This PDF file contains the front matter associated with SPIE Proceedings Volume 7389, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

The demand for achieving smaller and more flexible production series with a considerable diversity of products complicates the control of the manufacturing tasks, leading to big challenges for the quality assurance systems. The quality assurance strategy that is nowadays used for mass production is unable to cope with the inspection flexibility needed among automated small series production, because the measuring strategy is totally dependent on the fixed features of the few manufactured object variants and on process parameters that can be controlled/compensated during production time. The major challenge faced by a quality assurance system applied to small series production facilities is to guarantee the needed quality level already at the first run, and therefore, the quality assurance system has to adapt itself constantly to the new manufacturing conditions. The small series production culture requires a change of paradigms, because its strategies are totally different from mass production. This work discusses the tight inspection requirements of small series production and presents flexible metrology strategies based on optical sensor data fusion techniques, agent-based systems as well as cognitive and self-optimised systems for assuring the needed quality level of flexible small series. Examples of application scenarios are provided among the automated assembly of solid state lasers and the flexible inspection of automotive headlights.

Multi-scale measurement systems utilise multiple sensors which differ in resolution and measurement field to pursue an active exploration strategy. The different sensor scales are linked by indicator algorithms for further measurement initiation. A major advantage of this strategy is a reduction of the conflict between resolution, time and field. This reduction is achieved by task specific conditioning of sensors, indicator algorithms and actuators using suitable uncertainty models. This contribution is focused on uncertainty models of sensors and actuators using the example of a prototype multi-scale measurement system. The influence of the sensor parameters, object characteristics and measurement conditions on the measurement reliability is investigated exemplary for the middle-scale sensor, a confocal microscope.

In this paper a distributed intelligent system for civil engineering structures on-line measurement, remote monitoring, and data archiving is presented. The system consists of a set of optical, full-field displacement sensors connected to a controlling server. The server conducts measurements according to a list of scheduled tasks and stores the primary data or initial results in a remote centralized database. Simultaneously the server performs checks, ordered by the operator, which may in turn result with an alert or a specific action. The structure of whole system is analyzed along with the discussion on possible fields of application and the ways to provide a relevant security during data transport. Finally, a working implementation consisting of a fringe projection, geometrical moiré, digital image correlation and grating interferometry sensors and Oracle XE database is presented. The results from database utilized for on-line monitoring of a threshold value of strain for an exemplary area of interest at the engineering structure are presented and discussed.

Resolution is an important issue in inspection of objects on microscopic scale. Various approaches have been investigated to increase the optical resolution behind the diffraction limit of an optical imaging system. However every time the optical resolution of a fixed optical system is overcome it is possible to speak of super-resolution. Demonstration that super-resolution have been deeply investigated in interference microscopy through various approaches. Here we discuss briefly the different techniques that have been adopted in interferometry and specifically in digital holography (DH). Then we illustrate a novel method that uses a dynamic diffraction phase-grating for increasing synthetically the aperture of a DH imaging system in lens-less configuration. Consequently the optical resolution of the DH systems can be increased of a factor of 3. The aim of the study is to demonstrate that super-resolution is possible and is a practical and viable method for a coherent optical microscope. We take benefit of the numerical reconstruction properties of DH in combination with diffraction grating to get super-resolution. The approaches could be used for metrology and imaging application in various fields of engineering and biology.

The resonator of a solid state laser is a very well aligned optical system. As the resonator may be as much as a meter or more in length and precise alignment of the optical elements is required, the whole system needs to be exceptionally stable in order to guarantee reliable function. On the other hand, the laser crystal is pumped by light from a focused laser diode with significant optical power. This energy is only partly converted into optical energy as the required laser light. Most of the pump energy is lost as heat. The heat is dissipated within the laser crystal and into the mounting system of the crystal. Due to the thermal expansion of material, the crystal and its mounting system are deformed. The deformation of the crystal will cause a so-called thermal lens effect while movement of the mounting system can lead to disalignment of the laser resonator. In this paper, we describe an experimental set-up to measure the thermal lens effect by means of digital holography. A digital holography microscope was positioned above the laser resonator. The surface of the laser crystal was observed by the microscope via a selectively reflective mirror while the crystal was being pumped and the whole laser system was operating. By changing pump current and laser power, it was possible to monitor both deformation of the crystal surface and deflection of the crystal holder. We present the results of this experiment including an estimate of the stresses and temperatures on the laser crystal induced by its thermal deformation.

Digital holography (DH) has been employed in the retrieval of three dimensional images of bull's sperm heads. The system allows a three dimensional analysis of the sperm morphology by means of a Digital Holographic Microscope (DHM). Microscopic holography measurements are performed by projecting a magnified image of a microscopic hologram plane onto a CCD plane. This could constitute the basis of an alternative method for the zoothecnic industry aimed at the investigation of morphological features and the sorting of the motile sperm cells. Indeed, one of the main advantages of digital holography consists in its full non-invasivity and in the capability of investigating the shape of the sperm cells without altering their characteristics. In particular the proposed technique could be applied to investigate the frequency of aberrant spermatozoa. Until now, in fact, such industrial investigations have been mainly performed by means of specific painting probes: unfortunately this technique dramatically reduces the vitality of the sperm cells and can even cause chromosome aberration, making them useless for the zootechnical applications.

Digital holography and TV holography is the most promising tool for industrial applications. For a successful industrial measuring system automated evaluation is necessary. To develop this kind of measuring system the fringe compensation principle can be used. Because both digital holography and TV-holography operate with images recorded with a digital camera, several computer based compensation methods can be applied. In our investigations automated compensation techniques were investigated to develop industrial measuring systems. In digital holography the compensation method can be easier, using digital compensation, performing the compensation process in the computer using the recorded complex amplitude of the scattered light from the investigated object. In this case the compensation is based on the phase manipulation of the reconstructed waves. Digital compensation method was chosen for TV holography too. Previously developed fringe synthesizing method was applied in Tv holographic measurements. In this method a set of phase shifted fringe patterns of the investigated object is recorded. Using the recorded fringe systems new contour fringe pattern can be generated. Based on these methods, the evaluation program in digital holography or in TV holography can set the sensitivity of the measurement, can separate different deformation components (e.g. rotation, local deformation) after the measurement was performed. Measuring the separated deformation components new alternative output of the measurement can be generated: a list of the deformation components with its features.

