Holographic Plate Research Articles

Holographic inspection of plates with regions of local thinning as defects

This paper describes the use of double-exposure holography on the detection and assessment of plates containing locally thinned regions as artificial defects. The artificial defect is programmed by thinning locally a plate to various depths with a milling cutter. During testing, the plate, illuminated by an expanded laser beam, is clamped along its periphery and an incremental uniform pressure applied between two exposures on the holographic plate. Local thinning is revealed from anomaly in the reconstructed fringe pattern—the boundary of the anomalous fringes is larger than the boundary of the actual artificial defect, and the amount of thinning is deduced from the number of fringes within the boundary. Artificial defects with eccentric local thinning are more readily revealed from the reconstructed fringe pattern than the artificial centric defects. A simple theoretical model is developed so that when the experimental fringe-counts are compared with the theoretical ones, any discrepancy between them reveals not only the presence of centric and eccentric artificial flaws but also their sizes and depths.

All white-light process for pseudocolor encoding of depth information

A new and simple optical method for encoding depth information is proposed which is based on the localization of interference fringes phenomenon. In this process the various depths of a 3D object are codified by means of interference fringes with different orientations. The recording of the fringes on a holographic plate allows a subsequent decoding step in which each orientation is pseudocolored with a different color, thus the result obtained is the conversion of depth information into pseudocolor. The whole process is performed with white-light illumination thus the drawbacks introduced by a coherent process are avoided. Experimental results are shown.

Object, Image, Space and Light: Paula Dawson's Artwork 1974-1990

Paula Dawson's holographic artwork entices the viewer and confounds critics with a complex web of meanings. Her work demonstrates an absorption with technical experimentation and plays with notions of art and the role of the artist. She explores aspects of the unique characteristics of holography as well as broader concepts related to her own experiences and ways of seeing. Her sense of humour and energy are apparent in everything she creates. Dawson exhibited her first holograms in 1974 [1]. One of these, Toy Boat, comprised technical descriptions of a hologram juxtaposed with a holographic plate that seemed to merely present stains from poor developing. Although a laser was directed at the plate, its beam was not diffused and so no image was visible. The work played on a characteristic approach of hologram viewers that fascinated Dawson,

Pulsed holographic vibration analysis on high-speed rotating objects: fringe formation, recording techniques, and practical applications

The pulsed laser holographic vibration analysis on high-speed rotating structures presents several difficulties due to the rotational movement of the object between the two laser pulses recording the holographic interferogram. Apart from the vibrational motion, the recorded holographic fringes can be additionally modulated due to the object's rotary motion. Beyond small angles of rotation, a decorrelation of the recorded object waves occurs, preventing the formation of high-visibility interference fringes. To overcome these effects, different holographic recording techniques were used, including an interferometer in which both the reference wave and the holographic recording plate are rotated simultaneously in relation to the object and an interferometer incorporating an image derotator. Conditions for the practical application of these experiments are outlined, and examples of vibrational studies of high-speed rotating components, i.e. , cantilever beams, disks, cooling fans, and radial impellers, are presented. The radial impeller vibration investigation was done on a compressor test facility up to object speeds of more than 13,000 rpm, corresponding to a circumferential speed of approximately 200 m/s.

A Toast to Nick Phillips

dramatic increases in brightness could be achieved. What is most remarkable about this process, and a tribute to Phillips's genius, is that conventional photographic wisdom would dictate that this type of system should not work! Holographic plates initially contain a homogenous distribution of silver-bromide grains, and if all the developed silver were changed back into its original form, the plate would regain its virgin condition. In this condition, there would be no modulation of the incoming reconstructing light, since there would be nothing to differentiate where a bright fringe had been and where the dim ones had been. In reality, this process works really well, and the theory is that the developed grains migrate into the dim fringe areas as they are being rehalogenated. The bright fringe areas are represented by pure gelatin, and the dim fringe areas contain silver bromide, but the increase in modulable material in those areas increases efficiency. Since nothing leaves the emulsion-its elements are merely rearranged-the original thickness of the emulsion layer is preserved along with the spacing of the fringes during recording, so that it is possible not only to replay a reflection hologram with the laser that made it but to replace the hologram onto the object and generate real-time interferometric fringes with it. At first I doubted that this migration-diffusion mechanism would work, but its effectiveness was proven to me when I was making some extremely low frequency gratings. Ed Wesly (researcher, educator, artist), Center for Photonics Studies, Lake Forest College, 555 North Sheridan Road, Lake Forest, IL 60045, U.S.A., and the School of the Art Institute of Chicago, 280 South Columbus Drive, Chicago, IL 60603, U.S.A. Received 22 Febrtuary 1991. LEONARDO, Vol. 25, No. 5, pp. 439-442, 1992 439 This content downloaded from 207.46.13.169 on Mon, 04 Jul 2016 04:13:41 UTC All use subject to http://about.jstor.org/terms

One-step, full-view rainbow holograms with conventional plates of 6 μm emulsion

A method of one-step full-view rainbow holography using conventional holographic plates of 6 °m emulsion as recording materials is described aand experimentally demonstrated. The requirement for the inter-beam angle to avoid cross-talk between two images is discussed. The simplicity and low cost of this method make it particularly suitable for the full-view white light holographic display of moderate-sized objects.

