Various unsolved problems in holography are described, along with some long-standing problems that have been at least partially solved in recent years. In particular, the problems of making holograms in white light are discussed.

Microwaves incident on finite dielectric structures, such as slabs and hollow wedges, excite a variety of fields that produce complicated interference patterns. This paper describes calculations with the moment method and measurements with a small, probe antenna. The interpretation identifies guided waves, plane waves, and cylindrical waves, and it gives relative amplitudes of these waves. The intensity distribution is a hologram because the guided waves and internal refracted waves are coherent but with distinct propagation constants. Images are formed by reconstruction. In addition, describe a new, angle scanning interferometer that determines angular distributions of fields about dielectric gratings. Mechanismus, which include grating lobes, and specular reflections, are identified.

After reviewing the advantages and shortcomings of already existing holographic recording techniques which offer a full 360° view of an object, a new possibility of recording geometrical quantities in a cylindrical space is described. This technique is based on our recently developed toroidal lens which allows 360° panoramic speckle photography.

A cylindrical holographic stereogram with white light reconstruction, or a multiplex hologram can be conveniently used as a tool of non-destructive testing if the original picture is taken with X-rays. Along the lines of that purpose, it is discussed making holograms, optical properties of reconstructed images, mainly with regard to distortion and resolution, and a proposal of applying to medical purposes.

The multiplex hologram was used to observe the internal structure of the human body three-dimensionally with the naked eye. The hologram was synthesized by the use of a He-Ne laser from cine-film taken with X-rays by rotating both the cinecamera and the X-ray tube. The three-dimensional image was reconstructed by a small white light source. The three-dimensional hologram images of a dry human skull, the skull of a living body, the ERCP and laryngography were satisfactory. The three-dimensional image obtained by those multiplex holograms proved to be clinically useful.

Examples like the holographic vibration analysis to study the influence of gun and cannon shots on the function of tympanic membranes, or the optimization with in-line holography of spray nozzles that were used in defoliation actions in Vietnam show that today even in such highly specialized fields like biomedical applications of holography, where you normally would not expect military applications, you are confronted with the question of the interlacing of science with military. This demonstrates, that there is no way to avoid taking a stand on this question - which seems anyway to be very obvious especially when you are involved in laser research and optics. But it seems that many colleagues knowingly or unconsciously put this problem out of their minds and many - if not most - of the scientific societies support this attitude by giving increasing public recognition to such type of research without any critical discussion of its consequences.

Equations of homology and of fringe visibility for transparent media (gas) are established in such a way as to illustrate their similarity with the equations which were derived for opaque objects. Time dependance is taken into account at the end.

Real time measurement will be reported on the time variations of both the refractive index and geometry of transparent samples. The temperatures of the samples were varied while they were in a parallelism interferometer and the two independent sets of fringe patterns were monitored. One pattern gave the geometric variation, while the others gave the optical path profile. Resolution of quarter wave are readily realized.

Pressure shock wave is created in a shock tube which ends with visualization chamber with two transparent glass windows. Different kinds of obstacles to the shock wave are placed in the chamber. Double-exsposure holographic interferometry realized by a Q-swit-ched ruby laser is applied to investigate the events happening in the chamber. Some preliminary results of experiments are presented in the report.

Thermal and mechanical strains have been measured on samples of a common material used in jet engine burner liners, which were heated from room temperature to 870°C and cooled back to 220°C, in a laboratory furnace. The physical geometry of the sample surface was recorded at selected temperatures by means of a set of twelve single-exposure speckle-grams. Sequential pairs of specklegrams were compared in a heterodyne interferometer which allowed high-precision measurement of differential displacements. Good speckle correlation was observed between the first and last specklegrams also, which showed the durability of the surface microstructure, and permitted a check on accumulated errors. Agreement with calculated thermal expansion was to within a few hundred microstrain over a range of fourteen thousand.

The use of sandwich hologram interferometry makes it possible to investigate objects of interest to an engineer that was not possible to investigate before. The paper presents some different applications of the technique. An application is a study of an object one meter in length, where the object was removed from the holographic setup between exposures and holes were drilled in one wall of the object. The deformation around the drilled holes could be studied, after a second recording of the object repositioned in the holographic setup was performed. Other applications of holographic non-destructive testing are shown where the fringe manipulation possibility is important.

