The holographic interferometry will be starting out the next decade with an anniversary: 1990 it will be 25 years ago since Stetson und Powell first published their utilization of the new technology for vibration analysis /0/. The new testing method quickly gained interest for the use in both industry and research. Holographic inferometry was proposed for applications such as construction optimization, damage analysis and non-destructive testing. Back then, the author of this report pointed out four main application areas which are still of the most interest today /1/: - non-destructive testing of materials and parts- static and dynamic construction optimization -measuring outlines and contours -examination of transparent materials and mediums A whole range of solutions for industrial applications were found, some of which, although slightly modified, are still in use today. For example: tire testing is a recognized testing procedure, fig.1; damage analysis has been developed by SchOnebeck to a standard practice for turbines /2/; Felske and Happe used vibration analysis to study noise sources /3/ and Brown used holographic interferometry to solve problems connected with the construction of automobiles /4/. But still these advances, which were more or less the results of pioneer work, could not be considered the real practical break-through. This was due to the fact that time was technically not yet ripe for holographic interferometry. At that time almost none of the components were available or even existed which now are obvious parts of any professional set-up. CCD-cameras could not be conceived yet, large computer systems did not even have the power of a modern day home computer and the optical components which were needed were just starting to be developed. Because of these problems, holographic interferometry was more or less restricted to research labratories There slowly but constantly fundamental advances were made which later opened up the wide range of areas in which holographic interferometry can be used now.

Optical sensors have the intrinsic advantages over electronic sensors of complete safety in hazardous areas and absolute immunity from both transmitting or picking up electromagnetic radiation. However, adoption of optical sensors in real-world applications requires a sensor design which has a sensitivity, resolution, and dynamic range comparable to an equivalent electronic sensor and at the same time must fulfill the practical considerations of small size and low cost. While sensitivity, resolution and dynamic range can be easily achieved with optical heterodyne sensors, the practical considerations make their near-term adoption unlikely. Significant improvements to optical heterodyne vibration and velocity sensors (flexibility, reliability and environmental immunity) have been realized with the use of semiconductor lasers, optical fibers and fiber-optic components. In fact, all of the discrete optical components in a heterodyne interferometer have been replaced with much smaller and more rugged devices except for the optical frequency shifter, acousto-optic modulator (AOM). The AOM and associated power supply, however, account for a substantial portion of both the size and cost. Previous work has shown that an integrated-optic, serrodyne phase modulator with an inexpensive drive circuit can be used for single sideband heterodyne detection. This paper describes the next step, design and implementation of a heterodyne interferometer using integrated-Optic technology to provide the polarization maintaining couplers and phase modulator. The couplers were made using a proton exchange process which produced devices with an extinction ratio of better than 40 dB. The serrodyne phase modulator had the advantage over an AOM of being considerably smaller and having a drive power of less than a milliwatt. The results of this work show that this technology is an effective way of reducing the size of the system and the cost of multiple units without sacarifying performance.

This device utilizes single mode polarization maintaining optical fibers to generate the pair of laser beams required by diffraction moire interferometry. Design of the device permits extremely rapid and convenient setup for measurement of in-plane displacement distributions on the surfaces of specimens. The device, applications, and typical data are described.

Currently, high spatial density/high resolution data bases of the deformation of structures are available using Computer Aided Holometry (CAH) for (1) static deformation, (2) periodic motion and (3) dynamic deformation at widely separated instances of time. However, many practical structures are nonlinear and there exists a need to measure how a surface moves as a function of time. This paper presents a high frame rate, shifted phase video holographic method for measuring surface motion as a function of time. The theory, hardware, simulation results and limitations are discussed.

