The last few years have seen major advances in laser interferometry. The use of laser diodes whose output wavelength can be controlled by varying the injection current has led to the development of several new techniques in interferometry, as well as new methods for multiplexing fiber-interferometer sensors. New fields have also been opened up by phase- conjugate interferometers and the use of squeezed light. This paper will review some of the current trends in laser interferometry and discuss some future possibilities.

A white light interferometer was developed for measuring polarization extinction ratios in proton-exchanged, integrated-optic (IO) chips. Usually, such measurements require expensive strain-free polarization components. The instrument which was developed at United Technologies Research Center measured extinction ratios in excess of 95 dB using only interferometric quality optics. The system used a superluminescent diode operating at 825 nanometers as the illumination source and two interferometers combined in series, a measurement interferometer and an analyzing interferometer. The measurement interferometer relied upon the two axes of polarization in the IO chip having different optical pathlengths and the analyzing interferometer was a modified Mach-Zehnder. Results using this system on the IO chips showed that the extinction ratio was 58 dB.

A compact optical displacement sensor is reported which is based on the light undulation caused by the optical feedback on a frequency modulated laser diode. For applying this effect to the metrology, the relationship between the feedback rate and the oscillation behavior of the laser diode was investigated experimentally. As the result, it was found that the higher order of the output undulation could be suppressed by keeping the feedback rate low, and displacement measurement was performed with a resolution of 25 nm for the target distance between a few cm and 30 cm. In addition, an improved current modulation scheme for a laser diode as well as a new signal processing techniques for improving the performance is reported. As a further application, this sensor system was extended for precise measurement of two-dimensional displacement by utilizing a spherical retro-reflector.

An Integrated Beam Control Demonstration (IBCD) is being fabricated by Hughes Danbury Optical Systems (HDOS) for the Strategic Defense Initiative Organization under the direction of the Naval Surface Warfare Center. The IBCD will validate critical technologies for the space based laser Advance Beam Control System (ABCS) Program. One of the system requirements is to provide a means of independently sense and record the wavefront of the main infrared test beam during highly dynamic beam control demonstrations. HDOS developed a design concept and specification for a High Speed Diagnostic Interferometer (HSDI) to meet this requirement. Phase Shift Technology finalized the design and produced the instrument described in this paper under a subcontract from HDOS. The HSDI is an IR phase measuring interferometer operating at 1.321 microns using a PtSi array at 950 frames per second. The system collects up to 256 frames over a 64 X 64 array. A long travel (40 micron) phase shifting device moves the reference mirror to cause a 90 degree phase shift per frame. The data collected is digitized in real time and may be played back, stored to disk or analyzed immediately. Details of the optical system, high speed PtSi camera, long travel phase shifting device, electronics and software are given. Data collection, PZT calibration, and analysis techniques are discussed and results are presented. Examples of this system using menu driven PC based software are presented.

Modified wavefront analysis concepts for interferometric optical testing are presented, specifically: a moire fringes version of the temporal phase-shifting method and spatial-carrier phase-shifting. These techniques require working with a finite fringe observation field in the interferometer; therefore, additional analysis of the imaging optics is necessary. The influence of the interferometer construction and the chosen method of analysis upon the measurement error is discussed. Extended experimental and theoretical comparison of the techniques presented is given in order to fulfill a wide range of user requirements.

Two moire techniques are described which are based on Talbot projected fringes. They are applied to the study of three-dimensional contouring of diffuse targets for absolute shape measurement. One basic system relies on modulating the test target surface by projecting the Talbot image of a linear grating. A second grating, similar to that used for the Talbot image, is employed to obtain the demodulation or moire fringes. These fringes represent surface contours of equal depth. Using a phase measurement technique and digital image processing algorithms, the surface shape information is obtained from the contour maps. The technique is extended using a white light Talbot interferometer that produces a set of real color moire fringes. Each color represents a particular Talbot plane associated with a single wavelength. Subsequent interpretation of these colors allows the selection of a discrete set of contour planes, which suggests the possibility of profile measurement without using conventional fringe analysis techniques. Experimental results, merits and limitations of the systems are discussed.

