The application of holographic interferometry to determine large deformations of opaque bodies by compensating when reconstructing has been treated previously in several publications. This contribution concerns a similar investigation in the case of a domain with a strong spatial change of the index of refraction as for instance in a fluid or also in combination with different media. Firstly, the general theory about the analogy between both fields as well as the image aberration and the fringe modification is outlined. Secondly, a development of the fringe vector in the case of a moderate index gradient is performed.

Tomography is a technique known for integrating two-dimensional projections into three- dimensional objects. In our application, tomography is used to determine the three- dimensional gas density distribution from a set of two-dimensional interferograms. In an Aeroballistic Range, tomography can be used with multiple-view interferometry to obtain the density field between the shock wave and the model surface. A supersonic flow model is generated by computer code for a 10-degree half angel sharp cone traveling with an angle of attack. Two freestream Mach numbers, 3 and 5, are tested. The calculated indices of refraction are projected two-dimensionally to simulate the results obtained from projected holographic interferometry. Three algorithms based on pixels, a triangular mesh, and polynomial/Fourier decomposition, are used to invert the results tomographically into its three-dimensional flow field. The proficiency and the accuracy of each algorithm are compared under the same matrix inversion process.

Holographic interferometry is a differential technique used to detect small changes that can be translated to phase variations in the light transmitted or reflected by the object. Phase fluctuations are shown as interference fringes produced by the superposition of the wavefront in its original state, reconstructed by the hologram, and the modified wavefront coming from the real object. In order to reconstruct the original beam, the hologram is illuminated with the reference beam used to record it. Making the analysis ofthe resultant interference pattern is not easy. At first, a bidimensional mapping of the phase distribution along the interferogram must be performed. Then using fringe positions, the interference pattern must be interpreted. The detection of the phase in each point of the interferogram and the location of its individual position require a complicated detection system or a well trained operator. In this work we analyze the sensitivity of holographic optical correlation, a technique that gives a global evaluation of the changes in the object through the measurement of intensity variations in a single position. This technique combines the three-dimensional storage capacity ofholography with the integrated response given by the correlation of two wavefronts. Utilizing a Van der Lught type filtering system and a common path holographic interferometer the changes introduced in the object wavefront were studied. To do so, the reference object wavefront is recorded in the hologram. Afterwards the modified object wavefront is used to illuminate the hologram plate. Using a lens the intensity variations associated to the correlation of both object wavefronts is obtained in the direction of the reference beam used to record the hologram. The detector is positioned at the image point related with the collimated reference beam used to record the hologram. The intensity variations measured there give us a global evaluation of the changes in the object beam. Experimental results considering different objects and sources of change are shown.

This paper describes the theory and design of a low frequency omnidirectional hydrophone array. Calculations determining key design parameters are reviewed and new materials were examined to match target specification. A design addition to the sensor is also described to adapt the sensor to the array.

A mathematical model relating surface and bulk behaviors of metals in aqueous solution has been developed. The model was established based on principles of holographic interferometry for measuring microsurface dissolution, i.e., mass loss, and with those of electrochemistry for measuring the bulk electronic current, i.e., corrosion current. The model is utilized to predict the corrosion behavior of metals subjected to anoodic reaction in aqueous solution. Furthermore, the model was plotted versus experimental data of aluminum samples in 0.25 N sodium hydroxide solution.

The measurement of strains at high temperatures has become a very important field of research. Advanced technology applications such as structures for high speed aircraft and high efficiency thermal engines are examples of areas requiring measurements of strains at temperatures well above the capability of present day strain gage technology. In a recent paper by one of the authors1 references on the application of optical techniques to field measurement of strains at high temperatures are given. Of the different techniques that are used, speckle and holographic interferometry are of particular interest. Both techniques are remote sensing and do not require elaborate preparation of the surfaces being investigated. From the view of practical applications the use of TV cameras for recording purposes and electro-optical data manipulation and processing are of great interest. Simplicity in handling the recording process, speedy data collection, and automatic data processing are the main advantages of using electro-optical methods. Some more developments in this field can be found in Reference 2-6. Reference 4 contains quantitative results proving the feasibility of making accurate measurements at temperatures up to 1000°C.

A technique for simultaneous independent measurement of temperature and magnetic field is demonstrated using a low finesse Fabry-Perot interferometer probe. The probe is completely passive and is linked by optical fibers allowing remote operation. Absolute temperature measurement is demonstrated using a two wavelength technique. Unlike all previously reported techniques, the temperature is measured over the same optical path as that experiencing the magnetic field.