Reconstruction of sequential cardiac in-plane displacement patterns on the chest wall by laser speckle interferometry

Time-average speckle interferometry has been applied to obtain displacement patterns on the chest wall produced by cardiac action, in the absence of breathing, during various phases of the cardiac cycle. This has been achieved by an electronic shutter, controlled by the electrocardiogram of the subject. The recorded holographic plates processed under identical conditions are scanned by the pointwise method to obtain the absolute displacements at various locations corresponding to the activities of the various cardiac chambers and values. These data are transformed to a 40 x 30 matrix by an interpolation method and, from this, three-dimensional displacement plots are reconstructed by an IBM PC/AT computer. These patterns shown the displacements over the entire cardiac area corresponding to the activities of various regions during the cardiac cycle. The apex and aortic valve areas show the maximum displacements during the systolic phase. During the diastolic phase the activities over the low pressure atrial regions are also observed. The results obtained outline the functional details of the normal heart and the activities over various areas are in agreement with that of other noncontact techniques.

Improvement in high-speed, large-area, multiple-exposure holography

The method of encoding more than one large-area hologram on a single recording medium by changing the angle between the object beam and the reference beam between successive exposures is well established. We report an extension of this technique to record over 16 individual large-area holograms on a single emulsion plate by taking advantage of the characteristics inherent in a solution physical developer. The tests were carried out on 8E75-HD holographic plates with a short-pulse ruby laser for high-speed recording. Multiple-image-plane doubled-exposure holographic interferograms were also obtained, and the results are presented.

Practical system for time-resolved holographic interferometry

An easily implemented and easily manageable system for timeresolved holographic interferometry is presented. The system consists of a multiple-pulsed <i>Q</i>-switched ruby laser and a rotating disk having radial slits with a constant angular separation. The disk is used to scan the reference beam along a holographic plate, thereby achieving spatial multiplexing. Since the influence on the beam is negligible and a single slit is illuminated by every laser pulse, there is no need for synchronization. The interferometric pattern is achieved by removing the disk and exposing a reference image on the holographic plate. The system may serve as an excellent tool for full-field dynamic measurements. A simple experiment has been performed showing a sequence of momentary interference patterns on a vibrating plate.

Mixed mode crack propagation in quasi-brittle materials

Crack propagation in rectangular blocks of mortar containing a central notch and subjected to uniaxial compression were studied. Four different notch orientation angles (18°, 36°, 54° and 72°) with respect to the loading direction were used. Holographic Interferometry was used to observe crack initiation and propagation. It was possible to detect crack extensions during the experiments, hence the load vs crack extension curve for each notch orientation angles could be obtained. A separate Holographic Interferometry method was used to measure crack opening and sliding displacements by making four independent observations of holographic fringes from the same holographic plate. Crack initiation theories were employed to study their relative merits for predicting crack initiation angles and loads. A Finite Element Method (FEM) using quarter point singular crack tip element was used to calculate Stress Intensity Factors (SIF) and crack surface displacements for different inclinations and extensions of the propagating cracks. It was found that while crack initiation was predicted well by some of the theories, it was necessary to account for the traction forces on the crack surface before any propagation criterion could be identified. Opening and sliding of the crack faces determined by Holographic Interferometry (HI) and clip gage measurements were used to find the normal and shear traction applied to the propagating crack faces. The SIFs for the traction free cracks were corrected by taking into account normal and shear tractions along the propagating crack. It was concluded that the Maximum Hoop Stress Criterion was reasonable and K I stress intensity factor at the tip of the propagating crack was dominant in the failure mechanism.

Fabrication of holographic microlenses using a deep UV lithographed zone plate

Holographic microlens arrays and elliptical zone plates are fabricated on holographic plates and photoresists by interference between the first- and second-order diffracted waves from an ion etched Fresnel zone plate, which is made by electron-beam scanning and deep UV lithography. This method of fabrication is simple, and a holographic lens with a large numerical aperture and short focal length is obtained. Experimental results of focusing and imaging by a lens array and an elliptical zone plate are given. Two methods of fabricating holographic zone plates for an IR or UV wavelength are also proposed.

Digital holographic interferometry in flow research

A plane-wave holographic interferometric set-up for the quantitative determination of the density distribution existing in the flow field around arbitrarily shaped objects using digital image-processing is presented. By utilizing two reference/reconstruction beams, generated by a slightly misaligned Twyman-Green (T-G) interferometer in the reference/reconstruction beam path, the wavelength used to reconstruct the holographic plate is allowed to differ from the recording wavelength. To obtain again an infinite fringe pattern after such wavelength change, one of the two mirrors constituting the T-G interferometer is slightly rotated. Phase-stepped interferograms are generated successively by piezo-electrically translating the other mirror of the T-G interferometer. Overlapping cross reconstructions, which are inherently induced in such a set-up, are eliminated by a spatial filter in the focus generated by the imaging lens. By applying plane traversing waves instead of diffuse light, automatic distinction between the foreground pixels (i.e., the pixels not lying in the shadow of the object) and the background pixels is made, starting from the modulation intensity as a discriminating parameter. The above procedure is demonstrated by measuring the density distribution in an axisymmetric supersonic jet of air.

