During the last national meeting of the Holographic Club of the French Optical Society held at SAUMUR, 22-23 November 1990, on `Vibration analysis with the help of holographic and associated methods,' more than 80% of attendees were industrialists. Some scientists who specialized in coherent optics said that it is not necessary to be an optician to use holography in the industry. That means that veritable progress has been achieved since the discovery of holographic interferometry in 1965. But, on the other hand, too few industrialists use holographic techniques. This paper critically examines the evolution of holographic interferometry through concrete examples and shows that hopes of industrial uses of holography are more credible today than yesterday because of new developments expected in hardwares (lasers, recording materials, etc.) and softwares.
In recent years, various methods for computer-aided phase reconstruction from phase-shifted interferograms have been developed. The acceptance of these techniques for practical utilization mainly depends on their degree of automation, reliability, and robustness. The main problems to be solved occur in the inverse-modulo process (phase unwrapping). There are already many solutions differing in robustness and complexity. This paper deals with the description and classification of the processing difficulties and some strategies to avoid them or to diminish their influences. First results of a new procedure considering the phase discontinuity field in a global way are presented. This topology-based approach opens the possibility of model- and knowledge-based processing of phase-shifted interferograms.
The spatial-carrier phase shifting (SCPS) technique that is related to both Fourier transform and phase-shifting methods of calculating the phase is analyzed. In this technique, a large amount of tilt is introduced into an interferogram, so that the phase difference between successive pixels equals (pi) /2. Three successive pixels are used to recover the phase using the adequate standard phase shifting formula. The detailed error analysis is presented. Examples of application of this method in conventional and moire interferometry, as well as in optical triangulation, are shown. As the SCPS technique requires a single frame only for phase calculation, it is capable of making high-speed measurements or performing testing in adverse environments.
The relative fringe order in a holographic interference pattern can be measured with high accuracy by means of methods like heterodyning or phase shifting. The determination of the absolute fringe order from the interferogram has not been solved satisfactorily. In this study, the absolute fringe order is determined through the employment of several wavelengths. Two interferograms are recorded with different wavelengths of a dye-laser. The mathematical treatment and an experimental application are reported.
This paper deals with the problems encountered when unwrapping a noisy phase map obtained in connection with phase shifting speckle interferometry. Due to decorrelation of the speckle patterns obtained before and after loading the object, these phase maps are very noisy and unwrapping requires smoothing. Traditional procedures based upon averaging or median filtering in a window have some disadvantages. Averaging tends to smooth the jumps to be identified in the phase map and median filtering is very slow. A new fast-edge preserving approach is presented and compared to some traditional methods by means of evaluating their performance when filtering and unwrapping a computer-generated noisy sawtooth pattern.
In quantitative investigations of heterogeneities in transparent media in such fields as experimental gas dynamics, ballistics, thermal physics, physics of plasma, control of large optical elements, etc., classical interference and holographic techniques are most effective. They make possible the a posteriori analysis of the object waves reconstructed from holograms by shadow, color, and interference methods with the change of initial tuning of the device and with the increase of measurement sensitivity. The recording of the object initial hologram or interferogram, for example, on a gas-dynamic stand or during the control of large mirrors, can be hampered by the external vibrations or by difficulties of joining together the object and the interferometers. This is conditioned, as a rule, by the off-axis location of the reference beam in the interferometer circuit, for example, Zehnder-Mach type, and by the existence of the relatively distant large optical elements. This paper presents a new interferometer that doesn't have those drawbacks.
The adhesive bonding, especially the overlap adhesive bonded joint, is used in many sectors, such as 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 the entire specimen deformation to be measured. 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.
During the past few years, the number of intraocular lenses that have been implanted has grown considerably, thereby creating the need for an exhaustive study of the characteristics of such lenses as image-forming systems. This paper discusses the spheric aberration of flat- convex intraocular lenses as measured by a holographic interferometer and compares the results with the technical data on the aberration that said lens presents. The match between theory and experimentation is good.
Nondestructive testing (NDT) of near-surface component regions is of great importance, because functionality, loading capacity, and lifetime of components often depend on material condition and discontinuities (flaws) in these regions. It is therefore necessary to provide reliable and problem-matched testing techniques to monitor material condition and to detect relevant inhomogeneities. This especially is true of the NDT of hot surfaces of continuously casting slabs in the steel industry. With respect to NDT, several surface and subsurface testing techniques have been developed. The classical methods of surface testing (e.g., visual inspection, dye penetration testing, magnetic particle testing) reveal a series of shortcomings, but these techniques often have the inability for hot surface testing. Fast and noncontact methods are required, especially in the field of hot surface testing. In the following a special NDT-technique, based on holographic interferometry and ultrasonics is presented which can reduce some problems in hot surface testing. By this technique, free-running ultrasonic waves insonified at the surface to be tested are visualized holographic-interferometrically. Disturbances of the otherwise homogeneous acoustic wave fronts, as they are depicted in the soundfield image, indicate near-surface flaws, which can be described with regard to their location and size.
