数字全息显微像平面相位畸变的自动补偿研究

对离轴数字全息显微相位畸变的自动补偿进行了理论和实验研究。首先对由CCD记录的数字全息图采用平均梯度自聚焦方法确定最佳再现距离,然后将修正的虚拟参考光作用于切趾滤波后的全息图进行数字再现,经像平面相位自动补偿后得到无畸变的物体相位分布。该方法仅需记录一幅离轴数字全息图就可以自动快速地重建物体的真实相位信息。     

远心同-离轴混合数字全息高分辨率重建方法

现存的同-离轴混合数字全息技术可同时解决同轴全息共轭像消除困难和离轴全息分辨率受限的问题,但需预测衍射距离,不仅复杂耗时,且精度有限;而远心成像技术可获得非衍射图像,无需预测衍射距离,并具有可消除球面像差和散焦像差等特性.因此,本文将远心成像技术引入同-离轴混合数字全息技术中,提出一种远心同-离轴混合数字全息高分辨率重建方法.该方法利用远心同-离轴混合数字全息系统,分别采集聚焦的离轴全息图和同轴全息图;进而将离轴全息图获得的低分辨率相位信息与同轴全息图获得的振幅信息相复合,作为迭代恢复过程的物光复振幅初始值,并分别在空域和频域进行约束迭代,实现高分辨率重建.实验结果表明,该方法无需衍射距离等先验信息,便可很好地消除共轭像和系统畸变的干扰,并可充分利用图像传感器的空间带宽积,实现物体的高分辨率重建.     

提高数字全息再现像像质的两步相移迭代算法

在两步相移数字全息术中,相移误差直接影响着零级像和共轭像的消除.为了消除相移误差,获得实际相移值,提出了一种基于相位统计特性的两步相移迭代算法.首先利用全息图的相位统计特性计算出初始相移值,然后用数字全息图再现像抽样点强度偏差之和作为评价标准,通过迭代计算寻找参考光的真正相移值.该算法能对任意未知相移量进行提取,从而有效地消除零级像和共轭像,提高了再现像质量.理论分析和光学实验结果证明了该方法的可行性和有效性.     

载波全息干涉图的自动分析

用正交相干相位检测法实现了载波全息干涉图的自动分析.讨论了分析载波条纹图的边界效应,提出了一种易于在微机上实现的条纹图外插算法.最后给出了一幅实时法载波全息图的分析结果.     

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。     

同步相移数字全息综述（特邀）

相移数字全息技术将相移技术与数字全息技术相结合,为微观物体的三维形貌和折射率分布检测提供了一种快速、无损、高精度手段。与离轴数字全息相比,相移数字全息采用同轴光路,可以充分利用CCD相机的空间带宽积。然而,传统相移数字全息需要依次记录多幅不同相移量全息图,才能消除零级像和共轭像,再现出无混叠的相位/振幅图像。同步相移又称瞬时相移,可在同一时间得到多幅不同相移量的干涉图样,克服普通相移干涉不能实时观测的缺点。介绍了相移的概念和实现方式,基于多CCD记录、像素掩膜、平行分光的三种同步相移技术,对同步相移数字全息在生物医学、流场测量、表面形貌测量、微纳器件检测等领域的应用进行综述,为从事同步相移数字全息技术及其应用研究的学者提供有益参考。     

双步相移光栅投影测量轮廓术

双三步相移算法证明可以较大地减少数字光栅投影测量轮廓术的测量误差,基于理论分析与实验验证,针对常用的四步、五步相移算法,提出了相应的双四步、双五步相移算法。通过两次传统相移算法得到两幅主值相位图,直接融合两幅主值相位图即可获得测量所需的相位信息,与已有的针对两幅展开相位进行相位融合方法相比,此方法实现简单且更加有效。相较于双三步相移算法,双四步和双五步相移算法实现简单且能够极大地减少测量误差,仅需通过投影2倍数目传统相移算法所需的投影光栅,且可保持常用三步、四步及五步相移算法固有的优点。     