There is a variety of well developed methods to measure diffusely reflecting free-form surfaces. For instance fringe projection based systems are commonly used for the contactless optical measurement of such surfaces. The calibration procedures used in these systems are well understood and state of the art [10,4]. However, contactless measurement of specular free-form surfaces requires new measurement techniques along with the corresponding calibration methods. In this paper a multi-sensor approach for measuring specular free-form surfaces using stereo based phase measuring deflectometry (PMD) combined with a fringe projection sensor unit will be presented. With the stereo enhancement over classical PMD techniques it is possible to measure the shape of the specular free-form surface and not only the slope of the surface. However, the major challenge is the necessary calibration. We present a new calibration method to obtain the orientation information of the deflectometry screen and the measurement cameras needed to calculate the shape of the object from the observed phase values. To solve this task we combined the calibration/measurement principles of fringe projection and phase measuring deflectometry into a single measurement cycle. The developed calibration algorithm will be described in detail along with an analysis of the calibration accuracy using simulated data.

Accuracy and robustness of 3D inspection methods, which are based on structural lightening, strongly depend on surface reflectance and its geometry. If the intensity of light profile undergoes disturbances or the image is interfered with reflection artefacts, then the algorithms for height determination fail. The paper presents a method for predictive light profile line segmentation which employs information from 3D model of inspected object. Besides calculation of profile position, based on confidence intervals, the advantage of surface normal pitch and surface scattering are utilized. The necessary information is calculated based on STL object model and surface description extension. The developed algorithm includes error model of camera and laser optics, what corrects distortion and vignetting. The developed solution increases accuracy and robustness of machine vision quality inspection systems especially based on laser triangulation.

In this paper, a quality-guided phase unwrapping method is proposed for a modified Fourier transform method, which utilizes a fringe image and a flat image. The proposed method takes advantage of the additional information provided by the flat image to calculate the visibility of the fringe pattern, which is difficult to obtain in the conventional Fourier transform method. The phase unwrapping process includes two steps. First, the pixels with unreliable phase values in the wrapped phase map are masked out. Then, visibility is chosen as a quality index to assist the quality-guided unwrapping. Experimental results show that the proposed method is an effective method to unwrap complex surface's phase map generated from dense fringe patterns.

Classical 3D inspection systems require users to coat transparent objects before measurement. Experimental techniques via non contact measurement, suggested in literature, do not treat inter reflections. The aim of our work is to develop a non contact 3D measurement system for transparent objects by using a polarimetric imaging method in far infrared range. The classical approach relies on the use of orthographic model generated by a telecentric lens in practical setup. However telecentric lenses working in far infrared range are not available. Therefore, we have to adapt pinhole model corresponding to non-telecentric lenses for shape from polarization. In this paper we introduce a 3D reconstruction method to exploit polarimetric imaging with perspective model. We also propose two mathematical approaches in order to reduce reconstruction error: data analysis method to better estimate Stokes parameters and a validation method after Stokes parameters estimation. These techniques are applicable irrespective of the nature of the selected model and any linear system resolution.

A fast and efficient technique for full-field dynamic 3-D measurement with color three-frequency fringe pattern projection is proposed. The technique is based on RGB color fringe pattern projection and empirical mode decomposition algorithm Using temporal unwrapping method the true phase distribution with high precision is acquired to recover the height distribution of the object. The technique permits the three-dimensional shape measurement of objects that have large height-discontinuity or spatially isolated surfaces. Owing to requiring only a single snapshot; it makes possible the instantaneous three-dimensional shape measurement of discontinuous objects in fast motion.

The development of a modified stripe-pattern projection system that uses linescan cameras is presented. The system measures complex-shaped sheet metal parts (>3 m²) and enables the detection of dents (>30 μm) and other defects. Therefore, the measurement system is moved and the parts are scanned line by line. The parallel investigation of a simulation environment in order to optimize the system is shown. The simulation combines optical ray tracing based on the matrix formalism [1] and projective transformation to get an image equivalent to the measured image in the laboratory setup. In order to extract the object's shape from the measured and the simulated line Fourier-Profilometry is used [2]. Therefore a FFT is applied to the data. The power spectra show a central frequency phase modulated with the object's shape. A filtering algorithm, an IFFT and a phase unwrapping algorithm deliver the shape. Both, experimental data and results from the simulation are shown and the noise effects are considered.

Digital speckle pattern interferometry is potentially capable to solve a large variety of measurement and inspection demands in industrial applications. However, it is not so widely used in industry due to some special requirements that are not easily fulfilled on the shop floor. This paper presents some reflections about what would be necessary for an interferometer to be successfully applied in industrial environments: it must be robust, flexible, compact, stable, friendly and cooperative. Next, a case study, that fulfills those requirements, is presented in details. It involves a digital speckle interferometer designed to measure residual stresses in-field. It was developed using an axis-symmetrical diffractive optical element in such a way that it is not sensitive to the laser wavelength at all. It produces radial in-plane sensitivity on a circular region. The interferometer was accommodated in a compact construction that made it robust enough for infield applications. A magnetic kinematic mounting base is used to firmly attach the interferometer to the surface where residual stresses have to be measured. The same kinematic base is used for positioning an ultra-high speed pneumatic drilling unit. In order to measure residual stresses, a reference phase pattern is first acquired from a sequence of four 90° phase-shifted images. After that, a small blind hole is drilled on the surface to be measured. The residual stresses are then relieved at the borders of the blind hole, what produces a local displacement filed. A second phase pattern is then acquired. The radial displacement filed is computed from the phase difference and it is fitted to a mathematical model. The principal residual stresses are then determined. The interferometer was used outside of the laboratory for residual stresses measurement in a gas pipeline in a risky area. The goal was to investigate the effectiveness of a repair.

