重建彩色数字全息图时不同色光物光场的准确重叠研究

将数字全息检测物体表面视为散射面,球面波为参考波,使用角谱重建算法对不同波长照明情况下物平面光波场重建位置进行研究.结果表明,不考虑图像的物理意义时,衍射的一次傅里叶变换重建像中心与物光场频谱的中心相对应,以一次傅里叶变换重建像为参考,可以较好地确定物光场频谱位置,按照可变放大率的角谱重建算法实现不同色光重建场的准确重叠.     

显微数字全息中物光波前重建方法研究和比较

根据全息理论和线性系统理论,采用离轴无透镜傅里叶变换全息记录光路,对利用菲涅耳近似法、基于瑞利—索末菲衍射积分的卷积法以及角谱理论方法数值重建全息图进行了比较研究,并做了计算机模拟验证.结果表明：菲涅耳近似法和角谱方法重建像质比较好,且菲涅耳方法重建速度快;在记录距离极小的情况下,尽管记录距离不满足通常的菲涅耳近似条件,菲涅耳近似公式仍然成立;自由空间脉冲响应的快速傅里叶变换的性质与距离有关,由卷积方法得到的再现像只在某一特定距离下比较理想;对于极小物场、大孔径显微数字全息来说,菲涅耳近似重建方法是较为有效的方法.     

一种基于角谱理论的光学FRFT的数值模拟算法

以角谱传播理论和分数傅里叶变换(FRFT)的单透镜和双透镜光学实现单元为理论基础,提出了一种基于实际光学结构的光学FRFT的数值模拟算法,推导了该算法中采样间隔的选取方法,并利用Matlab语言编写了相应的处理程序,将该程序对方孔分数傅里叶变换的计算结果与实际实验结果相比较,结果表明该算法是实际光学结构在理想情况下的模拟,因此,该数值计算在一定程度上可以代替柱面镜对光场实现分数傅里叶变换,也可以为实际实验提供很好的参考和指导。     

应用二维窗口傅里叶变换实现全息图数值再现

应用二维高斯窗口傅里叶变换对全息图进行局部分析。首先定义二维窗口傅里叶变换,并从理论上证明通过二维高斯窗口傅里叶变换所获得的叠加频谱与傅里叶变换所获得的频谱是一致的。对菲涅尔全息图进行数值再现时,通过提取窗口区域内局部全息图的＋1级频谱信息,并随着窗口中心在整幅全息图上逐点移动,将窗口傅里叶变换局部分析所获得的＋1级频谱叠加求和,可有效地重构出与＋1级衍射像相对应的完整频谱信息,在一定程度上改善了0级以及±1级衍射像所对应的不同频谱之间的串扰,提高了再现像的质量。     

基于空间光调制器的动态全息再现技术研究

为了使空间光调制器实时产生大景深的再现像,运用GS算法计算出不同参数下的全息图。通过计算全息重建算法仿真得到不同傅里叶全息图下的再现像。在无傅里叶变换透镜的情况下,利用计算机将不同参数下的傅里叶全息图输出到空间光调制器,通过分析二维实时动态显示的再现像表明,当傅里叶全息图的采样点数为1 024×768,采样间隔为18μm时,再现像景深为275 cm,该参数下再现像景深最大;通过分析不同参数的傅里叶全息图再现像,实验结果表明相位图像元尺寸越小再现像景深越大,并且在相同参数下有傅里叶变换透镜时的再现像景深小于无傅里叶变换透镜时的再现像景深。     

像面滤波技术在无透镜傅里叶变换数字全息中的应用

无透镜傅里叶变换数字全息波前重建主要采用全息图的一次快速傅里叶变换方法,重建图像不能充分占有重建平面.本文基于像平面滤波技术,提出对物体局部区域光波场进行放大重建并让重建图像布满重建平面的方法,给出具有精细结构物体的数字全息波前重建实例.此外,将数字全息光波场重建视为具有方形出射光瞳的光学系统的相干光成像过程,导出了物体放大图像的分辨率与光学系统相关参量的关系,并通过实验给予证明.     

像面滤波技术在无透镜傅里叶变换数字全息中的应用

无透镜傅里叶变换数字全息波前重建主要采用全息图的一次快速傅里叶变换方法,重建图像不能充分占有重建平面.本文基于像平面滤波技术,提出对物体局部区域光波场进行放大重建并让重建图像布满重建平面的方法,给出具有精细结构物体的数字全息波前重建实例.此外,将数字全息光波场重建视为具有方形出射光瞳的光学系统的相干光成像过程,导出了物体放大图像的分辨率与光学系统相关参量的关系,并通过实验给予证明.     