A system capable of generating several tens of diffraction moire interferograms at rates on the order of 1 MHz is described. The interferometer consists of a specially modified, segmented ruby rod laser capable of producing a long train of 40-mJ pulses each with a width on the order of 20 to 50 ns. The interferograms are recorded on film using a high speed turbine camera capable of 2,000,000 frames per second for a total record of 80 frames. The interferometer is used in conjunction with any of several devices for impulsively loading a variety of materials so as to study dynamic material deformation, fracture, delamination, or other response to dynamic stress. This apparatus is the latest in a series of dynamic diffraction moire systems built at the Idaho National Engineering Laboratory.

A device that provides a very convenient facility for the manufacture of holographic diffraction gratings is described . The system employs single mode polarization maintaining optical fibers and a simple optomechanical design to permit great flexibility in grating manufacture. The intended application of these gratings is diffraction moire interferometry. A variety of gratings ranging from less than 100 to more than 2000 l/mm can be made with minimal time required for changing between grating frequencies. Furthermore, the rational design of the device permits one to easily generate more complex gratings, including crossed gratings, gratings having two or more superimposed groove spatial frequencies, or gratings having other unusual features such as induced aberrations.

This paper describes a technologically advanced version of a multidirectional holographic interferometer (MHOI). A new MHOI set-up with fiber optics is under development in order to decrease the size of the experimental apparatus while maintaining a good optical output. The use of fibers has several advantages such as: more flexible arrangements less optical equipment needed a wide total angle of view same intensities for all object rays. The first step in creating a fiber optics MHOI set-up is to build a monodirectional holographic interferometer. Some tests have already been performed using this innovative optical fiber device providing one-directional holographic interferometry. A new MHOI set-up scheme and expected performances are'presented. In this new scheme six object rays are used to illuminate the sample, and six reference rays record the image on the holographic plate. The spacing between object rays is 30°, and the total view angle is 150° . The aim of this work is the development of a multi-user facility for space experiments. MHOI could be used not only for crystal growth experiments, but also for any experiment involving transparent media in a quasi-equilibrium state.

An electronic holographic computer has been developed that generates both time-average and two exposure holographic interferograms. The interferograms are continuously updated at a rate of 30 frames per second and the image quality can be enhanced with both temporal frame averaging and spatial speckle averaging. The results rival the quality of film holography for resolving interference fringes. The electronic image processor allows immediate enhancement of the resultant images as well as flawless, compact digital storage on magnetic media. Details of the algorithms are given and results are discussed. Two applications of the system are also mentioned and sample images are included.

The experiment results of FFPI with the fineness more than 100 at center wavelenth 0.63um and throughput of 40-50 percent have been achieved.The relations of fineness N and peak transmissonT to coupling loss g and mirror reflecticity R are descussed here.

The use of a laser diode for phase-stepping interferometry is very attractive, because the wavelength can be shifted by changing the injection current. However, several problems have to be overcome if high precision measurements are to be made. This paper analyses some of the sources of error and shows how they can be controlled.

By using a multiphase detection technique, unambiguous shot-noise-limited measurements of unwrapped (i.e. not limited to modulo 21) interferometric phase may be made at data rates in excess of 1 MHz. This technique is ideally suited for use with laser diodes. We describe the technique and associated algorithms which facilitate the rapid processing of data, and we present experimental data obtained with different types of laser diode interferometers--including an imaging interferometer in which phase is digitally measured for each pixel at TV frame rates, and an interferometric linear encoder head which achieves a 1-microinch resolution with a 1250 line/inch linear scale and a 1 MHz update rate.

Optical sensing technology with laser interferometry have been used in industrial metrology. Usually, frequency stabilized lasers have been used for the accurate measurement of length or surface roughness. (1' However, the length reference of the laser inter-ferometer is the wavelength of light, so optical measurements with a frequency stabilized laser have the disadvantage that the error induced by fluctuations in the refractive index of air must be compensated for. A wavelength stabilized optical source with a laser diode( LD ) is proposed for distance measurements, and a compact, precise light source developed using an air-gap etalon as a length reference ( wavelength reference ). (2) A new and simple method to control the wavelength has been devised, and spectral linewidth reduced simultaneously using this method. Important characteristics of the optical source are wavelength stability and narrow spectral linewidth. Experimental results for wavelength stability were 3x10^-9 estimated from the square root of the Allan variance( integration time T is 10 sec ). Experimental results for spectral linewidth were 700KHz( with feedback ) and 10 MHz( free running ). Satisfactory results were obtained for the other characteristics( output power and point stability ).