This paper describes measurement of magnetic field using magnetic fluid. Magnet fluid shows a strong magnet-optical effect: a birefringence is induced by the magnetic field. Optical heterodyne method has high sensitivity to measure the birefringence. This measurement system consists of a stabilized transverse Zeeman laser, an optical isolator consisting of a Faraday rotator and a half wave plate and the sensor part. These optical components are connected by the polarization maintaining fiber (PMF) and bundle fiber. The two-frequency orthogonally polarized light from light source is led to the sensor part by the PMF. This light is divided into the measurement and the reference light. The probe light passes through the magnetic fluid twice by the mirror. Then it traces back through the bundle fiber to the photo detector after passing the polarizer. The beat signal is compared for the phase difference with the reference signal that is obtained from reference lights behind polarizer transmitted by another bundle fiber. This fiber sensor is independent of temperature and external stress. The magnitude of the magnetic field is received from the phase difference. The results are received sub-Oersted of the resolution and 500 Oersted in the range of the measurement.

A system has been developed and tested for optical noncontact measurement of displacement. The system consists of a light source, an objective lens, a quadrant pattern and a quadrant photodiode. The principle is based on the detection of the contrast variation of the projected quadrant pattern as a function of defocus. This system has coaxial projection and observation axes and is hardly influenced by the color and inclination of the surface. The direction of displacement can be identified by using one pair of detectors. Experimental tests verify the principle of the method and some tests of the system in applications are tried with expected results.

Automated interferometer equipments are described which can be used for calibrations of gauge blocks and line scales with lengths up to 1000 mm. For the gauge blocks, the scanning measurement method utilizes a white-light source and one stabilized 633-nm laser. White-light interference signals from the reference flat and from the front surface of the gauge block mark the distance to be measured with the laser. The final length is determined from the laser-signal phase shifts between the gauge and the reference flat. Environmental conditions are measured and the necessary corrections are made automatically. The repeatability of the measurements is +/- 3 nm for a 400-mm gauge block and the estimated relative uncertainty (1 s) is about 10^-7. The variation in length of the gauge block is obtained by computer-aided analysis of the digitized interference fringe patterns. For the line scales, a new measurement method has been developed which can utilize the same electronic units as used for gauge-block calibration: images of the graduation lines replace the white-light interferences. The two fields constituting a video frame (image) are recorded by a moving microscope and by a ccd camera with 1-ms charging time interval. The exact distance between the microscope positions at the time of charging the ccd pixels is deduced from the interference and video synchronization signals. It is expected that a total uncertainty of about 100 nm for a 1000-mm scale will be reached.

To prove the possibility of detecting internal inhomogeneities in thick walled structures by holographic interferometry we measured the deformations of the outer surface of a thick walled pressure vessel above an internal weld point. The measured deformations were confirmed by calculations of the deformation field by the method of finite elements.

Distributions of in-plane displacement vectors and strain of a laser illuminated diffuse surface are obtained by detecting a distribution of speckle displacement at its image plane. The speckle displacement is determined from the peak position of two dimensional cross-correlation function of the intensity distribution taken by a CCD camera and divided into many subblocks in a computer. First speckle displacement due to general surface deformation is derived theoretically for an imaging system including oblique observation. It is shown that speckle displacement at the gaussian image plane is proportional to object displacement transverse to the optical axis. In experiments in-plane displacement distribution of a plane metal specimen subject to extension is examined. Resolution of displacement is improved by subpixel interpolation of the peak, while range of measurement is extended by integrating small displacements before serious speckle decorrelation. The resolution in displacement and strain are several micrometers and several hundreds of microstrains, respectively. The measurement range is extended up to plastic strain.

This paper discusses the measurement of in-plane displacements on discs driven at high rotational speeds using an optical technique called Electronic Speckle Pattern Interferometry (ESPI). Some of the basic theory concerning rotating components is discussed followed by an explanation of how interference fringes are generated on the test specimen. The interpretation of the fringes and method of analysis using a well established fringe analysis technique based on the two dimensional Fourier transform is then discussed. The extracted data is compared with mathematical models in the results section.

A scanning laser Doppler vibrometer is used to investigate the dynamic characteristics of a tensioned wire specimen. A mathematical formulation and solution is presented for comparison. The ultimate application, investigating the filament behavior in quartz lamp heaters, is also discussed.

