An optical method is proposed which generates the two-dimensional out-of-plane partial contours of silicon wafers and requires only a single numerical differentiation to compute the whole-field residual stress distribution. The optical arrangement for the method requires the use of either a linear or a crossed grating and two large lenses. At the recording stage, this arrangement results in an instantaneous reconstruction of the grating lines into the contours of partial slopes of the wafer. Visual inspection of these contours allows an immediate qualitative evaluation of the local stress variations. Contours with good contrast are obtained even for wafers with circuits printed on them. The partial curvatures are obtained by numerically differentiating the slope contour data. The wafer is modelled as a composite structure consisting of a thin film deposited on the silicon substrate. The two-dimensional residual stress distributions in the film and the substrate are obtained from the curvatures using a plate bending theory approach. The proposed method was used to follow the development of residual stresses in silicon wafers during integrated circuit fabrication using an n-MOS silicon gate process. It was found that the local oxidation step introduced maximum residual stresses whereas the metalization step had a small counter influence on the stresses. The local residual stress variations were enough to cause the conventional average measure to be in error by a factor of two even for wafers without stacking faults. This method can be a valuable tool for a fast and accurate quality control of incoming and outgoing wafers, and can provide useful guidelines for wafer fabrication process research.

Correlation between two speckle patterns obtained by successive exposures has been extensively studied by many researchers. The correlation coefficient is associated with the roughness of the measured surface, the angular offset of the incident beam between two exposures, and the diffraction distance from the rough surface ( or its image ) to the photographic plate. The correlation degree can be estimated by measuring the contrast of the Young's fringes, in turns, the fringe contrast is used for determining roughness of the measured surface. If the fringe contrast is high enough, the interfringe spacing can be measured, which contains a great deal of information about the surface displacement, the surface rotation and the phase distribution.

A modified shearographic (speckle-shearing) method for the rapid detection of residual stress in elastic engineering materials and components has been introduced. A coherent monochromatic light source (laser) is required to enable interference fringes to appear in the recording medium as a result of path length changes occurring between the two separate exposures during the evaluation. The path length change is a function of the objects surface displacement. The method employs a special image-shearing camera permitting quasi-full field measurement of surface displacement. A surface displacement, which occurs due to altering the specimen surface in the test area between the two exposures of a double exposure method, produces a fringe pattern which is visible using a high-pass Fourier filtering device. The viewed fringe pattern is directly related to stresses that are changed due to the surface alteration. The stresses altered are those present due to either a live-load or those resident in the specimen.

A simple but practical optical technique for automated surface inspection of car bodies is presented. The method which is based on light reflection is applicable to inspecting specularly reflective surfaces such as painted car bodies. A structured light signal consists of linear grating is imaged by a video camera via the surface to be inspected. With this arrangement, the surface being inspected acts as a mirror. Presence of surface flaws causes the grating to be locally perturbed. The grating-image is digitized and analyzed by a computer. Several algorithms are developed which automatically identifies the surface flaws by analyzing the perturbation in the grating-image. The technique allows surface flaws to be quantified in terms of slope deviation or depth variation. The sensitivity of the technique is very high permitting minute flaws to be detected. In the paper the theory of the technique will be presented together with experimental validation. The technique possesses numerous practical features such as requiring no special surface preparation, allowing evaluation in place, requiring minimum environmental safeguards, allowing rapid testing and evaluation, providing reliable and quantitative results, and it can be automated. Therefore the technique has clearly exhibited a great potential for being developed into a production-line inspection tool.

Unity vision equipment, such as periscopes and vision blocks, is used in combat vehicles to furnish the vehicle crew with a wide-angle, closed-hatch surveillance capability. The addition of filters to eliminate laser hazards from affecting crewmembers' eyes makes the testing of such filters essential in order to assure their physical and optical integrity. The hazard filters are glass with a thin-film coating and, depending on the application, cemented to polycarbonate or acrylic. This paper presents some preliminary results in the applicability of shearography for flaw detection in thin-film coatings and bonded optical components used in combat vehicle unity vision devices.

