The holographic method and experimental results for recording two-dimensional modulation transfer functions (MTF) of lenses are described. The conditions for hologram-filter recording are determined. The existence of optimum ratio between reference and object beam intensities, at which the results of measuring MTF match with those expected, will be demontrated. The cause of formation of parasite intensity modulation in correlation distribution will be revealed and the way to eliminate it will be suggested. The requirements for granularity of the recording medium for hologram-filters are determined. It will be shown that the results of measuring the two-dimensional MTFs of lenses with symmetrical and nonsymmetrical point spread functions by the holographic method are satisfactorily matching with the expected results and the evidence obtained through harmonic analysis.

We plan to develop hybrid picture processing applications, (photonics and electronics). We started by optimizing, for given applications, first photonics processing and then electronics processing, combining both in order to obtain a maximum of advantages.

Speckle photography is a new technique for measuring e.g. in-plane-deformations of objects. Till now the Young's fringes diffracted from the double-exposure specklegram are in most applications evaluated manually. With the aid of a microprocessor-system data recording is performed via a TV-system and data are processed by an appropriate software. This way object-deformations are evaluated automatically and yield fast and relieable results.

An application of the multiple-exposure speckle photography to the Rayleigh-Benard flow is described. A fluid seeded with a minute concentration of diffusing particles is illuminated by a laser light sheet. The multiple-exposure photograph of this sheet is analysed by the well-known techniques of speckle photography to obtain a bidimensional map of the instantaneous velocities.

The method of tandem speckle photography has been successfully applied to the measurement of vibratory strain on an actual turbine blade. Several procedural changes have been implemented in the mechanics of the experimental process to both improve and simplify the technique: 1) Increasing to four toe number of specklegram pairs to reduce the effect of data errors by overdetermination; 2) Increasing the spacing between specklegram pairs; 3) Locating the point of zero speckle motion between the pair of tandem specklegrams; and 4) Improing equipment stability and measurement of the sensitivity vectors. In addition, the data reduction program nas been modified to calculate standard errors for the strain parameters. Finally, a computeraided TV analysis of toe nalo fringes, as recorded photographically, has been employed. Tne influence of the above changes on performing strain measurements, via the tandem speckle photographic process, will be reported, along with comparisons between the results obtained with computeraided TV analysis acid manual evaluation of the halo fringe data.

Elastic diffusion of light on moving objects is affected by Doppler effect ; coherent detection of this effect gives the opportunity to reach high resolutions (10¹⁰ to 10¹¹). This light beating spectroscopy provi-des a frequency modulated signal proportional to the velocity of the diffusing object. The main characteristics of this optical heterodyne detection are : . a coherent mixing of two colinear waves of different intensities and frequencies, . a detected waves etendue limited by the coherence Otendue, . no sensitivity to thermal noise. Laser noise (mode beating and plasma noise) which usually limits coherent detection sensitivity is removed with a balanced heterodyne detection which improves greatly the signal to noise ratio. Common mode noise is removed in the same time the signal is multiplied by a factor two. Application of these methods to different optical measurements is presented. The first one, an infrared 8 watts CO2 laser anemometer is able to perform remote measurements of atmospheric wind up to 500 meters. The second one, a vibrometer using a 1 mW red laser is able to perform vibration measurements on a poor diffu-ser at distances of several meters with a resolution of half a wavelenght. Main advantages and limitations of these methods are discussed. Industrial applications are presented.

The two wave field widened interferometer of "Institut National de Metrologie" (I.N.M.) is controlled by Micral R2E microprocessor (Intel 8008) for data acquisition and real time signal processing. Two different methods are described, one involving a servo controlled step by step scanning of the path difference, in the second one this scanning is approximately linear with time, and the microprocessor samples interferometric signal at a high rate. In both methods a real time signal processing is achieved. We compare the results of phase measurements by the two methods ; the reproducibility may be in both cases within a few 10^-4 of a fringe.