A simple electronic speckle pattern interferometer (ESPI) using a transmission holographic optical element (THOE) is presented. The THOE is designed to create a speckled reference beam in the interferometer. It is a transmission hologram of a diffusely transmitting glass plate. A specific requirement for the fabrication of the THOEs is for them to be recorded at one wavelength, at which the recording material is photosensitive and reconstructed using a near-infrared laser diode which can be current modulated for phase shifting purposes. A partially reflective glass plate provides illumination of the object along the normal to its surface, ensuring that the system is sensitive only to out-of-plane displacement of the object. The intensity of the object beam can be controlled by using reflective glass plates with different reflection coefficients. It is demonstrated that the HOE based system can be used for vibration measurements and modal analysis. A big advantage of the system is its simplicity.

Temporal carrier has been introduced to electronic speckle interferometry (ESPI) in order to produce virtual speckle patterns. Dynamic deformation measurement with a large deformation is performed by using virtual speckle patterns. However, it takes a long calculating time to produce virtual speckle patterns, because the method requires Fourier transform operation at each pixel of CCD. In the proposed method, virtual speckle patterns are produced by algorithm without Fourier transform. As the results, it is confirmed that the calculating cost of virtual speckle patterns is improved remarkably, and that the new method also is equal to the ordinary methods in measurement accuracy.

We present a white-light spectral interferometric method for measuring the chromatic dispersion of microstructured fibers made of polymethyl methacrylate (PMMA). The method uses an unbalanced Mach-Zehnder interferometer with the fiber of known length placed in one of the interferometer arms and the other arm with adjustable path length. We record the spectral interferograms to measure the equalization wavelength as a function of the path length difference, or equivalently the differential group refractive index dispersion over a wide wavelength range. First, we verify the applicability of the method by measuring the wavelength dependence of the differential group refractive index of a pure silica fiber. We apply a five-term power series fit to the measured data and confirm by its differentiation that the chromatic dispersion of pure silica glass agrees well with theory. Second, we measure the chromatic dispersion for the fundamental mode supported by two different PMMA microstructured fibers, the multimode fiber and the large-mode area one.

The refractive index distribution over a cross-section of an optical fiber can differ between core and cladding, can vary over the core in graded index fibers, or may even have a more complicated form in polarization preserving fibers. Besides this intended variations the refractive index may vary due to a loading of the fiber like pressure or bending or due to a faulty production. Digital holographic interferometry is a suitable means for measuring the refractive index distribution. In the experiments reported here the fiber is embedded into an index matching fluid, which is mixed so as to match the index of the cladding. Phase-shifted digital holograms are recorded and the interference phase distribution is calculated. From a single demodulated interference phase distribution the refractive index field is determined by an algorithm based on a model which takes into account the known symmetry of the fiber. It can be shown that the obtained accuracy is better than that of classical two-beam interferometry. Results of experiments with step-index, with graded index, and with polarization preserving fibers are demonstrated.

Digital holography is one of the most versatile tools for the whole field imaging of wavefronts. Since numerical reconstruction provides both the amplitude and phase of the wavefronts it finds immense potential applications ranging from shape measurement to microscopy. The method is useful especially for phase objects, which otherwise does not produce any change in the amplitude of the interacting wavefront and hence is difficult to image. The wavefronts passing through a region having non-uniform refractive index distribution will carry the information about this distribution as a spatially varying phase. Digital holography can be used for measurement of this phase. Here the use of digital holographic interferometry coupled with tomography is investigated for mapping of spatially as well as temporally varying refractive index distributions.

Optical deflectometry, likewise many other optical methods, permits to reconstruct the wavefront deformations induced by a refractive or a phase object. In this paper, a Fourier based deflectometry method is presented. A telecentric imaging system acquires pictures of a grating being the superposition of two crossed Ronchi rulings of the same spatial frequency. The object under test is inserted in the optical path between the grating and the telecentric imaging system. The presented Fourier based image analysis permits to extract the wavefront derivatives, and therefore permits to reconstruct the wavefront or the local power of the object. In this paper, the method is illustrated on several free form thermoplasic elements, the sensitivity is determined experimentally, the precision is analyzed and the ability to characterize cosmetic defects is evaluated.

The extraction of 3D shape and roughness by optical measurement techniques become more and more import in industrial applications. Optical systems are measuring fast with high accuracy and give reliable information about the workpiece form or surface roughness. The classical systems based on triangulation, white light, confocal, shadow or fringe projection techniques and are applied with a great success in recent years. In future there will be a growing interest in robust inline measurement techniques to monitor the manufacturing process. E. g. some automotive manufactures are using confocal systems to characterize the surface of cylinder liners inline. But there is another robust and powerful technique suitable for inline measurement purposes: scattered light sensors. In this paper, a special type of a scattered light sensor based on the former Rodenstock RM 400 sensor is considered. The sensor enables the user to measure form and roughness in a robust manner. The properties of the sensor are analyzed system-theoretically.

The interferometric length measurement value in multi-axis positioning and measuring systems is directly influenced by the topography of reference mirrors. Form deviations of the mirror plane can cause systematic measurement errors because the specimen geometry is superimposed upon the topography of reference mirrors. This article discusses the complete acquisition of the topography of a special mirror arrangement with the help of a Fizeau interferometer to correct systematic measurement errors after the raw measurement using the expanded three-flat test. Furthermore, other influencing factors are presented in the article, e.g., measurement errors caused by the Fizeau interferometer. Additionally, temporal changes of the reference mirror topography are detected by regularly occurring measurements, and the topography data used as the correction reference are updated accordingly.

