Several processes of image formation through inhomogeneities are compared: double-pass phase conjugation, single-pass phase conjugation, and superresolution. The phase conjugation processes can each be combined with the superresolution process, giving rise to more generalized methods of image formation through inhomogeneities.
An erythrosin-doped polyvinyl alcohol (PVA) film can generate phase-conjugate (PC) waves simultaneously by degenerate four-wave mixing (DFWM) process with a fast response time and holographic process with a slow one. The DFWM component with a response time of about 1 msec results from saturable absorption in erythrosin dyes, while the holographic component with a response time of tens sec is generated from a hologram recorded in the erythrosin/ PVA film. The PC reflectivities for both components exceed one percent. In combination of these two processes, we demonstrate that the erythrosin/PVA film is available for real-time and double exposure PC interferometries with a cw argonion laser.
Structural integrity could now be assessed in the field environment with static test loads using pulsed holography and computer vision. Previously, we made holograms of pressurized components on a vibration isolation table with a cw laser. Now, they have been obtained without vibration isolation using pulsed ruby or YAG lasers to freeze motion. Instead of viewing the holograms with a separate cw laser as is usually done, the pulsed laser itself was used. A video camera and frame grabber were used to capture the image and hold it between laser pulses for continuous viewing of the image on a monitor. To obtain a fringe pattern which indicates strain, two separate holograms are made for initial and final load conditions and are viewed together, or one hologram is made for the initial condition and is viewed together with the component itself in its instantaneous condition. Techniques to overcome unwanted motion of the component under test are described, so that fringes due to deformation alone can be seen.
Expressions of the maximum displacement measurable by holographic interferometry is presented in the paper. From spectrum analysis of an image-hologram, a model of speckle statistics is established in reconstruction viewing system. The results show that the displacements much larger than the mean size of the speckle at holographic plate or at surface of fringe localization can be obtained by holographic interferometry when the viewing aperture is small enough. Methods of increasing the upper-limit of range are also proposed.
Holographic correlation filters have been used for a variety of recognition tasks, generally related to military applications. In these applications, the holographic correlation filter is made in the Fourier transform plane of some known subject, then compared to an unknown to determine degree of correlation or fit. Correlations of this type have the properties of very high speed, near insensitivity to position of the subject, and tolerance to small variations in the subject. The output from a correlation operation of this type is typically a single point of light, the intensity of which is a measure of the degree of correlation. Classical holographic interferometry, on the other hand, is unique to a particular diffuse subject and very intolerant to any rigid body motions of the subject. When a subject is moved in a holographic interferometry system, the interference fringes quickly decrease in contrast and vanish as the hologram becomes decorrelated. Positioning a subject with a real-time holographic interferometry technique can be very difficult as the fringes, which must be found, are moving very fast and are changing in character and shape as the object is moved through the referenced position. The use of a correlation filter simplifies this registration task by creating a single, unmoving correlation point, which can appear and vanish with the sensitivity of holographic interferometry, yet also be made flexible enough to determine near registration conditions. The use of a single element detector permits the reference position to be determined to a very high accuracy, with the very high speeds associated with optical correlations. Experimental results of using this technique for high accuracy registration of a zero position of a rotational shaft will be presented in this paper.
Many of the properties of dichromated gelatin (DCG) holograms such as diffraction efficiency, spectral bandpass and reconstruction wavelength can be understood by measuring various optical parameters of the DCG film at various stages of the hologram production process. In this paper, the influences of the optical nonuniformity of the substrate and the photosensitive layer, changes in the thickness and the refractive index during exposure and processing, the light transmissivity through the interfaces and absorption in the photosensitive layer, on the hologram properties are investigated and discussed.
For correct size and shape analysis of very small micro-objects by holography, aberrations play an important limiting role. A unique characteristic of in-line Fraunhofer holography with collimated beam recording is that each object can be considered to be on the optical axis. During the reconstruction, the hologram center can again be made to pass through the optical axis. With this arrangement, all the off-axis aberrations practically disappear. This aspect has been discussed in this article for practical size ranges encountered in far-field holography. Spherical aberration can also be removed by proper sphericity of the reconstruction beam in terms of reconstruction-to-recording wavelength ratio and the object-to-hologram distance. These conditions are obtained by equating the third order spherical aberration to zero. The situation is then described for object space ranges for tolerable aberrations satisfying Marechal's criterion.
