Computer-generated line holograms using an xy plotter

A new method is presented for constructing a computer-generated Fourier-transformed line hologram using an xy plotter. Phase and amplitude of the complex amplitude in the hologram plane are represented by varying, respectively, the position and height of triangles formed in the cells composing the hologram. An image reconstructed optically from the hologram can be moved arbitrarily from the optical axis since the hologram contains information about the phase and amplitude of the complex amplitude in the hologram plane. A three-dimensional hologram from which an image was successfully reconstructed is also presented.     

基于液晶空间光调制器的全息显示

在传统的纯相位全息显示系统中, 一般基于快速傅里叶变换(FFT)算法来计算相位全息图, 在FFT的计算中需要遵循Nyquist采样定理, 因此, 重建图像的尺寸往往受限于空间光调制器的固定采样率. 这个限制可以通过卷积算法或者两步菲涅耳衍射算法来解决, 但是需要使用多个FFT的计算, 导致计算量增大. 鉴于此, 提出了一种基于透镜的纯相位全息图计算方法. 在全息图的计算中, 通过透镜的成像原理建立一个采样率可变的虚拟全息面, 通过调节相应的距离参数使得在全息图的计算中可以任意调节原始图像的采样率, 摆脱了传统方法中液晶空间光调制器带宽积对重建图像尺寸的限制, 并且这种算法只需使用一次FFT就能达到变采样率的衍射计算, 大幅提高了全息图的计算速度. 数值模拟及光学实验结果证明了此方法可以在全息显示光学系统中清晰地重建不同尺寸的图像. 同时该系统可以有效地消除由空间光调制器的像素化结构带来的零级衍射.     

Reconstruction of digital hologram of small particles on arbitrarily tilted plane using digital holography

Digital holographic off-axis geometry is presented for the reconstruction of the digital hologram of small particles in an arbitrarily tilted plane. A single hologram is sufficient to obtain a well focused clear image. We can't obtain clear images of small particles in the case of plane tilted to the detector plane by ordinary reconstruction method because of the rotation of the hologram plane. Rotational transformation based on coordinate rotation in Fourier space makes it possible to reconstruct holographic images on any plane in the object space. The reconstruction of digital hologram is based on the plane wave expansion of the diffracted wave fields, using Fourier optics and the two-axis rotation of the wave vectors. With this method, the object-to-hologram distance can be any small distance because the minimum distance requirement does not apply.     

Holographic image projection using fractional Fourier transformation

A new method of image projection based on fractional Fourier transformation is presented. This method can project an image at any distance after a lens plane. We use a modified Gerschberg–Saxton (GS) iteration algorithm to compute a phase-only hologram. The amplitude distributions both on the hologram plane and image plane are restricted while allowing their phase distributions to drift into an optimum value. The quality of the image projected by fractional Fourier hologram is close to the image projected by Fourier hologram. The RMS error between the projected image and the constrained image is computed in our experiment. A comparison in flexibility of the two projection methods is also discussed.     

Phase-only hologram generation based on integral imaging and its enhancement in depth resolution

We introduce a phase-only hologram generation method based on an integral imaging,and propose an enhancement method in representable depth interval.The computational integral imaging reconstruction method is modified based on optical flow to obtain depth-slice images for the focused objects only.A phaseonly hologram for multiple plane images is generated using the iterative Fresnel transform algorithm.In addition,a division method in hologram plane is proposed for enhancement in the representable minimum depth interval.     

大尺寸物体彩色全息图制作的研究

通过分析两步法制彩色全息图中全息图空间带宽积与物体大小、全息图记录距离的关系,提出了一种拍摄大尺寸物体彩色全息图的方法。经编码,设置参数,在视窗处平面记录下三分色全息图, 以保证用最小的幅面记录下物体的完整信息,并且H1rgb处于同一平面经原参考光的共轭光再现时,他们的再现像能完全重合;将H1rgb再现,获得大视场的物光波信息,三基色物波信息重合后,用光学方法记录大幅面的彩色全息。该方法能提高全息图再现像的视场和解决大尺寸物体的全息图难拍摄问题。 经实验验证,该方法能将全息图再现像的视场提高6倍左右。     