基于空间光调制器的非相干数字全息单次曝光研究

菲涅耳非相干相关全息术(Fresnel incoherent correlation holography,FINCH)利用在空间光调制器(spatial light modulator,SLM)上加载双透镜模式对同一物点光分束自相干,并通过改变加载的相位因子得到不同的相移全息图.本系统利用SLM可分区编码调制特性,将FINCH成像中SLM上分三次加载的0°,120°,240°相位双透镜掩模各提取1/3组成一幅复合相移模式加载,并研究了三种相位分布方式对FINCH成像质量的影响.结果表明:三个相位在SLM上分布间隔越大,再现像越清晰.在此基础上,提出了一种新的掩模加载方式,在SLM加载透镜阵列,每一个相位因子对应一个双透镜,具有一个光轴.实验表明,通过这种加载方式,通过SLM后形成的三个相移图能够一次在电荷耦合器上记录,并且三个相移图不重叠,然后通过MATLAB编程计算将不同相移角度的全息图分别提取出来,通过三步相移计算合成一幅包含有物光波的复值全息图,最后通过数值再现算法重建待测样品.此系统可用于对光源相干性较低的实时成像系统,也为微小形变测量、动态物体的观测提供了新方法,为非相干数字全息术的发展提供了新思路.     

一种消除数字离轴全息零级像的实验方法

提出一种消除数字离轴全息零级像的实验方法.这种方法是将全息衍射光栅作为分光元件,形成数字离轴全息记录系统,通过调节记录光路系统中平面镜,改变物光波到达CCD的入射方向而引入相移,从而得到不同记录参数的全息图.再通过对不同记录参数全息图的数字处理,即可达到零级像消除的目的,并对这种方法进行了理论分析和实验验证.给出了利用这种方法获得的实验结果.实验结果证明了该方案的可行性,并且具有光路系统简单、操作和处理容易等特点.     

基于离轴数字全息改善散斑自相关重建效果

针对在成像物体没有超出散射介质记忆效应范围的情况下,提出一种结合数字离轴全息术减少散射介质成像中散斑自相关噪声的方法。当成像目标经过散射介质时,使用自相关技术结合相位恢复算法能够从散斑中重建成像目标。但在实际成像的过程中,为了有效抑制环境噪声和热噪声等对重建效果的影响,设计利用离轴全息中的相移法消除噪声项中静态噪声项的干扰,再利用散斑自相关与相位恢复算法重建去噪后效果更好的成像目标。采用结构相似度对重建效果进行定量评估,仿真结果表明对于给出的成像目标,去噪前后的结构相似度从0.8796提高到0.9875,验证了该方法的有效性。说明所提出的方法能够改善散斑自相关法重建效果。     

Fast phase retrieval in slightly off-axis digital holography

In this study, three efficient algorithms are proposed for fast phase retrieval in slightly off-axis digital holography using spectrum cropping, spatial multiplexing, and complex encoding. In the first algorithm, the real spectral order of the subtracted hologram is filtered and cropped, and the number of pixels is decreased in the subsequent retrieval operations. In the second algorithm, two sequential subtracted holograms are digitally phase shifted and spatial multiplexed into one synthetic hologram, and thus only one inverse Fourier transformation is then required. In the third algorithm, two sequential subtracted holograms are encoded separately into the real part and the imaginary part of a complex hologram. Two cross-correlations can be used to reconstruct the phase, thereby improving the utilization of the spectrum. The three new algorithms speed up our previously proposed retrieval method with the assistance of specimen-free holograms. Our experiments demonstrated the validity and improved time requirements of the proposed methods.     

Derivative method for phase retrieval in off-axis quantitative phase imaging

We present a method for phase retrieval in off-axis interferometric systems. By numerically calculating the transverse 1st and 2nd order derivatives of the interferogram, we show that one can directly retrieve the quantitative phase image, without the need for Fourier or Hilbert transformations. Because of this, the method is significantly faster than the current approaches. We illustrate our method using biological specimen data from three different off-axis quantitative phase imaging techniques.     