The sensitivity of laser diodes to small amounts of optical feedback provides the basis for a remarkably simple and versatile tool for interferometric metrology of optical elements and systems. The tool uses a simple optical scanner and phase tracking to analyse wavefronts and is particularly useful for obtaining surface profiles of strongly aspheric mirrors. Surface profiles have been obtained to an accuracy of 100 nm in the presence of extremely high (1011/mm) departures from spherical.

The Fourier-transform method pointwisely determines the interference phase distribution out of a single digitally recorded and stored interference pattern. By using suitable filter parameters in the spatial frequency domain, speckle noise and known as well as unknown background variations can be suppressed. The paper presents a description of the Fourier-transform method, a discussion of the effects of filter parameters like orientation and cutoff-frequencies, and experimental results.

Multidirectional holographic interferometry makes it possible to obtain a three-dimensional concentration distribution by means of a series of interferometric observations along different directions. The aim of this paper is to describe a multidirectional holographic interferometer (MHOI) and to present a mathematical technique for interferometric data processing. The numerical algorithm of reconstruction from projections is the "sine" method used by Sweeney and Vest, modified by a singular values analysis of the problem, for a discrete data collection over a limited range of view angles. In order to prove the effectiveness of the "sine" method, the reconstruction from projections of some a priori known functions, similar to the expected experimental results, has been performed. These computer simulations make it possible to confirm the validity of the chosen algorithm, and yield the information needed for the design of a multidirectional holographic interferometer (MHOI) using a fiber optics system. In particular, tests of the analytical treatment of data extracted by computer simulation have been made in order to assess the optimum view angle, the number of views and the spacing among views in the fiber optics MHOI. This research has been done under ESA sponsorship.

Holography concepts have been evaluated as nonintrusive tools that can measure earthquake effects and earthquake resistance of structures. The methods offer potential for removing limitations currently obstructing the application of advanced design techniques in civil and earthquake engineering. Methods under study can result in a capability to holographically monitor large, distant surfaces such as the face of a building, bridge foundation, liquid storage tank, or dam during interaction with geological or meteorological forces. This work included the successful demonstration that holography could be used to obtain modal information from a 3.4-meter-tall, liquid storage tank at a distance of 20 meters.

Optical whole-field testing techniques have been carrots dangled in front of engineers' noses for a considerable period of time. The promise of acquiring meaningful data without upsetting the component nor its environment, has significant attractions. ESPI technology has been modified and pursued with these goals in mind. This paper presents some of the recent work containing several developments which now make the engineering realisations a near term possibility. An overview of the correlation imaging mechanism is presented with a discussion on how this principle type of optical interferometer can be configured to provide the data necessary for analytical use. Attempts to produce instrumentation able to function outside the laboratory have required replacement of continuous wave lasers with Nd.YAG pulsed lasers. The new pulsed lasers are able to be combined with the computer based fringe pattern analysis which has been produced to suit the requirements of the engineer. Experimental results using such equipment are presented and further work is included which demonstrates the ability for speckle interferometry to produce three-dimensional analysis with the data being presented in conventional cartesian form.

A miniaturized electronic speckle pattern interferometry system (ESPI) has been developed for in situ measurements of microdeformations on buildings and monuments. Direct coupling between object and the compact optical head of the system enabled detection of microdisplacements even in non laboratory environments. Several examples of applications in deterioration investigations are presented.

A setup is presented allowing simultaneous application of ESPI and holographic double exposure interferometry in the study of microdeformations of climatically stressed natural stones. High sensitivity to deformations is obtained by introducing a suited reference fringe system, while high spatial resolution is achieved using the real image for evaluation. Problems of the method are discussed and several example applications to natural stones are described.