Combining surface interferometry of limited aperture with automatic evaluation by phase shift and with ultra precision kinematics allows to scan large surfaces or bodies of revolution and produce a composed interferogram covering the entire surface.
A review of the current state of phase-measuring interferometry is presented. Emphasis is placed on the broadening field of applications for the technique including; micro-surface topology, non-destructive testing, and surface contouring. Advance techniques of extending the range of phase-measuring interferometry and high speed data sampling are presented, along with two other techniques of interest.
Performance parameters describe a phase-measuring interferometer's system operating conditions, its ability to acquire information in a given testing environment, and the quality of that information. This paper presents a review of these parameters, their definitions and quantification. Additionally, a self-referencing technique is presented for the absolute calibration and removal of an interferometer reference wavefront signature.
The interpretation of interferometric test data frequently involves fitting sampled data points to some set of polynomials and the removal of a reference wavefront. Random uncorrelated sampling errors introduces inaccuracies into the polynomial fit. This process is complicated when testing a large component with multiple non-overlapping apertures by the need to reconstruct the total surface shape from the related subaperture data sets. This paper examines the error introduced into the polynomial fit by random uncorrelated sampling errors. The error, expressed as an rms value, is represented as a projection onto the reference and total polynomial spaces.
A new method for the wavelength dependence of the index of refraction has been recently proposed. It is based upon an accurate determination of the positions of dark bands which appear in the source spectrum observed in the focal plane of a spectroscope while a phase plate is partly inserted in its field. After the method has been reminded, experimental results obtained with known glasses and liquid crystals are reported proving the efficiency and the reliability of the method. In addition of those experimental data, a discussion is devoted to the versality of this new method also the accuracy of the results is considered.
An interference microscope enables visual inspection of optically smooth surfaces in order to obtain quantitative data on surface roughness, size and depth of defects. We modified such an instrument into a phase-shifting interferometer. Some measurement results are presented and commented.
The self-imaging property of the SIS has been utilized for transferring information from extended objects placed at certain distances from the SIS to its self-image planes. The concept of 'reverse shadow magnification' has been introduced, and the most important result is that full object information may be encoded in the self-images by changing this magnification. Typical computed and experimental results for incoherently illuminated objects have been presented in support of some of the conclusions. A simple illustrative application has also been described.
The process of moire interferometry is given mathematical description in terms of the classical theory of optical interference. The governing relationship between displacement and fringe order is derived, and the analysis is extended to cover carrier patterns, double exposure methods, and initial fringe pattern elimination. Various processes for obtaining patterns of displacement derivatives are also described mathematically.
We have considered the image formation due to a number of single and multiple apertures in their immediate vicinity. Under incoherent illumination the images are produced with an extremely high demagnification, typically of the order of 103. Analyses based on geometrical optics, Fresnel-Kirchhoff diffraction theory and the optical transfer function (OTF) have been used to characterize the images produced by pinholes, rectangular slits and rectangular transmission gratings. The high factor of demagnification has been advantageously utilized for numerous applications including image subtraction and phase object characterization. The reverse geometry producing highly magnified images has been discussed and applied to displacement metrology.
Computer moire deflectometry (CMD) using onegrating, a TV camera and a computer image processor (CIP) was developed. The TV camera is located in a Talbot plane allowing the recording of a (disturbed) image of the grating with maximum contrast and without any other optical component. CIP is used for obtaining, processing, as well as automated interpretation of the fringes. Double exposure, real-time , time-average and phase-measuring methods of CMD for transparent and reflective objects are equally demonstrated.
Moire interferometry in this paper is extended to topographic contour measurement of an arbitrary object. The principle of the proposed method is different from that of projection moire and shadow moire methods in both the moire fringe forming mechanism and the w displacement evaluation. The advantage of the present method over the others is that it has a very high sensitivity which can be the order of Amm. As an experimental verification, the method is applied to the topographic contour measurement of a cylindrical shell with and without a diametric point loading.