Requirements on high-performance of ball bearings in terms of the loads they experience and their reliability are increasing as the automotive, aerospace, and power generation industries look to cut costs, reduce emissions, and improve efficiency. Most bearings are evaluated with a stylus profiler or with a bright field scopes or microscopes for form, roughness, and defect classification. Two-dimensional stylus measurements captures only very localized surface profiles unless multiple scans are performed which slow the measurement time unacceptably; this leads to inadequate sampling and sometimes greatly varying results based on location and directionality of the line scan. Bright field microscopes deliver only the lateral information about defects but not their depth, volume or surface roughness. White light interferometry can be very successfully utilized in the measurement of full field form, roughness and defect detection and is gaining adoption. They provide rapid, accurate, three-dimensional imaging compatible with the newly developed ISO 3D surface parameters which are expected to rapidly displace traditional 2D metrics. These surface parameters allow for better characterization of surface structure and better understanding of the production process and bearing and race wear. New 3D filtering techniques allow effective separation of form, waviness, and roughness for highly accurate and repeatable bearing qualification.

Wave front sensing is an optical method allowing non-contacting topography measurements of flat surfaces. Applications of the method are, for instance, the characterization of optical components, semiconductor surfaces, or subcomponents used in semiconductor manufacturing equipment. The method developed here is covering the characterization of flatness on mirror-like surfaces within three orders of magnitude from micro- to nanometer scale. This is due to the high range of detectable surface slopes from very low to relatively high values. Therefore, the method is applicable to both, micro- and nanometer scale height deviations on surfaces. The wave front sensing is capable of studying the topography in a real-time operating mode. The technique enables vertical resolution of approximately 10 nm at a lateral resolution of 0.6 mm on bare silicon wafer surfaces. Moreover, highly reflective surfaces with height deviations of 10-15 μm could be easily resolved at a lateral resolution of 2.4 mm. In this study, we focused on the application in semiconductor surfaces and manufacturing equipment: measurements were performed on bare wafers as well as on the mirror-like surface of a wafer holder used for wafer polishing (a 'polishing head'). An obstacle for measurements is a low reflectivity of surfaces. Both, metallic surfaces and silicon wafers, however, show high surface reflectivity.

We studied the shape measurement of semiconductor components by holography with photorefractive Bi₁₂TiO₂₀ crystal as holographic medium and two diode lasers emitting in the red region as light sources. By properly tuning and aligning the lasers a synthetic wavelength was generated and the resulting holographic image of the studied object appears modulated by cos²-contour fringes which correspond to the intersection of the object surface with planes of constant elevation. The position of such planes as a function of the illuminating beam angle and the tuning of the lasers was studied, as well as the fringe visibility. The fringe evaluation was performed by the four stepping technique for phase mapping and through the branch-cut method for phase unwrapping. A damage in an integrated circuit was analysed as well as the relief of a coin was measured, and a precision up to 10 μm was estimated.

Optical scatter measurements are the basis for efficient methods in the quality management of optical components in all production steps. Especially, the Total Scattering (TS) of an optical surface can be evaluated in respect of the roughness and the state of cleanliness. In many applications defects on the surface or the imperfections in the bulk of the components are of major interest and have to be controlled systematically. In this paper a fast TS measurement procedure is presented for flat components, which can map a surface completely in the timescale of few ten to hundred seconds. The mapping covers the entire test area with spatial steps of less than one micron. The set-up can be adapted to wavelengths from the UV- to the IR- spectral ranges. The present study is dedicated to the technical specifications, problems during implementation and the resolution limits of the Fast TS set-up. TS measurements on samples with defined micro structures are employed to demonstrate the spatial resolution. Results of TS measurements in forward and backward direction will be presented for selected samples with defined particle distribution and sizes.

When integrating optic measurement systems into or next to the production line for part inspection and control of the production process requirements for measurement devices like the measurement time and the measurement uncertainty have to be expanded by a requirement for the robustness of the measurement system. A novel optic measurement system will be presented which is designed for the robust measurement of roundness of shafts next to the production line which is not influenced by residues of the manufacturing process, e.g. cooling lubricant. The measurement system is based on projecting the shadow of a shaft onto a detector and measuring the cast edges to derive the roundness of the shaft. The main parts of the measuring system consist of a soft X-ray micro focus tube, a highly precise angle measurement system and a CCD-detector. In contrast to roundness measurement instruments which are based on visible light and a telecentric optical path, new algorithms to calibrate the soft X-ray measurement instrument are being developed because of the divergent ray distribution of the soft X-rays. This paper will introduce the design and the main elements of the novel soft X-ray projection system as well as algorithms needed to conduct the roundness measurements. An estimation of accuracy and precision for small diameter shafts is presented as well as possibilities to achieve the invariance up to residues of the manufacturing process.

We developed a gauge block interferometer which utilizes the frequency tunable laser diodes as both light sources and phase shifters of a phase shifting interferometer. By using a confocal Fabry-Perot cavity made of ultra low expansion glass, and linearly modulating the laser diode current, the laser frequency could be injection locked to the resonant modes of the Fabry-Perot cavity consecutively. These equal spaced frequencies produce equally phase shifted interferometric images which are ideal to be analyzed by the Carré algorithm. Two frequency scanning lasers at the wavelengths of 636 nm and 657 nm are used as light sources for the gauge block interferometer. The system takes only 10 ms for a single measurement which acquires two sets of four equally phase shifted images with 640×480 pixels in size. Central lengths of gauge blocks are measured by using the phase shifting interferometry and exact fraction method. The performance of the high speed interferometer could be checked by comparing the measurement results on the same gauge block made by two different methods. Two results agreed well within the measurement uncertainty.