To gain the advantages of both spatial and temporal heterodyne techniques, and to make efficient use of the limited spatio-temporal frequency bandwidth of image detection systems, we propose a novel technique of spatio-temporal heterodyne interferometry using both spatial and temporal carrier frequencies. By means of spatio-temporal frequency multiplexing, the technique enables simultaneous recording of multiple phase objects on a single space-time interferogram.

We propose a phase locked interferometer where tunability of the wavelength of a laser diode is utilized. A CCD image sensor detects an interference signal electrically scanning a measuring point along a surface of an object. The phase of the interference signal changes according to the surface profile. This phase is kept at a constant value by controlling the injection current of the laser diode with a feedback control system. The surface profile is obtained from the change in the injection current. The feedback signal is generated directly from the output of the CCD image sensor, which enables us to make high-speed measurements in real time. The scanning time required to complete the measurement for one measuring point was from approximately 2 msec to approximately 10 msec. External disturbances such as mechanical vibrations cause phase variations in the interference signal, and accurate measurements become impossible. Detection of the phase variation at a fixed point on the surface of the object is added to the phase locked interferometer. The feedback control of the injection current is done alternately for the fixed point and the measuring point. An exact surface profile is obtained by subtracting the phase variation detected at the fixed point from the surface profile detected at the measuring points. We could improve the measurement accuracy from approximately 20 nm to approximately 5 nm in surface profile measurements of diamond turned aluminum disks.

Recently, we proposed a new method called orthogonal coherent phase-lock detection (OCPLD) for demodulation of the phase distribution of photo-carrier fringe patterns. In OCPLD, if carrier fringe is introduced along the x-axis, orthogonal coherent phase detection technique is used to demodulate the phase distribution along the x-axis, while the phase-locked technique is used to track the phase variation along the y-axis. In this paper, OCPLD technique is presented, and its mathematical model of phase demodulation and phase transfer function are derived. The error analysis of OCPLD is also given. Experimental results show that OCPLD is a precision and rapid method.

We describe a transmission video processing microscope that uses a temporary hologram recorded in real time to provide phase-conjugate illumination of phase and mixed phase and absorption objects. It uses the aberration-removal capabilities of phase conjugation to (1) produce phase contrast in phase objects, (2) make motion in phase objects visible by creating contrast only for moving elements, and (3) eliminate phase background due to an embedding medium or to phase-modulating structures in absorbing (intensity) objects.

This manuscript outlines a continuing effort to validate and verify the performance of an airborne autonomous wavemeter for tuning solid state lasers to a desired wavelength. The application is measuring the vertical profiles of atmospheric water vapor using a differential absorption lidar (DIAL) technique. Improved wavemeter performance data for varying ambient temperatures are presented. This resulted when the electronic grounding and shielding were improved. The results with short pulse duration lasers are also included. These lasers show that similar performance could be obtained with lasers operating in the continuous and the pulsed domains.

A position-measurement type of laser Doppler velocimeter is proposed. While many conventional LDV systems get information on velocity from the frequency of a Doppler signal, the system proposed in this paper obtains that from the instantaneous phase change. The phase of the Doppler signal is obtained from two signals proportional to sine and cosine of the position of a target, respectively. We get the two signals by using linearly polarized beams. Differential configuration of the measurement system enables us to remove pedestal components of detected signals. This system makes it possible to measure rapidly-changing velocity including direction change and zero velocity without any special devices.

Some years ago we realized that a number of flow velocity measurements we were carrying out using a LDV based on the VISAR principle, could be done faster if instead of measuring the velocity at only one point of the flow field in each experiment, we could measure the instantaneous velocity in the whole plane of interest with only one photograph, called Doppler-picture. The Doppler-picture technique allows the measurement of the velocities of tracers passing through a light sheet that cuts a flow, as well as the measurement of the instantaneous velocity of a fast moving reflecting solid surface.

A new correlator which outputs 48 correlation values around the correlation peak is described, and several interpolation methods for the detection of the displacement of a speckle pattern with less than one pixel resolution of the linear image sensor are experimentally compared. The correlator is capable of computing the correlation function between the current frame and a reference frame. The use of the new correlator in conjunction with interpolation methods makes it possible to obtain the best value of the resolution for the speckle displacement of less than 0.2 pixels.