An ever increasing variety of automotive component vibration testing is being pursued at Ford Motor Company, U.S.A. The driving force for use of hologram interferometry in these tests is the continuing need to design component structures to meet more stringent functional performance criteria. Parameters such as noise and vibration, sound quality, and reliability must be optimized for the lightest weight component possible. Continually increasing customer expectations and regulatory pressures on fuel economy and safety mandate that vehicles be built from highly optimized components. This paper includes applications of holographic interferometry for powertrain support structure tuning, body panel noise reduction, wiper system noise and vibration path analysis, and other vehicle component studies.

Vibrational characteristics of a model of NASA's GAW-2 airfoil are studied computationally and experimentally. The computational procedures are based on the Finite Element Method. The experimental procedures are based on the Laser Hologram Interferometry methods; more specifically, the methods of stroboscopic Heterodyne Hologram Interferometry and time- average Electro-Optic Holography are used. Comparison of the computational results with the experimental results shows good correlation.

The velocities at which elastic vibrational waves propagate in an aluminum cantilever beam are studied analytically, numerically, and experimentally. In order to predict these propagation velocities, both beam theory and modal analysis have been employed. Experimental results are compared with theoretical results in order to determine the degree of correlation. This comparison shows that the holographically observed velocities concur with the analytically determined velocities. Problems with the particular numerical approach employed in this work are presented and discussed.

The overall breast cancer mortality rate has remained unchanged the last 50 years. The most significant factor in the treatment is its early detection which will alter the mortality rate. In this investigation, the feasibility of holographic interferometry for the purpose of detecting breast cancer was examined. Optical setups were developed to enable the collection of holographic interferograms in vivo of asymptomatic breasts and those containing cancerous lesions. Different stressing concepts of holographic nondestructive testing and their applicability for the detection of breast cancer were tested.

An apparatus for measuring the mechanical properties of thin living biological membranes such as pericardium (the sac which encloses the heart) is presented. The apparatus, using 16 actuators to apply stresses in the plane of the membrane, measures in-plane displacements and strain by means of electronic speckle pattern interferometry (ESPI). As opposed to conventional speckle interferometers which use light reflected from the surface under test, the apparatus presented here collects the light transmitted through the membrane, as pericardium is translucent and reflects very little light. Furthermore, in order to be preserved in a healthy state, the biological membrane must be kept immersed in a bath of physiological solution during the measurement experiments. Results of mechanical stretch experiments are presented where the infinitesimal strain tensor components were measured over the entire surface of a 10 mm diameter circular specimen of pericardium.

The calibration of the novel laser heterodyne interferometry system for measurement of vibrations of small amplitude in the audible frequency range is described. A frequency-shifted reference beam is compared with an unshifted test beam that is phase modulated by a vibrating surface. Vibration displacements down 10 nm in the frequency range from 150 Hz to 10 KHz are measured. The system is ideally suited for biological movement analysis, for example, the acoustic emission evaluation from human cochlea excited by electrical stimuli.

An adaptation of holographic interferometry to microscopic systems is described. The adaptation is suitable for studying motion even at the molecular level. The interferograms are fringeless, and they are presented in a form that discriminates against bulk translation, while mapping local displacements directly. The mapping is inherently insensitive to inhomogeneities in the illumination beam. Statistical interrogation of the maps is therefore unusually free of propagated error; and the effect of reconstruction noise, whose explicit calculation is given, is made transparent. The methods are illustrated by analyzing the motion of force-generating molecules of muscle. It is shown that their movements are correlated to a high degree.

In the course of using holographic interferometry to test a wide variety of specimens, the staff at MetroLaser has acquired a variety of 'tricks' or procedures that has made this practice quick and easy to perform. A few of these procedures are presented here for the benefit of the industry in an effort to further the art of HNDT. In general there are no real technical revelations made here but the simple practical application of basic principles.

The shearographic and holographic interferometry were employed as nondestructive testing (NDT) methods for detecting flaws and delaminations in fiber reinforced composites. Different nondestructive loading techniques were utilized to stress the composites. Using shearography two states of deformation are recorded by double-exposing a Holotestfilm in an ordinary camera. In the tele-lens of the camera a shearing element inside resp. outside the focus is integrated. Rigid body motions of the specimen are not recorded. Local deformation irregularities caused by a defect under the surface of the specimen are not superimposed by an interference pattern, e.g., in the case of the internal pressure differential. The shearogram shows dark and bright fringes which can be interpreted as the gradient of the deformation. The represented shearograms compared with the equivalent holograms show the detection of the irregularities which can be analyzed by an image processing system.

