A new and novel technique is discussed that provides non-contact high resolution absolute measurements with moire interferometry. Field shift moire provides both a course absolute measurement and a high resolution relative measurement similar to a vernier caliper. Combining these measurements yields absolute high-resolution range information.

We propose a sinusoidal phase modulating laser diode interferometer which is insensitivity to vibrations of optical devices and fluctuations in the optical wavelength of the laser diode. We analyze the sinusoidal phase modulation in a laser diode interferometer, and describe the principle of the feedback control of the injection current of the laser diode to eliminate the fluctuations in the phase of the interference signal caused by external disturbances. We construct two sinusoidal phase modulating interferometers for movement measurements and surface profile measurements, respectively. The experimental results make it clear that the interferometers can be used in mechanically noisy circumstances.

Major advances in imaging technology have seen the advent of 3-dimensional imaging systems, and the ensuing advantages that they have over 2-dimensional systems in many situations. Both passive and active systems for 3-dimensional image production have been widely used for robot control, and for high accuracy measurements in engineering metrology. This paper will concentrate on a discussion of the development of a new instrument employing dynamic fringe projection techniques, capable of simultaneously measuring the range at each point in the field of view of, say, a CCD camera in real time. The instrument, called the Dynamic Automated Range Transducer, (DART), uses a method of fringe projection based upon the principle of triangulation. The current investigations aimed at automating the ranging process will be described, and an error analysis and theoretical maximum resolution of the system will be included.

A method for a phase detection of Young's fringes is applied to a high-precise retardation measurement. A simple common-path polarizing interferometer is used with a birefringent wedge and a polarizer. The birefringent wedge introduces a spatially linear phase difference between orthogonally polarized light and Young's fringes are formed on an image sensor. The phase difference between orthogonally polarized light is proportional to the phase of Young's fringes. Thus, the retardation is equal to the phase change of Young's fringes before and after the insertion of the retarder into the common-path interferometer. The phase of Young's fringes is calculated from Fourier cosine and sine integrals of the fringe profile. , The experimental results for wave plates, a Soleil-Babinet compensator and a Pockels cell are presented with error estimations. The accuracy of the retardation measurement is estimated experimentally to be higher than X/2100.

A hexf lash phase analyzer is an electronic circuit that solves the common phase from a three-phase input. Two applications are described, one being an interferometric angle encoder having unprecedented resolution, and the other being a real-time television fringe pattern analyzer.

The concept of hexflash phase analysis described in a previous talk' has been extended to two dimensions. The associated phase unwrapper also works in two dimensions, making the device useful for high speed wave front sensors. A wave front sensor is described which uses high speed 32 x 32 arrays at each focal plane, enabling real time phase measurment at up to 1024 points. These measurements are acquired at a nominal frame rate of 5 KHz. The processing electronics which will be described adds a transport delay of less than 1/20th of a frame.

A sequence of algorithms for processing interference patterns generated by a phase-shifting speckle interferometer is discussed. The processing yields the computation of in-plane displacement and strain components on the surface of an object, using a phase-shifting algorithm to compute the phase. Accurate phase measurement on a 512*512 grid is achieved by pixel-synchronous digitizing of four interference patterns and subsequent calculation of the phase modulo 2n radians, using a two-dimensional look-up table. A pipeline of Datacube image processing modules is configurated to perform this measurement. Digital image processing algorithms have been developed for phase unwrapping, phase restoration and smoothing. During these processing steps, invalid pixels due to low modulation or saturation are neglected. For phase unwrapping an algorithm has been developed that, starting at a chosen start pixel, propagates a "wavefront" of unwrapped phase data through the data set and that takes a set of neighbouring pixels into account to detect 2n steps. Subsequently, phase restoration is done by averaging valid neighbouring pixels. Basic binary image processing techniques are used to solve the problem of irregularly shaped objects due to holes and shadows. The measured phase change is used to compute the in-plane displacement and strain components of the deformed object. Results of a measurement of in-plane displacement and strain components on the surface of a simple aluminium object are shown.

Moire technique using projected fringes is a suitable method for full field measurements of out-of plane deformations and object contouring. In many applications however, the sensitivity of the method is often too low. To overcome this problem, one solution is to apply interpolation tech-niques by means of precise location of the fringe maxima. In this paper we present a method of fringe location by means of a zero crossing algorithm. The system is based on a digital image processing module plugged into a PC/AT using a CCD camera as the imaging sensor. In this way, the positions of the maxima are located with an accuracy of a fraction of one pixel width.