A novel technique for enhancing the time-average ESPI vibration fringes is presented in this paper. The technique is based on the use of wavelength modulation of a laser diode which is adopted in the interferometer as a coherent laser source. The wavelength modulation of the laser diode gives rise to both the additional phase shift and the speckle decorrelation by which the time-average ESPI vibration fringe quality is improved.

Substitution of common lasers by small laser diodes gains increasing popularity since it serves for compactness of measurement systems. The possibility of tuning the emitted wavelength simply by changing the injection current is very attractive for systems applying phase shift methods. Usage of optomechanical elements to produce the required phase shifts is superseded. Phase shifting by laser diode tuning was implemented into the presented electronic speckle pattern interferometry (ESPI) setup. Automatic evaluation of fringe systems is done using the Carre phase shift method. Influences of variations of laser power due to changed injection current and decorrelation of speckle patterns due to the altered wavelength are found to be neglectable.

Applications of holographic interferometry to earthquake prediction studies, such as field measurements of crustal stresses and strains as well as laboratory experiments of rock deformation and failure, are first reported. Advantage and disadvantage of holographic applications to geophysical studies are then discussed. Finally, a new type of ESPI borehole stressmeter is introduced.

There is a need to perform modal analysis upon large structures such as buildings and bridges to understand and predict their behavior during earthquakes. Conventional holographic techniques cannot practically be used. Time average holography on glass plates and thermoplastic film requires vibration isolation. Double pulse holography on glass plates is time consuming in the processing of the plates and locating resonance frequencies and requires an in field darkroom. Conventional electronic speckle pattern interferometry (ESPI) normally requires vibration isolation and is limited to frequencies above 30 hertz. And also ESPI normally produces undesirable noisy looking images. Techniques for performing double pulsed ESPI with fringe enhancement and no vibration isolation have been developed to study these large structures. The work in progress on these techniques is presented.

A statistical interferometric theory for smooth-reference-beam ESPI is presented in this paper. It reveals the effects of all system parameters to the abstracting of information.

In this paper, computer image processing techniques for the extraction of numerical data of vibration amplitude are presented using stroboscopic phase-stepping speckle interferograms. An automated analysis system based on IBM-PC microcomputer and PCVISION-plus Frame Grabber is developed which is able to acquire quantitative displacement information with high speed and accuracy. Effect of time integration during light pulses and f-number of image lens are discussed. Experimental results with out-of-plane resonant vibration metal plate are also given.

Although fully automated phase unwrapping of stepped phase interferograms is a worthy goal and is receiving considerable attention, this Utopian circumstance has not yet been uniquely achieved in a reasonable time on complex real life structures such as an automotive powertrain. The method presented here uses a binary bad spot mask and a seed point mask to phase unwrap the underlying modulo 2(pi) phase map of very complicated structures. Fringe amplitude, modulation, and triangular unit cell path dependence are used to automatically create a portion of the mask. Partition lines are added manually to the mask to separate sheared fringe systems, structural boundaries, and regions of sampling theorem violation.

Phase-measurement interferometry (PMI) techniques enable quantitative measurements to be performed in optical testing, holographic interferometry, and speckle metrology. This paper will present results of error analyses of the most common errors in phase-measurement techniques. These errors include miscalibrated and nonlinear phase shifters, detector nonlinearities, detection quantization, vibration and air turbulence, and frequency mixing. Simulations providing the magnitude and form of these errors are shown for a number of different phase-measurement algorithms.

In an effort to improve the signal to noise in an interference experiment, we have developed a method to remove systematic phase drift between data sets acquired over long time intervals. Using this technique, it is possible to average repeatedly acquired phase measurements and improve the phase estimate without sacrificing spatial resolution. Results from tests using real-time phase stepping holographic interferometry applied to cantilever bending of a piezoelectric bimorph indicate that white noise has been reduced from 3 to less than 1 deg (lambda/360) by averaging 36 phase compensated data sets before object bending and 36 data sets after bending.

