If optical methods are long time ago used in metrology, coming of laser sources has improved drastically the impact of optics in metrology. The progressive existence of more and more industrial optoelectronic components on the market is responsible of the actual introduction of optical technics in industrial processings like interfero-metric control, wide-ranging optical sensors , visual inspection.... Further partial coherence and guiding properties of the light field, non linear optical comportment of the medium offer also interesting metrological applications. The aim of this paper is not to give a full description of all the optical methods used in metrology, but to draw some general specific properties and ideas illus-trated by representative applications.

A frequency-doubled Nd:YAG laser with an unstable resonator is explored for its capabilities as a coherent light source for, holographicmeasurements. Test objects are cavitation nuclei (small air bubbles and particles in water) whose size distribution is to be determined in a water tunnel. The ultimate resolution of the system including size determination by the digital picture processing system designed at the Drittes Physikalisches Institut is at present limited to 30 μm by the aberrations caused by the windows (thick PMMA) of the cavitation tunnel. The Nd:YAG laser proved to be a good alternative to a ruby laser. Bright phase holograms with high resolution could be made. The evaluation of the holograms shows as a result that the density of bubbles with a diameter greater than 30 μm was less than 0.1 per mm3 even in gassy water.

A new biphotonic process providing a means for recording holographic patterns produced by laser sources emitting in the near infra-red is presented. This recording process, known as the "two-photon-two-product" technique, works according to the following basic ideas : a first photon of coherent light promotes oxygen dissolved in the reactive medium into its singlet form through a photosensitization process. The excited species oxides then an adap-ted chemical trap which becomes converted into a carbonyl compound. The latter absorbs a second photon-coherent or not- and acts as a photoinitiator of polymerization. A spatially inhomogeneous photoreaction develops in the active medium, thus, inducing changes of refractive index which can be used to record holographic pictures. The attractive advantages of this system are its outstanding light sensitivity and the gating property associated with the two-photon process.

In this paper we present and discuss new results concerning the dependence of the diffraction efficiency of holographic gratings on the state of polarization of the reconstruction wave. The results were obtained during the investigation of polarizing beam splitters manufactured in dichromated gelatin. The aim of this investigation was to fabricate holographic gratings of the transmissive and reflective types, which diffract the component polarized perpendicularly to the plane of incidence, whereas the parallel component will pass the hologram unaffected. Experimentally determined diffraction efficiencies for both types gratings are presented and discussed. The results are compared with the predictions from Kogelnik's theory.

The possibility of storing lightwaves on holographic material can not only be used for recording and reconstructing of three-dimensional objects, but also to deflect lightwaves in an unconventionally manner and for divergent an focusing properties. This kind of specific holograms, which hold imaging properties are called Holographic Optical Elements (HOE). Moreover one can store several features of conventional optical functions in one HOE.

Some properties of the OTF of a scanning acoustic microscope (SAM) have been measured With the help of a glass-water-edge, a grating and Siemens star spoke target of chromium on glass, a layered gold-glass-edge and a microelectronic circuit. After explaining the special conditions for image formation in the SAM, which is a confocal ultrasonic scanning device, concerning the defocussing and interaction effects with the specimen, we regard it as a linear system, and the influence of the testing object is included as a part of the imaging system. We deconvolve SAM micrographs with the help of synthetic holograms, produced by an analogue electron-lightoptical device, inserted in a 4f coherent optical image processor. We show that the edges of the objects become sharper and that the image structure is more clearly related to the light microscopical image impression.

More and more the media of holography is being used in security measures, against counterfeiting. This presentation will especially deal with the mass production of suitable embossed holograms. In the field of credit cards rainbow holograms are used predominentely as a security measure against counterfeiting. Although these holograms possess a relativ high degree of security it is still possible to copy them.

New and simplified processing procedures and formulations for Silver Halide Sensitized Gelatin (SHSG) holographic recording materials have been developed. Holographic gratings, with high diffraction efficiencies (DE) of over 70% and signal to noise ratios (SNR), greater than 100, have been obtained. Further insight into the mechanism of hologram formation was gained.