Holographic metrology of the cavitation bubble field has being successfully applied for the inter alia determination of its statistical properties.Bubble diameter's spatial distri-bution is deduced through measurements of each bubble diameter in the reconstructed field. Data reduction procedure is seriously tedious when the inspected volume and its cross-section is in a realistic range usually seen even in the smallest hydrodinamic tunnels.For the development of a hybrid Opto-Digital set-up, which distinguishes bubbles of a specific size from others, and from other particles in the inspected volume, it is of major importance to synthesize the appropriate SMF (Spatialy Matched Filter) for the FPC (Fourier Plane Corrlator). The large dynamical range of the bubble signal spectrum and the limited dynamical range cf photoemulsion combines into a weighting function by which the signal spectrum is multiplied in the holographically synthesized SMF. This weighting function is, to some extent, controlled by the selection of exposure and photo-processing parameters. The coherent optical correlation technique is used for the investigation and measurement of surface wear. Tappet's head surface wear from an IC (Internal Combustion) engine exhibits exponential decay of the optical cross-correlation of its initial and intermittent phases, in relation to the number of wear cycles. The Fourier spectrum of tappet surface shows in addition to a very pronounced DC component, an even spatial distribution.Nevertheless,the weighting function inherent to SMF synthesis must be controlled. Dimensional and statistical metrology of the granular structure of the photosphere of the solar disc is performed fast and easy through optical Fourier analysis. Through appropriate synthesis of optimally weighted SMF, temporal behaviour and decay half-times of the solar granular structure are obtained. In order to achieve acceptable control of the weighted SMF through the holographic procedure, a detailed theoretical and experimental analysis is carried out and empirical models are established for the FPC signal analysis based on the Vander Lugt filter.

Pulsed dye lasers are representing a most important group of tunable lasers that can used for high resolution photographic, interferometric, holographic or spectroscopic apr cations. For our investigation we developed a multichannel nitrogen laser emitting trair of short duration light pulses (five or ten ns-pulses at repetition rates up to 100 MHz which is used either directly as UV source or as a pumping source for dyes. The waveleng can thus be converted throughout the large spectral range of dyes available and can be changed from pulse to pulse within a few ns. Some examples are given showing the applicE bility of the system for the study of rapidly expanding phase objects by means of cineme ographic techniques such as shadowgraphy or multiwavelength-interferometry.

A new passively mode locked laser source developed at the Center for Laser Studies yielded pulses shorter than 0.14 ps, at a rate of 250 MHz or 0.3 ps pulses at a rate of 500 MHz. The laser and its modes of operation are described. With this source and a second order cross correlation technique similar to the autocorrelation used to determine the pulse duration, time domain reflectometry measurements can be made with a resolution of 40 µm. Three dimensional images can be made by time resolving the backscattered radiation of a beam scanned through a medium. The depth resolution of 0.1 µm can be carried over to the other two dimensions by computer reconstruction. The new technique should have important applications in medicine and biology. Because of the short duration of the laser pulses, high peak intensities can be used without damage to the tissues. Therefore, light measurements can be conducted through a larger depth than with continuous radiation.

A variety of cotton fabrics (twills, velvets, moleskin, and satin) have been analyzed by means of Frauenhofer patterns. While determination of geometrical parameters is possible, it appears that cotton fabrics, and for that matter, most fabrics made of natural fibers, are less suited for analysis by optical methods than spun filaments (i.e. artificial fibers and silk) due to an important contribution to scattering of the small fibrils which give the yarns their shagginess.

The method presented for evaluating size distributions of small objects makes use of the Fourier transformation performed optically by a lens. The objects are stored in a transparent photographic recording whose spatial frequency pattern (far field diffraction pattern) is investigated.The method is first tested with patterns of model objects and then successfully applied to real particles, namely photographs of small air bubbles in water.

We propose a new opto-electronic method permitting the study of ordered structures in the optically transparent mediums and particularly the measurement of their phase speed. The validity of the process associating the optical Fourier transformation and interferometry is experimentally verified in applying it to the study of different modes propagating in an acoustic wave guide.

With stable silicon-photovoltaic-cells corrected very accurately to the light weighting function V(λ) or the tristimulus functions x(γ), y(λ), z(λ) in connection with modern electronics, it was possible to develope high precise meters for photometry and colorimetry.The construction of these instruments as well as their application for the measurement of photometric or colorimetric quantities is described.

We present a new device, utilizing a He-Ne 5 mW laser as a light source, and including a Mach-Zehnder interferometer coupled with schlieren systems with defocalised phase plates permitting the measurement of the dalembertian of the optical path along a trajectory of the laser beam in a transparent medium. This device which required a long development, as much optically as electronically, is used for the study of noise sources in the air jets. The particularities of the system are described and its performances are illustrated by applications in aerodynamics.