We present a symmetric heterodyne interferometer as a prototype of a highly sensitive translation and tilt measurement system. This compact optical metrology system was developed over the past several years by EADS Astrium (Friedrichshafen) in cooperation with the Humboldt-University (Berlin) and the university of applied science Konstanz (HTWG-Konstanz). The noise performance was tested at frequencies between 10^-4 and 3 Hz, the noise levels are below 1 nm/Hz ^1/2 for translation and below 1 μrad/Hz^1/2, for tilt measurements. For frequencies higher than 10 mHz noise levels below 5pm/Hz^1/2 and 4 nrad/Hz^1/2 respectively, were demonstrated. Based on this highly sensitive metrology system we also developed a dilatometer for the characterization of the CTE (coefficient of thermal expansion) of various materials, i.e. CFRP (carbon fiber reinforced plastic) or Zerodur. The currently achieved sensitivity of these measurements is better than 10^-7 K^-1. Future planned applications of the interferometer include ultra-high-precision surface profiling and characterization of actuator noise in low-noise opto-mechanics setups. We will give an overview of the current experimental setup and the latest measurement results.

We propose a common-path two-wavelength intereferometric system based on a single optical element, a Savart Plate, able to obtain profile measurements at frame rate. To improve precision up to the sub-micron levels from safe working distances (beyond 100 mm), we use a speckle reduction system based on a rotating holographic diffuser. The interferometric signals of the two wavelengths are obtained simultaneously and their phase signals are combined to extend the measurement range. The system's common-path interferometry nature, and the possibility of acquiring a distance profile in a single frame, make it ideal for surface inspection in industrial environments.

Sequentially recorded intensity patterns reflected from a laser illuminated diffuse object can be used to reconstruct the complex amplitude of the scattered beam. Several iterative phase retrieval algorithms are known in the literature to obtain the initially unknown phase from these longitudinally displaced intensity patterns. When two sequences are recorded in two states of the object in similar experimental setups, as is digital holographic interferometry - but omitting the reference wave-, displacement, deformation, or shape measurement can be done. Although the object-beam-only setup is not so sensitive to vibrations, several other factors influence the success of the measurements, the position or angle alignment of the linear stage. The results of initial simulations and measurements of displacement are presented, and the convergence of the phase retrieval is examined.

In this report, lens testing method for small lenses is discussed. Cylindrical or aspherical lenses are included to the scope of this report in addition to spherical lenses. A shearing interferometer is applied for the measurement. That consists of a plane parallel plate for inducing lateral shear for the test beam. This method is robust to disturbances because it is a common path interferometry. Moreover it is not necessary to prepare reference lens. For these reasons it can be said that this method is practical and is good for using at actual factories.

PURPOSE. To assess a new method of power measurement of soft and rigid contact lenses. The method is the phase shifting schlieren method, as embodied in the Nimo TR1504 instrument. MATERIALS and METHODS. Three Nimo TR1504 instruments were used to measure the power related dimensions of: a) a range of custom toric rigid lenses; b) a range of commercially available spherical hydrogel lenses; and c) a commercially available range of toric silicone hydrogel lenses. The measurements were carried out using a standard ISO ring test protocol where independent tests were carried out under conditions of reproducibility. The analysis of the measurements was carried out using ISO methods which enabled the reproducibility standard deviation, SR, of the method to be calculated. RESULTS. The results show that this new method has a reproducibility standard deviation SR of 0.048D for spherical soft (hydrogel) lenses. This means the back vertex power of spherical soft lenses having a power in the range ±20.0D can be determined to current ISO product tolerances with a single measurement. The method has SR of 0.059D for sphere power and 0.093D for cylinder power for toric soft lenses having powers in the range ±10.0D and cylinder powers in the range ±2.0D. A single measurement will determine sphere power to current ISO tolerance limits with 95% confidence while two measurements are required to determine the cylinder power to the same confidence level.

We propose a new method for reducing ripple phase errors in the fringe analysis by the Fourier transform method. Object profiles obtained by the conventional Fourier transform method tend to have ripple errors at the boundary edges of the fringe pattern. The shape of these ripple phase errors are found to have certain systematic relations to low order components of the phase and intensity distributions, which can be modeled by polynomials (such as Zernike polynomials). We estimate the systematic ripple errors by analyzing a virtual interferogram which is numerically created with models of the intensity and the phase. Starting from a rough initial guess, the virtual interferogram is sequentially improved by an iterative algorithm. Results of simulations and experiments that demonstrate the validity of the proposed method are presented.

Determination of parameters of the lens like the focal length, radius of curvature and refractive index are important from its application point of view. Many interferometric as well as non interferometric methods exist for this. But most of these methods require a visual inspection of the resulting interference pattern. Confocal imaging has very high axial resolution and it permits three-dimensional observation of object. This same property also enables one to determine the axial position of a specularly reflecting object. Here this capability has been applied, in reflection case, to the determination of lens parameters. This method is explained with simulation using diffraction theory and experimental results.

It is well known that manufacturing of lens systems featuring concentric design is a difficult task mainly due to nontrivial testing required for optical surfaces sharing their center of curvature. We propose an inexpensive imaging method, which can be used to test the alignment, concentricity, the axial length of air gaps and figure errors of the optical surfaces in concentric lens systems. Our setup consists of a laser, collimating lenses, a beam splitter, testing and imaging arms. We demonstrate the functionality of this scheme by testing an artificial eye with concentric design. During the experiment, the laser beam travels along the optical axis of the testing arm until it is focused onto the surfaces of the artificial eye. The light is then reflected and directed into the imaging arm to the camera. We perform tests in two positions: first, when the focused beam hits the vertex of the convex lens of the eye, and second, when the light comes into the system perpendicular to the optical surfaces. By finding the distance between these two positions, we can obtain the radius of curvature of the lens surfaces. In addition, the images formed on the camera give us accurate information about the alignment and the quality of the optical system under the test. Our results also show that this method is a powerful technique to determine the position of air gaps in compound optical systems.

