粒子场数字全息诊断中的再现算法研究

 粒子场的数字全息诊断中,良好的再现算法能够在较短的时间内给出高质量的再现像。利用标准粒子板模拟单层面的粒子场,使用大面阵CCD实现同轴数字全息记录,得到了大尺寸的数字全息图。针对4种数字全息再现算法,本文从再现图像的质量、再现全息图的大小和计算速度3个主要方面进行了比较研究,结果表明角谱算法(FFT-AS)具有再现图像背景均匀,再现结果中无物理图像压缩,可以再现大尺寸的全息图且具有较快计算速度的优点,适合于粒子场同轴数字全息图的再现计算。     

大尺寸物光波面彩色数字全息高质量重建研究

为解决检测面尺寸较大时CCD难以得到高质量数字全息图的问题,本文利用负透镜设计光学系统让CCD接收来自物体的缩小虚像,以球面波为参考波,使用单色CCD近距离得到三种色光照射下的大尺寸彩色物体的数字全息图,然后采用可控放大率波面重建算法得到同一尺寸的数字全息重建像,合成彩色数字全息重建像.同时,使用两种消零级方法去除零级干扰,提高重建像质量,一种方法利用空间光调制器相移技术在参考光中加入一次任意相移,记录两幅数字全息图,消除重建零级像|另一种方法使用“无干扰全息图”消除重建零级像及共轭像.本文讨论结果可为大物体彩色数字全息及多波长数字全息检测应用提供有益的参考.     

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.     

二步法大景深反射全息图

以开拓反射全息图的景深表达能力为目的,从反射全息图的共轭物像关系出发,利用反射全息图的均匀介质耦合波理论和布拉格条件,对其白光再现像模糊作了具体的分析和讨论,得到色模糊和线模糊的表达式.指出反射全息图上不同各点对任意白光再现像点的色模糊和线迷糊的影响均存在差异,给出反射全息图白光再现像的景深表达式.实验利用二步法制作了一张景深为83 cm的反射全息图,与大景深彩虹全息图再现像相比,其再现像的立体感更加强烈.理论分析和实验结果表明,光源的再现角度和观察距离对反射全息图的再现像景深大小影响显著.在再现光垂直于反射全息图平面照明情况下,反射全息图具有最好的景深表达能力.     

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。     

Intensity equalization for elements for binary-object images reconstructed using synthesized hologram projectors

The influence of the nonlinearity of synthesized hologram projectors on the dependence of the intensity of the images reconstructed using these projectors on the image size has been investigated. A way for reducing the aforementioned dependence, based on choosing the optimal (from the point of view of providing equal intensities of images of different sizes) binarization level for holograms synthesized is proposed. It is proposed to perform this choice using a specialized software package for synthesis and digital reconstruction of hologram projectors. The results of experimental study are indicative of workability and efficiency of the technique proposed.     

透射型彩色全息图的拍摄与再现

提出一种透射型彩色全息图的拍摄与再现技术,所再现的图象可以突出物体的三维立体感和原有色彩.同时提出一种透射型彩色全息图的象素化显示方法,并用全息光栅作为全息光学元件(HOE)进行了实验验证,这种方法特别适合于大尺寸彩色全息图的显示,它将为显示全息的广泛应用和市场开发提供一种新的方法和途径.     

Controlling image size as a function of distance and wavelength in Fresnel-transform reconstruction of digital holograms

A method for controlling the size of amplitude and phase images reconstructed from digital holograms by the Fresnel-transform method is proposed and demonstrated. The method can provide a constant reconstruction pixel width in the reconstructed image plane, independent of the recording and reconstruction distance. The proposed method makes it possible to maintain the size of an object for a sequence of digital holograms recorded at different distances and, therefore, to subtract phase maps for an object recorded at different distances. Furthermore, the method solves the problem of superimposition in multiwavelength digital holography for color display and holographic interferometry applications.     

Multi-wavelengths digital holography: reconstruction, synthesis and display of holograms using adaptive transformation

A method based on spatial transformations of multiwavelength digital holograms and the correlation matching of their numerical reconstructions is proposed, with the aim to improve superimposition of different color reconstructed images. This method is based on an adaptive affine transform of the hologram that permits management of the physical parameters of numerical reconstruction. In addition, we present a procedure to synthesize a single digital hologram in which three different colors are multiplexed. The optical reconstruction of the synthetic hologram by a spatial light modulator at one wavelength allows us to display all color features of the object, avoiding loss of details.     

从线全息图分析彩虹全息

本文从彩虹全息固有的线全息图出发,不采用传统狭缝像的概念来分析彩虹全息的成像机理.论述了线全息图的宽度与再现像最小分辨距离及体视极限的关系;讨论了几种典型彩虹全息术中线全息图的特征及其对再现象的影响,提出并实现了不通过狭缝实像来观察再现像的新方法.     

数字显微全息重建图像的景深扩展研究

显微物镜的景深问题限制数字显微全息在大纵深视场中的应用. 本文充分利用数值重建的特点, 采取低频和高频系数子图上的最大亮度梯度的局部方差作为聚焦判据, 在小波分解域内对显微全息重建图像的景深扩展问题进行了研究. 对倾斜的连续物体碳纤维进行三维重建, 分析了重建距离与直径测量误差的关系. 以超声波雾化器生成的微液滴颗粒场为例, 对离散颗粒场的重建图像进行了景深扩展. 利用基于广义洛伦兹-米散射理论的模型分别模拟1-15 μm 的非透明与透明离散颗粒的显微全息图, 分析了该方法重建的颗粒场的纵深定位误差与夫琅禾费系数的关系, 对比了非透明与透明颗粒纵深定位误差的异同点. 实验和模拟结果显示出该方法对于连续物体和离散颗粒场的显微全息重建图像的景深扩展能力, 且能由此准确重建物体信息.     