This paper will discuss and display results of my experimentation to produce a holographic stereogram from scenning electron microscope. (S.F.M.)

This paper describes the contact copying of volume phase transmission gratings. Master gratings are written in silver halide since this material is well understood and relatively simple to use. Masters are then copied into either silver halide, primarily to characterise the copying, or into DCG for a high efficiency end product. The gratings are characterised in terms of their diffraction efficiency as a function of the angle of incidence of a collimated monochromatic beam. Results are presented for copies in silver halide and DCG to demonstrate the quality of the copy process.

Kinoforms were manufactured by transferring computer-calculated phase-data into a photo-resist layer applied to a glass substrate. This transfer was carried out with conventional photolithographic techniques, using one single photomask exposed in discrete grey scale levels. The photomasks were generated in a specially designed PC controlled exposure system. We present kinoforms manufactured in ten levels with a pixel width of 20 μm. About SO% of the totally transmitted power was diffracted into the desired intensity distribution, and a few percent were undeflected at λ = 632.8 nm.

Since the beginning man has attempted to transfer his capability of three-dimensional viewing, into equivalent imaging techniques. He developed the techniques of painting, photography, and televisions. But these techniques only offer a flat projection of our three-dimensional reality.

The methods used for automatic evaluation of interference patterns are presented and compared. These are the fringe tracking, the heterodyne, the phase step or phase shift, and the Fourier transform methods, especially the Fourier transform method without additional carrier frequency. The special advantages of the individual methods are described. Experimental results of holographic interferometric deformation measurement at a thick-walled pressure vessel by phase stepping, Fourier transform evaluation of an object not covering the whole frame, and Fourier transform evaluation of a speckle interferogram are presented.

We describe a new holographic method called THI (Total Holographic Interferometry) allowing the measurement of non-interferometric displacements in holographic interferometry.

A modified optical system and computer image processing software is presented, to automate the analysis of holographic fringe patterns for applications in measurement of transient events is presented. Two fringe pattern analysis techniques are considered; a phase stepped method and a 2-D Fourier transform method. Both of them rely on spatial separation of phase information, although they are based on different physical principles. In the phase stepped method a grating is introduced into the holographic interferometer to separate three phase shifted images into the spatial domain instead of the time domain. In the Fourier transform method a spatial heterodyning frequency is added to the interferogram to isolate phase information in the spatial frequency domain. A comparison between the two methods is given, together with several refinements.

Today, holographic interferometry is successfully employed in many branches of industry as a powerful measuring procedure. Nevertheless, it remains an extremely laborious, expensive and time-consuming process, and, as a result, its use is limited mainly to large concerns.

Multi-directional holographic interferometry, combined with the techniques of computed tomography, can provide 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 such a holography-based computed tomography system for laboratory measurements, with emphasis on the accuracy attainable with such a system. The design of the homographic measurement system is presented, and the data-taking procedure described. Data reduction using two Hartley transform-based computed tomography algorithms is described. The first of these is similar to the single-step Fourier extrapol-ation technique developed by Sweeny and Vest. The second is an iterative technique based on Gerchberg's spectral extrapolation algorithm. The performance of these algorithms is compared using numerical "phantom" temperature distributions. Preliminary measurements of the temperature distribution in an asymetric convective hot air flow were made using the holographic system. These are compared to measurements made in the same flow using an array of fast-response thermocouples.

Holographic ultrasound imaging is a non-destructive testing method for the detection and description of surface-near flaws. This method is based on the combination of the ultrasonic measuring technique with holographic interferometry. The possibilities of imaging oscillating surfaces by the use of holographic interferometry were already demonstrated shortly after the development of holography /1/. Three different illumination techniques are employed: the time-averaging technique /2/, the stroboscopic technique /3/ and the double-pulse technique. The time-averaging and stroboscopic techniques are performed with the aid of cw-lasers (cw = continuous wave) such as ionized argon lasers. Owing to the relatively low laser power, exposure times lie in the region of seconds so that particular vibrational isolation measures must be taken to realize the required measuring accuracy. This, however, excludes the application of these methods in on-site workshops, and other techniques must be employed, such as the double-pulse technique which has the advantage of rapid and therefore vibration-insensitive imaging.