The critical stress intensity factor K_I is a material property for crack evaluation. The holografic interferometry is shown to be a good measuring method that is capable to determine the K_I-factor even for large specimen and without knowledge about the characteristic defect properties like size and location.

Small size blisters and vacuoles in industrial paint films, which are induced by corrosion or insufficient curing, can not be observed by simple means. A holographic method is presented which visualises small deformations of the paint surface, on the places of these defects, after lowering the pressure over the paint film. In experiments with Alkyd-Satin paint films, with a thickness between 0.03 - 0.18 mm, appplied on a Washprimer, blisters with diameters between 0.1 - 1 mm were detected after a maximum of 24 hours of vacuum-stressing.

Computer generated holograms have not been widely used for metrology and nondestructive testing because the required accuracy was beyond the state of the art and the cost of the best available hologram writer was prohibitive. Both of these barriers have now been removed. We have designed and built an adequate writer (the holowriter) and made it available at no cost (except for labor) to all workers on U.S. Government contracts. This paper describes the Holowriter design and performance.

A technique is described to observe shape development and particle displacements of fast moving solidifying particles during stir casting. The optical set-up consists of a Ruby la-ser (generating pulse pairs), a frequency doubled Nd³+:YAG laser (generating single pulses at a 10 Hz repetition rate), a model device of an actual metal stir casting apparatus filled with a transparent organic alloy and three different recording systems. Double exposure holograms and microphotographs are used to analyse the three- and two-dimensional particle displacements, respectively. Simultaneously recorded videotapes, microphotographs and holograms provide the opportunity to study the shape development at a repetition rate of 10 Hz over periods of 10³ seconds in an imaging volume of 3 x 2 x 2 mm³. We found that a NPA-water alloy nucleates initially as equiaxed dendritic particles. After a period of stirring, the dendrite tips become more rounded. Finally the particles obtain the shape of a bunch of grapes. This final state is in good agreement with the morphology of stir casted metal alloys. Further we found that the flow behaviour at the start of the experiment can be decisive for the solidification process. We observed Taylor vortices and measured particle displacements, that occur in the direction of rotation and also along the axis of rotation (although there was no flow pressure excerted in that direction) and in the radial direction, too.

Interference holography with a pulsed ruby laser is used for analyzing the vibration pattern of an acoustic source. In our experiments the pattern was composed of two different vibrational modes. The pattern pertaining to a single mode can be obtained from the interpretation of a set of two holographic interferograms, taken under electronically controlled conditions. The interpretation methods that have been used were a moire-technique and an automated digital technique. Applications of these techniques in a few cases are discussed, and the effect of small timing errors in the electronic system on the results is determined.

Theoretical and experimental analysis of two methods for obtaining time average holographic interferometry in Fourier plane was done. The fringe patterns are always localized in Fourier plane. From one hologram, it is possible to obtain simultaneously all components of vibration amplitude vector on the entire surface of the object. In both methods, the measuring range can be controlled by the parameters of the Fourier lens and covers tens to hundreds micrometers for in-plane vibrations and hundreds to thousands micrometers for out-of-plane vibrations.

The coherent optical correlation technique was applied for measuring the surface wear of a tappet (part of car engine), worn by friction with the camshaft. It was found that maximum correlation intensity decays exponentially with the number of wear cycles (i.e. camshaft revolutions). Tappets of the same make have an identical rate of correlation decay. Tappets of different makes have different rates of correlation decay which are in agreement with observed long term wear.

The fast noncontact testing of quality of the 11-12th metal working surface plays an important part in the mechanical engineering, and especially in the bearing industry. At present, the optical testing devices used in industry are based on the intensity measurement of white light reflected from the surface. Such devices have a simple optical scheme, which permits one to detect a wide class of surface defects. However, using of incoherent light does not allow one to detect defects with the size less than 20-30 microns. This can not satisfy the present-day technical requirements. It should also be noted that devices of this type are not sensitive to geometric-shape defects of the object surface.

The terms "biomechanics" and "bioengineering " are often employed in the same sense and some authors seem to believe that they are describing the same reality. None the less there exist two different ways of applying the methods of physics to the living matter, and for not confusing them, two different terms are needed.