A system employing closed-loop phase-stepping is used to measure the out-of-plane deformation of a diffusely reflecting object. Optical fibers are used to provide reference and object beam illumination for a standard two-beam speckle interferom-eter, providing set-up flexibility and ease of alignment. Piezoelectric fiber-stretchers and a phase-measurement/servo system are used to provide highly accurate phase steps. Intensity data is captured with a charge-injection-device camera, and is converted into a phase map using a desktop computer. The closed-loop phase-stepping system provides 90° phase steps which are accurate to 0.02°, greatly improving this system relative to open-loop interferometers. The sys-tem is demonstrated on a speckle interferometer, measuring the rigid-body translation of a diffusely reflecting object with an accuracy of -±100, or roughly ±15 nm. This accuracy is achieved without the use of a pneumatically mounted optics table.

We have improved stability and temporal response of the laser speckle strain gauge. In the gauge a narrow laser beam is incident on a diffuse surface and speckle patterns appearing in the light scattered to certain directions are detected by linear image sensors. The correlator computes the correlation peak between the current frame and a reference one of the sensor which is driven at 1000 frames per second. The reference frame is fixed until the correlation peak becomes lower than a threshold. By employing a pair of the correlators and a laser of output power of a few tens of mW, we could measure dynamic strain of polymer films, between a fraction of Hertz and one hundred Hertz. The resolution of the gauge which only depends on geometry of the optical system and the sensor pitch, is a few tens of microstrains. The upper limit of the measurement can be extended arbitrarily much because small incremental strain is integrated.

A new speckle-shearing interferometric method that allows the cancellation of unknown rigid body displacements in shearography is presented. The technique, referred to as sandwich shearography, combines the advantages of sandwich holography and conventional shearography, to measure displacement derivatives directly. The method involves the recording of two different speckle patterns on separate photographic plates. The plates are then sandwiched together and placed in a Fourier filtering setup, to obtain fringes depicting contours of constant strain. A method to cancel rigid body translations and rotations is described. Experimental verification of the method is presented and discussed.

Speckle patterns can be used as natural surface markings which are printed by high coherence of laser light. Speckle displacement caused by linear or rotary motion of a surface is detected with a linear image sensor whose outputs are analyzed by a correlator. By using an image sensor of the pitch 15 pm and 1024 elements, resolution of a micrometer and 1/1000° have been attained. Main advantages of the encoders are extreme simplicity in optical configurations and wide ranges of measurement.

Speckle interferometry has been used to monitor the change of strain in a hydride blister in a specimen of zirconium pressure tubing used in a nuclear power reactor. The change of in-plane strain due to migration of hydrogen in the heated sample was observed through use of two illumination beams. Day-to-day speckle interferograms were obtained using a computer to control the relative optical phase of the two beams. Good qualitative agreement was found between strain measured in this work and that predicted by a metallurgical model.

An optical velocimeter using a double-exposure specklegram is proposed and studied. In the method, a double-exposure specklegram is used to produce Young's fringes over a probing area, instead of forming the fringes as the result of interference of two beams in the case of a differential-type laser Doppler velocimeter. The method has special advantages over the conventional laser Doppler velocimetry such as simplicity in the optical arrangement together with high stability for mechanical shock. The power spectrum to be obtained in the present method was first theoretically derived, especially under the existence of speckle noise. Next, the velocities of the solid objects having continuous surfaces as well as the fluid flow or particles in the fluid were measured to show the usefulness of the method for actual objects. In the study, two types of the specklegram were considered in relation to the improvement of the signal-to-noise ratio (SNR) of the detected signal. The velocity of the solid object having relatively small variation of the surface brightness was accurately measured with an error less than 1 in the experiment.

