Electro-Optic Holography System For Vibration Analysis And Nondestructive Testing
01 Dec 1987-Optical Engineering (International Society for Optics and Photonics)-Vol. 26, Iss: 12, pp 1234-1239
TL;DR: In this article, a TV system was developed for detecting and displaying a two-dimensional hologram image that permits concomitant (real-time) hologram interferometry, where a uniform reference field interferes at zero offset angle with a speckled image of an object.
Abstract: A TV system has been developed for detecting and displaying a two-dimensional hologram image that permits concomitant (real-time) hologram interferometry The optics employed are the same as for electronic speckle pattern interferometry (ESPI), wherein a uniform reference field interferes at zero offset angle with a speckled image of an object Rather than detecting spatial modulation to indicate interference, as in ESPI, this system modulates the phase of the reference beam by 120° between picture frames to vary speckle irradiance Each incoming frame is compared with the two previous frames, and only pixels that vary in brightness are passed as white pixels in the video output The use of binary-valued pixels allows inexpensive data processing at standard video rates
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TL;DR: The principles and major applications of digital recording and numerical reconstruction of holograms (digital holography) are described, which are applied to measure shape and surface deformation of opaque bodies and refractive index fields within transparent media.
Abstract: This article describes the principles and major applications of digital recording and numerical reconstruction of holograms (digital holography). Digital holography became feasible since charged coupled devices (CCDs) with suitable numbers and sizes of pixels and computers with sufficient speed became available. The Fresnel or Fourier holograms are recorded directly by the CCD and stored digitally. No film material involving wet-chemical or other processing is necessary. The reconstruction of the wavefield, which is done optically by illumination of a hologram, is performed by numerical methods. The numerical reconstruction process is based on the Fresnel–Kirchhoff integral, which describes the diffraction of the reconstructing wave at the micro-structure of the hologram. In the numerical reconstruction process not only the intensity, but also the phase distribution of the stored wavefield can be computed from the digital hologram. This offers new possibilities for a variety of applications. Digital holography is applied to measure shape and surface deformation of opaque bodies and refractive index fields within transparent media. Further applications are imaging and microscopy, where it is advantageous to refocus the area under investigation by numerical methods.
1,171 citations
01 Jan 1994
TL;DR: Quantitative data can be extracted from holographic interference fringes using Phase-Measurement Interferometry (PMI) techniques using spatial and temporal techniques, which process the data analytically on a point-by-point basis.
Abstract: Quantitative data can be extracted from holographic interference fringes using Phase-Measurement Interferometry (PMI) techniques. These techniques are used to determine the phase of the secondary interference fringe pattern and can be divided broadly into spatial and temporal techniques. Temporal techniques introduce a known phase shift between the object and reference beams in an interferometer and take a series of data over time as the phase shift is varied. Spatial techniques rely on encoding the phase shift information spatially in a single interferogram by using a large number of fringes as a carrier for the phase information which are generated by tilting the reference wavefront relative to the test wave front. Temporal techniques which process data in electronics are known as heterodyne techniques and were discussed in the last chapter. The processing of spatial phase-measurement data will be discussed in the next chapter. Temporal techniques which process the data analytically on a point-by-point basis will be the concentration of this chapter.
87 citations
TL;DR: A technique for nondestructive testing based on phase shifting TV holography and digital image processing is presented, which calculates the phase modulation of the object light caused by object deformation and smoothed the resulting deformation phase image to obtain a better signal-to-noise ratio.
Abstract: We present a technique for nondestructive testing based on phase shifting TV holography and digital image processing With this technique we calculate the phase modulation of the object light caused by object deformation The resulting deformation phase image is smoothed to obtain a better signal-to-noise ratio Smoothing is done by a new low pass filtering procedure we call phase shifting convolution This procedure is based on smoothing of two phase images: the original phase image and a second image obtained by spatial phase shift of the original phase image By combining the two smoothed images we obtain an image without smoothing errors close to the 2π phase ambiguities in the deformation phase image To detect surface areas with local inhomogeneous deformations indicating material defects, we calculate and display the deformation phase gradients Examples with testing of composite materials are shown
69 citations
TL;DR: Two methods for vibration measurement are presented, based on phase shifting TV-holography and digital image processing, developed to optimize fringe contrast and quality.
