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.     

Phase retrieval for off-axis digital holography using multiplexing with hologram rotation and complex encoding

Optical Review - An efficient method of reconstructing the phase distribution for off-axis digital holography is proposed using hologram multiplexing with hologram rotation and complex encoding. A...     

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     

Elimination of zero-order and conjugate images in off-axis digital holography

In this paper, a new digital method has been developed for eliminating the zero-order and conjugate image in off-axis digital holography. The method consists of filtering the spatial frequencies associated with these undesired terms (the zero-order and conjugate images) in the computed Fourier transform plane of the hologram multiplied with computer simulated original reference wave (written as (RI_h)). An important conclusion is that, without the need for additional shift-spectrum process, the spectrum of real image always appears in the center of the spectrum plane and never shifts. This brings us some convenient to design a filtering window. The theoretical analysis and the corresponding simulation and experiment results are given. As the zero-order and conjugate image are eliminated, both the contrast and brightness of the real image are enhanced and the image quality is improved. Meanwhile, the process of designing a filtering window is simple and convenient.     

通过保留相位进行全息图信息压缩的方法

从全息图的特点出发,研究了全息图的记录和再现原理,提出了一种对离轴菲涅耳全息图信息压缩的方法。对全息图进行傅里叶变换,滤除零级噪声及物光波的共轭波前,仅仅保留物光波的相位信息,而后以采用较低的采样频率对全息图重新抽样,从而大大减少了数字全息图的信息冗余。压缩后的全息图也可以获得良好像质的再现像。理论和实验均证明了该方法的可行性,为全息图的信息存贮与传输提供一条新的途径。     

合成孔径数字全息的分析模拟及多参考光合成孔径数字全息

分析了合成孔径数字全息的理论和实现方法,提出了多参考光合成孔径数字全息方法及其应用前景,以双狭缝为例,模拟了单幅及单参考光、多参考光两种合成孔径数字全息术的记录和再现方法,对三种方法再现像的分辨率进行了比较.     

复数滤波器在数字全息图处理中的应用

数字全息图在微电路检测、粒度分析、透明场测量等小孔径、小视场对象测量和细胞观测等显微测量方面有着广泛的应用前景。根据离轴数字全息图的频谱特点,提出采用复数滤波器,利用计算机及相关算法对离轴数字全息图进行滤波,消除其零级及共轭像,同时可以得到全息图的相位分布。讨论了复数滤波器的设计方法,给出了实验结果。为数字全息图的压缩、再现和相息图制作提供了方便。     

一种有效解决离轴数字全息相图倾斜畸变的数字参考平面方法

离轴数字全息中使用倾斜的平面参考波以消除成像中的零级衍射和共轭像是一种简捷和常用的方法,然而该方法遇到的一个困扰是,由于倾斜参考波引入了附加的载波频率并很难通过实验测量准确地获得附加的载波频率值或倾角,因此会导致重建的相图出现一定的倾斜畸变而无法完全修正.本文提出了一种数字参考平面算法以解决这一问题.该算法利用重建相图的平坦区域选点构建一个能准确表征相图倾斜的数字参考平面,并建立该平面参量与参考波载波频率的数学关系和作为随后相图畸变修正迭代计算的判据.该算法简单有效,不仅能实现对倾斜相位畸变的准确修正,而且能准确地获得倾斜平面参考波的附加载波频率.由于在相位解包裹重建中结合了抑噪处理,因此该方法在环境和系统噪声的影响下仍然有效,实验结果验证了理论设计的有效性.     

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     

结合线性回归的离轴数字全息去载波相位恢复算法

为实现仅用一幅离轴数字全息图便能直接恢复相位,提出一种利用空间载波相移技术(spatial carrier phase shift, SCPS)和线性回归相结合的离轴数字全息去载波相位恢复算法.首先,利用SCPS将一幅离轴数字全息图分为四幅含有载波相移的全息图,其中载波相移由沿行、列两个方向的正交载波所引入;然后,将四幅载波相移全息图作为输入,将所求物体相位和两个正交的载波作为未知量,结合最小二乘法和线性回归同时求出载波和相位信息.相较于已有的去载波技术,本算法无需背景全息图作为参考,便可准确地去除载波,实现高质量的相位重建.本文结合数值仿真和具体实验结果验证本算法的有效性和优越性.     

Curvature measurement using phase shifting in-line interferometry,single shot off-axis geometry and Zernike's polynomial fitting

This paper describes the difference between phase shifting in-line interferometry, single shot off-axis geometry and Zernike's polynomial fitting methods for measuring the curvature of a spherical smooth surface by using the Michelson interferometer. In phase shifting in-line interferometry, four interferograms shifted by a piezoelectric actuator (PZT) were captured by a digital detector and corrected by using the flat fielding method. In off-axis geometry, single shot off-axis interferogram was obtained by tilting the reference and the object wave of the off-axis interferogram was reconstructed in the central region of the observation plane by using the digital reference wave concept. The demodulated phase map was obtained and unwrapped to remove the 2π ambiguity. The unwrapped phase map was converted to height and the sagittal length that used for curvature measurement was calculated accurately. The results extracted from phase shifting in-line interferometry and single shot off-axis geometry methods were compared with the results extracted from single shot Zernike's polynomial fitting method and the results were in excellent agreement. A new trial was done to overcome the fringes produced from the object interfaces. Some factors of uncertainty which affected on the measurement were estimated in the order of 6.0 × 10^?5 mm or 0.003 dioptre (▽).     