The interference fringe known as the Lau image is produced at the infinite image plane when two transmission gratings are located in tandem and are illuminated incoherently. We have studied this imaging by analyzing the optical arrangement in which the second transmission grating is replaced by a reflection grating. Unlike the transmission Lau imaging, the new set of fringes become changeable in their profile when one of the gratings is subjected to an inplane translatory motion in the direction perpendicular to the grating lines. The phenomenon is investigated theoretically and experimentally from the viewpoint of displacement sensing. Using the combination of the binary gratings having duty cycle of 1/2, two fringe maxima with different intensities are obtained in a single period of the fringe pattern. Introducing the lateral displacement of the grating, one of the maxima decreases in its intensity while the other increases. The change of the fringe profile has been used for an alignment method. Using 25pm gratings and an automatic alignment system with piezo-electric actuators, alignment precision of about ±50nm has been obtained.
Two optical moire methods for curvature measurements are presented:
a) A new method was developed, based on projection moire, in which the fringes relate directly to the second derivative of displacement. The method was applied on cylindrical shell segments (CSS).
b) Rasterography was extended for the measurement of changes in the radius of curvature. It was also demonstrated here for CSS, under static loading.
The two methods were examined and compared with theory and strain gauge measurements, and were found to be with similar results.
Projected fringe contouring, projection moire, shadow moire, and two-angle holographic contouring all measure surface height relative to a reference surface. A single theory can be used to describe all of these techniques. This paper compares these techniques with each other and with conventional interferometry. Quantitative data are obtained from projected fringe contouring and two-angle holographic contouring using phase-measurement interferometry techniques with a surface height measurement repeatability of 1/50 of the contour interval rms.
An interferometric profilometer with fiber transmission of the 1-D surface profile is presented. The system works in real time by purely optical means. A CCD linear array is used as a light detector. The received interferogram is processed by a microcomputer. Depth resolution is up to λ/256.
Improved signal processing procedures have been developed for determining surface microtopography from interference microscopy. These are illustrated by comparing the finish of a precision-machined surface measured with the research Linnik microscope at Imperial College with corresponding results obtained using the digitized Talystep at the National Bureau of Standards. Excellent agreement is obtained.
This paper describes a commercial optical profilometer, the UB 60, and several of its industrial applications. The operating principle of the instrument is based on the dynamic focussing of a confocal microscope, a technique adapted from known CD player technology. The paper begins with a brief description of the profilometer itself, concentrating on the optical system, and then continues with a brief description of four applications. Finally some encountered measurement problems and their solutions are discussed.
The use of the DiffractoSight (D Sight) technique, is shown to be an effective inspection method for the observation, rating and cataloguing of defects on sheet metal and plastic automotive body panels. Using a standard television camera and a high intensity light source, in conjunction with a retroreflective screen, small localized slope variations in a surface can be converted to grey scale information. The benefits of the system are highlighted by its essential simplicity, high sensitivity to contour changes, low sensitivity to part positioning and its wide field of view capability. The technique is shown to have much to offer in improving process control and monitoring product quality in the stamping, composite and molding industry. Results from laboratory and field installations are used to verify the advantages of the D Sight' approach to surface quality inspection.
This article describes an instrument capable of making precision smoothness measurements on optical surfaces. The feasibility of extending the use of this new measurement technique and instrument into the domain of high precision machined parts and surfaces will be discussed. Such techniques and instruments will provide moderate cost tools for use in evaluating surfaces where defects can cause friction and/or stress failure. Particular applications in machined part and automotive industries are anticipated.