Reconstruction of synthesized holograms-Fresnel projectors at angles of incidence of reconstructing wave that exceed the angle of incidence of the reference wave in hologram synthesis

The possibility of the aberration-free reconstruction of a synthesized hologram-Fresnel projector in the case when the angles of incidence of the reconstructing plane wave exceed the angle of incidence of the plane reference wave during hologram synthesis is shown. The character of the dependence of admissible angles of incidence of the reconstructing wave on the parameters of the synthesis of hologram projectors is revealed and described mathematically. The results of an experimental study that confirms the possibility of the aberration-free reconstruction of hologram projectors at angles of incidence of the reconstructing plane wave that exceed the angle of incidence of the reference wave of the plane are presented. The results of the successful implementation of the projection photolithography process using a synthesized relief-phase reflection hologram-Fresnel projector are demonstrated.     

单幅同轴全息图两步迭代收缩重建

利用压缩传感理论中的两步迭代收缩重建算法,开展单幅同轴全息图重建实验研究,实现单幅同轴全息图共轭重建像的消除并克服数字全息技术在轴向聚焦平面识别能力的不足。以数字图像和标准分辨率板为记录物体,比较分析了基于两步迭代收缩算法和菲涅尔近似衍射重建算法的重建质量;以两根裸光纤为实验样本,分析了两步迭代收缩重建算法对记录物体轴向不同焦平面的识别能力。实验结果表明两步迭代收缩重建算法可得到清晰度高于68.73%的重建信息,同时对直径为125 m的两根光纤在9 mm的轴向间距条件下,显示出了比全息菲涅尔近似算法更好的聚焦平面识别能力。这一轴向聚焦识别能力有助于数字全息技术应用于功能材料梯度参数或功能涂层光学器件涂层厚度检测。     

传像光纤束单丝芯径大小对光纤像面全息图的影响

光纤像面全息可以获得较高衍射效率的全息图和再现较大的物像。文中分析了相干光激励下传像光纤束单丝芯径的大小对其输出光场的影响，以及输出光场中低阶模与高阶模对全息照相的不同作用，在此基础上，提出缩小传像束单丝芯径，增多单丝根数，可以提高光纤像面全息图衍射效率和分辨率的观点，并通过实验进行了验证。     

Diffraction efficiency of a dynamic hologram in a reversible photochromic medium with allowance for diffusion of photochromic particles

Spatial resolution of a dynamic hologram in a reversible photochromic medium is analyzed, with allowance made for diffusion of photochromic particles. It is shown that the bandwidth of spatial frequencies of a thin hologram decreases over time, approaching the value determined by the diffusion coefficient and the hologram recording/erasing time. The optimum relationship between the intensity of the beam that records the volume hologram and the parameters of the photochromic particles is found for which the difference between the limiting value of the bandwidth of spatial frequencies of the volume hologram and the value of the band-width of spatial frequencies of a thin hologram located in the plane z=0 is the greatest.     

Astigmatism free holographic lens elements

By applying the s and t formula for a hologram lens on a curved surface the conditions which must be satisfied for astigmatism free imagery are derived. It is shown that for hologram lenses formed on surfaces which are conic sections or on a plane surface, astigmatism free imagery can be obtained for extended objects.     

位相恢复法重现软X射线同轴全息图

在物平面和全息平面上分别施加限制条件,实现了同轴全息图的位相恢复重现,基本消除了孪生像的干扰。提出了一种软Ｘ射线同轴全息实时成像的方案     

Fast calculation of wave front amplitude propagation: a tool to analyze the 3D image on a hologram (Invited Paper)

A simple approach to calculate the amplitude component of a wave front propagating in space from a hologram is proposed. It is able to calculate the amplitude distribution on a plane at any distance rapidly using a standard GPU. This is useful for analyzing and reconstructing the 3D image encoded on a hologram.     