数字显微全息中二次项相位误差的补偿

针对预放大式数字离轴显微全息技术中二次项相位误差,提出一种基于单幅全息再现的补偿方法.该方法是在显微物镜后焦平面处实现该相位误差的数学补偿,相位误差补偿过程具有调整参量单一化的优点.同时,利用显微物镜的后焦平面上物点特征实现了最佳再现距离的自动判断.该文以相位光栅为实验样本,对该方法进行了实验例证,实验结果验证了本文所提出二次项相位误差的补位误差的补偿方法的正确性和有效性.     

计算全息检测离轴非球面的离散相位计算

为了设计检测离轴非球面的计算全息图（CGH）,需要对采样点的相位进行计算。通过平移和旋转,将离轴非球面几何中心的法线作为检测光路光轴。在此基础上,采用光线追迹法,对离轴非球面上采样点的相位分布进行了研究,详细推导了离散相位的计算方法,给出了在3维空间坐标系中,离轴非球面上任意一采样点的相位计算公式,并通过计算、对比同一旋转对称非球面的相位分布对该算法进行了验证。结果表明该计算方法正确,且计算精度能够满足CGH的要求。     

Phase aberration compensation by spectrum centering in digital holographic microscopy

Firstly, an approach is proposed for eliminating the tilt phase aberration introduced by the tilt reference wave. It is based on the argument distribution of the hologram spectrum to locate exactly the position of the carrier frequency of the virtual image. This tilt aberration will be corrected by shifting the filtered hologram spectrum to the coordinate origin of the frequency domain, without knowledge of the focal length of the imaging lens or distances in the setup. Then the subsequent quadratic phase aberration compensation is performed only by adjusting a single parameter. The method is demonstrated by the phase contrast imaging of the cervical carcinoma cells.     

Aperture synthesis based solely on phase images in digital holography

Aperture synthesis is an important approach to improve the lateral resolution of digital holography(DH) techniques. The limitation of the accuracy of registration positions between sub-holograms affects the quality of the synthesized image and even causes the failure of aperture synthesis. It is a major issue in aperture synthesis of DH. Currently intensity images are utilized to find the registration positions of sub-holograms in aperture synthesis. To improve the accuracy of registration positions, we proposed a method based on similarity calculations of the phase images between sub-holograms instead of intensity images. Furthermore, a quantitative indicator, degree of image distortion, was applied to evaluate the synthetic results. Experiments are performed and the results verify that the proposed phase-image-based method is better than the state-of-the-art intensity-image-based techniques in the estimation of registration positions and provides a better synthesized final three-dimensional shape image.     

Digital off-axis holography without zero-order diffraction via phase manipulation

By means of manipulating the phase information of the object beam in an off-axis digital holographic setup, we show that it is possible to fully eliminate the zero-order diffraction (ZOD) from numerically reconstructed holograms. Two different approaches are presented. In the first method, we introduce a ground glass on the object path beam to provide a random phase illumination. The subtraction between two holograms recorded with different positions of the ground glass yields a ZOD free hologram. In the second approach, a piece of window glass inserted on the path of the object beam produces a constant phase shift. The subtraction of two holograms, one recorded with and one without window glass generates a new hologram whose numerical reconstruction is ZOD free. Theoretical models and experimental results are shown to validate our proposals. They show that the proposed methods totally remove the ZOD without ruining the object information.     

High-efficiency detour-phase holograms

We suggest a new approach to the fabrication of detour-phase holograms. By combining the concept of the detour phase with highly efficient carrier gratings it is possible to overcome the major drawback of detour-phase holograms, i.e., their low efficiency. We call the new hologram type a kinoform detour-phase hologram (KDPH). KDPH's facilitate the implementation of diffractive elements with high phase complexity. Especially if off-axis reconstruction is desired, the number of degrees of freedom for the design of the phase component is increased significantly.