A digital phase shifting speckle interferometric technique for measuring the 3D displacement vector field and the in-plane strain components of a deformed object is presented. The displacement components at each point on the surface of the object are calculated by subtracting the measured phases before and after deformation. Accurate phase measurement in each detector point is achieved by using reference beam phase shifting, fast digitizing of the interference patterns and image processing techniques. The 3D displacement vector can be calculated from measurements of the displacement components along four sensitivity vectors. Application of a special gradient filter enables the determination of the in-plane strain components. Special purpose hardware allows a complete measurement of the phase change modulo 2n on a 512*512 grid every 240 ms. The measuring system and its performance will be discussed and results of measurements of the in-plane strain components in a simple experimental aluminium object are shown. For small loads the estimated inaccuracy amounts to 0.3 listrain r.m.s..

A statistical distribution model for point information in speckle photography is established using statistical approach. It is shown that the recognition of information is to recognize the space and direction of the Young's fringe from a random metrological field statistically. Based on the model, a 1-D recovnition technique is presented, in which the homomorphic filtering technique is used to elliminate both the speckle and the diffraction hole effects. Experiments show good accuracy and fast recognition speed.

TV-holography is used in vibration analysis and surface inspection of very hot objects. Vibrational behavior (resonant frequencies, phase and amplitude of vibrations) has been studied as a function of increasing temperature. To reduce the effect of turbulence we use continuous averaging of TV-frames. Among typical applications of this technique is the testing of turbine components. We also show some examples of deformation measurements for various temperatures up to about 3000°C. The temperature limits are mainly set by the accessible laser illumination to suppress the background radiation. To block the background radiation we use narrow-band interference filters centered at the laser wavelength.

Mono-mode fibre optic components, including directional couplers and piezo-electric phase control elements, have been used to construct a TV holography system. The instrument has advantages of simplicity and ruggedness of construction and, with a 40m fibre optic link to a 600m' argon ion laser, has proved to be an ideal tool for studying the structural behaviour of automotive assemblies. The TV holography system is described and two examples presented of its use: analysis of the deformation of a petrol engine cylinder bore due to head bolt forces, and the vibration study of a vehicle bodyshell subjected to wheel induced inputs. Limitations in the application of the technique are identified and future work to address these shortcomings outlined.

Holometry studies of automotive body and powertrain components have become a very useful high resolution test methodology to knowledgeable Ford engineering personnel. Current examples of studies that represent the static or dynamic operational conditions of the automotive test component are presented. Continuous wave laser holometry, computer aided holometry (CAH) and pulsed laser holometry were the holometric techniques used to study the following subjects: (1) body in prime (BIP) vibration modes, (2) transmission flexplate stud-torque converter deformation due to engine torque pulses, (3) engine cylinder head and camshaft support structure deformation due to cylinder pressure and (4) engine connecting rod/cap lift-off. Static and dynamic component loading and laboratory techniques required to produce usable and valid test results are discussed along with possible conclusions for the engineering concerns.

With the development of the portable diffraction moire interferometer, it became possible to imagine the use of subtly distorted or aberrated diffraction gratings as unique markers. The portable system, described in another report, provides a simple and convenient method for accurately measuring the degree of distortion of an aberrated diffraction grating so as to uniquely determine the identity of the grating. The concept, technique, devices, and data reduction are described for this unusual application of diffraction gratings, interferometry, and optical fibers.

Continuous local basis function (CLBF) methods have been formulated for three-dimensional reconstruction of phase objects from multidirectional interferometric data. In a method, identical CLBFs, having support only in their local domains, are employed. Three methods tested include the polynomial, the convoluted Hanning function, and the cubic B-spline. Unlike the conventional methods, they represent higher-order approximations. The polynomial and convoluted Hanning function allow relatively simple expressions. All the CLBFs can fit a constant function with proper overlaps. The methods are evaluated through computer simulation of experiments. They demonstrate comparable power of approximation. The CLBF methods show better reconstruction accuracy than the traditional methods as noise level or degree of limited data (incomplete projection and limited view angle) increases.