For a multi-sensor machine vision system, relating each sensor's measurement to a master gage coordinate system has been a difficult task. This is especially true for sheet metal gaging in the automotive industry where sensors may be separated by four or five meters. The current approach used to establish this master coordinate system, which is difficult at best, has been the following. First, the part is placed in the gage. The exact location, that is being measured by each sensor, is marked on the part. Then the marked part is transported to a coordinate measuring machine (CMM), where the location of each of the marked points is measured. These CMM measurements establish a master coordinate system. The procedure just described has major drawbacks including: the accuracy of marking the exact location being measured; the sensors orientation must be known with respect to the master coordinate system; and deformation of the sheet metal part when it is transported to the CMM. The mastering process can be significantly improved by optical coupling a theodolite pair with each machine vision sensor. This optical coupling is established by locating a target in a position that can be accurately measured by both a sensor and the theodolite system. First, the theodolite system is calibrated in gage coordinates by sighting on reference points placed on the machine vision gage. Then, for each sensor, the target location is measured by both the sensor and theodolite pair at three or more positions (or alternately one target may have three or more points that can be measured). From this data, the transforms from sensor coordinates to gage coordinates can be calculated. This report will present the configuration and calculations for coordinate mastering using optical coupling.
Laser-aided spherometer is a novel designation for a flexible and high performance instrument to the measurement of curvature radii of spherical surfaces. Combining the well established technique of Laser interferometer for linear displacement measurement with the principle of a classical spherometer frame, an accuracy of one order of a magnitude better than current type of precision interferometers is reached. This stays as the first mark on the development of an all-optical high precision spherometer.
An improved Fourier transform profilometry for the automatic mesurement of 3-D object shapes is presented. Because of using a defocused Rouchi grating to get a qusi-sinusoidal optical field and using grating π-phase shifting technique, the fundarmental spectrum modulated by 3-D object shapes can be extended from 0 to 2f. theorily Cf. is the carrier frequency of the optical field). Consequently,the measurable rate of hight variation can be extended three times more than the unimproved FTP. This article gives the theory and experiment results of the improved FTP.
A technique for the measurement of surface roughness using a non-contact optical profiler is presented for the measurement of surfaces having RA's of up to 2.5 μm (100 μn). The optical profiler uses phase-measurement interferometry to directly measure surface height profiles at a single wavelength of illumination. By utilizing information from surface height measurements made at two different wavelengths, surface profiles with peak-to-valleys of up to 20 gm (800 μn) can be determined. The technique presented is non-destructive, quick, and has an rms repeatability of better than 25 nm (1 μn). Results of measurements made with both linear and area detector arrays on calibrated roughness standards as well as on machined surfaces are presented.
This paper describes the theory and implementation of automated optical roughness inspection. This work is being conducted at the Inspection Workstation (IWS) in the Automated Manufacturing Research Facility (AMRF) at the National Bureau of Standards. The Surface Roughness Instrument Controller (SRIC) supervises the automated optical roughness inspection of parts. This controller is an integrated, data-driven, hierarchical control software system. The SRIC controls two pieces of equipment-the surface roughness instrument (SRI) and the automatic dial indicator (ADI). The SRI is a photo-optical surface roughness inspection device which monitors surface roughness by measuring the angular distribution of light scattered from the surface of a part. Its tasks are coordinated with those of the IWS inspection robot. Using the SRI optical signals as sensory input, the robot properly aligns the part in front of the SRI so that a valid optical scattering reading is obtained. The ADI is used to help the robot position the part in front of the SRI for its initial reading. The SRIC uses the optical data obtained to estimate values of root mean square roughness (Rq) for parts machined in the AMRF.
The characterization of surface microtopography by Nomarski Differential Interference Microscopy, using digital image processing, is compared with measurements obtained from contact profilometry. The limitations of the two techniques for characterizing rolled-metal surfaces are discussed. The advantages of using the distribution of surface slopes for evaluating surface quality in rolled aluminum sheet is highlighted.
An optical/digital approach to the classification of rough surfaces is described. The setup consists of a coherent optical system to generate the Fourier irradiance of a rough sample and a digital computer to process data. The sampling of Fourier spectra is achieved with a wedge ring detector. The extraction and measurement of specific statistical parameters of Fourier spectrum are done for two typical mached samples. An analysis of the efficiency of these parameters in roughness classification is also carried out.