The skiers access-control to skilifts requires to work unconstrainedly. Therefore, an optical remote control has been considered. A very low-power laser scanning allows to locate the user's skipass and read data barcodes printed on a reflective tag. Optical and electronical filters associated with a microcomputerized decoder allow informations reconstitution and the label validity checking. Each item of this product has been designed to aim the desired performances in the easiest and lowest-cost means.

The real image of an "off-axis" hologram recorded with a separate reference beam reproduces the spatial structure of the recorded. objects. The application of this real image as an "analogue 3-D picture storage" to digital image processing has been successfully applied to the computer-controlled analysis of fast moving particle distributions.

New possibilities for engineering uses of hologram interferometry are shown by two experiments. Sandwich holography has been used for measurements of in-plane displacement of an object. The sign of the displacement is found by tilting the sandwich hologram during reconstruction. Fringes caused by in-plane rigid body motion can be compensated for, and local displacements evaluated. It is shown that an inplane motion of more than 1 mm of the object placed at a distance of about 1 m from the plates can be compensated for and a local tilt of 1.5 x 10-3 degrees evaluated. An object, 1 m long was placed in a fixture and a recording of the object was performed on one of the plates in the sandwich pair. Then the object was removed from the fixture as well as the holographic laboratory and holes were drilled in one wall of the object in a workshop. Then the object was put back in the fixture and the second plate in, the sandwich pair was recorded. At reconstruction the influence caused by a slight reposition error was compensated for by tilting the sandwich hologram and then the deformation around the drilled holes could be studied.

Holographic interferometry using a Q-switched double pulse ruby laser has been applied to study the out-of-plane vibrations of rotating objects. The elimination of fringe patterns due to the rotary motion of the object was achieved with a holographic interferometer in which the observation point coincides with a virtual position of the illumination point. In the second method described the rotary motion is optically removed with a reflective image derotator. Experimental results of the vibration analysis including standing and travelling waves of rotating disks, sawing blades and an automobile cooling fan with speeds up to 13.000 rpm are given.

Double beam illumination is used to obtain contourline maps for the in-plane and out-of-plane deformation of reinforced concrete test specimen. Generally large rigid body movements hinder interpretation and have to be eliminated. The rigid body rotations of the test specimen are measured by means of a Michelson interferometer. The unwanted effects are eliminated by rotations around three axes of the holographic plate.

The application of the holographic measuring method it cherdcal enginecrirg surpluss information in the study of dispersoids. Its advantages are its three-dimersionality, possible separation of particles covering one another, storage of rapid processes fcr later evaluation, and the fact that it can be used "in-situ", without the disturbing of the phenomenon investigated.

Interferometry is a very precise measurement technique which has the great advantage of not disturbing the phenomenon being studied. The basis for measurement is generally a photographic print on which the interference fringes are recorded. The measurement itself is derived from the displacement of the fringes between two consecutive interferograms. So the operator must evaluate this displacement by fixing the position of the same fringe in the two photographs. A method of automatic analysis has been developed which uses a television camera linked to a microcomputer, in a system whose overall cost remains relatively modest. The interferogram is formed directly on the vidicon of the T.V. camera. At a moment fixed either by the operator or by a timer program, the signal delivered by the camera is digitalized for the space of one half-image, then stored in memory. The interface linking the camera to the computer was built up around an analogue-digital converter. The encoding distinguishes 16 shades of grey (4 bits), which are sufficient for an interferogram and allow a saving in memory space. An original program for picking out the position of the fringes provides a refinement in accuracy up to one hundredth of the fringe spacing, since it uses all the information contained in each "line" of the T.V. image, when fixing the position of the fringe. This system of analysis has been applied and tested with the holographic interferometry bench designed for studying solar heat collectors.

We have built a compact and mobile holographic camera capable of recording holograms by double exposure, the time lapse between the 2 laser impulses (duration 20 ns, energy 100 mJ approx.) being adjustable from 0.1 is to infinity. The successful "in situ" experimentation of this device took place during a stay in the facilities of the Aerospatial Company at Suresnes on test bars of aeronautical structures being tested for fatigue (periodical tensile stress).

