Holography and its application to acoustic imaging

This paper briefly reviews some aspects of holography and its application to acoustic imaging with an emphasis on concept. Included age discussions of the identity of holography, the principle of optical holography, holography applied to the acoustic domain and holography by linear detection, the applications of optical and acoustic holography, the concept and front-end embodiment of acoustic imaging systems that can be considered holographic, and the limitations of acoustic holography. This paper is intended to be tutorial and to provide discussions on relevant topics not covered by other papers in this issue on the subject of holography.     

Acoustic imaging and holography

Applications of active and passive devices employing the characteristics of sound to obtain results have been known to investigators for many years. However, in addition to these sonar or pulse-echo methods of analysis, there exist a variety of techniques in which a sound image is obtained in a way more analogous to optics. This analogy has, in the last few years, been extended to include holographic techniques, and has led to the inception of a new discipline?acoustic holography. In this article, we trace the development of this new field as it originated from a fusion between ``conventional' acoustic imaging and optical holography; and we see how, in the few years of its existence, it has already generated its own unique methods and problems.     

利用声全息方法实现自由场局部有源噪声控制

对声全息技术进行了研究,提出将声全息技术应用在近场误差策略的自由空间局部有源噪声控制中。主要从理论出发对此方法进行了推导论证,证明了方法的可行性,并提出了实现中可能遇到的一些问题,最后以点声源为例,应用声全息的方法对自由场有源噪声控制进行了仿真实验,结果表明,利用声全息实现自由场局部有源噪声控制的方法是一种有效的局部噪声控制方法。     

基于平滑l_0范数的压缩感知近场声全息方法

传统平面近场声全息(CPNAH)是一类典型的不适定问题,采用波数域滤波或Tikhonov正则化等方法都无法彻底解决,因此,提出一种基于平滑l_0范数的压缩感知平面近场声全息法(SL0-CS-PNAH)。根据全息面上测量声压的特点,采用symlets8小波函数构建正交小波变换矩阵,将其作为重建面质点法向振速的稀疏基。将CPNAH中使用的瑞利(Rayleigh)第一积分公式离散化,确定SL0-CS-PNAH中满足约束等距原则的测量矩阵,设置合适的压缩比,利用测量矩阵对稀疏信号进行压缩采样。在由感知矩阵、全息面测量声压和稀疏向量共同构成的约束条件下,建立稀疏向量的最小l_0范数优化模型,采用平滑l_0范数重建算法求解此模型下的最优化问题,得到质点法向振速的最优稀疏解,再将最优稀疏解和稀疏基相乘恢复重建面质点法向振速。在数值仿真实验中,将测量点由64×64减少到32×64的情况下将传统CPNAH、基于正交匹配追踪算法的压缩感知近场声全息(OMPCS-PNAH)、基于子空间追踪算法的压缩感知近场声全息(SP-CS-PNAH)和SL0-CS-PNAH进行比较。实验结果表明,在相同采样率和压缩比条件下,采用SL0-CS-PNAH的声场重建质量较好且重建效率较高。     

太赫兹数字全息成像的研究进展

随着太赫兹成像技术的发展,人们对太赫兹成像系统的成像性能如分辨率、成像速率、成像维度等均提出了越来越高的要求。为了消除衍射对太赫兹成像的影响,提高太赫兹成像系统所能达到的性能指标,许多学者已针对太赫兹数字全息技术进行了研究。首先对太赫兹数字全息的基本原理进行了概述,阐述并分析了目前国内外有关太赫兹数字全息成像的研究进展,这些研究显示太赫兹数字全息技术在提高成像分辨率、扩展成像维度等方面具有很大的发展潜力,且具备实时成像的能力,具有十分广阔的应用及发展前景。     