A high precision mark position sensing method for image position sensing detector (PSD) with kaleido scopic mirror tunnel (KM-PSM) is introduced. To increase the image position detecting precision of a sensor element itself, hybrid ( analogue and digital ) type position sensitive device (R-HPSD) is invented. In order to realize high precision and miniaturized 3-D position measuring system, 1-D mark direction sensing method (PM-DSM) which consist of a 1-D image position sensing element, a cylindrical lens and a parallel mirror tunnel is proposed. Furtheremore, an optical range sensing method (RORS) which is suitable to realize a miniaturized optical range sensing probe based on the triangulation, is proposed. In addition, an optical range sensing probe for advanced 3-D coordinates measuring machine is considered.
A simple optical triangulation based electro-optical sensor with 0.01 µm resolution has been successfully used for the interferoretric calibration of 1m end gauge. Two independent illuminating and detecting arms were mounted together to gauge both the faces of the gauge alternately. The null photo-signals defined the gauge planes and the in-between displacement was measured by a laser interferometer. A precision of 0.25 μm was obtained which was limited by the mechanical vibration found to be present in the machine bed. The experimental set-up details, procedure adopted and the results arrived at are presented.
An interferometric system, based on heterodyne principle is described and which enables profile measurements of a surface with a high accuracy. It is possible to measure height variations of 4 Angstroms with a spatial resolution of 1 micrometer. Fran the surface height measurements, there were calculated its statistical properties, such as the R of the heights, the slopes and also its spectral density. The last one identifies the spatial frequencies of the surface, caused for example by the diamond turning mad-line and also by the measuring maChine. For an electro-magnetic wave with a Gaussian profile, which is incident the surface under test, the reflected complex field amplitude (CFA) near the focal region was calculated. jibe have defined the "Macroscopic wavelength" A, which was found to be constant for variations ▵z of the focal distance from the plane under test, for variations of the bean diameter wo in the focal region, while the complex index of refraction (CIF) of the surface under test was kept constant.
The basics, the working principle, the advantages, and the names of ESPI are reviewed. Syntheses and analyses of the optical system set-ups, emphasizing the speckle reference ESPI, of the past and present developments are made. Future development directions are discussed. The optical system set-up requirements and techniques are listed and emphasized. Light economy analyzing method is described and Michelson-type speckle reference ESPI set-up and two other new set-ups are analyzed.
A new technique for fully automatic diffraction fringe measurement in point-wise speckle photograph analysis is presented in this paper. The fringe orientation and spacing are initially estimated with the help of 1-D FFT. A 2-D convolution filter is then applied to enhance the estimated image . High signal-to-noise rate (SNR) fringe pattern is achieved which makes it feasible for precise determination of the displacement components. The halo-effect is also optimally eliminated in a new way. With the computation time compared favorably with those of 2-D autocorrelation method and the iterative 2-D FFT method. High reliability and accurate determination of displacement components are achieved over a wide range of fringe density.
A method that achieves automatic measurements of the orthogonal components of the motion of optically rough surfaces is described. An optical set-un that implements a speckle rotation is used to extract the components of 2-D displacements, which are obtained from simultaneous data recording performed by a single 1-D CCD line. A temporal analysis of speckle patterns related with a given inspected area of a moving structure is then possible. The movement trajectory is reconstructed. The principle of the method and the experimental set-up are described. Experimental results are shown with a specific application to the deformations of a video film structure under directional traction and dynamic analysis of thermal deformations of mechanical parts.
A new method of contouring 3-D objects in real-time is suggested. The technique makes use of Digital Speckle Pattern Interferometry (DSPI) alongwith an in-plane sensitive optical configuration. The contour interval can be varied in real-time by varying the tilt applied to the object. The variation of the contour interval with the tilt angle and the angle between the illumination beams is discussed. The decorrelation of speckle pattern due to tilt and consequently the disappearance of the fringes is also discussed. Experimental results have been presented for a variety of objects.
Auto-correlation and cross-correlation methods have been proposed for the detecting of point information in digital speckle pattern photography(DSPP). With the spatial auto-correlation the magnitude and the direction of the deformation can be obtained and with the spatial cross-correlation the deformation vector can be known. The principles of the two methods have been presented and the analytic expressions of the signal have been derived, from which the measurable minimum and maximum have been predicted. The two methods have been implemented on an IBM-PC/XT based image processing system in the author's work and the experiment results have been shown in this paper.