An algorithm for evaluating overlapping bubble images recorded by double pulsed laser holography

The present paper describes a method for evaluating images of a bubbly flow in stirred aerated tanks which are typical when pulsed laser holography is applied as the measuring technique. Features of the brightness histograms of reconstructed bubble images are discussed. A procedure is presented to evaluate the bubble images taken from a reconstructed hologram in order to determine the center of gravity of the bubble image. Double pulsed holograms were taken to measure bubble velocities and diameters simultaneously. In this case, overlapping bubble images are sometimes observed in the reconstruction. This significantly impedes the evaluation of the characteristics of the bubbles. Thus, an algorithm is presented in this work to distinguish between single and overlapping bubble images and to separate the overlapping bubble image in a two-dimensional image for a bubbly flow at low void fraction recorded from double pulse holograms. This algorithm was confirmed to be effective if the bubble images are extracted from the entire image.     

基于数字闪耀光栅的位相全息图光电再现优化

针对利用液晶空间光调制器（LC-SLM）进行全息图光电再现过程中,再现像面存在多级衍射像造成单一像能量利用率低的问题,提出了一种在位相全息图中加载数字闪耀光栅的方法,以提高全息图光电再现中单一衍射像的衍射效率.分析了闪耀光栅作为衍射光学元件的特性及其对光波进行位相调制的原理,并阐述了在LC-SLM中加载数字闪耀光栅对位相全息图光电再现时像面能量分布的影响.搭建了基于LC-SLM的位相全息图光电再现实验系统.理论分析表明：在其他条件不变的情况下,加载竖直（或水平）槽向周期为2 pixels的数字闪耀光栅可使 关键词： 全息光电再现 位相全息图 数字闪耀光栅 液晶空间光调制器     

Optical-path-length-shifting color digital holography

We propose an in-line color digital holography that can suppress a 0th-order diffraction image and a conjugate image. This technique reconstructs the image of an object from two holograms that are formed at two different distances from the object for each primary color. We numerically simulated the proposed technique and confirmed that it enabled the reconstruction of higher-quality images of an object than the Fresnel transform alone, which is the simplest reconstruction algorithm in digital holography. The effectiveness of the proposed technique was also quantitatively shown by evaluating the reconstructed images using root-mean-square errors. Thus, it was confirmed that the proposed technique was capable of recording and reconstructing both three-dimensional information and color information of an object.     

大尺寸物光波面彩色数字全息高质量重建研究

为解决检测面尺寸较大时CCD难以得到高质量数字全息图的问题,本文利用负透镜设计光学系统让CCD接收来自物体的缩小虚像,以球面波为参考波,使用单色CCD近距离得到三种色光照射下的大尺寸彩色物体的数字全息图,然后采用可控放大率波面重建算法得到同一尺寸的数字全息重建像,合成彩色数字全息重建像.同时,使用两种消零级方法去除零级...     

基于DMD的数字全息显示及其再现像质增强

采用DMD作为空间光调制器构建了一套数字全息显示系统.分析了数字全息图光学再现中影响再现图像质量的因素,提出了一种采用频域滤波重建高条纹对比度滤波全息图来改善其光学再现图像质量的新方法.采用信噪比及图像亮度作为评价参量,对原始全息图和滤波全息图的数值再现像进行定量分析表明,滤波后全息图的再现像质量明显优于原始全息图的再现像.基于DMD数字全息显示系统的光学再现实验也验证了理论分析结果.     

Multidot recording of rainbow and multicolor holographic stereograms

A new method for rainbow and multicolor holographic stereograms is described using the technique of multidot recording, which was originally developed for the syntheses of full-parallax holographic stereograms. Instead of recording vertical parallax, an image of horizontal slit is synthesized for rainbow holography. It becomes possible to obtain large images by a compact optical system, since the hologram is composed of many small elementary holograms. Multicolor image is also produced by the same system introducing a simple image processing. Experimental results of three-dimensional and color imagery are demonstrated.     

Reflection hologram for reconstructing deep images

A method to record deep and blurless images as a reflection hologram is proposed. A slit was used in the recording process in the same manner as for a rainbow hologram. The reconstructed image was monocolor and could be observed from wide longitudinal angles when it was illuminated by an extended white-light source such as a fluorescent lamp. One can easily obtain multicolor images by multiplexing the holograms with different wavelengths.     

Fraunhofer holography of small particles

The reconstruction of an in-line Fraunhofer (far-field) hologram is re-examined, and an analytical solution of the intensity distribution throughout the entire reconstructed image is presented. The solution bridges the gap between previously documented solutions which are limited to the plane-of-focus image and distant out-of-focus images. The analysis is motivated by a particle velocity measurement technique which attempts to distinguish the focussed image by photographic thresholding. The general methodology is presented for objects of one- and two-dimensional cross-section. Specific results are presented for the single exposure holograms of a long wire and a small particle of circular cross-section. The one-dimensional solution is verified experimentally. The results show precisely how the Fresnel diffraction term creates peaks in the intensity distribution, both upstream and downstream of the focussed image. This characteristic limits the resolution of methods which use thresholding as a means of distinguishing focussed images from their out-of-focus neighbors.     

White-light Fourier holography

This paper describes a technique for generating broad spectral band Fourier holograms with an encoded white light source. Since this technique utilizes primary white-light construction and reconstruction process, it is quite suitable for color Fourier hologram image reconstruction. Experimental results are also given.