全息技术在散射成像领域中的研究及应用进展（特邀）

散射是光学成像中普遍存在的现象,成像路径中存在的烟雾、水体、生物组织等散射介质导致光束发生随机散射效应,使得像面处目标信息以杂乱无章的散斑形式存在,如何应对散射介质对成像的限制是当前光学成像领域的研究热点。全息技术能够记录和重建物体全部信息,是获取和解译光场信息的有力工具之一。近年来,传统全息以及相关全息理论被推广应用至散射成像领域,取得了一系列突破性成果,文中主要介绍与归纳了散射成像领域中应用全息技术的理论原理、发展历史及最新进展,并展望其发展前景。     

连续太赫兹波合成孔径数字全息成像方法

太赫兹波数字全息成像技术结合了太赫兹成像技术和数字全息成像技术的优势,是一种新型相衬成像技术,具有光源相干性要求低、光路结构简单、实时定量获取物光波复振幅信息等特点,非常适用于太赫兹波段成像。影响数字全息成像技术分辨力的因素有多种,其中一个主要因素是探测器靶面尺寸的大小,因此,提出合成孔径方法扩大探测器靶面尺寸,提高太赫兹数字全息的成像分辨力。文中搭建了连续太赫兹波同轴数字全息成像装置,获取了样品高质量、高分辨力的振幅和相衬图像。实验结果有效说明了合成孔径方法可以提高太赫兹数字全息成像分辨力。     

声场全息重构方法与实验研究

声场全息重构是通过近场声全息重构声源的声辐射特性的一种声场反演方法,是近年来的研究热点问题.基于近场声全息声场重构模型,研究声场全息重构方法;再运用LabVIEW虚拟仪器软件平台,开展了传声器阵列各通道标定校准、数据采集、全息面复声压的获取和声场可视化等声场全息重构实验研究.实验结果表明,声场全息重构实验具有较高的定位精度,同时也验证了声场全息重构方法的有效性和实用性.     

Phase-only acoustic holography

A simple system for producing acoustic holograms is described, which linearly records only the phase of the object wave rather than both the phase and the amplitude, as in conventional holography. An example of a phase-only acoustic hologram and its optical reconstruction is included.     

Three-Dimensional Imaging and Processing Using Computational Holographic Imaging

Digital holography is a technique that permits digital capture of holograms and subsequent processing on a digital computer. This paper reviews various applications of this technique. The presented applications cover three-dimensional (3-D) imaging as well as several associated problems. For the case of 3-D imaging, optical and digital methods to reconstruct and visualize the recorded objects are described. In addition, techniques to compress and encrypt 3-D information in the form of digital holograms are presented. Lastly, 3-D pattern recognition applications of digital holography are discussed. The described techniques constitute a comprehensive approach to 3-D imaging and processing.     

透过高散射介质成像的超短脉冲激光电子学全息系统

分析了超短脉冲激光透过高散射介质的电子学全息成像原理;编制了数字再现和图像处理软件;结合ＣＣＤ摄像机、图像采集处理机,建立了一套完整的适于透过高散射介质成像的电子学全息系统;给出了实验结果,实验证明系统是可行的。     

Surface-wave nondestructive testing using 1-dimensional acoustic holography

A new method of surface nondestructive testing using 1-dimensional acoustic holography has been demonstrated. A simulated defect 0.5 mm in diameter and 1 ?m thick has been clearly resolved using 60 MHz acoustic surface waves, propagating along a quartz substrate.     

Optical scanning holography

This paper provides a tutorial on the principles of holography, followed by a review of a newly developed 3-D imaging technique in which 3-D optical information of an object cam be extracted by a 2-D optical scan of the object. The technique is called optical scanning holography (OSH). In the context of optical scanning holography, we discuss some of its potential applications such as holographic information transmission and television (TV) system, 3-D image coding and decoding, 3-D microscopy, and 3-D optical remote sensing. In most cases, feasibility has been proven but awaits broader application     

Seismic imaging by holography

During the last half century, seismic imaging techniques have seen steady improvements. With the recent advent of relatively cheap and readily available computers, many complicated algoriths for obtaining seismic images that were formerly only theoretical curiosities can now be implemented. This paper reports on the applications of yet another imaging technique, namely holography, with particular emphasis on Fourier transform holography. A variety of laboratory, field, and computer experiments ate described together with several anticipated practical applications, and it is shown among other things that certain image enhancement techniques based on holography can significanfly improve siesmic images and image-related data.     

