傅里叶变换数字全息图的记录与 再现及实时化研究

为了有效的记录和再现物体的数字全息图,搭建了以液晶光阀(LCD)为透镜的傅里叶数字全息装置。根据全息理论,分析了傅里叶数字全息的记录、再现及实验原理,并进行了相应的数字图像处理,结果表明,傅里叶变换数字全息再现算法简单,缩短了再现周期,可实现准实时化。并成功应用傅里叶变换全息来对字母和数字进行实时相干识别。     

三维物体全视差全息体视图的快速计算

针对传统全息技术对三维数据源要求高、计算量大以及实现速度慢等问题,提出了一种三维物体全视差全息体视图的快速计算方法。该方法对全息面和再现面分别进行空间分割和频谱采样,通过迭代傅里叶变换算法计算多个基元全息图,叠加构成全息图单元。由摄像机获取三维物体不同角度的二维视差图像,基于人眼双目视差立体视觉原理,构建视差图像与全息图单元的对应关系。最后,利用全视差图像调制全息图单元中对应衍射方向的基元全息图,快速合成三维物体全视差全息体视图。基于液晶空间光调制器构建的光学系统对全息体视图进行了再现实验。结果表明,与传统全息图计算方法相比,本文方法容易获取数据源,计算量较小,能够快速计算全息体视图,实现三维物体不同视角图像的再现。     

加密同轴全息数字水印

在研究数字全息技术的基础上,提出了一种新的加密的同轴全息数字水印方法。该方法包括加密和解密两个过程。加密过程首先将原始二值水印图像经过输入面和频谱面上分别放置随机相位模板进行调制加密,生成加密的复数图像,将其作为物光信息,再与参考光信息叠加生成同轴全息图像,然后将其作为水印嵌入到载体图像中;解密过程是加密过程的逆过程,水印重建不需要原始图像的参与,属盲检测过程。在理论分析部分证明了该水印技术的有效性,在仿真实验部分证明了该水印技术具有抗随机噪声干扰、剪切干扰、有损压缩和低通滤波等常见的干扰能力。文中还详细研究了全息数字水印的嵌入强度及对应恢复水印的效果。     

基于傅里叶变换和Gyrator变换的图像加密

基于傅里叶变换和Gyrator变换对图像进行加密。将原始图像和第一个随机相位函数叠加后做傅里叶变换,然后将频域信息减去第二个随机相位函数后得到一个复函数。复函数经过Gyrator变换得到加密图像,将第二个随机相位函数作为相位密钥,同时将Gyrator变换角度作为密钥,由此增大了密钥空间和增强了系统安全性。通过数字方法对图像进行加密,解密过程用光学装置实现。计算机模拟结果表明,该加密方法解密图像质量好,系统安全性良好。     

分数阶全息的转子起停车故障特征提取方法

针对传统起停车过程分析采用短时傅里叶变换提取瞬时幅值和相位会损失瞬变信息的不足,提出了基于分数阶全息原理的转子起停车故障特征提取方法。该方法利用分数阶傅里叶变换从转子起停车振动数据中提取随转速变化的各倍频分量,并通过Hilbert变换求取幅值和相位,克服了傅里叶变换的平均效应,保留了转子振动的瞬变信息。通过结合全息谱理论绘制分数阶全息瀑布图,提取出转子起停车状态下的故障特征。实验结果表明,该方法能够有效提取出起停车过程中振动信号的典型故障特征,对于常见的典型故障有很好的区分能力。     

彩色全息的进展

本文介绍真彩色全息技术的进展。包括早期的彩色全息术，白光处理彩色全息术，透射彩色彩虹全息术，彩色傅里叶变换全息术，反射彩色全息术。阐述全息图的构成与再现过程，给出了这些技术的实验例证。     

基于随机分数梅林变换的光学图像加密

为了实现光学图像的非线性加密,设计了一种基于随机分数梅林变换的光学图像加密方法,构造了相应的光学加密装置。该装置采用混沌映射生成一对共轭随机相位掩模放置于分数傅里叶变换光学装置的两端,对分数傅里叶变换的核函数进行随机化处理,得到随机分数傅里叶变换。随机分数梅林变换由对数-极坐标变换和随机分数傅里叶变换组成,光学图像经随机分数梅林变换得到复值密文,从而完成图像的像素值和像素点位置的双重加密。对应所有密钥计算了输入图像和解密图像的均方误差,混沌映射的初值增大10-16时,解密图像的均方误差放大200倍以上,其作为密钥扩大了加密算法的密钥空间;随机分数梅林变换的分数阶次作为密钥也具有很高的敏感度。数值分析验证了该光学加密系统的可行性和有效性,噪声叠加和抗裁剪性能分析表明该算法具有良好的鲁棒性。     

