基于偏振位相调制的位相轮廓测量

本文介绍了一种用来测量三维物体面形的位相轮廓方法，它是通过将正弦光场投影到被测物面，该光场被物体表面调制后发生位相改变，利用偏振位相调制及位相检测算法计算物面的位相分布，再根据几何关系实现对物体三维形貌的测量。实验装置采用一种偏振位相调制的干涉光场投影装置对光场进行简便而精确的移相，采用ＣＣＤ摄像机记录畸变光场，并用计算机处理和显示测量结果。文中给出了有关实验结果。     

声悬浮过程的激光全息干涉研究

利用二次曝光全息干涉术实现了对单轴式声悬浮声压场的研究.分别拍摄了悬浮不同物体和 不同输出功率情况下声悬浮场的多幅全息图，并进行了对比分析.结果表明，实验中获得的 声压分布图样与由声波动方程获得的理论声压分布基本一致，其相应中轴线的强度分布也具 有很好的一致性.与以往的声场测量方法相比，二次曝光法非接触、无干扰及全场测量的优 势在声悬浮场测量中得以充分体现，该方法的引入不但简化了声悬浮场测量的实际操作，而 且可以更直观地获得全场信息，为优化声悬浮系统提供了实验依据. 关键词： 全息干涉术 二次曝光法 声悬浮 谐振     

彩色全息显示中液晶空间光调制器位相调制偏差的矫正方法

采用三基色激光照明并结合时分复用或空间复用技术,可实现基于液晶空间光调制器(LC-SLM)的彩色全息显示.但由于在不同激光波长入射条件下LC-SLM的位相调制特性曲线不同,难以同时满足多波长入射条件下2π线性位相调制的要求,致使彩色全息再现结果受到共轭像和零级斑的干扰.针对该问题,本文通过实验测试获得LC-SLM在不同波长入射时的位相调制特性曲线,并分析了RGB激光器各分量的位相调制特性曲线非线性偏差和调制幅度偏差对多阶位相型傅里叶变换相息图再现效果的影响.根据"查表法"建立了各波长入射条件下满足2π线性位相调制的灰度映射关系,并对RGB分量相息图进行修正.通过对修正前后RGB分量相息图的数值模拟再现和光电再现实验与分析,结果表明:该方法有效地克服了LC-SLM位相调制特性曲线偏差的不利影响,从而改善了彩色全息显示中各分量相息图的再现质量.     

位相恢复法与X射线激光等离子体密度诊断

 详细介绍了XUV波段Gabor全息及位相恢复法去除Gabor全息孪生像的全部过程,分析了X射线激光Gabor全息术对等离子体和实验条件的要求,编程对全息图的制作、反演以及位相恢复法的全过程进行了模拟,并对三个模型进行了计算比较。     

全息术诊断激光产生蒸汽羽等离子体

介绍了用脉冲激光全息二次曝光法诊断Q开关钕玻璃激光脉冲与LY12铝靶(φ50×3)耦合产生蒸汽羽等离子体的原理和实验。在打靶激光脉宽约50ns,功率密度约5GW/cm~2条件下,拍摄了激光产生蒸汽羽等离子体的全息干涉图。运用Abel变换和Saha方程,对全息干涉图进行数据处理,得到对激光与物质相互作用机理研究的有用参数。     

利用计算全息技术重构激光超声的激发面源

把计算全息技术引入激光超声无损检测系统,此系统借助直接搜索算法生成计算全息图,利用空间光调制器液晶器件代替传统全息干板再现全息图像,并将此生成、再现方法具体用于空间调制的脉冲激光源的产生,以辅助固体表面的窄带超声波的激发。由于算法的稳健性和重建方法灵活性,大大简化了激光超声实验系统,缩短了实验周期,在激光超声无损检测领域有广泛的应用空间。     

位相型物体全息干涉计量的计算机全场数据处理

全息干涉法是一种无损、灵敏的新型测量技术。用其测量具有不均匀折射率分布的位相型物体时,可由全场无限条纹图得出全场折射率分布。本文采用图象处理技术进行干涉图的数据处理。文中对测温和计算的某些细节进行了详细的讨论。实验证明,本文采用的方法便利、迅速,编写的FORTRAN及C语言程序可用于同类型问题的处理。     

DYGQ—Ⅰ型多用途高速全息摄影机

多用途高速全息摄影机是研究高速动态过程全息干涉计量的必备仪器,它可在无暗室条件下对透明物体和非透明物体进行全场非接触测量,如:微粒的大小、分布、运动速度、流场、燃烧场特性研究、工作状态下机械动力设备的振动、应力、应变、各种材料结构力学的实验,以及各种材料的无损检测。除此之外还可做高速摄影的激光光源,     

利用激光全息干涉测量梁的微小位移

全息干涉测量利用二次曝光记录物体在不同载荷状态下的相对位移场.通过在干板上记录和比较不同状态产生的光波的干涉,可以得到在不同载荷时干涉条纹随物体位移的变化情况,实现对物体微小变形、微小位移量的测量.本文利用激光全息干涉技术测量了金属梁的微小位移量,计算得到金属梁的弹性模量和挠度.     