Spatial filtering of the diffractional field of a double-exposure hologram of a focused scatterer image. Part II

Analysis is made of the interferometer sensitivity to transverse or longitudinal displacements of a diffusively scattering surface under double-exposure recording of a focused image hologram, where the distribution of the complex field amplitude results from two Fourier transforms of the distribution in the object plane. It is shown that in the case of transverse displacement of the scatterer, the interference patterns are localized in two planes, with each plane characterized by different interferometer sensitivity. In the case of control of the longitudinal displacement, the interference pattern is localized in one plane, however, in order to record it, it is necessary to perform spatial filtering of the diffraction field in the hologram plane. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 78–85, October, 2007.     

单波长编码计算机制彩色彩虹全息图的研究

提出计算机制三维物体彩色全息图的新方法.通过理论分析表明，在满足一定的条件下，三个不同原色的点光源所产生的全息图光栅结构和距全息图不同距离的三个同色物点的光产生的全息图光栅结构是等价的.根据这一原理并参照彩虹全息技术，研究了物体三原色信息光分布的编码方法和全息图的算法，用单波长计算实现彩色全息图的制作，同时，较为完满地解决了全息图叠加和色串扰问题.实验结果证明了该方法的可行性及有效性.     

An image-plane hologram with non-image-plane motion parallax

Image-plane holograms, made using the two-stage process of Rotz and Friesem, provide achromatic or near-achromatic images only when the image straddles the plane of the second hologram. It is shown that in certain circumstances it is possible to generate nearly-achromatic images which appear to lie completely behind the second hologram plane.     

Waveguide holograms: A new approach to hologram integration

A new class of holography is proposed, in which (1) the evanescent part of a guided wave, or (2) the guided wave in a thin-film hologram is utilized as the reference wave and/or the illuminating one. The hologram was designated as “wave-guide hologram” and has advantages in the possibility of integration, wide field of view, and compactness and high reliability of the reconstructing system. The possibility of the waveguide hologram has been proved through reconstruction experiments with a guided wave of a waveguide hologram recorded with a plane reference wave.     

Extension of planar nearfield acoustic holography for sound source identification in a noisy environment

Planar nearfield acoustic holography (NAH) is extended to identify the sound source in a noisy environment. The extended method requires the knowledge of the pressures on two closely spaced parallel hologram planes and the plane wave reflection coefficient on the target source surface. First, the incoming field coming from the back side of the microphone array and the scattered field due to the incoming wave falling on the target source are correlated through the plane wave reflection coefficient on the target source surface. Then, the mixed field on the hologram plane can be represented by the field that would be radiated by the target source into free space and the incoming field. Finally, the field that would be radiated by the target source into free space can be extracted by using the pressures measured on two hologram planes, which will be further used to accurately identify the sound source via planar NAH. The validity of the proposed method is demonstrated by simulations and experiment, and the influence of the relative strength of the disturbing source to the target source is also investigated.     

电子全息法三维物场逐层分析

本文叙述了一种三维物场的定量再现、分析方法,其中采用了电子全息法,它包括:1)三维物场全息图的数字记录,2)全息图面上复振幅分布的数字再现,3)三维物场的逐层再现。由此可以获得整个三维物场的信息,这一方法以CCD摄象机作为记录介质,然后把由CCD采集的数字全息图输入计算机,利用频谱滤波法经过傅里叶变换、频谱分离、反傅里叶变换再现出全息图面上的复振幅。在此基础上借助频域衍射公式可再现出任何一层(平行于全息图面)上的图象。这样,我们用这一数字再现和逐层分析的方法便可研究三维物场的一些特性,如物体在其中的位置等。整个再现过程是由计算机软件实现,其中采用了二维快速傅里叶变换算法,再现过程可在几分钟内完成。本文同时还给出了这一数字再现方法的空间分辨率,并且通过计算机模拟展示了一个理想三维物场的再现过程及再现结果。最后指出了这一方法存在的问题及未来的应用前景。     

Spatial Filtering of Lateral-Shear Interferograms in the Case of Double-Exposure Recording of a Lens Fourier Hologram of a Mat Screen. II

Distortions of lateral-shear interferograms in fringes of infinite width due to hologram aberrations are analyzed in a third approximation for a complex field amplitude. The interferometer sensitivity range in the field is shown to increase in the case where a Fourier hologram of a mat screen is recorded using a negative lens, two identical subjective speckles of two exposures are superimposed in the hologram plane, and errors of control are eliminated.