The use of a new type of steady-state energy exchange that can be realized in media with a local response during anisotropic self-diffraction accompanied by a change in the plane of polarization, permits optimization of selection of environments and conditions of the record of interferograms. Some of these results were applied in modern industry to determine the residual stresses in welded structures and size instability of materials of air-space industry.
Several pulsed TV-holography techniques exist. Single-pulse techniques give good fringe visibility but a large sensitivity for environmental instability. Double-pulse techniques are much less sensitive to instabilities but normally yield a poorer fringe quality. New subtraction techniques improving visibility are introduced, and their features compared to the conventional pulsed TV-holography techniques.
The probability density function of detection of a speckle of a fixed size in the classic pattern of a fully developed random field is studied. The notion of spatial speckle size is defined. The results obtained for the one- and two-dimensional case and the possibility of practical application of spatial speckle-field statistics are discussed.
This paper presents qualitative and quantitative results obtained from measurements on specimens of different composite materials and one ceramic-ceramic joint. Characterizing anisotropic material properties, extensive investigations have been carried out to measure effective thermal coefficients of expansion and to determine thermal shear based on correlation fringe patterns. Carbon-fiber materials reinforced with epoxy and metal matrix have been subjected to thermal cycles. A further DSPI application concerns residual stress analysis on a ceramic pipe that is laserbeam welded.
A diode seeded Nd:YAG pulsed laser is used in conjunction with ESPI to study targets undergoing resonant in-plane and out-of-plane vibrations. The Nd:YAG laser is capable of operating in a single- or twin-pulse mode. At a repetition rate of 50 pulses/sec, the single- and twin-pulse operations are used to create subtraction fringes, and the twin-pulse operation (at 50 twin pulses/sec) to produce additional fringes. Results are presented for phase determination from in-plane and out-of-plane subtraction fringes, and also results on noise reduction for additional ESPI fringe patterns.
The method of measurement of a derivative of a function of phase distribution in the object plane is dealt with in the paper. The method consists of recording in the phase object image plane of a one-dimensional grating defocused image and in subsequent coherent optical processing. As a result of grating image repeated coherent re-recording with filtering of lateral orders of diffraction, increase of measurement sensitivity is obtained. Experimental results, characterizing 16-times sensitivity increase of measurements, are shown.
The operational advantages of the complementary techniques of electronic speckle pattern interferometry (ESPI) and laser Doppler velocimetry (LDV) are combined for out-of-plane vibrational analysis. A cw laser was used in a fiberoptic system to generate time-averaged ESPI fringes. By mutual phase-locking of the ESPI and LDV signals, automatic heterodyning of the ESPI signal was achieved, together with compensation for unwanted nondeterministic out-of-plane whole body motion of the object under study. Automatic heterodyning extends the operating range of time-averaged ESPI systems to higher vibrational amplitudes, and reveals phase relationships in the object vibration. A practical demonstration of this new technique is described.
Real time speckle photography using B112S1O20 (BSO) crystal for the recording media of specklegram has been investigated for measuring deformation of a object in a real time. First, it is shown that the ratio of a periodic distance of the generated Young fringes to the average diameter of speckles forming the fringes must be kept larger than 1.1 in order to obtain the fully developed Young fringes with a high contrast. Next, it is shown that the BSO used In photorefractlve type has enough potential to be recording media for the double exposure specklegram. Finally, displacements due to deformation on a surface of rectangular pole of a rubber have been measured by real time speckle photography
Advantages of moire holography with single illumination beam as a real-time method to detect vibrational modes of diffusing objects have been already experimentally demonstrated by several authors. The main obstacle to automatizing the analysis of the moire pattern is the difficulty in filtering the carrier pattern. At the present, it seems affordable to realize filtering in quasi-real time by means of a digital image-processing system. However, several problems arise in this operation, for example, the spread of the spatial frequency spectrum of the carrier fringes. Different filtering algorithms, with and without FFT, are compared. Different ways to combine both carriers are examined.
The free electron laser (FEL) amplification mechanism is discussed in this paper, including the influence of electron beam quality (energy spread, emittance, stability) on the FEL performance. Considerations regarding the choice of the electron accelerator are presented and some characteristic properties of laser radiation are discussed. An overview of FEL-facilities for the infrared spectral region, which are being designed and built worldwide, is given.