角谱衍射公式的快速傅里叶变换计算及在数字全息波面重建中的应用

从取样定理出发,对角谱衍射公式及逆运算的快速傅里叶变换(FFT)进行了研究.基于研究结果.讨论数字全息研究中物光通过一个光学系统到达CCD探测器的波面重建问题.提出物光场的逆运算追迹重建及像空间波面重建两种方法.最后,通过数字全息实验及波面重建计算,对两种波面重建方法的可行性作出证明.     

傅里叶变换轮廓要中频谱泄漏的讨论

讨论了频谱泄漏对傅里叶变换轮廓术测量精度的影响.由于用傅里叶变换轮廓术进行三维面形测量时,测得的变形光场是空间有限函数,故离散傅里叶变换时先要进行周期拓展,如果拓展周期选择不当,拓展后的条纹将不连续,对之进行傅里叶变换会产生频谱泄漏.文章从理论上推导了拓展周期与变形结构光场频谱泄漏之间的关系.给出了由泄漏引起的视场边缘误差的计算模型和定量分析.提出采用条纹外插以减小泄漏误差的方法,计算机模拟及初步实验证实了该方法的有效性.     

基于相位重建的叠栅层析技术

针对叠栅层析研究中采用基于相位重建方法处理叠栅条纹图像的问题,用标量衍射理论对叠栅偏折仪的叠栅条纹形成原理进行分析.通过小孔滤波分别提取光场的零级和一级频谱,分析结果与传统的通过几何叠加原理的结果一致,在形式上更加精确.结论表明,叠栅条纹是多波面剪切干涉的结果,且一级频谱滤波下的叠栅条纹图像满足严格的余弦强度分布.采用基于多重网格相位展开的傅里叶变换方法和叠栅层析滤波反投影算法对丙烷燃烧场进行了层析重建.     

Design of the spatial filter window for digital holographic convolution reconstruction of object beam field

In the convolution reconstruction process of digital holographic object beam field, the object beam fields with different magnifications can be obtained when the reconstructing beams are spherical waves with different wave curvature radii. This paper presents a theoretical and experimental discussion on the useful spatial frequency spectrum of the hologram numerically illuminated by the spherical wave. The result shows that there would be an image in the spatial frequency spectrum of digital hologram, which is completely the same as the object, if the wave surface radius of the spherical wave is equal to the distance from the object to the CCD sensor. Taking this image as a reference and designing a filter, the position of the reconstructed images with different magnifications can be predicted correctly in the reconstructed plane. Additionally, since the spectrum distribution of zero-order diffraction can be forecasted accurately in theory, its contribution can be effectively eliminated through changing the spatial filter shape; then a reconstructed object field containing more high-frequency information can be obtained.     

Recording and reconstruction of digital Gabor hologram

This paper looks at some as yet undisclosed observations in the recording and reconstruction of digital Gabor hologram. Small particles on the specimen plane diffract the illuminating spherical wave to form the object wave which interferes with the un-diffracted reference to form the in-line hologram. The interference is similar to that between two spherical wavefronts. It is shown that resolution enhancement can be achieved in the recording process through the use of wavefronts with different curvature. Numerical reconstruction of this hologram with a conjugate of the illuminating (reference) wave provides the in-focus real image at the object plane. It is exemplified that the proper choice of the reconstruction wavefront can optically magnify the reconstructed image enabling one to better visualize the resolution enhancement. Both theoretical analysis and experimental confirmation are provided for these observations.     

基于滤波成像的大视角数字全息技术

为提高数字全息再现像视角,提出一种基于滤波成像的数字全息技术来实现大视角的三维物体面型测量.利用离轴像面数字全息技术,通过在4F相干图像处理系统的空间频谱面处放置可移动的低通滤波器,使满足CCD分辨率的物光波与参考光波干涉形成全息图,并控制低通滤波及成像区域分别记录不同谱段的子全息图.再现时,首先对子全息图进行数字傅里叶变换,重构对应频谱段,并对频谱段进行拼接形成完整的物光频谱|而后通过数字再现获得大视角的数字全息再现像.利用该方法测量了圆柱形表面（光滑的缝纫针）的三维形貌,并取得了较好的实验结果.     

