X射线荧光全息术中记录全息图的角度范围对原子像的影响

X射线荧光全息术,通过记录样品的荧光全息图并利用计算机重构,能够得到晶体内部原子的三维排列信息,这对于材料科学将有着非凡的意义.理论上,在一个X射线荧光全息实验中,实验者必须在4π立体角范围内高角度分辨率地探测荧光的强度,才能得到高空间分辨率的三维的原子像.但在实际的X射线荧光全息实验中,因为实验的装置安排限制,不允许探测到整个球面上的荧光强度振幅.因为取样范围的不完全而引起的全息信息的损失将直接导致重构的原子像失真.本文通过数值模拟在不同角度范围和取样步长情况下铁单晶的X射线荧光全息图并对其进行数字重构,研究了记录全息图的角度范围及取样步长对重构得到的原子像的影响.方位角范围的不完全导致原子像在x和y方向上被拉长,而且导致原子像的亮度不均匀.而极角范围的不完全则导致了原子像在z方向上被拉长.至于步长的影响,则是可以忽略的,如果步长不是太大的话.     

无透镜傅里叶变换全息图数值再现中的图像处理

针对无透镜傅里叶变换全息图数值再现过程的特点，提出了一套不同于以往的削弱或消除全息图0级衍射和孪生像的数字图像处理算法。该算法分为三步。首先，对所拍摄的数字全息图通过高通滤波实现衬比度增强预处理，以提高全息图的衍射效率并消除再现图像的0级衍射斑；其次，对再现图像进行带通及Ⅴ型滤波，以降低背景噪声并使再现视场均匀；最后，对所得到的再现像进行平滑处理，通过小波滤噪和中值滤波进一步提高再现像的信噪比。实验结果表明，该方法只需记录一幅数字全息图，通过简单的数字图像处理，便可明显改善图像质量，尤其适用于无透镜傅里叶变换全息图的数值再现，并且更加实用化。     

光学扫描全息术中的孪生像噪音及消除

阐述了光学扫描全息术的基本原理,分析了孪生像噪音的来源,提出了一种新的数字滤波方法.计算机仿真结果表明:孪生像噪音以振荡形式传播,降低了重构图像的信噪比,影响了重构图像的分辨率;用电子复用技术,即用复全息图函数代替实全息图函数的方法可以有效地消除孪生像噪音;采用单一通道对信号进行处理,即只用一个实全息图函数,通过数字滤波方法同样可以消除孪生像噪音,该方法简便、实用而有效.     

X射线荧光全息术中消除光源偏振效应和孪生像的重构新算法

以27个铁原子成立方排列的晶体结构为模型,通过数值模拟和重构,讨论了入射光源的偏振性对原子像的影响.结果表明,入射光源的偏振性对原子像的可观测性有非常重要的影响.为此,提出了一种能同时消除光源偏振性影响和全息成像所固有的孪生像的数字重构新算法,并通过数字模拟及重构,结果证明了这是一种有效的数字重构算法,能够解决实验过程中光源偏振性和孪生像对原子像的影响. 关键词： X射线荧光全息术 同步辐射 偏振性     

一种消除数字离轴全息零级像的实验方法

提出一种消除数字离轴全息零级像的实验方法.这种方法是将全息衍射光栅作为分光元件,形成数字离轴全息记录系统,通过调节记录光路系统中平面镜,改变物光波到达CCD的入射方向而引入相移,从而得到不同记录参数的全息图.再通过对不同记录参数全息图的数字处理,即可达到零级像消除的目的,并对这种方法进行了理论分析和实验验证.给出了利用这种方法获得的实验结果.实验结果证明了该方案的可行性,并且具有光路系统简单、操作和处理容易等特点.     

超短脉冲数字全息泵浦-探测系统的能量测算

提出了一种测算探测系统所需能量最低值的方法.利用该方法分别针对子脉冲能量不均匀和子脉冲能量均匀的脉冲数字全息光路系统进行讨论,计算得到其探测系统对入射光强的能量利用率分别为41.3%和28.8%.用马赫-曾德干涉仪测出用以记录干涉条纹的电荷耦合器件能够有效记录全息图的能量临界值为56.7mW.根据能量临界值和入射光能量利用率反推出两种探测系统所需的最低能量分别为0.86 W和1.575 W.     