An approach to radar imaging using the spherical projection density concept*

High resolution radar imaging is used to perform target signature analysis. In this paper, we present a comparative study of diverse 2- D imaging methods on spherical waves, such as sar processing and its modes, ssar and isar as well as holography, whose mathematical formulation is identical by using the spherical projection density function, although the measurement technique are quite different. We show that azimuth processing is unified, and under some conditions range processing can be unified. In order to reconstruct the fixed target side looking radar image, we have developed an idea based on the transformation of antenna lateral displacement as a function of equivalent angular displacement, and then the 1- D images coherent summation algorithm of classical holography can be used.     

同轴数字全息自动聚焦与再现像的融合

由于数字全息采用相干光成像,当再现距离偏离焦点时,再现像的边缘会出现振荡现象,采用传统的清晰度评价函数不能准确实现自动聚焦。通过对再现像进行小波分析可以发现,偏离焦点时的小波变换高频系数的幅值比聚焦时要小得多。针对这一特点,对拉普拉斯算子和小波变换清晰度评价函数进行了改进,将原来利用高频系数之和改为利用聚焦窗口中高频系数的最大幅值为清晰度评价依据。为便于同时观察到数字全息三维空间内的目标,还提出了将不同层面上的再现像进行融合的算法。进行了模拟数字全息自动聚焦及再现像融合实验和用数字全息观察生物标本的实验。实验结果表明,改进后的清晰度评价函数可以准确实现数字全息的自动聚焦;提出的融合算法可以将数字全息再现后得到的一系列再现像融合到一幅图片中。     

Research on Reconstruction Algorithms in 2.52 THz Off–axis Digital Holography

To eliminate the diffraction effect on Terahertz (THz) imaging and improve imaging system performance, digital holography has been investigated. The size of the common THz digital hologram and the recording distance are in the same order of magnitude, which does not satisfy the Fresnel approximation conditions. Meanwhile, diffraction has a great impact on free–space propagation behavior. So the research of the influence on reconstruction performance with different reconstruction algorithms is necessary. In this paper, the numerical simulations of the recording and reconstruction process of 2.52 THz off–axis digital holography imaging have been done, and the reconstruction performances of Fresnel angular spectrum algorithm, Rayleigh–Sommerfeld convolution algorithm and angular spectrum algorithm have been compared and analyzed as the reconstruction reference wave is different. The real experimental reconstruction results have also been presented.     

飞秒全息术

介绍了飞秒全息的分类、工作原理和进展，讨论了飞秒全息的实验要求和分辨率。对飞秒全息术在光信息处理、成像技术和微加工技术等方面的应用进行了详细介绍。     

An introduction to the principles and applications of holography

Holography has strong historical ties with electrical engineering and potential application to many electrical engineering problems. The basic problem addressed by holography is introduced in both physical and mathematical terms. The analogy between the hologram of a point-source object and the linear FM signals of chirp radar is stressed, and the first-order imaging properties of holograms recorded in arbitrary geometries are derived. Various types of holograms are described, including thin, thick, transmission, reflection, amplitude, and phase holograms. The important properties of each type of hologram are introduced. A survey of various applications of holography is presented, with introductions to the use of holography in interferometry, microscopy, imaging through distorting media, optical data processing, and optical data storage. The use of simple holograms as optical elements is also described.     

基于波叠加法的近场声全息重建参数选取研究

基于波叠加法近场声全息的基本原理,分析了使用波叠加法进行声场重建时结果不准确的原因。研究了重建距离、重建频率、等效源的数目、等效源的半径及信噪比等参数变化对重建精度的影响。研究结果表明,与空间傅里叶变换法的平面近场声全息相比,波叠加法近场声全息拓展了重建距离的适用范围;波叠加法近场声全息对5 kHz以下声源的重建效果较好;等效源半径最好选为辐射体半径的0.8倍以下。