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.     

Method for eliminating zero-order diffraction in lensless Fourier transform digital holography

A method to induce phase shifting in lensless Fourier of digital holography system is presented. In this method, by computer simulation and theoretical analysis on the technology to eliminate the influence of zero-order diffraction in force, it can be found that, a reference light induced in a random non-2π integral number of phase shifting shooting to get the second hologram, and wave reconstruction can be got by the difference value image of the two holograms. And, the method of different digital holography record system with different phase shifting should be used. In this paper, theoretical analyses have been done in detail to discuss the problems that exist in the unsuitable phase-shifting methods. Furthermore, some experiments have been done to prove the reliability of this method. This method can significantly improve the image quality and give better resolution of the reconstructed image.     

点源参考光数字全息的频谱和记录能力分析

基于最高空间频率分析法,对点源参考光数字全息的空间频谱进行了分析,得出了使空间频谱分离的条件。结合全息成像系统的分辨率,推导出了同时满足采样和再现像分离的记录条件以及CCD对被记录物体的数据记录能力。结果表明,对给定的物体和CCD来说,采用点源参考光比采用平面参考光更容易满足采样和分离的条件,并可以记录到更多的物体信息,从而可使再现像获得更高的分辨率。     

Aplanatic hologram lenses on spherical surfaces

It is shown that if an off-axis Fresnel hologram is formed on a spherical surface the hologram as a lens will be aplanatic if the position of the reference and object points satisfy the condition (l′)^?1 + l^?1 = R^?1.     

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.     

用Stokes参量法实现数字同轴偏振全息的研究

提出了一种基于Stokes参量的数字同轴偏振全息方法.在实验中用一束线偏振光和一束椭圆偏振光作为参考光, 分别与物光进行干涉,通过拍摄在两个相互垂直方向上的全息图,计算出物光在这两个方向的振幅和相位信息, 从而得到物光的Stokes参量和物体的全偏振信息,实现对各向异性物体偏振态空间分布的图像重建. 实验结果表明,该方法可用于物体的全偏振特性的测量.这种方法在求出物光Stokes参量的同时, 也可消除零级像和共轭像的干扰,因此也可用于同轴或离轴全息.     

Digital holographic image fusion for a larger size object using compressive sensing

Digital holographic imaging fusion for a larger size object using compressive sensing is proposed. In this method, the high frequency component of the digital hologram under discrete wavelet transform is represented sparsely by using compressive sensing so that the data redundancy of digital holographic recording can be resolved validly, the low frequency component is retained totally to ensure the image quality, and multiple reconstructed images with different clear parts corresponding to a laser spot size are fused to realize the high quality reconstructed image of a larger size object. In addition, a filter combing high-pass and low-pass filters is designed to remove the zero-order term from a digital hologram effectively. The digital holographic experimental setup based on off-axis Fresnel digital holography was constructed. The feasible and comparative experiments were carried out. The fused image was evaluated by using the Tamura texture features. The experimental results demonstrated that the proposed method can improve the processing efficiency and visual characteristics of the fused image and enlarge the size of the measured object effectively.     

Single-shot phase-shifting digital holography with a photon-sieve-filtering telescope

A method of single-shot phase-shifting digital holography with a photon-sieve-filtering telescope is proposed. Three copy images with different phases are first generated by use of a monofocal photon-sieve filter in Kepler telescope, and then interfere with the reference plane wave by a beam combiner. The hologram is captured by a charge-coupled device(CCD)in one single exposure. The complex-valued amplitude of the test object can be reconstructed by three-step phase-shifting interferometry through three frames of extracted sub-interferograms from the single-exposure hologram. The principle and simulation experiments are carried out and verified the validity of our proposed method. This method can be applied for snapshot imaging and three-dimensional object construction.     

用一幅离轴菲涅耳数字全息图重建物光波的局域算法研究

基于对离轴菲涅耳全息干涉条纹强度分布的分析,根据CCD记录数据的特点研究了从一幅全息图重建物光波波前、再现物体像的一种新方法.以记录面上某一点（CCD靶面上某一像元）为中心取一个小邻域,假设在该邻域内参考光的振幅、物光的振幅和相位是慢变化的,全息图的强度变化仅是由倾斜入射的参考光的相位变化引起的,从而可用最小二乘法构建一个线性方程组,通过求解该方程组可求得该点物光波的振幅和相位.文中给出了该方法的基本思想和理论分析,并通过计算机模拟和初步的光学实验,验证了该方法的正确性和有效性.