Measurement of Slopes of a Deformed Object Corresponding to Different Directions with Digital Holography

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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.     

基于数字全息及复用技术的全场偏振态测试方法

提出了一种在数字全息记录系统中利用偏振和角分复用技术对光场进行偏振态检测的方法. 将全息系统中的一束参考光分为偏振方向相互正交、初相位相同的两束光, 并分别与物光相同偏振方向的两个分量干涉, 形成两幅子全息图, 同时记录在一帧画面中. 为了分开记录到的物光两个分量, 系统中利用了角分复用技术, 即在两束参考光中引入不同载频, 使物光两分量的频谱位于全息图频谱面的不同区域. 通过滤波、逆傅里叶变换和衍射计算, 获取距离全息图不同位置处物光两正交分量复振幅信息. 利用复振幅信息, 可以构建被测物光的斯托克斯参量和琼斯矢量, 从而表征物光的偏振态. 实验中, 通过对一束椭圆偏振光进行偏振态测量以及对该光束在不同空间位置处的偏振态进行表征, 表明该方法可以实现光束偏振态全场测试, 并且具有较高的可靠性. 关键词： 数字全息 偏振态 琼斯矢量 斯托克斯参量     

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.     

壁面结构对非定常薄膜流动表面波特性的影响

采用VOF方法,在入口处引入周期扰动,对沿矩形结构底板下落的二维非定常薄膜流动进行直接数值模拟.计算结果表明,不同频率的外加周期扰动在流场中激发出不同波长的自由表面波.当壁面结构的波长与之相比较小时,由于壁面结构引起的静态波骑行在外加扰动形成的行进波上.若这两个波长相近,非线性效应将促进附近的表面波之间的合并.当薄膜无...     

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.     

Illumination-angle-scanning digital interference holography for optical section imaging

We propose and experimentally demonstrate a new (to our knowledge) digital holographic method to reconstruct section images of objects with wavelength-dependent reflectivity. A number of holograms of an object are taken as the illumination angle of the laser beam with a specific wavelength is changed in regular intervals. The complex object fields reconstructed from the holograms are numerically superposed to show the image of a sliced section of the object, whose position and thickness can be chosen arbitrarily. By changing the wavelength of the illumination beam, wavelength-dependent section images can be obtained with our method.     

长工作距离显微成像数字全息合成孔径方法(英文)

提出了一种用于长工作距离下显微成像的数字全息合成孔径方法。首先,在不同斜入射照明条件下记录多幅包含不同物光频谱范围的数字全息图。然后,利用每一幅全息图通过数字方法重构并放大物体强度像。最后,通过非相干叠加这些强度像得到分辨力提高且散斑噪声减小的合成物体强度像。理论分析和实验结果表明,此方法可应用于长工作距离下的原位显微观测。     

Resolution improvement of digital holographic images based on angular multiplexing with incoherent beams in orthogonal polarization states

We present a method to improve the resolution of digital holographic images based on angular multiplexing with incoherent beams from two orthogonal polarized components of natural light. Two incoherent subholograms are synchronously recorded by two pairs of incoherent object waves and reference waves with orthogonal polarization states, in which the object is illuminated by two incoherent beams from different directions. The increase in resolution is obtained through phase correction and superposition of two reconstructed object waves. Experimental results show that the resolution and quality of the reconstructed image can be effectively improved.     

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。     

Quantitative evaluation of two-dimensional dynamic deformations using digital holography

An optical system for the parallel evaluation of in- and out-of-plane dynamical deformations will be described. A double pulse laser with pulse separation in the microsecond range is used for the investigations. Two separate interferograms of an object under test, in its undeformed and deformed state, are recorded in a few microseconds. The object is illuminated from two different directions and imaged onto a CCD sensor. This produces two sensitivity vectors. The reference beams have different directions in order to produce two directional spatial carriers. The Fourier method is used for quantitative evaluation, and the measurements along different sensitivity vectors are separated in the Fourier domain. The phases of the two interferograms are obtained from the complex amplitudes and the two dimensional deformation is calculated from the phases. Experimental results are presented.     