The joints of the assembled concrete frame structure are studied by the white light speckle method. Compared with the results of whole-body casting frame structures, the joints of the assembled frame have the weak stiffness. The conclusions provide a reasonable mechan-ical model of the assembled frame structure to the engineers. The in-plane rotations are expressed as the function of the displacement distribution in the paper. The white light speckle provides the local displacement distribution about the joints and the in-plane rotation can be obtained. Some photocarrier techniques are used to improve the accuracy of the white light speckle method. Besides, both the assembled and whole-body casting frame structures are are studied after the cracks appear. The variation of the mechanical model is discussed.

A liquid crystal display (LCD) is very convenient as spatial light modulator and seems to be a promissing device for interfacing computers with holographic imagine. We discuss some of the potential applications such as transforming a computer displays to a coherent image, generating multiplex holograms from CAD-systems, and generating holographic read-only memories directly from computer displays. Other possibilities for the LCD device are fast control of slit-width and slit position in multiplex holography, and for the control of aperture position and size in facet holography. Optical properties of a transmissive LCD screen (640 x 200 pixels) has been tested. Application of the device for interfacing a CAD-system to a holographic camera for generating composite holograms (stereograms) are discussed.

Phase holograms offer interesting possibilities to realize generalized optical components as well as optical data storage and display devices, because of their high diffraction efficiency. Phase holograms reconstructing a desired intensity distribution in the Fourier plane of the hologram are the subject matter of the presented paper.

A technique is described to generate Fresnel holograms using a computer. A modification is introduced which reduces the number of calculated complex values by orders of magnitude. In a display situation, the resulting slight astigmatism can be kept almost unresolvable.

Holometric testing of vehicle components to improve their structural characteristics is now a proven methodology. The inherent advantages of a full-field, high sensitivity measurement capability are emphasized for the iterative improvement of prototype structures (static and dynamic) and the timely application to understanding structure related concerns on vehicles in production. Successful acquisition of usable and valid test results requires considerable thought and effort to create a test set-up that recreates as closely as possible the test subject boundary and loading or excitation conditions existing in-vehicle. The recent addition of advanced Computer Aided Holometry (CAH) has significantly enhanced the understanding and utilization of holometric testing by Ford engineering. Recent examples of studies that address both the static and dynamic behavior of components are presented. Continuous wave and pulsed laser holometric techniques have been applied to study the following subjects: (1) self generated brake noise, (2) engine block noise radiation, (3) steering column vibration, (4) engine structure deformation under fastener torque loads and (5) cylinder head deformation under simulated combustion chamber pressure loads.

The holographic moire technique is reviewed and adapted to the measurement of the Poisson's ratio of specimens which are submitted to a uni-axial tension.

In modern assembly techniques in order to contact a large multilayer circuit board,complex connectors are necessary. To guarantee a sufficiently high, uniformly distributed contact pressure the knowledge of the deformation of the components under working conditions is indispensible. In the first part of the investigation the deformations were measured with the aid of holographic interferometry. The load on the components was increased in steps and therefore through summation a large total of the stresses in the components via the finite element method (FEM) can be combined with the results of the component surface and the values ob tained experimentally agree well with each other. With the help of this experimentally confirmed model the stresses and deformations can also be calculated for places inside the component that can not be measured at all or only with very costly, time-consuming methods.