Recently, the photomechanics employed to measure displacement, strain or stress has been developing rapidly. In photomechanics, the identification of interference fringe order and the density of interference fringe are attractive to the researchers in this field. It deals with the quantity analysis of the measured object, the accuracy and sensitivity of measurement and the real reflection about the whole nature of the measured value, etc. Moreover, the automatic'. identification of interference fringe is also the technical basis of automatic process of interference fringe pattern. At present, the identification and increase of interference fringe can be divided into three groups in which one is the new photocarrier methodc(1-2) , the second one is the optical heterodyning method and the third one is the changed parameter method presented here based on the paper(3). This paper presents the formulas, the physical sense and the applications about the changed parameter method.
Using a modelocked frequency doubled Nd-Yag laser it has for the first time succeded to make a light-in-flight recording using one single pulse. New experiments have become possible such as the contouring of a fast moving object and recording through a scattering moving medium. It is hoped that the timeshift in the arrival of a light pulse that has passed through living tissue can be developed into a new diagnostic tool.
The integral-equation formalism previously used by the present authors to describe the elastic scattering of monochromatic light from a rough metal surface is reviewed. By taking the scattering of light from a plane metal surface as the zeroth order solution to the integral equation, the selvedge field and the diffusely scattered field outside the selvedge are determined in the first and second order Born approximation. On the basis of a generalized Huygens principle, the electromagnetic coupling between two source points located inside the selvedge is briefly discussed. Within the framework of the integral-equation approach, we consider the diffuse scattering of light from a few atoms outside a flat metal surface. By treating the light-induced radiation from an atom in the electric dipole approximation, a set of linear equations is established which allows us to determine the electric fields on the atomic sites, selfconsistently. In the case where only two atoms are placed outside the surface a detailed description of the interatomic coupling is given, and the exact solution for the selfconsistent field on the atomic sites is compared with that obtained in the second Born approximation. The contributions to the selfconsistent field from radiative and non-radiative modes, from self-field effects, and from the excitation of surface polaritons are investigated. With knowledge of the selfconsistent field on the dipole sites we examine the diffusely scattered field. We close our theoretical treatment by outlining how the present work can serve as an adequate starting point for elaborated studies of the diffuse scattering of light from small clusters of atoms on a perfectly flat metal surface. In the final chapter of our paper we present a number of numerical results for the case where one has two atoms outside the surface. Using dielectric data for aluminium a detailed analysis of the frequency dependence of the diffuse scattering process is undertaken.
The need for aspherics has been brought out in optical systems and an effort has been made from the technologist's view point to ascertain the difficulties involved. An appreciation has been done of some of the methods for aspheric generation which have been considered suitable for accurate, reliable and repetitive production. Miniature aspherics for integrated optical systems have also been referred to.
In [I], "Optical flatness standard," by W. Primak, published in Optical Enneerie 23(6), 806-61,5 (1984) , the ultimate precision of determining figures of optical flats was considered for an investigation of dimensional stability and stress relaxation, where any increase in precision of measurement is significant in shortening these investigations, usually extending over months and years. Although it might have been adequate to examine the contour along a single traverse, an attempt was made to combine such measurements to determine the figure of the whole surface in order to choose a traverse away from abrupt contour variations to avoid the errors of placement. With the equipment then at hand, it was difficult to handle more than a few traverses at a time. Now, with the advent of microcomputers with large memories and faster computational speeds, it has become practical to configure data loggers capable of handling data for the whole surface at once, thus greatly simplifying the task of combining the data for the interference patterns of sets of flats in pairs to determine their individual figures, and also giving access to a variety of methods. Several methods of reducing the interference patterns, including two using Fourier series expansions and one using substitution are given, and the problems of such determinations are discussed. A mathematical error in [I] is corrected.