Correlation recognition of Chinese character is much more difficult than that of English word. After the investigation of digital method and optical method, we take the MSF (matched signal filter) in UGH (computer generated hologram) form as a compromising method. Based on a simple computing-plotting system, the MSF mentioned above is prepared. The example is that of a Chinese word - "light".

A sandwich technique is presented. Two white light speckle patterns corresponding to the two different loading states of the structure are recorded. Analysis can be carried on in the Fourier transformation optical system as well as the point diffraction optical system. The coherent conditions of the speckle sandwich patterns are derived. The mismatch of the two corresponding speckle patterns can be made use of to introduce the linear photo-carrier with which the sensitivity and accuracy of the white light speckle are improved, meanwhile the measurement scale is enlarged.

Interferometric measurements in high vibration environments or in a turbulent medium can be impossible because of alignment problems and induced phase noise on the signal. Significant improvements to interferometric sensors have been realized with the use of a semiconductor laser as the light source and by enclosing the beam paths in optical fibers. These two advances make the transducer more flexible while improving reliability. Problems unique to fiber-optic interferometers have also been solved resulting in a rugged instrumentation package for measuring localized vibrations in manufacturing environments. In all of these techniques, however, the beam leaves the fiber to probe the surface of the object and is subsequently collected by a lens for return via the fiber. During this process, most of the light is lost, drastically reducing the signal-to-noise ratio. Also, while outside of the fiber, the phase of the beam can be perturbed by index variations in the surrounding medium. These perturbations can destroy the signal in applications where measurements are made on surfaces at elevated temperatures or on objects located in a turbulent medium. A new design for an interferometric sensor has been devised and implemented in a remote bearing vibration monitor where the light does not leave the fiber. In this particular application, the sensor and bearing are in a highly turbulent medium and are located over 100 meters from the laser light source and processing electronics. The design of this transducer and preliminary test results will be presented.

In this paper a new technique is presented. Using grating strain method, we can directly obtain the amount of strains. It does not need to be shock-proof and any darkroom, which is convenient to strain measurement on spot, and it is also very easy tc measure and take the experimental data as well as to treat them. We use a prefabricated orthogonal grating as strain rosette, and then stick it on the surface of the object measured. It can measure directly the value of strain of 2 orthogonal lines on all points of the object and a shear strain. So we may obtain the value and direction of the main strain and main stress on all points. The orthogonal grating is made by means of holographic interferometry.

In Talbot effect, the change of the refractive index along the direction perpendicular to grating lines causes the change of fringes. In the other hand, the intensity of fringes is relative to the principal refractive index and its direction of birefringent object. This paper analyzes the two kinds of Talbot effect mentioned above. The result obtained is suitable for image processing.

Based on research of image photocarrier Talbot effect, some important conclusions are presented in the paper. It is proved that the fringes patterns possessing different characteristic can be modulated with each other to form the photocarrier images. Obviously the conclusion is corrected that the necessary condition of fringe modulation was supposed that two fringe images must have the same fringe characteristic in the previous photocarrier theory. The relationship of difference and direction of the principal stress with the Talbot fringes is derived.

The physical conception of shearing photoelasticity is established on the base of the image photocarrier Tablot effect and shearing moire method. The mathmatical formula is derived. The theory and technique of the shearing photoelasticity is presented . The information of ∂n/∂Si can be dirived to separate principal stresses in 3-D photoelasticity.

Holographic interferometry was used to measure the instantaneous temperature distribution of a premixed flame propagating through a cylindrical tube. In spite of the crude assumptions employed, the combined inaccuracy and imprecision of the measurements was estimated to be less than ±5 percent. The sources of error, the techniques used to minimize the errors, and the magnitude of the residual errors are described.

The present paper proposed a complete method to obtian whole-field displacements information at the curved surface of a body by using carrier-holography and rasterstereography. In the carrier-holography,the fringe pattern of interferogram consists of two parts. Ons is the displacement due to surface deformation, another is a straight fringe family with equal pitch produced by artificality and rigid body moving (if exist). the components of a displacement at every point are given from demodulating carrier-isothetics pattern by means of image processing. The space curvatures of a curved sueface are measured by the resterstereograph method. All the procedure from collecting image to printing result are completed automatically by a personal computer. For example, a model of a hyperboloidal arch dam is nonuniform heated,the thermal displacements on the arch suface are measured.