We describe a multiplexed form of phase-step interferometry suitable for measuring and mapping deformations at the nanometric and subnanometric level. Differential holograms of an object under stress are obtained by twin exposures sandwiched about a phase shift of (pi) (1 + 2(delta) ) or (pi) (1 - 2(delta) ) radians in the reference wave. Two reference waves are employed, and a conjugate pair of such holograms is recorded simultaneously, with (delta) < < 1, on high-resolution medium. The differential holograms of the pair are read individually. The interferograms reconstructed therefrom, once placed into accurate registration, are electronically reconstituted into an image in which small displacements are mapped linearly into intensity. An improved registration method used in the present work permits us to map displacements smaller than 0.4 nanometer within the optically sparse specimens that we use for calibration.

Optical measuring systems, such as holographic interferometry, speckle interferometry and speckle correlation make it possible to achieve the graphic, 3-dimensional surface area and very accurate measurement of deformations and vibration amplitudes. These systems are suitable tools for the optimizing of construction features.

Strain measurement using interferometry requires an efficient way to extract the desired information from interferometric fringes. Availability of digital image processing systems makes it possible to use digital techniques for the analysis of fringes. In the past, there have been several developments in the area of one dimensional and two dimensional fringe analysis techniques, including the carrier fringe method (spatial heterodyning) and the phase stepping (quasi-heterodyning) technique. This paper presents some new developments in the area of two dimensional fringe analysis, including a phase stepping technique supplemented by the carrier fringe method and a two dimensional Fourier transform method to obtain the strain directly from the discontinuous phase contour map.

The Fourier-transform method determines the interference phase distribution from an interference pattern. If evaluating only a single pattern, the sign remains unknown. Methods for interactive sign correction and for determination of the sign by two phase shifted interferograms are presented. For demodulation of the wrapped phase, a path independent algorithm is described.

Application of the 2D Fourier transform method of fringe analysis to Electronic Speckle Pattern Interferometric fringes produced from a specimen in high speed rotation is presented. Some of the problems arising through the shape of the fringes and method of analysis are discussed. Experimental results are included.

The use of Fourier fringe analysis as a tool for surface characterization has been well documented. However, there remain several grey areas in the implementation of this technique as a practical tool. Principal among these is the catalog of errors associated with the backbone of the technique--the Fast Fourier Transform. These errors are well known, but their nature and form in this context are not fully understood. This paper gives a detailed review of these problems together with their impact on quantitative measurements and presents possible routes to their elimination and solution.

The light deflection characteristics of the measuring beam rays passing through the laminar thermal boundary layer developing along a heated flat plate is theoretically analyzed, and the additional fringe order shift and fringe displacement are compensated to estimate exact values of temperature and Nusselt number. The obtained values compensated for the deflection effect agree with the exact ones of a laminar forced convective heat transfer. The optimum image focal position of the TV-camera taking real-time interferograms is also determined to minimize the measurement error, and is found to be not fixed but to depend on the thermal condition.

Phase shifting and logical moire (PSALM) is used to process fringes obtained by holographic interferometry. A moire is generated between the holographic pattern and a computer generated reference via logical operations. The computer grating is shifted to give the required number of shifted patterns to solve for the unknown deformation induced phase. Comparison with FFT is demonstrated.

Different software codes useful in fringe pattern analysis are described. The problems of achieving, digitizing and analyzing are briefly discussed with reference to a new software code, completely written in our laboratories. Some applications of numerical processing to holographic interferometric fringe patterns are described.

Adhesive bonding, especially the overlap adhesive bonded joint, is used in many applications, as in aircraft construction. For the development of new kinds of adhesives, there must be a testing technique which allows a fast and reliable detection of the stress distribution in the adhesive layer. In BIAS a method was developed which allows measurement of the entire specimen deformation. This deformation can be split into two parts: the adhesive layer and the two plate deformation. It has been shown by FEM calculation that in regions where the adhesive layer strain has its maximum, the entire specimen deformation is almost exclusively composed of the adhesive layer deformation. With this knowledge it is possible to determine the adhesive layer stress distribution by measuring the total deformation of the specimen.