长工作距离显微成像数字全息合成孔径方法(英文)

提出了一种用于长工作距离下显微成像的数字全息合成孔径方法。首先,在不同斜入射照明条件下记录多幅包含不同物光频谱范围的数字全息图。然后,利用每一幅全息图通过数字方法重构并放大物体强度像。最后,通过非相干叠加这些强度像得到分辨力提高且散斑噪声减小的合成物体强度像。理论分析和实验结果表明,此方法可应用于长工作距离下的原位显微观测。     

基于Matlab的计算全息图的制作与数字再现的研究

 应用Matlab语言,结合博奇型计算全息的编码方法,利用计算机分别绘制了菲涅耳全息图和傅里叶变换全息图,实现了计算全息图的快速制作,讨论了制作计算全息图的原理、方法和步骤。利用CGH技术和数字全息技术所生成的全息图再现出原始图像,完成了全息图的数字重现,实现了整个全息记录和再现过程的计算机模拟。与传统的编程语言和绘图方法相比较,该算法在实现上更加简单和快捷,并且带有一系列提高计算全息图质量的措施,有效地消除了零级像和孪生像的影响,获得了清晰的数字再现图像。     

基于有限脉冲响应滤波器的数字全息零级像消除

针对数字全息中零级像的存在影响数字再现像的质量,分析数字全息图的记录、再现原理及频谱特性,提出了一种利用有限脉冲响应滤波器消除全息图数字再现中零级像的方法.该方法只需记录一幅数字全息图,不需要相移器材或其他辅助设备,直接利用数字图像处理对数字全息图在空域进行预处理,消除全息再现时的零级像干扰.对比了数字模拟和实验拍摄到的全息图在应用有限脉冲响应滤波器消除零级像前后的再现结果,表明该方法可消除零级衍射像,改善重建像质量,并且算法简单.     

相移同轴无透镜傅里叶数字全息的分析与实验

应用菲涅耳衍射和全息理论，详细分析了无透镜傅里叶变换数字全息图的记录、再现方法和再现像的特点，分析了相移数字全息图的记录和再现方法，并进行了相应的实验验证。结果表明：直接对无透镜傅里叶数字全息图进行傅里叶逆变换可同时得到与物体完全相同的再现像及其共轭像；同轴无透镜傅里叶数字全息术能最大程度满足CCD对采样条件的要求，从而可以增大记录物体的尺寸，减小记录距离，明显提高再现像的清晰度和分辨率；相移数字全息术能有效地消除数字再现光场中的零级光场和共轭像，显著提高再现像的信噪比。条件许可时，相移同轴无透镜傅里叶数字全息术是目前解决数字全息术中再现像的分离与满足采样条件之间矛盾的最佳方法。     

Complex gamma-ray hologram: solution to twin images problem in atomic resolution imaging

A new technique for high fidelity three-dimensional imaging of atomic structure with gamma-ray holography is demonstrated. A complex hologram was constructed from holograms recorded for different values of the nuclear scattering amplitude on both sides of the (57)Fe M?ssbauer resonance. The holographic reconstruction was applied to this complex hologram resulting in a twin-image-free image of the bcc Fe local structure. The proposed procedure allows the removal of the twin images for all real space, making gamma-ray holography an unambiguous tool for atomic and magnetic structure imaging.     

Wave front reconstruction of Fresnel off-axis holograms with compensation of aberrations by means of phase-shifting digital holography

Off-axis holograms recorded with a CCD camera are numerically reconstructed in amplitude by calculating through the Fresnel–Kirchhoff integral. A phase-shifting Mach–Zehnder interferometer is used for recording four-quadrature phase-shifted off-axis holograms. The basic principle of this technique and its experimental verification are described. We show that the application of this algorithm allows for the suppression of the zero order of diffraction and of the twin image and that the contrast of the reconstructed images can be further enhanced by digital compensation of the aberrations introduced by the holographic recording system     