Modern treatment of sceletal disharmonies and malocclusions utilizes application of external forces. In order to effectively use these therapeutic forces, knowledge of three-dimensional displacements of bones with correlation to biological changes is required. In the past, this problem has been studied in a number of ways using, for example, strain gauges, brittle coatings, photoelasticity, as well as clinical observations and mathematical modeling. Becouse of their inherent limitations, these techniques did not always provide all the information necessary for development of meaningful relationships between the applied force system and the resulting biological remodeling. However, recent advances in the field of la-ser metrology allowed to overcome some of the dificulties found in the earlier methods and permitted development of new techniques for non-invasive measurements of bone motions in three-dimensional space. These laser techniques are particularly useful in biomechanics because they provide for rapid and accurate determination of displacements over the entire surface of the investigate object. In this paper, application of laser techniques for quantitative in-vivo and in-vitro measurements in biomechanics will be discussed and illustrated with representative examples.

The invited lecture was presented at the conference, but author was not willing to publish it in conference proceedings.

Ten years have passed since the first articles appeared in this new field. The qualities of the laser light together with the need of contactless 3-D measurements for different dental purposes seemed to be extremely promising, but still just a few scientists have used the method and mostly for laboratory studies. For some reason there has been a preponderance for orthodontic measurements. This seems to be a bit peculiar from holographic view compared with measurements for engineering purposes, which usually are made on metals. So naturally holography can become a clinical tool for measurements in the field of fixed bridges, removable partial dentures and implants. One of the problems is that the need for holography in dental research must be fulfilled in collaboration with physicists. Only a two-way communication during an entire experiment can balance both technical and odontological demands and thus give practical and clinical important results. The need for an easy way of handling the evaluation to get all required information is another problem and of course the holographic equipment must be converted to a box easy to handle for everyone. At last the position of dental holography today is going to be carefully examined together with an attempt to look into the hopefully exciting and not to utopic future for this research field.

The use of two and three dimensional imaging techniques using color coding methods on specimens can provide additional detailed information which might otherwise go unnoticed. We have coupled a phase contrast microscope to a vidicon and image digitizer to collect the 256 x 256 x (256 gray level) pixels of data on biological objects. Both a mini-computer for data collection purposes and a VAX computer for color coded image studies have been used In this research. Two and three dimensional perspectives of the specimens which were color coded are presented.

The paper presents a physical model of the tympanic membrane system and illustrates its usefulness to study the influence of different parameters on the energy transmission of the system.

To get quantitative information about principal aspects of the near-field propagation of sound in bone conduction, model experiments were performed with transparent silicon rubber as a vibrating material. Using the transparent silicon rubber instead of the bone itself made it possible to measure amplitudes and phases on interior planes of a solid medium of finite extent. To this end several holographic techniques were employed, among them speckle interferometry for analysing in-plane vibrations. A theory was developed which describes the basic features of wave propagation and shows the influence of the viscosity of the material on propagation behaviour. The application of the results on pracitcal audiometry will be discussed.

Investigations were carried out on embalmed and fresh specimens of human pelvisis with preserved lumbar spines, hip joints and all the ligaments. Specimens were tested under static vertical loading by pulsed laser interferometry. The deformations and behaviour of particular pelvic parts were interpreted by providing computer interferogram models. Results indicate rotation and tilting of the sacrum in the dorso-ventral direction and small but significant movements in the cranio-caudal direction. Sandwich holography proved to be the only applicable method when there is a combination of translation and tilt in the range of 200 μm to 1.5 mm.

The role of investigation of peripheral vervous fibers in bitality state is of great importance when elucidating the mechanism of a stimulant low-energy laser radiation influence which is widely applicable, for example, in practice for curing lumbar osteochondros-is (1), trigeminal verve radiculitis, and in developing the processes of transmission and processing of the information required for sustaining organism homeostasis. Using both electrophysiologic and holographic methods simultaneously can increase total information and authenticity of these investigations.

In this work the method of optical correlation was used for the investigation of the morbid deformations of human b000d. A sample of the fresh blood was dituted in the physiological salt solution in the ratio 1 : 30 and was spread on a glass substrate by the vibration method.