This paper describes the in-process testing of optical components machined on a Pneumo Precision MSG-325 diamond turning lathe. An unequal path Twyman-Green interferometer mounted on the X slide of the lathe provides the means to test aspheric profiles and complex conic shapes and locate conjugates. The use of this interferometer, together with other mechanical methods, enables tooling to be set and centred to the required level of accuracy.
Radial metrology combines an optical measurement technique with fiber optics and a unique lens system to study material properties and deformations on the inner surfaces of the cavities found, for example, inside pipes, tubes, and boreholes. The equations considered in designing and testing a prototype for profiling are described along with tests conducted to demonstrate proof of principle. Digital image acquisition and processing techniques are used to interpret various features appearing in the images and to transform images for improved human viewing.
An optical device is described that performs height data acquisition by focusing a white light beam at a sample surface and processing the backscattered light. The principle of the operation is based on longitudinal chromatic aberration of the focusing lens and on spectral analysis of the image irradiance. The surface microtopography is reconstructed after automatic point by point scanning. A personal computer interfaced to the probe controls the operation and produces the roughness parameters. Highlights of the optical approach are presented, main system characteristics are given and examples of performance on selected objects are demonstrated.
Holography is known mainly as a photographic technique with the capability of storage and three-dimensional optical reconstruction of objects using a laser as light source. This does not at all cover the full variety of applications of laser optical methods based on the holographic principle. There are numerous applications in the fields of image processing and metrology, which have attracted the interest of research groups to evaluate the potentials of these methods in biomedical research.
Currently within decentralised clinical laboratories there is a need for simple and rapid techniques to detect antigens and antibodies of diagnostic significance. The interaction between antigen and antibody molecules may be extremely specific as a consequence of binding geometries and is a principal phenomenon of antibody-based chemical sensors, i.e. immunosensors. Direct optical monitoring of this interaction is an attractive alternative in the development of immunosensors, because optical sensors can be very sensitive, small in size, safe, and cheap. This paper reviews immunosensors based on optical sensing techniques including such methods like light reflectance (the Brewster angle reflectometry, surface plasmon resonance), and evanescent wave fluorescence. The basic principles and the current state-of-the art are discussed with emphasis on sensitivity, measurement range, shortcomings and problems to be solved. Some comments on miniaturisation and future developments will also be given.
An attempt is made to survey optical testing methods currently being investigated for biological research and/or clinical diagnostics. The notation "optics" is used in a broad sense, i.e., for wavelengths in which the flow of electromagnetic energy can be modified with mirrors, lenses and/or gratings. The reviewed optical testing methods are based either on the change of the prop.gation p rameters of the electromagnetic radiation or on the fact that optical radiation is provoking changes in the material to be tested and the resulting signals not necessarily of optical n ture are used for rating. When and how optical testing methods used already in engineering are applicable to biomedical testing is also discussed.
The methodology of digital image correlation of random white light speckle is applied to the measurement of strain in bovine retina tissue which is subjected to uniaxial tension loading. The digital image correlation compares an image of deformed "seeded" retinal tissue to an image of the same tissue in an undeformed state. The correlation of the deformed image with the undeformed image yields both the displacement and strain fields for the area of tissue which is being imaged. The "seeding" of the tissue is accomplished by randomly spreading micron sized steel spheres on the retinal tissue. The results of this study indicate that uniform strain fields are not obtained in simple tension tests of the non-homogeneous retinal tissue as one might assume in the mathematical modelling of such tests. The average strains in a center test section of the retinal strip are correlated and compared with the grip strains. In addition, the digital image correlation methodology is shown to have the capability to make predictions of strain in the proximity of blood vessels and other anomalies in the tissue. This feature of the digital imaging methodology yields valuable information concerning such problems as retinal tearing and separation. The mathematical and physical background of the digital image correlation methodology will be discussed. The limitations of this methodology to measure displacement and strain will be given. The experimental procedure which was used to test the bovine retina will be explained in detail and results from the uniaxial testing of this retina will be presented.
We nave made some investigations on the perceived size of laser speckles. It was found that the increase in the perceived size of speckles with the increase in the viewing distance, is closely relateci to the Size-Constancy effect.