Using a modulated-fringe technique with double exposure holographic interferometry results in a monotonically ordered fringe pattern. This monotonic feature removes the ambiguity in determining the fringe values. For relatively small flat objects, the carrier fringes are straight and parallel. Using a reference area around the object and in the same plane as the object allows for easy determination of the undeformed and deformed carrier fringes with a single hologram. For 3-D objects, the carrier fringes are curved and non-uniformly spaced. In this case, a single hologram can produce only one of the two necessary fringe patterns. This paper presents a method in which the undeformed and deformed carrier fringe patterns can be obtained and processed by computer. This technique utilizes real-time holography and computer imaging to produce the two fringe patterns without having to reproduce the exact motion of the point source which creates the carrier fringes. The removal of the ambiguity in determining the fringe orders in the two digitally stored fringe patterns allows for the automation of measuring surface deflections of 3-D objects.

Holographic pulsed interferometry was applied in this investigation to studies of an automotive brake squeal problem. Pulsed holograms made on a brake disc assembly which squealed in a simulated service test in a laboratory loading fixture gave a clear display of the vibrating characteristics of the brake assembly. A subsequent investigation on free vibrating brake rotors excited by piezo-electric actuators simulated the service vibration patterns and provided means to evaluate natural disc vibrational modes. This capability in turn would lead to the evaluation of the vibration amplitude damping characteristics of various brake disc designs and materials that could be used in reducing brake squeal. Due to the limited scope of the investigation the development of a low damped brake disc was not carried out.

Electronic Speckle Pattern Interferometry (ESPI) is a full-field and non-contact technique for measuring surface displacements. However, one difficulty in the use of the technique is the ambiguity in fringe interpretation. This paper presents a modulated-fringe technique which removes the fringe ambiguity. By strobing the laser light, two speckle images of an object in steady state vibration can be digitally recorded. Shifting the illumination beam between exposures produces a linear phase variation which is added to the phase change induced by the vibrational displacements. The result is a modulated-fringe pattern which has monotonically increasing fringe orders. This permits the fringe orders to be determined in a staight forward manner and without ambiguity. The phase change due to vibrational displacement alone is then obtained by simply subtracting the known linear phase variation. Elimination of fringe ambiguity has paved a way for automatic data reduction of the vibration mode shape by digital image processing.

Drill bit natural frequencies and mode shapes are investigated using holographic interferometry techniques. For these experiments a fixture is developed to simulate some of the most important process parameters. The drill bit is fixed using an actual drill holder, and a hole drilled by the given drill bit. Then it is loaded to a nominal thrust force typical of machining. The structure is then excited using a piezoelectric exciter at various natural frequencies. The mode shapes of the drill bit are recorded on a photographic plate. The results of the experiments are then utilized toward the development of an analytical model. The model is a twisted Euler-Bernoulli beam subjected to thrust force and trasverse cutting forces. It also includes the rotation of the drill bit. The analytical model is solved using finite element techniques. The results from the holographic experiments are then compared to the numerical results obtained from the finite element analysis, and good agreement is observed. The validated finite element model is potentially useful for design and process optimization in drilling, as well as for process control.

This paper demonstrates recent advances in automating the data reduction from holographically recorded displacements. The computerized data reduction process is based on the marriage of a carrier-fringe technique and digital image process implemented with a personal computer.

One problem in the quantitative evaluation of holographic interferograms is to measure the absolute fringe order and not only the relative one. This relative fringe order can be measured with high accuracy by means of methods like heterodyning or phase shifting. To get the absolute value a method using two different wavelength to perform the interferograms. The mathematical treatment and an experimental application is reported.

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. In the last few years, there have been major developments in the field of glass fibre technology, making it possible to eliminate at least some of the restrictions of holographic interferometry.

Two-reference-beam stroboscopic heterodyne hologram interferometry was used to study beams vibrating at frequencies up to 29.9 kHz. This method allows measurement of vibration amplitudes with an accuracy of 1/1000 of one fringe. As such it is particularly useful in studies of objects vibrating at amplitudes below one micron. Comparison between results obtained from holograms and those computed using the finite element method showed good correlation, in this study.