We introduce a simplified laser Doppler distance sensor comprising only one single fan-shaped interference fringe system for dynamic position and shape measurement of fast moving objects with micrometer precision. Due to its low complexity, it can be built very compact and cheap, which is crucial for many industrial applications. It will be shown theoretically as well as experimentally that its position uncertainty is in principle independent of the object velocity in contrast to conventional distance sensors. In order to evidence its capability, radial and axial shape measurements of rotating bodies are presented employing a miniaturized sensor setup. An average position resolution of 2.3 μm was obtained.

Several optical measurement principles have proven their potential for high-resolution surface measurements. Among a few others, white-light interferometry has proven its capability for the measurement of technical surfaces, but yet, white-light interferometer systems cannot be miniaturized enough e.g. for the measurement inside small boreholes. In this work, a fiber-optic measurement system is described. Since the measuring principle is based on lowcoherence interferometry (LCI), the system provides non-contact surface measurements with nanometer accuracy. We present a system set-up for surface profile acquisition as well as the application of the system for the determination of roughness and waviness parameters. An outstanding feature of the proposed system is the miniaturized fiber-optic sensing probe, which is built up in all-fiber design. With a probe diameter down to 800 μm, the system can be used for measurements inside small cavities, e.g. bearings or injection nozzles. Beam shaping is realized with graded-index (GRIN) fibers. Conclusively, the results of evaluation measurements are compared with ISO 5436-1 type A and D measurement standards.

For geometry measurement of high precision machined mechanical or optical workpieces a resolution in the nanometer range is generally required. This can be reached by interferometric principles. In addition, measurement at steep flanks can be achieved by optical systems with high numerical apertures. Unfortunately, a high NA is always accompanied by a small depth of focus leading to a very limited measuring range. A possible solution in this context is a so-called depth scan. We realized a pointwise measuring interferometric sensor and use a piezo driven bending beam for the depth scan. A micro-optical fiber probe with an integrated reference surface is mounted at the top of this beam. By use of a piezoelectric actuator driven close to the resonant frequency of several hundred Hertz the beam deflects with a few micrometers of amplitude. By this oscillation the optical path length of the measuring rays of the interferometer is modulated, while the reference path remains unchanged. This leads to an interference signal which shows characteristic changes in phase as the average distance between optical probe and measuring object changes.

The measurement of aspheric surfaces in a Fizeau interferometer implies a sometimes dramatic increase in dynamic range, in terms of acceptable slope and departure, which can run the risk of introducing substantial measurement errors. Common approaches to relaxing the dynamic range requirement include reducing the area of the surface measured in a single measurement and stitching together the partial results, or using compensation techniques with the help of additional components like null-lenses or computer generated holograms. This paper reviews these methods, with special attention to the questions of degrees of freedom for misalignment. These considerations lead to a proposed method that uses the inherent symmetry of the problem to scan along the optical axis, gathering measurements at zones of normal incidence. These measurements are independent from each other; their ensemble represents directly the surface-deviation in normal direction to the surface and the result is in the object coordinates of the design surface. Using an absolutely calibrated spherical reference surface, the result is absolute. It is shown that this is very different from the technique of stitching of zones, even when Intrinsic Coma is preserved through partially overlapping measurement regions.

The production process of aspheric lenses relies on the measurement results from interferometers and profilometers. A new type of machine setup combining a profilometer with a rotational measuring axis is presented. It allows to measure lenses in all production stages, i.e. from rough grinded surfaces, which can not be measured with interferometers up to polished surfaces. The setup is very flexible, as it does not need a specific hologram for each type of asphere. These properties provide new options to optimize the production process.

The established method to measure aspherical surfaces is interferometric testing with null optics, but due to economical reasons the applications are limited. A special null optic has to be calculated, fabricated and qualified for each individual type of asphere. This time- and money consuming method is only cost-efficient for large quantities or when tests require high accuracy. We propose a new and flexible technique for measuring an ensemble of different aspheres with only one measurement setup. The main idea is to use the wavelength as a tunable parameter. Because it is possible to change the wavelength without introducing new errors by mechanical movements, the wavelength variation results in a higher measurement flexibility without reducing the measurement accuracy. We present the chromatic Fizeau Interferometer with a diffractive element as null-optic for the measurement of a set of four aspheres. We will show the influence of unwanted diffraction orders and the expected measurement accuracy. As in the monochromatic setup, especially the area around the optical axis is problematic and can not be measured with the desired accuracy. The use of a small aperture stop on the optical axis is recommended because errors in other radial domains are filtered as well. The results show, that the chromatic Fizeau interferometer makes the established monochromatic method far more flexible and that different aspheres can be measured in the same setup.

Non-contact methods for testing of large rotationally symmetric convex aspheric mirrors are proposed. These methods are based on non-null testing with side illumination schemes, in which a narrow collimated beam is reflected from the meridional aspheric profile of a mirror. The figure error of the mirror is deduced from the intensity pattern from the reflected beam obtained on a screen, which is positioned in the tangential plane (containing the optical axis) and perpendicular to the incoming beam. Testing of the entire surface is carried out by rotating the mirror about its optical axis and registering the characteristics of the intensity pattern on the screen. The intensity pattern can be formed using three different techniques: modified Hartman test, interference and boundary curve test. All these techniques are well known but have not been used in the proposed side illumination scheme. Analytical expressions characterizing the shape and location of the intensity pattern on the screen or a CCD have been developed for all types of conic surfaces. The main advantage of these testing methods compared with existing methods (Hindle sphere, null lens, computer generated hologram) is that the reference system does not require large optical components.

We describe a glancing-incidence interferometric double-pass test, based on a pair of computer-generated holograms (CGHs), for mandrels used to fabricate x-ray mirrors for space-based x-ray telescopes. The design of the test and its realization are described. The application illustrates the advantage of dual-CGH tests for the complete metrology of precise optical surfaces.