基于虚拟光波场的菲涅耳衍射计算及应用研究

为满足特定观测区域光波场的较高空间分辨率要求,提出一种在衍射计算中引入虚拟光波场,利用初始光波场的取样数表示观测平面任意区域衍射场的计算方法。通过应用该方法对具体实例进行模拟计算,结果表明该方法在观测区域所获得的有效信息量增加,所获得的衍射场空间分辨率可以达到5.2×10-3 mm/pixel,而S-FFT计算获得的衍射场空间分辨率为26.6×10-3 mm/pixel。并且在基于该方法的彩色数字全息波前重建的实验研究中,所得结果表明该方法能够取得更好的重建效果。     

数值模拟微米粒子的体全息记录与再现

体全息对小粒子记录及再现的影响关系到体全息材料在粒子场检测领域的应用前景,提出结合角谱传播理论与多光栅耦合波理论进行体全息图衍射分析的方法,并数值模拟了微米量级小粒子衍射光场的体全息记录与再现。数值分析结果表明体全息理论并不能像薄全息理论那样精确的再现出原始物光。其再现光场的角谱分布相对于原始光场存在高阶衰减,这使得再现光场成像后的图像边缘模糊,而且模糊程度还会随着粒子尺寸的下降逐渐上升。虽然这一现象为粒子边缘判读带来困难,但是再现图像的径向强度分布可为提高判断精度提供有益的参考。     

像面数字全息的重建相位误差分析和改善

像面数字全息是数字全息技术中常用的测量和成像方式,它通常采用离散傅里叶变换和频率滤波的方法进行物光波的重建.本文讨论了这些算法对重建相位的影响.首先分析了频谱泄露对于相位误差的影响,结果表明当采样周期为整数时,重建相位误差很小,因此具有极高的相位重建精度;而当不满足整周期采样时,相位重建误差有了明显的增加.为了改善频谱泄露所引起的相位误差,采用Hanning函数对数字全息图进行了预处理,结果表明Hanning窗的加入能够有效地提高重建相位的准确程度.     

散射光波场卷积重建的三种方法研究

将数字全息检测物体的表面视为散射面,当物体投影尺寸远大于CCD面阵尺寸时用球面波为重建波,对物平面光波场卷积重建过程进行了理论研究.导出了重建物光场放大率与重建参量的关系.介绍了通过补零扩大CCD平面以及对物体局域重建组合的另外两种卷积重建方法.通过实验对三种方法进了行比较.结果表明,球面波为重建波的方法优于另外两种方法.     

Eliminate the influence of zero-order diffraction for wavefront reconstruction with selectable magnification in digital holographic

The objective surface is considered as the scattering plane; frequency spectrum of a digital hologram transmission light is studied when the reference light and reconstruction wave are spherical waves. The relation between relevant parameters and the object light, conjugate object light and zero-order diffraction wave frequency spectrum distribution. The research results show that: each frequency spectrum of the diffracted wave broadens to various degrees as the radius of the reconstruction wavefront decreases, and frequency aliasing is generated under certain conditions. Based on the research results, a new method that carries out high-pass filtering processing without zero-order diffraction interference upon digital hologram is proposed and the reconstruction experimental proof for eliminating the interferential changeable magnification wave is given.     

Numerical reconstruction and twin-image suppression using an off-axis Fresnel digital hologram

In this work we proposed a novel approach for the numerical reconstruction of digital holography that uses only an off-axis Fresnel digital hologram and can easily be carrying out in a personal computer. From the presented off-axis holographic principle, the reference wave accompanies to the numerically reconstructed image, also makes the separation to the zero-order and twin images. Therefore, the concept can be applied to suppress the blurring of numerical reconstruction by adding the extra reconstruction plane and the formularized numerically reference wave in the reconstruction procedure. As expected, the blurring images can be separated out and removed from the reconstructed image. Then, by performing the back propagating to the exact reconstruction plane, one can obtain the pure object image without the blurring. In contrast to the temporal phase-shifting digital holographic-based scheme that employs multiple exposures the technique can be more effectively and easily overcome the blurring problem, also provide the practical feasibility in the digital holographic application. PACS 42.40.-I; 42.30.Wb; 42.40.Ht     

Lensless imaging of an arbitrary object

A new class of imaging systems that do not require the use of lenses or similar optical devices is introduced and theoretically investigated. In particular, it is demonstrated that, if an arbitrary plane object is illuminated by an appropriate spherical wave front (generated from a monochromatic point source), then a magnified image of the object intensity distribution can be observed in any transversal plane along the light-propagation direction within the far-field (Fraunhofer) diffraction region. The phenomenon is based on the fact that, under certain conditions, the spherical wave front can modify the energy's angular spectrum of the field distribution in the object plane such that this spectrum replicates the spatial intensity distribution of the object.