Computerized tomography and magnetic resonance imaging nave revolurionalized analysis of vertebral anatomy and pathology. Further advances with 3-dimensional imaging have recently become an important adjunct for diagnosis and treatment in structural abnormalities. Facets are intimately related to their surrounding musculature and malalignment may cause pain directly or indirectly. High resolution 3-dimensional reformations of CT Scans give us new insight on structure and function of facet joints, since their motion and architecture are ever complex. It is well documented in the literature that facet joint biomecnanics is a partial contributor to the myriad at causes of low back The term "facet Joint syndrome" was coined in 1933 by GhorMley.3 The osteopathic lesion complex is well defined by LeRoy and McCole and comparison of roentgenographic findings before and after manipulation has teen described by Long and Lioyd.4,5 since alterations in facet biamechanics are an important aspect of osteopathic manipulative therapy (OT), 3-dimensional hign resolution imaging will prove to be a great asset in osteopathic research. Rotating the spine allows for different viewing perspectives to provide optimal and consistent measurements of the facet joint. Rotations are performed on the X, Y and 7, axis and measurements pre and post-manipulation are performed and compared on matching axis and perspectives. Rotation about the X, Y and Z axis help appreciate the 3-dimensionality of the vertebral column to project to the viewer a feeling that the spine is floating in space before them. This does give the viewer a 3-D understanding of the object however, only at a perspective at a Lime.

Advances in the technology of medical imaging have allowed doctors to peer into the humna body in a more realistic, less invasive manner. CT (Computerized Tomography) and API (Nagnetic Resonance Imaying) that usually obtain 2-dinensional slices of 'oatient anatomy, are alLx) capable of pi oducin 3-dimens1onal r&prosentations of in anatomy and pathology. 1,2,3,4,5,5 Further ddVaflCEO in computer data acquisition, hence decreaeo. scan times with better resolution, have allowed for cine MR and CT giving us repreentative motion in pseudotize and almost real time. We now have the capbility to construct interal holograms out of 3-dimensional reformatted CT and MR Cata that demonstrate anatorcy in "true" 3-dimensions, and in the near future, 4-cliensionL; about a single axis. 7,3 This woulC allow. a medical student to aiwciate not only still anatomy from a cavader or electronic cadaver, out also 3-dimensional interactive pseudotiae intergral holograms of moving anatomy. Holograp4 is currnLiy the only wEy of visually recording objects or camputer-graphic models into "true" 3 and 4-dimensions. Since diikensions were defined befate computer-generated graphics and co:aputer-baed igi% technologiez, subdivisiono of dimensions (factorials will be addressed for the purpose of explanation for this paper.

The use of a two-frequency, Zeeman effect laser permits simple, stable, rapid, and highly accurate interferometry. There are a number of interesting applications. Three of them are discussed here.

A flexible and versatile holographic interferometry system is being developed for the Rocket-dyne Hypersonic Flow Laboratory (RHYFL) which will be a free-piston shock tunnel operating in the reflected shock mode. The RHYFL's large test section allows testing of full scale engine components, simulating a true hypersonic flight speeds up to re-entry conditions. The holographic system incorporates a diffuse back-lighting along with both double plate and rapid double pulse methods to provide 3-D visualization of the flow field inside the test section, and it has been designed to obtain the qualitative data on mixing rates and density structures as well as the location and shape of the shock waves.