One of the most important properties of optical glass is the excellent spatial homogeneity of the refractive index of the material. Nevertheless, sometimes spatially short-range inhomogeneities are formed during the production process. These striae are strongly anisotropic due to the process of glass melting. In optical systems, they cause degradation of the performance with a complicated behavior. The quality specification of the glass homogeneity usually is given by simple values of phase differences along the main propagation direction of the light in an area of a certain size. For the measurement of these effects, interferometry can be used, which is a quite expensive method in reality. The observation of striae shadowgraph pictures is a faster and more frequently used method. The evaluation and quantitative reconstruction of the inhomogeneities in glass based on the striae technique are the main goal of this work. We revise the experimental setup and develop models to simulate the measurements for thin and thick samples. The results of the shadowgraph method are compared with interferometric measurements. A more refined evaluation which is not only based on the image contrast allows a unique and accurate reconstruction of the size and the phase height of striae with negligible axial extension. A simple procedure shows how one can estimate the effect in thick samples in practice approximately.

A measurement system for quantitative registration of transient and irreversible lens effects in DUV optics induced by absorbed UV laser radiation was developed at the Laser-Laboratorium Göttingen. It is based upon a strongly improved Hartmann-Shack wavefront sensor with an extreme sensitivity of ~λ/10000 RMS @ 193nm, accomplishing precise online monitoring of wavefront deformations of a collimated test laser beam transmitted through the laser-irradiated site of a sample. Caused by the temperature dependence of the refractive index as well as thermal expansion and compaction, the initially plane wavefront of the test laser is distorted into a convex or concave lens, dependent on sign and magnitude of index change and expansion. The observed wavefront distortion yields a quantitative measure of the absorption losses in the sample. Some results for fused silica and CaF₂ are presented.

Reflection digital holographic microscopy (DHM) is a very powerful technique allowing measuring topography with a sub-nanometer axial resolution from a single hologram acquisition. But as most of interferometer methods, the vertical range is limited to half the wavelength if numerical unwrapping procedure could not be applied (very high aspect ratio specimen). Nevertheless, it was already demonstrated that the use of dual-wavelength DHM allows increasing the vertical range up to several microns by saving the single wavelength resolution if conditions about phase noise are fulfilled (the higher the synthetic wavelength, the smaller the phase noise has to be). In this paper, we will demonstrate that the choice of a synthetic wavelength of about 17 microns allows measuring precisely a 4.463μm certified step. Furthermore, we will show the feasibility of a sub-nanometer resolution on a range higher than the synthetic wavelength by being able to map the dual-wavelength measurement on data acquired from a vertical scanning process, which precision is about 1 μm.

We show how thin liquid film on polar dielectric substrate can form an array of liquid micro-lenses. The effect is driven by the pyroelectric effect leading to a new concept in electro-wetting (EW). EW is a viable method for actuation of liquids in microfluidic systems and requires the design and fabrication of complex electrodes for suitable actuation of liquids. When compared to conventional electrowetting devices, the pyroelectric effect allowed to have an electrode-less and circuitless configuration. In our case the surface electric charge induced by the thermal stimulus is able to pattern selectively the surface wettability according to geometry of the ferroelectric domains micro-engineered into the lithium niobate crystal. We show that different geometries of liquid microlenses can be obtained showing also a tuneability of the focal lenses down to 1.6 mm. Thousand of liquid microlenses, each with 100 μm diameter, can be formed and actuated. Also different geometries such as hemi-cylindrical and toroidal liquid structures can be easily obtained. By means of a digital holography method, an accurate characterization of the micro-lenses curvature is performed and presented. The preliminary results concerning the imaging capability of the micro-lens array are also reported. Microlens array can find application in medical stereo-endoscopy, imaging, telecommunication and optical data storage too.

The paper presents the optical, mechanical, and electro-optical design of an interferometric inspection system for massive parallel inspection of MicroElectroMechanicalSystems (MEMS) and MicroOptoElectroMechanicalSystems (MOEMS). The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under test. The probing wafer is exchangeable and contains a micro-optical interferometer array. A low coherent and a laser interferometer array are developed. Two preliminary interferometer designs are presented; a low coherent interferometer array based on a Mirau configuration and a laser interferometer array based on a Twyman-Green configuration. The optical design focuses on the illumination and imaging concept for the interferometer array. The mechanical design concentrates on the scanning system and the integration in a standard test station for micro-fabrication. Models of single channel low coherence and laser interferometers and preliminary measurement results are presented. The smart-pixel approach for massive parallel electro-optical detection and data reduction is discussed.

Numerous processes, e.g. in semiconductor and optics producing industries require film thickness observation. These measuring systems depend on different working principles, e.g. spectral reflectometry or ellipsometry. The spectral reflectometry interrogation method can be evaluated by various algorithms depending on resolution and measuring range demanded. All methods require a broad spectral distribution of the light source in order to sample the signal sufficiently for parameter extraction. Spectral sampling is often realized using a spectroscope, which produces equidistant sampling points in frequency space. In contrast to conventional spectrally broad light sources, the one employed here emits several spectral lines, which are non-equidistantly distributed. It also introduces problems like variations of intensity in the output spectrum and narrow wavelength bands, in which the reflected spectrum can be investigated. Non-equidistant sampling points additionally imply problems in conventional analysis algorithms, e.g. a FFT anticipates equidistant sampling points. Narrow wavelength bands imply little information to interrogate at the same spectral resolution of the interrogator. Strong variations of intensity lead to high noise levels at wavelengths with low intensities. Therewith, accuracy, resolution and measuring range are limited. An interrogator based on a Hg-Ar light source, a fiber coupler and a commercial spectroscope is described in this work. Both, accuracy and measuring range, are investigated by simulation and are experimentally proven on a glass on silicon demonstrator. Introducing an advanced algorithm, uncertainties invoked by the source's spectral and intensity distribution are minimized and resolution as well as measuring range are increased.