激光全息无损检测实验

本介绍了利用激光全息干涉计量对物体进行检测技术。并给出了实验装置和对物进行检测的图片。     

Stokes参量数字全息法实现相位物体成像

为实现对相位物体的无损检测和成像,克服数字同轴全息相位物体成像技术在消除零级像和孪生像的干扰时存在的系列问题,提出一种基于Stokes参量的新的数字同轴全息技术。该方法区别于传统的利用干涉光场来记录原始像项的数字全息方法,通过测量物参光合成光束的Stokes参量来分别得到这两束光的振幅和相位差,从而准确、唯一地获得原始像项;再利用数字再现即可重构物光的振幅和相位信息。实验中对弱吸收的相位样品进行了测量,得到样品清晰的振幅和相位分布。结果表明,采用该方法对相位物体进行数字全息再现,可以克服传统同轴全息图中零级像和共轭像对相位物体信息的严重干扰,对于提取相位物体的振幅和相位信息是可行和有效的。     

Dynamic characterization of MEMS diaphragm using time averaged in-line digital holography

In this paper dynamic characterization of a MEMS diaphragm is investigated using lens-less time averaged in-line digital holography. The analysis and capability of the numerically reconstructed amplitude and phase information from in-line time averaged holograms as applied to MEMS vibration are presented. Particularly the effect of mean static state on the phase in time averaged digital holography is explored. A novel double exposure method is also demonstrated using a diverging object wave suitable for dynamic characterization of small size objects. A phase jump in the static deformation fringes in the vibrating regions is observed and described and can be used for precise analysis of vibration mode shape under simultaneous presence of mean static deformation. A simple and robust tool for dynamic optical metrology of MEMS devices and micro-objects using time averaged in-line digital holography is thus proposed.     

Three-dimensional-object recognition by use of single-exposure on-axis digital holography

On-axis phase-shifting digital holography requires recording of multiple holograms. We describe a novel real-time three-dimensional- (3-D-) object recognition system that uses single-exposure on-axis digital holography. In contrast to 3-D-object recognition by means of a conventional phase-shifting scheme that requires multiple exposures, our proposed method requires only a single digital hologram to be synthesized and used to recognize 3-D objects. A benefit of the proposed 3-D recognition method is enhanced practicality of digital holography for 3-D recognition in terms of its simplicity and greater robustness to external scene parameters such as moving targets and environmental noise factors. We show experimentally the utility of the single-exposure on-axis digital holography-based 3-D-object recognition method.     

Object recognition by use of polarimetric phase-shifting digital holography

Pattern recognition by use of polarimetric phase-shifting digital holography is presented. Using holography, the amplitude distribution and phase difference distribution between two orthogonal polarizations of three-dimensional (3D) or two-dimensional phase objects are obtained. This information contains both complex amplitude and polarimetric characteristics of the object, and it can be used for improving the discrimination capability of object recognition. Experimental results are presented to demonstrate the idea. To the best of our knowledge, this is the first report on 3D polarimetric recognition of objects using digital holography.     

Application of longitudinal multimode laser coherence properties to increase the holographic depth of field

It has been shown that the temporal coherence of a non-mode-locked laser is periodic in 2L/c. It has also been demonstrated that the limitations imposed on the depth of field in holography by the laser coherence properties may easily be overcome by illuminating the object with multiple beams. In such a system each object beam should travel the same distance to the holographic plate as the reference beam, or a multiple of 2L farther. For large objects (which would have large depths of field) multiple beam illumination is necessary anyway, to ensure uniform illumination of the object. In fact the limiting factor with regard to the size of an object and the depth of field should be the laser's power and not its coherence length. An advantage in this method of overcoming conventional limitations is that there is no reduction in the laser's output power as is involved in some other methods of coherence length improvement.     

相位特征在三维物体识别中的应用

提出利用物体的相位特征联合神经网络的方法对透明半透明三维物体进行识别.首先利用波长扫描数字全息技术和数字再现技术提取物体的相位特征，然后将物体的这些相位特征作为学习模式训练一个BP神经网络，最后利用训练好的网络对三维物体进行识别.实验表明，对于具有小尺度变化的透明半透明三维物体识别，该方法的正确识别率为100%. 关键词： 相位特征 波长扫描技术 数字全息 BP神经网络     

Ultrashort-pulse dual-wavelength source for digital holographic two-wavelength contouring

Digital holographic shape measurements using femtosecond laser pulses are reported. For contouring of very fast moving objects, the simultaneous generation of at least two spectrally separated ultrashort pulses is required. To deliver this particular spectral signature at high pulse energies, a chirped-pulse Ti:sapphire laser amplifier was modified to emit two spectrally separated pulses with energies above 1 μJ each. The wavelength separation of these pulses was adjustable within the 50 nm gain bandwidth, cutting out two distinct wavelength peaks by a variable double-slit assembly in a prism sequence. A Michelson-type interferometer was employed to perform the two-wavelength contouring. The phases of the holograms and the phase differences are calculated numerically, which allow us to deduce the contour lines of the topology of the object. The suitability of the light source for digital holography is demonstrated with contouring of stationary objects and the potential for high-speed applications is indicated. PACS 42.40.-i; 42.60.By     

Direct object-shape comparison by light-in-flight speckle interferometry

A method is proposed for direct optical comparison of the three-dimensional shapes of objects by light-in-flight speckle holography. The basic idea of this technique is to use an ultrashort laser pulse with a short coherence length to produce interference patterns that present a single contouring of the object. A simple experiment using plane diffuse objects was performed to verify the method.     

Essay Review-Scholarly froth and engineering skeletons

Holography is a two-stage process of photography using coherent light from a laser to illuminate the scene. In the first stage a hologram is formed by combining the light scattered from the object and the direct laser beam on a photographic plate. In the second stage a three-dimensional image is reconstructed without the use of lenses, by directing the laser beam through the hologram. Applications of holography include information storage, recording of images in depth, the use of holograms as optical elements, and as a means of performing precise interferometric measurements on three-dimensional objects of any shape and surface finish.     

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.