Digital spatially incoherent Fresnel holography

We present a new method for recording digital holograms under incoherent illumination. Light is reflected from a 3D object, propagates through a diffractive optical element (DOE), and is recorded by a digital camera. Three holograms are recorded sequentially, each for a different phase factor of the DOE. The three holograms are superposed in the computer, such that the result is a complex-valued Fresnel hologram. When this hologram is reconstructed in the computer, the 3D properties of the object are revealed.     

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.     

Fringe order determination and zero motion fringe identification in holographic displacement measurements

In addition to holograms of the underformed and deformed object, a third hologram is recorded during the deformation process, on the same holographic plate: this marks parts of the test object which have not moved. The zero order fringe, which corresponds to zero motion, is reconstructed from the triple-exposure hologram with much greater intensity than the fringes of higher order.     

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.     

Autofocusing of digital holographic microscopy based on off-axis illuminations

An auto-focusing method for digital holographic microscopy has been proposed by employing two off-axis illumination beams. When specimens are illuminated by two plane waves in different directions, it is found that the farther the reconstruction plane is from the image plane, the wider the two reconstructed images are separated from each other. Thus, the image plane can be determinated by finding the minimum of the variation between the two reconstructed object waves on both the amplitude and phase distributions. The feasibility of the proposed method is demonstrated by the corresponding simulation and experiment.     

入射和反射激波诱导重气泡变形和失稳的三维数值研究

 采用大涡模拟方法,对入射激波及其反射激波诱导球形重气泡的变形失稳过程进行了三维数值模拟,利用已有实验验证了计算模型的可靠性,重点考察了反射激波与已经失稳的气泡界面的再次作用,讨论了涡环的形成及其三维失稳的过程。研究结果显示：入射和反射激波与球形重气泡作用产生斜压效应,会在流场中产生旋转方向截然相反的多个涡环;反射激波诱导的涡环具有较小的强度,故更加容易失稳,甚至能完全形成具有流向涡量的复杂小尺度涡结构。     

Monitoring micro-mechanical changes in electronic circuit boards with digital holographic interferometry

The micrometric changes over the size of the objects produced by the temperature variations can create deleterious effects; the decoupling of soldering points in electronic circuits is one of them. In this work, we present a system based on digital holographic interferometry to quantify the magnitude of the changes produced on an electronic circuit board as it operates at very low electric currents. For the system to work, two digital holograms of the object are registered for different temperatures. These holograms are reconstructed numerically in a computer by using Fresnel's approximation to make a phase difference map. This map is converted into micrometer size variations by means of a lookup table. The implemented system allows for determining mechanical deformations in the range of 0.5–4 μm for a regular electronic circuit board drawing an electric current from 10 μA to 50 μA.     

Digital holographic shape measurement using Fizeau microscopy

We present a Fizeau interferometer using a microscopic objective as a tool for surface contouring without the need for a numerical lens for reconstruction. The interferometer is associated with a telescope system to feature the object with collimated light. The experiment is conducted on two objects possessing different step heights.The phase maps from the captured off-axis holograms are calculated numerically, which allows us to deduce the contours of the objects. The great advantages of the presented technique are that it can be done in real time and there is no need for numerical lenses for micro-objects reconstruction.     

Digital holographic tomography based on spectral interferometry

A digital holographic tomography system has been developed with the use of an inexpensive broadband light source and a fiber-based spectral interferometer. Multiple synthesized holograms (or object wave fields) of different wavelengths are obtained by transversely scanning a probe beam. The acquisition speed is improved compared with conventional wavelength-scanning digital holographic systems. The optical field of a volume around the object location is calculated by numerical diffraction from each synthesized hologram, and all such field volumes are numerically superposed to create the three-dimensional tomographic image. Experiments were performed to demonstrate the idea.