The extraction of fringe curves is the foundation of the automatic quantitative analysis of interferometric Images. This paper proposes an efficient method for interferometric fringe curves extracting. First, alt fringe curve points are detected. Then these fringe curve points are tracked. Finaly, the fringe curves are extracted by a linking algorithm. The detection principal of the fringe curve points and criterions for curve point tracking and Interrupted gaps linking are discussed In detail. In the paper. The experimental results show that the method is effective.

Interferograms with closed loop fringe patterns pose numerous difficulties while labeling. Most automatic fringe numbering routines fail while encountered with fringes of complicated shapes. An interactive fringe numbering routine which uses a gray scale coding technique in the form of pseudo coloring to help the machine to identify each order during data input is presented. Each fringe is traced individually and coded with different colors (gray levels) according to its order. The computer is informed of the order of each fringe and the corresponding gray level, so that while it scans the peak contours for data input, it identifies each order even if the fringes are concentric.

An automatic fringe tracking programme has been developed for use with holographic interferograms obtained for heat transfer and compressible flow studies at the City University Thermofluids Laboratory. This paper reviews the image enhancement routines which were considered for use to prepare images prior to the application of fringe tracking and fringe ordering procedures. Their relative performances are assessed qualitatively and the conclusions which were reached in these studies are presented. Data pre-processing aspects such as image masking and the selection and implementation of common point or fiducial marking are also described. An important aspect of the work described has been the necessity of operating with an optimised level' of image enhancement, trading off processing time and hardware costs against usable image quality. Maximum entropy and statistical enhancement methods were rejected in favour of more direct and speedier methods. The heat transfer experiments were carried out with more primitive equipment than that used for the compressible flow studies, yielding poorer quality raw data, so that a much more extensive image enhancement regime was required before adequate data was available for the fringe detection routines. The paper details the different routines required in these two cases, illustrating how experimental sophistication can be traded against image processor costs and processing time.

This paper describes recent developments on methods for quantitative analysis of holographic interferograms. Two areas are considered : the holographic system and the automatic processing of fringe images. The holographic system is based on a quasi heterodyne technique. Methods for reconstructing the image with a single beam are presented. This produces a continuously variable phase difference between the two images of the object. An analysis of the errors has been performed for the reconstructed phase maps. A tiling approach and graph theory have been applied to the fringe field processing problem. This has produced an automatic method for analysing fringes forming an optimum solution for a phase or height map.

The Moire Interferometric Strain Sensor (MISS) is based on the principle that gratings diffract light in preferred directions determined by their frequency. Hence by tracking the change in diffraction angle the frequency of the grating can be determined. In engineering applications, a grating attached to the specimen would change frequency as a consequence of the strain at that point. Thus the change in diffraction angle can directly be related to strain. Since for most elastic strain measurements the change in diffraction angle is very small, this paper describes the use of a CCD array to improve the sensitivity.

Profile measurement using phase-shifted interference fringe projection technique is described and discussed. This method realizes the measurement by projecting interference fringe patterns on the object surface and by observing the deformed fringe pattern at the direction different from the projection. To obtain the information finer than the fringe spacing, phase-shifting technique is adopted. This technique needs no fine fringe pattern to improve lateral resolving power as it gives height distribution at all the picture elements over the object image. Discussions are made on errors inherent to the method, including the error depending on intensity quantization and number of phase-shifting steps.

The equilibrium distribution of particles dispersed in an aqueous solute situated in a centrifugal accelerative field is routinely studied by means of an optical trace recorded photographically. Rayleigh interferometric fringe patterns have been widely used to give this trace, in which the displacement of the parallel fringes is directly related to particle concentration differences. We have developed a simple but highly efficient frameshift algorithm for automatic interpretation of these patternsl . Results obtained from extensive use and further definition of this algorithm confirm its validity and utility. We have also studied algorithms for the interpretation of Fresnel fringe patterns yielded by an alternative optical system. These more complex patterns involving non parallel fringes can be analysed successfully, subject to certain conditions, with a precision similar to that obtained using Rayleigh interference optics.

Recent work has shown the importance of the fast Fourier transform (FFT) in the automatic analysis of fringe patterns. Three problem areas are encountered when the FFT is used as an analysis tool in this fashion, namely, aliasing, the picket fence effect and leakage. The authors consider leakage to be by far the biggest problem in this application. The paper defines what causes leakage and suggests how leakage may be controlled using data weighting functions. Comparative results obtained using a variety of functions are presented.

The objectives and reasoning behind the specification of a new test instrument are analysed with brief reference to the instrument it was to replace. The theory, development and operation of a 150 mm diameter scanning multi-waveband phase interferometer is described. This entails a description of how the method of phase modulation evolved with reference to its linearity and ability to operate over a very wide range of wavelengths (.6 um - 10.6 um). The method of phase measurement and its resistance to vibration is described with a brief outline of the electronic building blocks required for the operation and calibration of the instrument. The requirements and choice of computer are discussed. It will then be shown how the above elements can be put together to form a very compact and versatile instrument. The functions of the associated software are also described both for data capture and display, which is real time, and also for analysis of the captured data. The analysis includes MTF, PSF, LSF, encircled energy, polynomial fitting, homogeneity measurement and the manipulation of stored interferograms. Results from the final instrument will also be presented.