Imaging of rotating objects by means of synthesized optical holograms

A scheme is presented for producing optical holograms of rotating objects by illuminating the object by a single-frequency coherent laser beam. Along one axis, the synthesis takes place due to rotation of the object; along the other axis, the hologram is synthesized by the coherent radiation field generated by a long linear optical antenna. Numerical simulation shows that reliable discrimination of object images from the accompanying background is possible, for point objects, using a single hologram recorded at one angular position and, for extended flat objects or thin cylinder-like objects, using holograms recorded at two or three angular positions. If the holograms are synthesized in the presence of normally distributed random phase noise, the quality of the reconstructed images of rotating objects remains sufficiently high for root-mean-square noise amplitudes exceeding π/2 and reaching the limiting value 2π/3.     

Holographic imaging with a nanometer resolution using compact table-top EUV laser

Holographic 2D/3D imaging with nanometer resolution using short wavelength extreme ultraviolet (EUV) light is presented in this paper. Gabor’s holograms were recorded with a highly coherent table top EUV laser with different numerical apertures demonstrating ultimately a spatial resolution of 46+/−2 nm, comparable with the illumination wavelength, in 2D holographic imaging. Three dimensional images were obtained from a single high numerical aperture hologram recorded in a high resolution photoresist and numerically reconstructed at different image planes, allowing numerical optical sectioning with a lateral resolution ∼170 nm and depth resolution of 2.4 μm. The holograms were recorded in a high resolution photoresist and digitized with an atomic force microscope. To assess the spatial resolution of the numerical reconstructions of the holograms a correlation method was used. The algorithm allows for simultaneous estimation of the resolution and the feature size of the image under analysis.     

彩色全息图的计算机产生和数字再现

提出了一种基于色彩合成以及菲涅尔衍射原理,用计算机产生全息图并用数字方法再现彩色全息图的方法。该方法的第一步是将物体的彩色RGB图像分离为三基色强度图,再利用博奇编码的方法制成修正离轴参考光分色计算机全息图;第二步是分别对分色全息图在频域进行调制以实现用原参考光真实再现原始物光波。通过滤波消除零级衍射及共轭像的影响,获得了所需要的实像并提高了像质。提供的实验是选用一幅RGB图像作为原始物体,给出了用博奇编码法制成的全息图以及最后经色彩合成获得的再现像。结果表明,该方法能使各分色全息图的再现像准确重合,解决了在色彩合成时容易出现的色串扰问题。     

Optical noise reduction for dc-removed coaxial holographic data storage

A method of reconstructing positive and negative images from Fourier holograms recorded without the dc components is demonstrated by use of a coaxial holographic storage system. Reconstructed images are obtained by adding a phase-modulated dc component of the signal beam on reading. Contrast reversal of the reconstructed images can be achieved by reversing the readout reference pattern. This method can realize not only optical noise reduction but also less consumption of the dynamic range of the recording medium, potentially contributing to increasing the number of multiplexed holograms.     

Twin image removal in X-ray fluorescence holography with two energies

In the last decade,X-ray fluorescence holography has been developed for the study of 3D atomic arrangements in solids.However,it encounters the twin image problem which may disturb the reconstructed atomic images.In this paper,the formation of twin image is discussed and we propose a modified two-energy algorithm to remove the twin image.The simulation shows that the method is valid and more efficient than the multiple-energy algorithm proposed by Barton.     

Twin image removal in X-ray fluorescence holography with two energies

In the last decade, X-ray fluorescence holography has been developed for the study of 3D atomic arrangements in solids. However, it encounters the twin image problem which may disturb the reconstructed atomic images. In this paper, the formation of twin image is discussed and we propose a modified two-energy algorithm to remove the twin image. The simulation shows that the method is valid and more efficient than the multiple-energy algorithm proposed by Barton.     

One-beam recording in a LiNbO3 crystal

We propose a new way to record images in a photorefractive LiNbO3 crystal. This method involves only a single object light without any reference light. We believe that the recording is attained by fanning holograms that result from interference between the object light and its scattered light. Although volume gratings are involved, the recorded pattern can be viewed not only with a laser light beam that is incident over a certain angular range but also with white light.