Holographic quarterwave plates

Quarterwave plates can be made as holographic gratings in positive photoresist. We studied the effect of the grating period and relief depth on the phase retardation and on the rotation of the polarization of the transmitted light. Experiments were performed with gratings of different periods, which also exhibit an antireflection property.

Recording the behaviour of an avian embryo using holography

A novel application of holographic interferometry to study the development of behaviour of an avian embryo in an intact incubating egg is reported. A holographic system is implanted astribe both the interior and exterior of the incubator. The observation of the movements of the embryo is obtained in the form of the evolution of fringes in real-time by means of a vidicon camera placed behind the holographic plate. Besides being useful in the study of the pre-natal motility cycle, the method allows one to follow the development of specific behaviour patterns, their onset, duration and frequency of repetition. The steady development of the intense movements leading to the first cracking of the shell is vividly displayed. Preliminary results confirming the experimental viability of the proposed application are presented.

Digital phase-stepping holographic interferometry in measuring 2-D density fields

This paper presents a holographic interferometer technique for measuring transparent (2-D or quasi 2-D) density fields. To be able to study the realization of such a field at a certain moment of time, the field is “frozen” on a holographic plate. During the reconstruction of the density field from the hologram the length of the path traversed by the reconstruction beam is diminished in equal steps by applying a computer controlled voltage to a piezo-electric crystal that translates a mirror. Four phase-stepped interferograms resulting from this pathlength variation are digitized and serve as input to an algorithm for computing the phase surface. The method is illustrated by measuring the basically 2-D density field existing around a heated horizontal cylinder in free convection.

Measurement of mixed-mode crack profiles by holographic interferometry

Holographic interferometry was used to study the mixed-mode fracture characteristics of mortar. The nature of crack propagation in such quasibrittle materials and the theoretical model used to interpret the experimental results indicated that a highly sensitive measurement technique was required. The gradual curvature of the propagating crack at different sections of the specimen necessitated full-field observation capability. The nature of the problem made holographic interferometry the ideal technique for this application. To measure the in-plane components of the opening and sliding of the crack surfaces during propagation, a single holographic plate was placed very close to the specimen. This allowed four independent observations of any point on the specimen from the four corners of the plate without any need for additional optics of exposures. Double-exposure holograms were made at different crack-propagation stages. The developed plate was illuminated by an unexpanded reference beam to form a real image of the object and observe displacement fringes. Fringe data were interpreted by using computer software written for this research.

Optical holographic characterization of a radio ear bone vibrator

Bone vibrators are driven by an electrodynamic transducer that is suspended from the upper portion of the vibrator's case; while the lower portion of the case is mounted on the area above the subject's mastoid. As a result, the structural response of the vibrator's case plays an important role in the overall transfer function from the electrical input to the mastoid input. Holographic investigations of the case mode shapes at resonances up to 5 kHz were performed to supply data for input into a semiempirical model of the bone vibrator. Optical holography was chosen since the small size and mass of this transducer precluded any type of measurement that involved contact. Measurements were performed for both hard mounting of the bone vibrator and with the bone vibrator mounted on a Beltone model MB5 artificial mastoid. Time-averaged holograms of the case resonances were recorded on a thermoplastic holographic plate and transformed into digital images in a microcomputer-based image processing system. They were then analyzed to determine the details of the vibrations.

Holographic analysis of the deformation of a diesel engine piston

Holography has been used to measure the deformation of a diesel-engine piston heated through a low temperature rise in order to confirm the finite-element modeling of an isoformic piston being developed by Wellworthy Ltd. Previous work relating to the study indicated that a body movement had occurred on the piston and one of the main features of the current study was to measure the absolute movement at diametrically opposite positions on the piston. A single holographic plate was used for this purpose and produced the required results which, when averaged, compare favorably with finite-element results.

Magnification effect and color blur behavior in holography

This paper describes the spatial behavior of the hologram image as a function of the geometric setup used in the recording and reconstruction steps. Given the equation of the holographic image and using paraxial theory and the synthetic division method, values of the longitudinal and lateral magnification are obtained. The location and magnification of the holographic image are found when the distance between the holographic plate and the object is changed. For white light reconstruction and 3-D scenes the effect of color blur can be expressed in terms of the parameters associated with the optical system that forms the image on the hologram and the recording geometry.

Polarized shearing holographic-moirè interferometry

A new holographic-moire method is presented to obtain the in-plane strain fringe patterns. During the recording, double object beams and dual reference beams of orthogonally polarized state are used to illuminate the object and the holographic plate, respectively. Two carriers modulated by deformation are obtained through double-exposure or in real time. Pure in-plane displacement derivative patterns are then obtained through twice filtering.