Both optical information processing and digital image Processing are used for the component separation of the displacement derivatives in speckle shearing interferometry. In recording, a single-beam illuminates normally the object surface and two photographic plate record symmetrically the speckle field. Fringe carriers are introduced during the double exposures, which result in the frequency difference between the in-plane and the out-of-plane information. Through the ordeminterpolation of the modulated fringe carriers, the in-plane strain fringes are separated by digital-image subtraction.

A Twyman-Green phase-shifting interferometer with a laser diode (LD) source was constructed for testing an optical element. An automated interferometric system was developed in which the laser current is continuously changed to synchronize intensity data acquisition with vertical drive pulses of a charge-coupled device (CCD). The intensity of interference pattern is integrated with a CCD detector for intervals of one-quarter period of one fringe. A microcomputer calculates the phase to be measured. To avoid the mode instability of LD, a feedback interferometer with extra TTL electronics is made to stabilize the phase shift using the frequency tuning of LD. The experimental result is shown to measure the profile of a diamond-turned Al surfa-ce.

We have developed a new computerized measuring system for interferometric testing of lenses and mirrors. A personal computer with an image processor controls a laser interferometer, stores interferograms, derives the wavefront shape, and evaluates such imaging performances of optical components as the Seidel and the Zernike aberration coefficients, the peak to valley(P-V), the root mean square(RNS) values of wavefront aberration, the spot diagrams, PSF, and MTF.

The subject of the inspection is a diesel spray jet nozzle ( fig 1. ). The jet is manufactured to spray diesel fuel in 8 precisely controlled directions inside a diesel engine. The angle of elevation of the jet as it leaves the nozzle and the angle between neighbouring jets about the nozzle are of particular importance.

Based on the practical experience gained during the development of an automatic fringe tracing and ordering programme at the City University Thermo-Fluids Laboratory, the paper presents a critical appraisal of available fringe analysis techniques, ending with a flow chart which delineates the necessary steps, and, where applicable, the viable alternatives for the one- or two-dimensional analysis of infinite fringe data. One dimensional fringe analysis can be applied where only single scan data is required and the fringe analysis routines can be run essentially normal to the fringes. In this case, a choice of five viable techniques is available for the analysis, but automatic fringe ordering is impossible without extensive a priori knowledge, because of the lack of whole field data. Two dimensional fringe analysis can be performed either by edge detection or by medial line extraction; the latter of these is time consuming but somewhat more accurate. Fringe ordering by manual, semi- or fully-automatic techniques is possible in this case. If only limited data storage capacity is available then it may be necessary to use a redundancy algorithm to reduce the amount of data to more moderate proportions.

Fiber-optic sensors are becoming increasingly popular. Their use is steadily expanding and a large variety of fiber-optic transducers were designed and are commercialized for measuring pressure, strain, temperature, etc.

Image processing applications are computationally expensive. The paper shows that the computational time required for an application such as correlation can be considerably reduced by using a hierarchy of images. Even with these optimisation techniques, speeds do not approach real time on a uniprocessor system, but significant speed increases can be obtained by using a multi-processor system. It is shown that choosing the correct processor for the desired application is an important decision and that for correlation a digital signal processor provides superior performance over conventional processors.

It is usual, in speckle photography, to set the optical axis of the photographic lens so that it is perpendicular to the surface being investigated. However if the photographic lens is set with its optical axis at an angle to the object surface then it is shown that the accuracy of separating out the in-plane and out-of-plane displacements can be improved. A further benefit is that the whole visual field of the photographic lens can be studied whether the object itself is flat or has a 3-D surface profile. This means that speckle photography can be applied to objects of any shape and of considerable size. Firstly the principle and theory of the oblique axis method is explained. In particular the method of correct focusing is shown; because of this the technique is not possible with simple 35 mm SLR cameras where lens and film planes do not have the necessary movements for differential focusing, none the less the potential of a mono-rail plate camera can be full realized. Secondly the validity of the technique will be seen by presenting results of tests on a simple structure. Finally it will be shown, using automatic fringe analysis, that the method can be applied to large 3-D structures, such as a machine tool.

In this paper, affecting factors on accuracy of fitting wavefron of light beam with orthogonal polynomials are given theoretically in terms of F-test method of statistics. The method availability to control accuracy has also been verified experimentally by an axial hologram reconstruction.