显微数字全息图相位的滤波法提取

显微数字全息的关键技术之一是其相位信息的提取。通过分析显微数字全息图的空间频谱特点,提出了一种新的相位提取方法。将数字全息图频谱进行搬移,使物光频谱中心移到频域坐标原点;设计有限脉冲响应(FIR)数字滤波器滤出物光频谱;求解滤波后信号的辐角得到全息图相位。对设计的实验系统进行了验证,实验结果表明采用提出的方法提取显微数字全息相位,完全可行,效果良好。     

基于相位计算全息的完美涡旋光产生和调控方法

空间光调制器模拟锥透镜法是目前最为广泛使用的产生完美涡旋光的方法,但是该方法无法调控光束环宽,为了解决这个问题,提出了使用傅里叶空间相位计算全息法产生、调控完美涡旋光。通过理论分析和实验测量证明,改变编码相位可以实时调控完美涡旋光的光环半径、环宽和拓扑荷数。该方法光路简单,产生的光束质量高,且光路只需进行一次调整,操作简便。另外,该方法还具有通用性强的优点,可用于产生各类变形完美涡旋光。实验产生了不同参数的椭圆形完美涡旋光,实验测量结果与理论结果吻合得很好。因此,傅里叶空间相位计算全息法是一种简便、通用、实用性更强的完美涡旋光产生、调控方法。     

基于HWPT-ZFFT的二维全息谱计算方法

精确的频率、相位和幅值识别是进行全息谱计算的必备条件,针对含3个及以上的密集频谱成分,提出一种基于谐波小波包变换的频谱细化方法(harmonic wavelet packets transform-zoom fast Fourier transform,简称HWPT-ZFFT),较传统的复调制细化傅里叶变换所利用的低通及带通滤波器相比,其盒型频谱特性可将感兴趣频段的信号正交,无冗余、无泄漏地提取出,提高了识别精度。首先,利用谐波小波包对密集频谱成分进行滤波;然后,频移进而重采样,进行傅里叶变换得到细化的频率、幅值及相位;最后,计算密集频率下二维全息谱,进行双盘转子全息谱计算,考虑高次分倍频,得到更丰富的故障特征。仿真及双盘转子实验结果表明所提出方法的有效性。     

统计最优柱面近场声全息

由于全息声压测量点的离散性,在基于空间傅里叶变换的柱面近场声全息中会引入混叠误差;另一方面,由于测量面尺寸的有限性,会在该种全息技术中引入窗效应和卷绕误差。为了克服窗效应及卷绕误差,提出了统计最优柱面近场声全息技术,它通过空间域中全息柱面上复声压的线性叠加来反演重建面上的声学量,不需要借助空间傅里叶变换来实现全息重建,故可以克服窗效应和卷绕误差。数值分析的结果表明,统计最优柱面近场声全息要优于基于空间傅里叶变换的柱面近场声全息。     

Dark-field electron holography for the measurement of geometric phase

The genesis, theoretical basis and practical application of the new electron holographic dark-field technique for mapping strain in nanostructures are presented. The development places geometric phase within a unified theoretical framework for phase measurements by electron holography. The total phase of the transmitted and diffracted beams is described as a sum of four contributions: crystalline, electrostatic, magnetic and geometric. Each contribution is outlined briefly and leads to the proposal to measure geometric phase by dark-field electron holography (DFEH). The experimental conditions, phase reconstruction and analysis are detailed for off-axis electron holography using examples from the field of semiconductors. A method for correcting for thickness variations will be proposed and demonstrated using the phase from the corresponding bright-field electron hologram.     