Presence and growth of edge delaminations in carbon-fiber/epoxy (CFRP) tensile specimens can be detected by shearography and by holographic interferometry. The in-plane component of the displacement field on the object surface lowers the contrast in the interferogram for either technique. This effect is analyzed quantitatively. The comparison shows that both techniques have about the same sensitivity against in-plane object movements. The influence of object creep motions and of mechanical setup vibrations is also compared. Our experiments have shown that the main advantage of shearography in this application is the intrinsic differentiation of the measured out-of-plane displacement field; it allows clear contour identification of the defective regions in the CFRP specimens.

The short exposure time and high framing rate of the TV-holography system allow for global interferometric measurements even in industrial environments. In this paper we report some experiences from failure tests on concrete and weak sedimentary rocks. In a set of rock cavity failure tests, TV-holography has been used to monitor the cavity deformations. The technique allows for a complete description of the continuous displacement and deformation of a surface, and has a potential to reveal important information about, e.g., symmetry-breaking processes. Combined with image processing, the technique has been used to study micro-cracks on the surface of concrete blocks during pressure testing. The purpose of these tests was to study the fracture mechanics of concrete, including crack initiation and propagation.

Subject of the investigation are time dependent processes that cause small particles in rough surfaces to displace or deform. These small particles must be identified in a region several cm2 in size. The method proposed is a simultaneous application of electronic speckle pattern interferometry (ESPI) and a holographic double exposure technique using suited carrier fringe systems. The time dependence of the process is observed by ESPI indicating suitable states of the process to be compared by the double exposure technique. Detection of displacement and identification of the particles takes place in the reconstruction real image of the double exposure hologram. The real image was chosen because of the better accessibility of the finely spaced carrier fringes. The resolution obtainable with this method is subject of discussion. The power of the method is illustrated experimentally.

There has been much recent interest in the application of optical tomography to the study of transport phenomena and chemical reactions in transparent fluid flows. An example is the use of multidirectional holographic interferometry and computed tomography for the study of crystal growth from solution under microgravity conditions. A critical part of any such measurement system is the computed tomography program used to convert the measured interferometric data to refractive index distributions in the object under study. Several of the most promising CT algorithms for this application are presented and compared here. Because of the practical difficulty of making multidirectional interferometric measurements, these measurements generally provide only limited amounts of data. Recent studies have indicated that of the several classes of reconstruction algorithms applicable in the limited-data situation, those based on the Multiplicative Algebraic Reconstruction Technique (MART) are the fastest, most flexible, and most accurate. Several MART-type algorithms have been proposed in the literature. In this paper we compare the performance of state-of-the-art implementations of four such algorithms under conditions of interest to those reconstructing multidirectional interferometric data. The algorithms are tested using numerically-generated data from two phantom objects, with two levels of added noise and with two different imaging geometries. A reconstruction of real data from a multidirectional holographic interferometer using the best of the algorithms is shown.

Holographic interferometry has been used in a large scale transonic wind tunnel to produce a 3D flow visualization. The experiments have been carried out on a model civil transport aircraft wing and turbine powered engine simulator combination. This study is significant industrially as the method forms a diagnostic for turbofan installations. The holograms show many relevant flow features including shock waves, flow interactions between the engine simulator flow and the freestream flow, secondary flows, and acoustic waves. Quantitative 3D position information has also been obtained for some of these features. A comparison to other flow diagnostic methods has been made in this paper.

Application of particle image velocimetry (PIV) to a scale transonic wind tunnel and to a cold burner spray is described. It is shown that diffraction limited imaging makes it possible to extend the working range of PIV systems to several meters enabling a broad variety of industrial applications and to determine particle sizes with a high magnification objective. In both cases diffraction limited imaging significantly reduced the laser energy required to form satisfactory particle images. Particle images were recorded onto 35 mm film and a CCD video camera.

A holographic interferometric study was made of the structure of a shock wave discharged from a square cross section shock tube. To visualize the present complex three-dimensional shock wave phenomena, two- and three-dimensional holographic interferometry was applied. The results indicated that the vortex which was generated from the shock tube exit changed its configuration from a square shape to a cylindrical shape and that the secondary shock wave has a complex three-dimensional shape. To compare the experimental results, a numerical simulation using the TVD finite difference scheme was conducted and good agreement was obtained. It is pointed out that quantitative holographic interferometry is particularly useful to validate the CFD code.