61 citations
TL;DR: A unique, compact, and versatile state-of-the-art fiber-optic- based optoelectronic holography (OEH) methodology is described, which has the capability to export the measure- ments data directly into CAD environments for subsequent processing, analysis, and definition of CAD/CAE models.
Abstract: Characterization of surface shape and deformation is of pri- mary importance in a number of testing and metrology applications re- lated to the functionality, performance, and integrity of components. In this paper, a unique, compact, and versatile state-of-the-art fiber-optic- based optoelectronic holography (OEH) methodology is described. This description addresses apparatus and analysis algorithms, especially de- veloped to perform measurements of both absolute surface shape and deformation. The OEH can be arranged in multiple configurations, which include the three-camera, three-illumination, and in-plane speckle corre- lation setups. With the OEH apparatus and analysis algorithms, absolute shape measurements can be made, using present setup, with a spatial resolution and accuracy of better than 30 and 10 mm, respectively, for volumes characterized by a 300-mm length. Optimizing the experimental setup and incorporating equipment, as it becomes available, having su- perior capabilities to the ones utilized in the present investigations can further increase resolution and accuracy in the measurements. The par- ticular feature of this methodology is its capability to export the measure- ments data directly into CAD environments for subsequent processing, analysis, and definition of CAD/CAE models. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)02601-5)
50 citations
References
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TL;DR: One application of phase-shifting techniques to speckle interferometry is finding the phase of deformations, where up to ten waves of wavefront deformation can easily be measured.
Abstract: Speckle patterns have high frequency phase data, which make it difficult to find the absolute phase of a single speckle pattern; however, the phase of the difference between two correlated speckle patterns can be determined. This is done by applying phase-shifting techniques to speckle interferometry, which will quantitatively determine the phase of double-exposure speckle measurements. The technique uses computer control to take data and calculate phase without an intermediate recording step. The randomness of the speckle causes noisy data points which are removed by data processing routines. One application of this technique is finding the phase of deformations, where up to ten waves of wavefront deformation can easily be measured. Results of deformations caused by tilt of a metal plate and a disbond in a honeycomb structure brazed to an aluminum plate are shown.
740 citations
TL;DR: In this article, the Lougborough group in England, headed by Butters and Leendertz, viewed the technique more as an off-spring of their speckle work and they also introduced the name ESPI as an abbreviation for electronic specckle pattern interferometry.
Abstract: Historically, the concept of replacing the photographic emulsion by video recording and display occured to several independent groups almost simultanously. Macovsky(1) in USA, Schwomma(2) in Austria and Kopf(3) in West-Germany considered the technique to be based on pure holography. The Lougborough group in England, headed by Butters and Leendertz(4) viewed the technique more as an off-spring of their speckle work and they also introduced the name ESPI as an abbreviation for electronic speckle pattern interferometry. Although the ESPI-name might be considered appropriately descriptive, its association with coarse, annoying speckles has undoubtedly hampered the general acceptance of the technique. Video holography might be a name with better sales appeal, but might be confused with techniques for direct transmission of three-dimensional holographic images(5).
139 citations
12 Jun 1985
TL;DR: In this paper, a number of experiments in vibration analysis are discussed where different methods like hologram interferometry, impact testing, acoustical recording, FEM-calculations are compared to results obtained by means of an instrument based on image-plane, time-average hologram recording on a TV-vidicon like ESPI.
Abstract: A number of experiments in vibration analysis are discussed where different methods like hologram interferometry, impact testing, acoustical recording, FEM-calculations are compared to results obtained by means of an instrument based on image-plane, time-average hologram recording on a TV-vidicon like ESPI (electronic speckle pattern interferometry) The instrument, "VibraVision", offers distinct advantages in vibration studies
6 citations