A grating shadow moire technique is used for morphometric studies of the feet as a quantitative contribution in clinical diagnosis. A coefficient of symmetry is defined and its interpretation is searched. Repeatibility of the results in view of the specific character of the method and the biomedical nature of the object is examined. Dispersion of the coefficient values within a clinical identical group is analysed. The method is passive of routine clinical practice in documentation, mas screening, follow-up and experimental studies,namely biomechanical research in pathological conditions through predictable changes.

The dependence of the diffraction efficiency and hologram writing rate of Bi₁₂Si0₂₀ crystals on bias voltage and write-beam irradiance was investigated. The diffraction efficiency was found to increase with increasing bias voltage, but displayed very little dependence on write-beam irradiance for bias voltages of 5 kV or less. The hologram writing rate was found to increase with increasing bias voltage and increasing write-beam irradiance.

Recent advances in laser metrology, based on the concept of projection matrices have to led to the development of a new method for quantitative analysis of holograms and specklegrams. Using this method, all necessary calculations can be carried out, in an interactive manner, on a hand held calculator. In this study, the HP4lC System was used, however, the existing programs can be modified to accomodate other hand held calculators. The parameters required to solve the governing equations of this method are determined directly from multiple observations of holograms, or specklegrams. The results, based on these parameters, provide complete three-dimmensional information on object's translations and rotations, including compensation for rigid-body motions, if necessary, as well as the information on object's deformations. The accuracy of the results obtained in these analysis will be discussed. Representative examples on the use of this method in engineering applications, will be presented.

The paper deals with experiments made to verify the theory of bending of plates and related problems by method of speckle shearing interferometry, which is proved to be highly sensitive. Tests carried out on rubber products: (such as tires)and thin-walled containers have demonstrated the prospects of using image-shearing camera in nondestructive in-situ testing of industrial products, suggesting a potentiality still wider than that of holographic interferometry.

An opto-digital interferogram evaluation system for quality control applications is presented. The system allows the recognition of certain predefined fringe configurations in the input data. Thus the processor is well suited to detect defects of an interferometrically recorded object.

A new method of holographic interferograms interpretation, based on the scalar diffraction theory is proposed. This method allows to determine the field of displacements only from measurement of fringe visibility in holographic interferograms. It may be also used as a new method of zero-order fringes localization. The general form of the light intensity distribution in interference field, dependent on the intensity-and-phase spatial spectrum of a light source illuminating an object and on the phase modulation function of object is given. Some cases of object illumination and object surface structure are discussed.

The pulsed laser in the picosecond and femtosecond range introduces totally new possibilities. Using light-in-flight recordings by holography the wavefront of a light beam can be studied in the form of a continuous frameless motion picture. Pulse shapes, pulse lengthening and pulse delays can be measured with high accuracy e.g. to study the quality of optical fibers and integrated optics. The light pulse also can be used as a radar pulse to measure the three-dimensional shape of industrial objects. This new technique should make possible absolute measurements down to a resolution of micrometers even when the objects are meters of size.

In pulse holographic interferometry it is very annoying to find out that hard work done in making interferogram has been spoiled. Posible reasons could be in the arrangement design itself, in the deteriorated or inappropriate photosensitive material or processing, and in laser malfunctioning. In this work the use of a simple device, block defocused spherical Fabry-Perot interferometer (BDSFP), for instant monitoring of the pulsed laser light frequency components as well as for transversal coherence monitoring, and its useful help in holointerferometry is described.

An on-line computer system for measuring a deformation of a diffuse object with a speckle interferometer is presented. Methods for evaluating a speckle interferogram using digital image processing techniques are also discussed. The system consists of an interferometric optical setup and a computer TV-image processing facility. A speckle interferogram is generated by arithmetic operation between two digitized speckle patterns before and after deformation of the object. The informations about the deformation are extracted by two modes of procedures in analyzing the interferogram. One of them is a method for automatic analysis using digital image processing techniques such as gray scale modification, linear spatial filtering, thresholding, and skeletoning. The alternative is a man-machine interactive method for a simple and high-speed processing of the interferogram by using a light-pen facility. The determined fringe order numbers are interpolated and differentiated spatially to give strain, slope, and bending moment of the deformed object. Some examples of processed patterns are presented.

