基于螺旋相位调制的非相干全息点扩散函数研究

分析了菲涅耳非相干相关全息(Fresnel incoherent correlation holography,FINCH)系统中纯相位空间光调制器(spatial light modulator,SLM)加载螺旋相位掩模时的点扩散函数.以氙灯为照明光源搭建了FINCH系统,电荷耦合器记录的点源全息图与点扩散函数模拟结果一致.采用该系统分别在SLM上加载双透镜掩模和螺旋相位调制双透镜掩模两种情况下对分辨率板和非染色洋葱细胞成像,给出了成像对比结果.结果表明:采用螺旋相位调制的FINCH系统可以在几乎不牺牲分辨率的情况下提高图像的边缘对比度;同样,对相位物体也可以实现图像的边缘提取和识别.该方法在实时监测活细胞的分裂、形变等方面具有重要应用前景.     

全息模拟再现像的三维重构

提出一种全息模拟再现像的三维重构方法，可以模拟再现得到三维再现像.计算机模拟再现许多幅在不同深度位置的二维光强分布；利用灰度级变化的聚焦度评价方法，通过寻找最大聚焦度值，确定再现三维像各像点的深度信息.实验证明,该方法能实现模拟再现像的三维重构，使数字全息术有希望成为一种全新的三维面形检测技术.再现像三维重构的实现可以更客观地对全息图进行像质评价，并验证计算机制全息术算法的正确性.     

Fast reconstruction of multiple off-axis holograms based on a combination of complex encoding and digital spatial multiplexing

An algorithm is proposed for the fast reconstruction of off-axis digital holograms based on a combination of complex encoding(CE) and spatial multiplexing(SM). In this algorithm, every two off-axis holograms recorded in sequence are first assembled into a CE hologram using the CE method, and then four of the CE holograms are again encoded into one complex spatial multiplexing(CSM) hologram based on the SM algorithm. It is demonstrated that the eight holograms encoded into such one CSM hologram can be quickly reconstructed by performing a two-dimensional(2D) Fourier transform(FT) on the CSM hologram. Using this method, the eight 2D FTs required for the reconstruction of the eight holograms in the conventional spatial filtering methods can be simplified to a process with only one 2D FT, which can largely improve the computation efficiency with the     

Effect of intensity quantization level in parallel phase-shifting digital holography

Parallel phase-shifting digital holography (PPSDH) enables the instantaneous recording of three-dimensional fields. The three-dimensional field can be reconstructed using a computer by numerical scalar wave propagation. In PPSDH, we record a space-division multiplexed hologram that includes the required phase retardation in the spatial distribution of the reference wave and then interpolate the data at blanked pixels for each phase retardation to obtain the complex amplitude distribution of an object wave. The recorded quality of the multiplexed hologram influences the reconstruction quality. In this study, we investigate the effect of the intensity quantization of a multiplexed hologram on the reconstruction quality. We compare the influence of intensity quantization in PPSDH with that in the conventional phase-shifting method. Random noise is also added to the multiplexed hologram. The required intensity quantization level is helpful for selecting a digital image sensor.     

利用数值再现实现彩虹全息色差评价

为了在计算机制彩色彩虹全息图输出之前定量得到再现像的色彩保真度,提出了一种采用数值再现进行色差评价的方法.首先对彩虹全息图进行了频谱分析,得到再现参量与频谱分布之间的关系;然后采用频域滤波算法实现彩色彩虹全息图数值再现,得到再现像的相对功率谱分布;最后采用CIE1976UCS均匀颜色空间对再现像色差情况进行了计算.设计了7个色块并制作了计算机制真彩色彩虹全息图,以金卤射灯作为照明光源进行了光学再现实验,给出实验结果及分析.研究证明了采用数值再现方法实现对计算彩虹全息再现像光谱分布和色差进行计算分析是一种快速经济的方法.     