Holographic interferometry has been applied to the visualization of shock wave phenomena. This paper describes the observation of three-dimensional shock wave reflection over cones and demonstrates that this flow visualization technique is more effective than other conventional techniques. It is well documented that, in a two-dimensional shock wave reflection over a wedge, regular reflection or Mach reflection occurs according to the shock Mach number and the wedge angle. Whereas in a three-dimensional flow field when a shock wave reflects from a cone with attack angle, depending on a local attack angle of the cone, either regular or Mach reflection occurs. Therefore, these two reflection patterns appear simultaneously on the cone surface. Very little is known about the transition from regular to mach reflection in three-dimensions. It is thus important to determine the three-dimensional shock transition angle between regular and mach reflection. In this paper, a shock wave reflected from a cone with attack angle was visualized quantitatively by using double exposure holographic interferometry and diffuse holographic interferometry.

A special technique has been developed, enabling large area and contactless ultrasonic inspection of components. Ultrasonic Rayleighwaves are excited by proper laser irradiation of the component surface to be tested. The interaction of the propagating Rayleighwaves with near-surface flaws is visualized within the holographic soundfield picture taken from the insonicated part of the component. Thus, flaws as e.g. bonding flaws and cracks can be detected and described as concerns their shape and size.

A holographic recording system has been developed in which a single pulse from a frequency doubled Nd:YAG laser is repeatedly split and delayed to provide up to 10 pulses which are separated both in time and in space. A custom graded beam splitter is used to help insure near equal amplitude of all ten pulses. A White cell provides adjustable delay between the sequential outputs of the system over a range from 28 to 170 nanoseconds. By appropriate design of the holographic recording geometry, up to ten distinct holographic frames may be recorded in sequence on a single 4' X 5' film plate. Using the system, studies have been performed on the dynamics of detonation of 100 micron explosive particles and on the acceleration and growth of cracks in brittle materials. CW reconstruction of each holographic frame permits microscopic examination of the reconstructed image so that precise measurements of shock front or crack length may be made as a function of time.

A holographic measurement system was used for the investigation of droplet size, density and velocity in the injection spray of a model diesel engine. The model engine consisted of a conventional injection pump and a test chamber that could be operated at high pressure and temperature to simulate the conditions in an operating diesel engine. The use of off-axis holography with a laser light sheet from a pulsed ruby laser helped to increase the maximum droplet density in the spray that could be resolved. Chromatic aberrations, introduced by the reconstruction of the holograms with a wavelength different from the recording wavelength, were minimized by careful choice of recording and reconstruction geometry. A new method for size determination was devised. The reconstructed images were recorded with a CCD camera and analyzed with the help of a personal computer. Software for automatic detection of 3-D particle position and velocity determination was developed.

Continued demands for higher performance and safer vehicles mandate use of new technologies for development of automotive structures. These structures are not only mechanical in nature, but also involve electronics. Durability of automotive electronics depends on their response to environmental and other loads that they encounter. Typically this response is characterized by force-displacement characteristics. Since displacements in electronic components are small, their determination is difficult. In this paper, analytical and empirical methodologies for determination of displacements of electronic components are outlined. It is shown that, using heterodyne hologram interferometry, displacements of electronic components can be measured on the scale of nanometers.

Addition fringe patterns are obtained in real time from Electronic Speckle Pattern Interferometry, using a twin pulse laser, when two pulses are fired within a single field of a CCD camera, i.e. within 1/50 s. The ability of being able to use ESPI in this manner means that target deformation can be studied even under very severe environments. A major drawback of the method is that the addition fringes are intrinsically noisy and of very low contrast impeding a full analysis of the deformation. One way of reducing the optical noise is by subtracting two addition fringe patterns from each other. This subtraction procedure has led to high contrast fringe patterns who may contain information of both target deformation and target motion produced by its surrounding environment. This paper presents results showing such a behavior and its analytical representation which no doubt will be the subject of future research.

In the study the investigation of spatial speckle characteristics is described. After binarization of classical fully developed speckle pattern a probability density functions of linear sizes and speckle areas, a ratio of areas occupied by dark and bright spots, average speckle area and size were calculated.

The interferometer model for measurement of the absolute refractive index of the optical media with the accuracy of 0.00001 has been developed, manufactured and researched. The sample for test to be manufactured as the flat parallel plate. The interferometer gives possibility to defined sample geometrical thickness with accuracy 0.0002 mm simultaneously with index measurement. The range of index and thickness measurements is not limited in principle. The interferometer allows testing of solid, liquid and gaseous media.

The application of the adaptive holographic interferometer based on photoanisotropic organic materials 'Biochrom' to nondestructive testing are presented.