The meniscus of liquid-air interfaces is studied by holographic interferometry. In non diffuse reflected light the technique yields interference fringes from which the surface shape is calculated. When the method is employed to a meniscus of well known theoretical shape the coefficient of capillarity is obtained by a fit to the experimental data. In the present study the water meniscus adjacent to a vertical wall is investigated. A special holographic setup incorporating a Michelson interferometer and producing a real image of the phase distribution above the liquid surface minimises aberrations and allows to account for them quantitatively. Thus values of the coefficient of surface tension are obtained with an accuracy of 1°/oo and better.

Non destructive testing of ballistic missiles engine has been industrially carried out in the Aquitaine plant of Aerospatiale for many years by means of the following methods : - infrared thermography - ultrasonics - radiography X which have been proving their complete efficiency. However, in the aim of still improving the investigation range, the sensitivity of detection and equally for decreasing the testing cost, new methods have been evaluated. Among these, holographic interferometry which is presented here in its industrially used form. The use of brand new pulsed lasers, has permitted getting rid of strict limitations of a production workshop. This article will treat in a quantitative way, the contribution of holographic interferometry to the global efficiency of the non destructive testing carried out..

A method is given of measuring the displacement vector components by simultaneously recording four double exposure holograms of 3 x 4 cm2 each that simulate the corners of a large hologram (in the present case 35 x 24 cm2). A very divergent beam of laser light originates from the centre of the simulated large hologram and illuminates the object as well as the four mirrors, two on each side of the object. These mirrors provide the reference beams for four holograms. Through this simple set-up four interferograms are obtained. Three of them suffice to calculate the displacement vector-under the condition of the zero-order fringe being known. Two efficient modes of meeting this condition have been investigated. In case of mechanically caused deformation the surface of both the object and the holographic bench are linked by a streched elastic tape, over which the interference pattern progresses to the zero-order fringe on the bench surface. In case of thermically induced deformation the object is kinematically mounted and a selected point anchored that determines the zero-order fringe. The significant feature of this method is the simplicity of geometry, the minimal number of optical components and the large viewing angles, gained by the interspace between holograms.

As part of a general study of heat exchange at the surface of solar energy collectors, we have assembled a real-time holographic interferometry apparatus with wide field. The interferograms are either recorded by photographic means and analysed manually, or else they are collected by a TV camera and treated immediately by a special system linked to a computer. Experiments using collectors heated to 40°C or cooled to 10°C, both in the vertical and inclined position have allowed the presence of a zone of laminar flow where the convection transfer coefficient decreases from about 5 to 3.5 WK-lm-2, followed by a zone of turbulent flow in which this coefficient remains constant at a value of 3 WK-lm-2. For tilted plates, the convection transfer coefficients are different for the two faces. There is some scatter in the measurements which is due to the nature of the natural convective phenomenon itself.

The diffraction phenomenon produced by a Fabry-Perot interference pattern record is analized. As a result of this analysis, a compact device for interferometric holography has been developed. It is presented as example an application of this device to the interferometric determination of deformations in a loaded metallic cantilever.

An automated quantitative evaluation of holographic interference patterns can be carried out by a microprocessor controlled system. The recorded images normally are disturbed by e.g. diffraction patterns of dust particles and speckle noise. We describe some image processing techniques which can be applied to these images in order to suppress the disturbances and to enhance the interference pattern. It is reported on the realization of these techniques by a microprocessor controlled system.

Results from a theoretical and experimental comparison study of the vibration of a cantilever beam are presented. A verified theory was used for the theoretical prediction and real time and time average holographic interferometry was used for the experimental verifications. The first 16 vibration modes were predicted and measured for each cantilever beam, and a detailed comparison is presented. Reasonably good quantitative agreement was obtained for both natural resonant frequencies and mode shapes.

Time average holographic interferometry is the common kind for vibration analysis. The heterodyne interferometry allows to achieve an over-all interpolation accuracy of 1/1000 of a fringe. This paper reports how this can be accomplished for moving objects.

More and more people are working in the domaine which is the subject of this panel discussion. What are the problems that arise, is holography becoming an effective method of control in industry? I can give an answer to this question insofar as I am myself, concerned, but I would prefer to have a response from the audience.