数字无透镜傅里叶变换全息术中非傍轴及离焦像差的校正

对数字无透镜傅里叶变换全息图直接采用逆傅里叶变换进行物场的数值重建时.需要满足两个条件:第一,全息图的记录过程必须满足傍轴近似条件,否则再现过程中会产生非傍轴像差;第二,记录全息图时物平面与参考点光源到全息图记录平面的距离必须相等,否则再现过程中会产生离焦像差.理论分析了非傍轴及离焦记录条件下数字无透镜傅里叶变换全息图的灰度分布特点,并提出了相应的非傍轴及离焦像差的数值校正方法.根据实际的非傍轴或离焦记录情况.分别给所记录的数字全息图灰度分布矩阵乘以适当的非傍轴或离焦校正因子,以消除灰度矩阵中非傍轴或离焦因素的影响.然后再对校正后的伞息图灰度矩阵做逆傅里叶变换处理.即可得到准确的数字再现像.实验结果表明.该数值重建方法能够有效地消除无透镜傅里叶变换全息术中数字再现像的非傍轴像差及离焦像差,提高再现像的质量.     

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.     

共轭对称延拓傅里叶计算全息

提出一种计算全息算法,将物光波进行共轭对称延拓,经快速傅里叶变换直接生成实函数,其中包含物光波的幅度和相位信息,可编码得到灰度全息图.利用此全息图可清晰地再现原物光波.通过共轭延拓生成计算全息图的方法与以往基于干涉的计算全息不同之处在于,这里并不需要模拟物光和参考光的干涉,计算效率很高.利用生成的全息图在数字再现和光电再现实验中均获得了良好的效果.理论推导和实验结果都验证了算法的有效性. 关键词： 计算全息 共轭对称 数字再现 光电再现     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H₁.然后将H₁作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

利用反射全息实现计算全息三维显示

计算全息和光学全息都可应用于三维显示,但各有自己的优势和缺陷.将计算全息和光学反射全息相结合,可以突破光学全息对记录物体的限制,进行虚拟物体或自然场景的全息图的制作,同时可以实现白光再现.本文首先用三维扫描仪获得实际物体的三维数据,用"点云算法"模拟得到其菲涅耳全息图透射率数据,采用计算全息打印机将其输出于全息记录介质,得到可光学再现的菲涅耳计算全息图H1.然后将H1作为光学全息的记录物体进行反射全息记录,将平面全息转化为体全息,实现了计算全息白光再现.     

用全息透镜记录多重分数傅里叶变换全息图

提出一种全息透镜记录多重分数傅里叶变换全息图的新方法，它能在三维空间不同位置和不同方向上分别再现所记录的多个物体的图象，分析了利用全息透镜记录多重分数傅里叶变换全息图的原理及特点，制作了多重分数傅里叶变换全息图，并获得了满意的再现结果。     

Sectional image reconstruction and three-dimensional microscopy of small particles by angular spectrum method

In this letter, we demonstrate sectional image reconstruction and three-dimensional microscopy of small particles. We demonstrate sectional image reconstruction and holographic methods to obtain 2D and 3D images of small particles. A single hologram is sufficient to obtain a section containing only the focused parts of the reconstructed image. One can obtain images of different plane sections of a specimen in addition to its 3D display. The reconstruction of a digital hologram is based on the plane-wave expansion of the diffracted wave fields using Fourier optics (this method is also known as the angular spectrum method). With this method, the object-to-hologram distance can be quite small because the minimum-distance requirement does not apply. Furthermore, numerical reconstruction of transparent objects by this method may be interesting for micro-structure measurement.     

