膜的制备方法,分析和测试了薄膜的偏光特性和热致收缩率.采用全息曝光的方法一次性制备出具有栅状结构的热致液晶弹性体薄膜材料.在此基础上采用偏光显微镜(POM)、He-Ne激光器对弹性体薄膜的嵌段式栅状结构和偏光特性进行检测,并分析了薄膜弹性体偏光特性和液晶分子取向的关系,对该...