This paper summarizes a continuing effort to develop, design, construct, and evaluate the performance of an airborne autonomous wavemeter for laser tuning. The wavemeter supports tunable solid-state lasers that are used for atmospheric remote sensing. This sensing approach is the Differential Absorption Lidar (DIAL) technique. One atmospheric species, water vapor is measured by tuning one laser to line center of a water vapor line and by tuning another laser off the line. The two sets of received backscattered radiation are ratioed and corrected to determine the vertical profiles of water vapor. On a spacecraft platform, an advanced system could monitor the global water vapor profiles. This would provide a technology improvement for meteorological forecasting. One experiment to make water vapor DIAL measurements from a down-looking airborne platform is the NASA-LASE (Lidar Atmos pheric Sensing Experiment) Project instrument1 to be flown on a NASA ER-2 aircraft. Breadboard results have been obtained that predict that a wavemeter can be built to survive the harsh air-borne environment of low temperatures and low pressures that exist in high altitude flight. Based on the breadboard results, the airborne wavemeter consist of three stages of Fabry-Perot interferometers. Stages #1 and #2 provide the necessary information to provide laser wavelength centroid measurements to the required accuracy of less than 0-.25 picometers. This provides the real-time information necessary for tuning the two tunable alexandrite lasers for the water vapor measurement. A high resolution stage #3 interferometer provides the laser spectral profile measurement with an instrumental profile less than 0.5 picometers full-width at half-maximum amplitude for the post-flight science data reduction. To maintain interferometric stability, the first two stages are thermally controlled and contained in a vacuum chamber. A two level control approach is used to stabilize the interferometers above the highest ambient temperature. Techniques have been developed to evaluate the accuracy of the wavelength centroid algorithms. By using a single wavelength stabilized He-Ne laser as a perfect source, the end-to-end random errors (short term stability) are determined in a period too short for any thermal/mechanical response. The end--to-end sys

An optical tomography system, combining multi-directional holographic interferometry and computed tomography, can be a powerful tool for the study of transparent media. With such a system, one can measure the three-dimensional distribution of index of refraction in a transparent medium at an instant in time. In many situations, the index of refraction can be uniquely related to other variables of interest, for example temperature or species concentration in a gas flow. This paper reports on the development of an optical tomography system for laboratory measurements, with emphasis on the accuracy attainable with such a system. The holograph is of the diffuse-illumination type, and provides a full 90 degree angle of view of the object. Data is extracted from holograms of transparent fluids using a high-resolution CCD video camera. The digitized images are treated semi-automatically to extract fringe number versus position information. This fringe number data is then treated by a computed tomography program to reconstruct the index of refraction distribution in the fluid under study. The CT program used is an iterative technique based on Gerchberg's spectral extrapolation algorithm. The purpose of this study was to measure experimentally the accuracy of such an optical tomography system. The temperature distribution in an asymmetric convective hot air flow was measured using the optical tomography system. An array of ten fast-response thermocouples was read simultaneously with the exposure of the hologram. The thermocouple readings for several configurations are compared to the reconstructed temperatures from the optical measurement.

Phase-shifting interferometry (PSI) is the generally accepted technique for data acquisition and computer analysis of interferometric patterns. General purpose instruments that use this technique for the measurement of spheres and flats are available from a number of vendors. Recent improvements in the fabrication of aspheric surfaces have led to interest in a similar instrument for the measurement of aspheric surfaces. This instrument must be able to measure large departures from a reference surface, which is a limitation of PSI. Sub-Nyquist interferometry (SNI) extends the range of PSI by using a priori knowledge of the test surface. This paper will review SNI, discuss its hardware implementation, and give the results of preliminary wavefront analysis.

A common-path polarization interferometer is constructed for measuring microscopic surface profile. A double-focus lens made of birefringent material is used to divide the wave. To detect phase difference smaller than unit fringe, phase-shifting technique is adopted. This optical system is expected to be insensitive to vibration, temperature variation and air draft because of its common-path geometry. With this system microscopic surface profiles of some samples are measured. The measurements confirm its insensitiveness to vibration. On the basis of the results of the experiment, some problems for this type of an interferometer are discussed.

A wavelength scanning interferometer is proposed for measuring both the shapes of the front and the rear surfaces and the inhomogeneity of the refractive index of an optical parallel plate. To separate the superimposed interferograms generated with many wavefronts reflected from the plate, it is utilized the property of a wavelength scanning interferometry that the phase shift associated with wavelength shift is in proportion to the optical path difference of the interfering beams. By an experiment, the rms error of the measurement is shown to be less than 1/50 wavelength.