By using an optical path delay set-up, the instantaneous process in which a Q-switched YAG laser induces breakdown on an aluminum surface is studied. A series of time-resolved Mach- Zehnder interferograms and optical shadowgrams of the plasma and the shock wave during the initial stage is obtained. Plasma refractivity distribution and electron density on the shock front are computed.

Phase object pattern analysis has shown the possibility of increasing considerable microscope spatial resolution. Experiment has revealed resolution enhancement of greater than a factor of ten. Some phase object images inside an Airy disk are presented.

Industrial applications of holography in France are briefly reviewed. Particular attention is given to nondestructive testing of helicopter blades at Aerospatiale Central Laboratory, the use of holography at Renault for car-engine vibration study, vibration characterization of turbo-jet engine components at SNECMA, and vibration analysis of plates in an industrial hemodynamic tunnel.

Testing of vehicle components with holometry to improve their structural characteristics is a proven methodology. Full field, high sensitivity holometric measurement capabilities are used for the iterative improvement of prototype structures (static and dynamic). The combination of modeling methods and Computer Aided Holometry (CAH) is just beginning to impact structural design. Current examples of studies of static and dynamic behavior of vehicle components using continuous wave CAH techniques are presented.

The validity of inertial-fusion experiments relies on precise and accurate knowledge of the characteristics of small (<1-mm diam) gas-filled shells, such as the wall thickness and outer diameter of the spherical microballoon and the density of the gas inside it. In the past, dual-beam interferometry has been utilized to determine these quantities. These techniques produce interference patterns which have a spatial intensity distribution that is sinusoidal. In contrast, multiple-beam interferometry produces interferometric patterns which are described by the Airy function, and they can have interference maxima that are sharp and narrow, depending on the number of interfering wave fronts. This work describes a technique that uses a scanning, plane Fabry-Perot interferometer to determine inertial-fusion target parameters to high accuracy using the increased precision of multiple-beam interferometry. The microballoon is inserted between the highly-reflective surfaces of an air-spaced Fabry-Perot etalon that is illuminated with monochromatic plane waves. As the separation between the end mirrors is varied continuously, the intensities of the light transmitted through the center of the microballoon and passing external to it are recorded simultaneously as a function of mirror spacing. From this data, the phase difference between these two wave fronts is determined and the appropriate inertial-fusion target parameters are calculated. Using a scanning Fabry-Perot interferometer in conjunction with computerized data acquisition and analysis techniques, phase measurements with precisions of the order of X/100 can be made. With proper refractive index calibration, this precision results in a wall-thickness measurement accuracy of about 0.1%; and the density of the gas inside the microballoon is found with an accuracy of about 1% of its measured value.

A real-time holographic interferometry system was developed to inspect disposable reagent containers used in a clinical chemistry centrifugal analyzer. The system features a commercial holographic camera and a specially designed machine vision apparatus for the manual or automated detection of bonding flaws which could result in field failure of the packages. Engineering analyses of the interferograms located the most probable debond sites and successfully guided the corrective redesign.

The feasibility of using holographic interferometry for the nondestructive testing of arc and flame sprayed coatings is studied by using thermal stressing technique. The detection of bonding flaws in several specimens has been demonstrated. The location and shape of flaws detected are closely related to the artificial defects. By employing fringe control technique, the thermal stressing method can be more effective for flaw detection. With thermalplastic recording and vision system, the size and location of flaw can be visualized and evaluated in a few minutes.

Optical methods become useful tools for dimensional measurements. Different techniques have been developed in the last few years. In addition to the well known time of flight and phase measuring principles other methods such as focussing and interferometric techniques are implemented. Today, laser interferometry is probably one of the most commonly used interferometric methods in metrology. A stabilized He-Ne laser is freque9tly used as light source with an absolute stability of better than 10 . The accuracy for length measurements is limited by the atmospheric conditions (humidity, temperature, pressure) rather than by the laser stability.