Study on the reduction of speckle noise in the reconstructed image of digital hologram

As one of the most important 3-D display technique, reduction of speckle noise in the reconstructed image of digital holography should be grounded on the digital hologram itself. Based on the whole process of the recording and reconstruction of digital holography, the optical distributions of recorded object and reconstructed image of digital holography have been studied. It has been proposed that the root formation cause of speckle noise in its reconstructed image is the speckle noise formed on the recorded object surface when illuminated by coherent light because of its optical roughness. A novel approach has been presented to reduce speckle noise in digital holography by changing the interference structure of hologram itself. First, by reducing the speckle noise in the reconstructed image, the distribution of ideal reconstruction light with reduced speckle noise is acquired. Then in turn, taking the ideal reconstruction light with reduced speckle noise as ideal object light, a new hologram can be rebuilt, which can reconstruct the ideal object light. The experimental results are given to confirm the proposed method. Therefore, it offers a brand-new thought and practical way to reduce the speckle noise in the reconstructed image of digital holography.     

基于空间光调制器的多层图像的构建与可视化研究

 为解决实时直观地观察多层再现图像的问题,提出利用发光材料实现其可视化.针对由沿光轴方向的二维图层组成的空间图像,利用高效、快速的三维Gerchberg-Saxton算法,得到位相型计算全息图,并通过计算机进行了数字模拟再现.阐述了三维Gerchberg-Saxton算法的流程,并搭建了基于液晶空间光调制器的位相全息图光学再现与可视化光路.利用液晶空间光调制器的灰度-位相曲线把计算全息图转换为灰度图,加载在液晶空间光调制器上,再现出高质量的三维光场,同时利用量子点材料的荧光特性实现了图像的可视化.实验结果表明,光学再现与计算机模拟结果较吻合.该技术在医学、军事、三维显示、微加工以及显微技术等领域有重要应用价值.     

Achromatic reconstruction of femtosecond holograms in the planar optical waveguide

Holograms were recorded by 30 fs laser pulses in 20 microm film of dichromated gelatin on the polished quartz substrate and reconstructed in the waveguide mode. The geometric-optical regime of waveguide hologram reconstruction was obtained: the direction of the reconstructed beam was observed to be independent on the reconstructing wavelength within the hologram spectral selectivity band. We discuss the possibility of producing achromatic waveguide optical elements containing only a few periods.     

电子学全息法再现三维物场

叙述了一种采用电子学全息法分析三维物场的定量方法，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）利用空间频域衍射公式计算其它平面上的复振幅分布，由此可以获得整个三维物场的信息。本文同时还给出这一数字再现方法的空间分辨率。最后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。     

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。     

余弦二值编码纯相位全息图的数字微镜器件显示

分析了采用错误减算法的迭代过程,在已知物波函数傅里叶谱的振幅和物波函数振幅的情况下恢复出纯相位的物波函数,最大限度地保留物波的振幅及相位信息.提出采用余弦二值编码生成二值全息图,即全息图的透射率函数取0或1.二值全息图通过数字微镜器件全息显示系统进行了重构显示,重构效果很好.理论分析了数字微镜器件的衍射效率,表明其最大衍射效率仅和微镜之间的间隔尺寸与微镜边长之比有关.余弦二值编码方法从理论上消除了零级衍射,可以制作像素较多的全息图.     

Wavelength-scanning digital interference holography for optical section imaging

We propose and experimentally demonstrate a simple digital holographic method that allows reconstruction of three-dimensional object images with a narrow depth of focus or axial resolution. A number of holograms are optically generated by use of different wavelengths spaced at regular intervals. The holograms are recorded on a digital camera and reconstructed numerically. Multiwavelength interference of the holograms results in images of the contour plane whose thickness can be made arbitrarily narrow. Objects at different distances from the hologram plane are imaged clearly and independently, with complete suppression of the out-of-focus images. The technique is available only in digital holography and should have useful applications in holographic microscopy.     

数字全息用于光波衍射传播理论教学研究

数字全息技术是基于传统光学全息原理,借助于光电探测和数字处理技术,通过单次曝光记录和再现物光场的振幅和相位信息,近年来被广泛研究和应用.将数字全息应用于光波衍射传播理论教学中,不仅能够使学生在学习过程中形象、直观的理解光波衍射传播理论,而且能够通过编程计算完成数字全息图的数值再现,锻炼他们的知识运用能力,从而拓宽专业知识面、了解科学的发展前沿.