In holographic interferometry, measurements on the fringe pattern using at least three different directions of illumination or viewing permit evaluating the displacement vector at any point. However, the use of holographic interferometry in stress analysis has been limited so far by the fact that interpolation between the fringe maxima and minima to determine the phase at a particular point is tedious and not very accurate. Accurate measurements are possible by heterodyne holographic interferometry, but there are problems in applying it to real-time measurements at a large number of points. This paper describes an improved system for real-time holographic stress-analysis, which uses a diode-array tele-vision camera to view the interference pattern and digital electronics to measure and store the irradiance levels at a 100 x 100 grid of points. The phase at each point is calculated from the irradiance values obtained from three successive scans of the array, made with the phase of the reference beam shifted in steps of 120° by means of a piezoelectric translator. The optical system permits four holograms to be recorded in quick succession, using a photothermoplastic camera, with the object illuminated from four different directions. Data from these holograms are stored on a floppy disc; they can then be transferred to a fast computer for further processing to determine the displacement vector at each point and, hence, the stress distribution.

In holographic interferometry, the "phase difference" governing the interference pattern appears to deviate slightly from the value that follows from the usual formula. This phase deviation δ is due to the nonvanishing detector aperture and can be calculated for double exposure holography in the case that the detector is focussed on the object surface. In practical situations delta; appears to be maximized by a function proportional to the longitudinal displacement and to the square of the angular detector aperture, moreover 1S1{ ff. Neglection of δ can cause relative errors in the calculated displacements in the order of per mills, while in large aperture observation systems the error may increase to several per cents. The maximal absolute error, however, is always smaller than a quarter of the wavelength.

Diffuse illumination of investigated diffuse object in holographic interferometry radically changes creation condidions of interference fringes. Particularly, at wide-aperture diffuse illumination, visibility of interference fringes decreases as displacement component perpendicular to the axis of diffuse illumination increases. It can be applied for identification of the local minima of fringes order in double-exposure or double-pulse holographic interferometry. The lethod has been used for node localization of singers' larynx and face during singing. At present, the double-pulse lasers are usually applied for holographic investigations of dyna is objects. These lasers are also used for investigations of living objects [1-6]. Particularly they are applied for investigations of vibration patterns of different parts of human body [3-6]. Contrary to the tile-average method, holographic double-pulse method gives interference fringes with constant contrast, namely it does not give any differences in fringe contrast for nodal and vibrating areas of an object. Investigations, performed in Central Laboratory of Optics, show that sole differences in the interference fringes contrast can be obtained when diffuse illumination of the object is applied [5-8]. Moreover, for some cases of the wide-aperture diffuse illumination contrast of interfe-rence fringes decreases as the displacement of the investigated object between exposures increases [7-9] . It is illustrated in Figure 1, where two interferograms of the plane rectangular plate are presented.

The first part of this paper presents some estimations of the sensitivity which can be attained by holographic heterodyne interferometry applied to objects which can only be recorded with a limited aperture as e.g. the tympanic membrane. The dependency of the interference phase error from image resolution is discussed. In the second part we give a simple method, insensitive to noise, for the measurement of the interference phase in heterodyne interferometry.

Basic formulas for the light intensity distribution of interference field in holographic interferometry with diffuse illumination are given. Comparison between theory and experiment for the case of plate rotation about in-plane axis is drawn and discussed.

Extraction of wanted parts from optical images is performed by matched intensity filters of spatial frequiencies. The aim of the procedure is to enhance the recognition power of similar images.

The influence of the non-linearity weighting function of a matched spatial filter (MSF) on the Vander Lugt frequency plane correlation is analysed. A pure correlation of two signals is convolved with the Fourier transformed non-linearity weighting function of the MSF which is due to the non-linear behaviour of the recording media used. The transfer function of the recording material is depicted by the transmittance vs exposure (t - E) curve, which is described by means of the Taylor series expansion and approximated by commonly used polynomials, or by some analytic functions. For investigating the output correlation amplitude distribution, certain analytic approximations of the t E curve appear better suited than others. A tractable model was obtained through the application of the direct method and the transform method analysis of the Taylor series coefficients.