The function of fiberoscopic optical systems in medical or technical research and diagnosis is to render the natural cavities of the body or other difficult-to-access environments as if these were being observed directly. The unique and useful features of optical fibers for endoscopic diagnosis will be presented. Some limitations of endoscopic imaging will be pointed out. The possibilities of obtaining more information from an endoscopic image by exploiting the interferometric techniques will be discussed.

Laser Doppler velocimetry is an interferometric technique which allows to provide rapid. objective and non-invasive measurements of the flow velocities. The accuracy of these measurements depends on the apparatus function of the velocimeter which is the apparatus broadening of the Doppler spectrum. This is defined by the parameters of the optical and signal processing units of the velocimeter alone. In the majority of technical applications the probe volume of the conventional velocimeters is much smaller in extent than the dimensions characterizing the flow system under study. On the contrary the flows of biological fluids (protoplasm, blood, etc. ) are usually spacially restricted, so that the probe volume can be comparable to the characteristic dimension, e. g. the diameter, of the vessel . In these conditions the velocity gradients introduce the additional gradient broadening to the Doppler spectra which can exceed the apparatus broadening. This reduces the possibilities of the velocimeter to measure the velocity profiles in the investigated flows which are sometimes the main objectives of the study. But at the same time the gradient broadening carries the information on the velocity gradients which in certain cases can be extracted.

In this paper a technique to optically excitate ultrasonic Rayleigh waves is presented, thus allowing a completely contactless ultrasonic near-surface inspection.

The operaUon of machines and plants often leads to a strong loading of near-surface regions. Consequently, the non-destructive testing (NDT) of these regions during production as well as inspection is of high interest. Besides flaw detection the used test method should allow an exact flaw description. Furthermore contactiess techniques and the possibility of automation are points of interest. One technique which fulfils most of these requirements is the holographic soundfield visualization /1/. This technique allows large area detection of ultrasound (US) surface waves by means of opto-holographic methods. The test result is given by an image of the object surface covered with interference fringes representing the soundwave fronts. Until now only visual evaluation of the recorded soundfield images is performed. Because of the superposition of flaw pattern with the pattern of the insonicated soundwave, an exact flaw analysis appears difficult. with respect to precise as well as automatic testing digital image processing can be applied. The main task of image processing of soundfield images should be the isolation of flaw information from the background which is given by the insonicated wave and the image of the object surface.

Fringe counting techniques are often used in modern laser interferometers for measuring displacement. These interferometers are essentially integrating devices, where the displacement is derived from an accumulated fringe count; that is, they measure travel rather than static displacement. If the interferometer optical paths are interrupted during a measurement cycle, the reference for the instrument is lost and accuracy suffers. In this paper, we describe a holographic technique whereby displacement is measured by analyzing a fringe pattern localized at infinity which is equivalent to Haidinger or Brewster fringes in conventional interferometry. The phase distribution of the fringe pattern is measured to high accuracy using phase-stepping interferometry, and then analyzed by computer. Using this technique, we were able to measure in plane displacements with an accuracy of about 0.2 micrometers , while the accuracy for out of plane displacements was about 2 micrometers .

A 3-D displacement general equation of moire interferometry for measuring 3-D displacement of the negative camber using a dual columnar light wave is put forward. The authors researched the interference field of the dual columnar light wave and its change over law, and they deduced the internal columnar round and axial and radial displacement equation for measuring them. Using an optical fiber for flexible transmission and a small volume columnar lens system to realize miniaturization of the optical system, this technique can find use in measuring internal pipeline.

In an effort to reduce the hardware requirements for phase shifting interferometry, we have developed two approaches to estimating the amount of individual phase shift between interferograms. This is intended to make possible phase shifting interferometry with unknown and varying phase shifts. This will reduce the cost of phase shifters by eliminating the need for precision calibrated devices. The first method of estimating the phase shift involves beam shuttering and requires a special hardware modification of the interferometer, while the second is a purely software implementation. Both methods are relatively inexpensive to install and use.

In this paper we describe the operating principle of three different optical fiber flow meters. The optical fiber sensors used for sensing the measurand delivered by a conventional flow rate converter are all of the intrinsic type. Thus there is basically no influence in the measurement results due to fluid cleanness or fluid transparency. We present in the following some experimental results that we achieved in the case of water flowrates on industrial test rigs.