数据融合技术在声全息测量中的应用

提出了基于神经网络和证据理论的数据融合技术。首先,根据声全息的测量原理,建立了由传感器子网和融合子网组成的数据融合模型。接着,给出了基于神经网络的传感器子网结构,实现了从目标特征参数到目标类型的映射,得到初步的输出结果。然后,采用证据理论将目标信息融合起来,达到对目标的有效识别得到最后的识别结果。最后,给出了数据融合技术应用于声全息法识别声源的实例计算。实验结果表明:数据融合后的声源识别率为94.2%,比融合前提高了11.7%。该技术减小了由于信息量不足或存在较大偶然误差而带来的不利影响,使声源的识别结果更可靠。     

A novel method for identifying the order of interference using phase‐shifting digital holography

In this paper, we introduced a mathematical method for measuring the optical path length differences (OPDs), which is suitable for large OPD values where the fringes connections are difficult to detect. The proposed method is based on varying the width of the fringes, without changing the wavelength of the used coherent source. Also, in this work, we discussed the need for such method in off‐axis phase‐shifting digital holography. Low‐resolution off‐axis holograms failed to detect the correct interference order. In general, off‐axis phase‐shifting digital holography is limited by the resolution of the captured holograms. The results obtained using our proposed technique were compared to the results obtained using off‐axis phase‐shifting digital holograms and conventional two‐beam interferometry. Holograms were given for illustration.     

Off-axis and inline electron holography: Experimental comparison

Electron holography is a very powerful technique for mapping static electric and magnetic potentials down to atomic resolution. While electron holography is commonly considered synonymous with its off-axis variant in the high energy electron microscopy community, inline electron holography is widely applied in low-energy electron microscopy, where the realization of the off-axis setup is still an experimental challenge. This paper demonstrates that both inline and off-axis holography may be used to recover amplitude and phase shift of the very same object, in our example latex spheres of 90 and 200 nm in diameter, producing very similar results, provided the object does not charge under the electron beam.     

Performance limits of electron holography

Transmission electron microscopy is wave optics. The object exit wave contains the full object information. However, in the usual intensity images, recorded either in real space or in Fourier space, the phases are missing. In many applications at medium and at high resolution, electron holography has shown its unique ability of solving the “missing phase problem” and utilizing the recovered phase for complete interpretation of the object structure. The question is “What are the performance limits?” with respect to field of view, lateral resolution and signal resolution. In this article, the performance limits are derived and discussed.     

基于数字全息技术的变形测量

全息技术在测量、防伪中有大量应用.数字全息技术采用数字记录和计算机处理,实现测量的方法上有其特点.本文重点对数字全息技术实现变形测量的方法和具体算法开展了研究.论文首先总结了数字全息技术应用中的基本问题,包括数字全息算法问题和噪声抑制问题等.叙述了基于数字全息技术的变形测量基本思想,及相位恢复算法,同时分析了几种变形测量的实现方法,并提出了"2+2"步变形测量方法.该方法相对于"1+1"步变形测量方法,提高了测量精度,同时比"4+4"步变形测量法提高了动态性.本文建立了实验系统,获得了硬币的数字全息图,实现了常用的"1+1"步变形测量方法、相移算法的变形测量方法以及"2+2"步变形测量方法,给出了"2+2"变形测量的实验结果.实验结果表明在数字全息技术中结合相移技术进行测量,可以提高物波再现精度,进而提高变形等的测量精度.     

Mapping the electrical properties of semiconductor junctions--the electron holographic approach

The need to determine the electrical properties of semiconductor junctions with high spatial resolution is as pressing now as ever. One technique that offers the possibility of quantitative high-resolution mapping of two- and three-dimensional electrostatic potential distributions is off-axis electron holography. In this study, we review some of the issues associated with interpreting phase shifts measured using off-axis electron holography, and we describe how a quantitative determination of the dopant-related electrostatic potential can be achieved for device structures. Issues that include the presence of surface "dead" layers, external electrostatic fringing fields, variations in specimen thickness and dynamical diffraction are discussed, and their impact on the quantification of results obtained using off-axis electron holography is examined.     

Non‐invasive,label‐free cell counting and quantitative analysis of adherent cells using digital holography

Manual cell counting is time consuming and requires a high degree of skill on behalf of the person performing the count. Here we use a technique that utilizes digital holography, allowing label‐free and completely non‐invasive cell counting directly in cell culture vessels with adherent viable cells. The images produced can provide both quantitative and qualitative phase information from a single hologram. The recently constructed microscope Holomonitor™ (Phase Holographic Imaging AB, Lund, Sweden) combines the commonly used phase contrast microscope with digital holography, the latter giving us the possibility of achieving quantitative information on cellular shape, area, confluence and optical thickness. This project aimed at determining the accuracy and repeatability of cell counting measurements using digital holography compared to the conventional manual cell counting method using a haemocytometer. The collected data were also used to determine cell size and cellular optical thickness. The results show that digital holography can be used for non‐invasive automatic cell counting as precisely as conventional manual cell counting