Relationship between correlation intensity and a bias exposure, a beam balance ratio ,and a spatial frequency band are determined experimentally. It is shown that a spatial frequency spectrum of wanted input signal, for which filter is opticaly matched, is affecting the synthesis procedure.

The moire phenomena can be defined as the macroscopic periodic effect obtained by the superposition of two microscopic structures which, individually, produce no macroscopic effect. This phenomena has been used empirically since a long time to observe phenomena invisible with the nacked eye. For instance if one superimposes on a microscopic reference structure a similar but deformed structure the moire effect enables us to visualize the nature of the deformation. Interferometry is fundamentally a Moirg effect: the macroscopic interference fringes are the result of the moire effect between the two microscopic phase structures (in space time) of the light waves. We can in this case notice that the microscope effect operates also on the time coordinate: when we observe interference fringes we look at the projection, on the plane of observation and during the reacion time of the detector, of the two four-dimensional-structures, each of which is completely undetectable by our eyes.

The holographic interferometry is more and more used in industry as a nondestructive testing method. It is competing with conventional testing methods, which are limited in use, especially when dealing with composites and reinforced materials. One has to refuse the opinion, that the application of holographic interferometry demands specially qualified personnel with long-time training. "Press button"-apparatus are proving, that serial testing can be performed by semiskilled operators even today. The examples, presented in the following text, are mainly suitable for three important fields of application: 1. The best known application of holographic interferometry is the nondestructive testing. For some tasks testing automata are constructed, that only for operation and interpretation of the interferogram need semiskilled operators. The examples shown here mainly relate to adhesive joints and reinforced plastics. 2. An important field of application of holographic interferometry is the optimization during the construction process, which is done to a great extent in the development laboratories of great companies. 3. Another wide field of application is the vibration analysis as a tool for noise reduction at motor vehicles and machines or for (preventive) damage analysis at turbine blades.

The paper deals with experience gained in employing holographic nondestructive tire tester of type JQL-120. It also depicts a panoramic (360°) holographic interferometer developed recently. By means of double-exposure holographic interferometry, 6 holograms are obtained in each test, with fringe patterns clearly recorded, from which information regarding hidden defects in a tire may be gathered in one stroke, thus raising the efficiency of nondestructive inspection of tires. The potential of this kind of holographic interferometer is considered to be promisingly wide.

Double exposure holographic tests on a panel of the "DOOR OF PARADISE" are reported. The fringe pattern is used to infer the overall bending of the structure under thermal disturbance. Such a deforuation is pointed out as an effective agent of mechanical decay, and demonstrates the relevance of thermal control for better conditions of conservation.

In this paper a holographic non-destructive testing (HNDT) method, by which cracks in bronze, earthenware and other cultural relics are detected, is described. The experiment results obtained by using a local thermal loading and double exposure technique to detect the Spring and Autumn Period's numbered bell, the Han Dynasty's mirrors and more than ten cultural relics are presented. The significance that this technique can offer to the conservation and restoration of cultural relics is emphasized.

Photonics can be considered from several points of view. Two of them are of special importance: the first one concerns the scientific content related to better understanding of light-matter interaction by use of computers and lasers to performe fast, accurate and care-fully analysed experiments. The second one is the technological content to be divided in three main areas: Measuring with light or through instruments where light plays a significant role. Emitting, sending, processing or displaying data with light or through instruments where light plays significant role. Transforming matter with light. Technological improvements caused by development of photonics systems are likely to have an important impact on industrial productivity. Consequently socio economic effects will de-velop increasingly. The present day situation is analysed in relation to the last ten years development. On the bases of this ten years time series period, the tendencies are infered for the near and longer future. Forcasting is made and it is demonstarted that the rate of economical growth of photonics is likely to bring this field to the role comparable to one which electronics plays today.

During this conference we have once heard a political view on optics. I would now like to present an optical view on politics. I want to demonstarte how persons from different worlds, persons with different experiences, can study the same optical phenomenon and not only give different interpretations but actually make different observations and really see different things. It is important that we understand and accept that one single observation can produce different results in the minds of different people. As an example we study the simple mirror image and prove that our interpretation depends on the type of world we come from. When this fact is true for a simple optical reflection there is no wonder we have problems in solving political problems.