The Computer Aided Holo-Photoelastic Method (CAHPM) is applied to the determination of the holographic and photoeldstic stress optical coefficients of a material. The optical fields used are the absolute and relative retardation light intensity distributions. For the former, real time holography is employed and for the latter, half fringe photoelasticity is used. The coefficients corresponding to the principal stress sum (C') and difference (C) are calculated from a least squares fit of experimental whole field stress optical data to the corresponding theoretical stress distribution ILL a L:alibration sample. The data presented were obtained from a diametrically loaded disk and the section employed for the calibration was the centerline perpendicular to the load axis. For the coefficient determinations, the method requires that a total of eleven images be collected; eight phase shifted images of absolute retardation data and three images corresponding to light and dark field circular polariscopic fields for the loaded sample and the light field for the unloaded condition. The theory for the method is reviewed and the experimental setup is also shown. Finally, the influence of retardation plate errors on the calibration results as well as for stress predictions is discussed. Once the coefficients are known, CAHPM which includes our automated isoclinic analysis can be used for exact and total stress analysis of transparent two-dimensional structures without resort to iterative techniques.

The pulsed laser holographic vibration analysis on high-speed rotating structures presents several difficulties due to the rotational movement of the object between the two laser pulses recording the holographic interferogram: Apart from the vibrational motion the recorded holographic fringes can be additionally modulated due to the object's rotary motion. Beyond small angles of rotation, a decorrelation of the recorded object waves occurs, preventing the formation of high visibility interference fringes. To overcome these effects different holographic recording techniques can be used including an interferometer in which both the reference wave and the holographic recording plate are simultaneously rotating with respect to the object, and an interferometer in which an image derotator is incorporated. Conditions for the practical application are outlined, and examples of vibrational studies of high speed rotating components are presented.

The method of double-exposure holographic interferometry was applied to study the mechanical behaviour of an embalmed human tibia under simultaneous torsion and bending loading. The tibia was considered as a cantilever beam fixed at the knee and loaded at the ankle. The deflections were calculated from obtained holographic interferogram. The simultaneous bending and torsion make it easy to obtain the information about derivative values of deflection functions. The bone rigidity was calculated from differential equation of beam being bent as the product of Young's modulus E and cross-sectional moment of inertia I along the long axis. The advantages of the holographic technique in biomechanical research were pointed out.

In digital holography the complex amplitude in the hologram plane has to be calculated. We consider an inclined object plane and an independently inclined hologram plane. The complex amplitude is determined under Fresnel conditions. The feasibility of the method is shown by optical reconstructions.

The physical conception of the shearing photoelasticity is presented. The mathematic model is found and the deduction of the shearing photoelasticity equation is given. In order to improve the sensitivity of the shearing photoelasticity, a new method is developed that is the carried mismatch method by virtue of the computer. Some interesting results are obtained.

Based on the research of photocarrier theory and Talbot effect, a new technique is presented to determine the principal direction and the important relationship of difference gradient and principal direction with Talbot fringes is derived. The important conclusion is that fringes possessing different characteristics can be modulated each other.

Several characteristics of the photocarrier are described and different photocarriers are discussed. The analogy to the carrier theory of the communication shows some interesting conclusions. The theory accuracy of the photocarrier is also discussed and the linear photo-carrier error formula is derived. The error control conditions are given.

Many kinds of vibration, of great concern, occur to rotating structures such as turbines, propellers and brake disks. This paper describes how an electronic speckle patter' interferometry (ESPI) system is combined with the image derotator for the real time investigation of rotating objects. The ESPI + Derotator system is now capable of replacing holographic counterpart in most rotating structure measurements in industry with dramatic improvements in convenience and simplicity of use. A double pulsed Ruby laser illuminates the rotating objects at two positions of its vibration cycle respectively, and a reflective image derotator is used to compensate the rotational motion of the object. The speckle patterns between two laser pulses are correlated as a series of interferometric fringes, which give a picture of the dynamic vibration distribution on the surface of the rotating objects. Such information is valuable for the optimal design or investigation of noise generation.

A new method is proposed for the fringe evaluation in electronic or digital speckle pattern interferometry (ESPI or DSPI). A series of interferometric speckle patterns, at least three, are recorded and stored during the deformation of the object. The subtraction of each two of the speckle patterns gives the correlation fringes corresponding to the deformation between the two exposures. These correlation patterns are interrelated. The phase differences between each two exposures can be determined by comparing the phase relationship between these correlation fringe patterns. The method is suitable for dynamic or large deformation measurement. The principle of this method is discussed and the computer simulation and experimental results are given.