Objects that vibrate at frequencies higher than 1.0 MHz usually have vibration amplitudes far below the first fringe minimum (about X/5) of holographic detection. To get a complete phase and amplitude map of such high frequency vibrations we have combined phase modulation with phase shift techniques, using an electro-optic modulator and a digital image processor. Results showing the vibrations of a ceramic crystal (3.8 MHz), with a complete phase and amplitude map, are presented.

This paper discusses the principles of tomographic reconstruction of three-dimensional temperature field from multi-directional interferometric data and presents a method of multi-directional image plane holographic interferometry, which solves the problems that interference fridges are not clear and viewing angle is small ( <90) in dif fused illumination holography. Using this method, an asymmetric three-dimensional temperature distribution in water has been measured. Furthermore, a multi-directional F-P interferometry is presented which has more practical value and can be used in dynamic whole process measurement.

The holographic non-destructive (HNDT) marketplace is potentially a S 1(X) million dollar a year business. It is not being addressed. Examples of untapped markets such as Aircraft inspection, bridge inspection and earthquake engineering, are given.

In order to improve conventional ultrasonic testing of near-surface component regions a holographic system has been developed, enabling sensitive detection and large area visualization of ultrasonic waves insonified at the component surface. Near-surface flaws, e.g. cracks, are thus indicated by distinct disturbances of the interference fringes representing the free-running ultrasonic wave in the interferogram. Besides the discussion of the basic principles of the system the inherent possibilities in nondestructive testing as well as the limitations of this technique with respect to flaw detection and flaw description (size, shape, location) will be discussed. Practical applications in testing thermally sprayed coatings and thinwalled components will be presented. First results with respect to visualization of laser-induced ultrasonic waves as well as developments in computer-aided flaw detection and description will be presented.

The displacement, strain, shear and rotation components of the deformation of a part cutted out of an adhesively bonded car body has been measured by a novel technique. The large deformation registered required the application of a compensation technique. Tne rotation components were always much larger than the strain components. Therefore a reduced quantitative analysis based on rotation alone can be performed for car bodies. Then, for this analysis, two, instead of three, directions of observation (or of illumination) are necessary.

Pulse Holography includes studies concerning time-varying phase objects as well as time-varying reflective objects involving the use of pulse ruby- and YAG-lasers. The paper is divided in two parts. One part concerns the direct use of 3-1) images reconstructed from holograms, i.e. applications to particle size analysis, 3-I) velocity measurements, 3-I) cinematography ... The second part describes applications using holographic interferometry in laboratory or in an industrial environment, i.e. applications to fluid mechanics, vibration analysis, non-destructive testing ... Recent developments including interferornetric cineholography, fiber optics, measurement of non-interferometric displacements ... , are also described. The future of holography depends to a great extent on data processing and interpretation of informations contained in holograms or holographic intericrograms. Therefore, we give the state of art in this field in Europe illustrated with some industrial applications.

The alexandrite laser^1,2, operating at 730-780 nm, is an efficient solid-state laser capable of generating holographic quality laser pulses at reasonable repetition rate (10 to 30 Hz) and can be built into a compact package. With the laser operating at a submultiple of the TV frame rate, the combination of a double pulse alexandrite laser with a solid-state camera and image processing techniques makes possible real time TV examination of small displacements in a dynamic situation.

This paper describes the use of an Electro-Optic Holography system for measuring vibration patterns on diffusely reflecting objects. The system provides a high-quality display of fringes for identifying modal frequencies and setting vibration levels after which image brightness data can be transferred to a host computer. A bias vibration is introduced into the illumination beam to shift the 0 fringes so that fringe shift algorithms can be used to determine vibration amplitude. Using this approach, high spatial density displacement fields for vibrating objects were obtained directly form the time-average interferograms recorded by the Electro-Optic Holography system. These results show good correlation with the reconstructions from the holograms and with the vibration characteristics predicted by the Finite Element Methods.