We report on the development of an all-interferometric sensor based on the laser-self-mixing for the simultaneous detection of multi-degrees-of-freedom displacement of a remote target. The prototype system consists only of a laser head, equipped with 6 diode lasers and a properly designed reflective target. Information on a single degree-of-freedom motion is extracted by the differential measurement of two linear displacements by means of two nominally identical self-mixing interferometers. The sensor has been experimentally tested to measure yaw, pitch, roll, straightness and flatness corrections over a continuous linear range of 1 m, with resolutions of 0.7 μm (longitudinal), 20 μm (straightness and flatness), 0.001° (yaw and pitch) and 0.015 °(roll).

A novel laser encoder is presented for sub-nanometer displacement measurement. It is based on optical heterodyne interferometry and two arms of compensation optics with a symmetric and quasi-common-path optical configuration in polarization space. High stability and resolution can be achieved for displacement measurements. The theoretical analysis shows that our method can effectively compensate misalignments resulting from the dynamic runout in laser encoders. Experimental results reveal that the laser encoder can measure a displacement in subnanometer scale and in millimeter travel range.

A vision system is used for measuring in-plane target displacement, position and orientation. Pseudo-periodic patterns fixed on the target forms a phase reference. Absolute position is determined with subpixel accuracy by phase computations. Various position encoding designs are proposed for different displacement ranges and resolution. Performances obtained are compared and discussed for both displacement and orientation measurements. The capability to resolve position on depth ranges larger than the lens depth of focus is demonstrated.

A novel approach to an established method to calculate the frequency spectrum of Lamb waves is introduced. Lamb wavetrains are generated with the wedge method in aluminium plates, and a sequence of instantaneous acoustic out-of-plane displacement fields at the plate surface is measured with a self-developed double-pulsed TV holography system. This is achieved by emitting two laser pulses synchronized with the piezoelectric transducer that generates the waves and conveniently delayed. As a result, a 2D optical phase-change map, proportional to the aforementioned acoustic displacement field, is obtained for the instant of emission of the second laser pulse. Then, a series of maps is acquired under repeatability conditions by successively delaying the second laser pulse, so that the resulting sequence of maps records successive instants of the propagation of the wavetrain. The frequency spectrum of the wavetrain is obtained from a 3D spatio-temporal Fourier transform of the whole sequence of optical phase-change maps, as the relation between the temporal frequency and the spatial frequency along the principal propagation direction of the wavetrain. The use of a 3D Fourier transform permits to calculate the frequency spectrum regardless of the propagation direction of the wavetrain, with non-perfectly plane wavefronts and also increases the signal to noise ratio with respect to the 2D spatio-temporal Fourier transform approach. Experiments show that the resulting branches for the Lamb modes existing in the wavetrain are in agreement with the theoretical frequency spectrum of Lamb waves in aluminium.

In the past, we developed a holographic interferometry technique based on photorefractive materials for high resolution measurement of structures deformation. In this paper we present the early results of development of a holographic technique and facility for deformation and expansion measurement of aerospace composites components. Here the holographic technique consists in using several illumination beams for retrieving different components of the displacement vector. In our case the components and structures to be measured in the future will undergo temperatures excursions up to 150°C typically. Since holographic techniques are sensitive to air turbulences, it is necessary to place the samples in a vacuum chamber. We will present some early examples of measurements with this facility, obtained for temperatures excursions ranged between ambient and 29°C as first steps before going further to higher temperatures excursions.

In-situ measurement of distances and shapes as well as dynamic deformations and vibrations of fast moving and especially rotating objects, such as gear shafts and turbine blades, is an important task at process control. We recently developed a laser Doppler distance frequency sensor, employing two superposed fan-shaped interference fringe systems with contrary fringe spacing gradients. Via two Doppler frequency evaluations the non-incremental position (i.e. distance) and the tangential velocity of rotating bodies are determined simultaneously. The distance uncertainty is in contrast to e.g. triangulation in principle independent of the object velocity. This unique feature allows micrometer resolutions of fast moved rough surfaces. The novel sensor was applied at turbo machines in order to control the tip clearance. The measurements at a transonic centrifugal compressor were performed during operation at up to 50,000 rpm, i.e. 586 m/s velocity of the blade tips. Due to the operational conditions such as temperatures of up to 300 °C, a flexible and robust measurement system with a passive fiber-coupled sensor, using diffractive optics, has been realized. Since the tip clearance of individual blades could be temporally resolved an analysis of blade vibrations was possible. A Fourier transformation of the blade distances results in an average period of 3 revolutions corresponding to a frequency of 1/3 of the rotary frequency. Additionally, a laser Doppler distance sensor using two tilted fringe systems and phase evaluation will be presented. This phase sensor exhibits a minimum position resolution of σ_z = 140 nm. It allows precise in-situ shape measurements at grinding and turning processes.

The interference measurement using the femtosecond optical frequency comb (FOFC) is in progress at present. We analyzed the temporal coherence function (TCF) of an FOFC since which is the fundamental description of the interference phenomenon. As a result, it has been understood that the same high coherence peak exists during the time which is equal to the repetitions interval in the traveling direction of the FOFC. The theoretical derivation has been used to model the TCF of an FOFC and shows good agreement with experimental measurements which is taken with a combination of an ordinary Michelson interferometer and an unbalanced optical-path Michelson interferometer.

An ultrasonic propagation imaging (UPI) system consisted of a Q-switched Nd-YAG pulsed laser and a galvanometer laser mirror scanner was developed. The system which requires neither reference data nor fixed focal length could be used for health monitoring of curved structures. If combined with a fiber acoustic wave PZT (FAWPZT) sensor, it could be used to inspect hot target structures that present formidable challenges to the usage of contact piezoelectric transducers mainly due to the operating temperature limitation of transducers and debonding problem due to the mismatch of coefficient of thermal expansion between the target, transducer and bonding material. The inspection of a stainless steel plate with a curvature radius of about 4 m, having 2mm×1mm open-crack was demonstrated at 150°C using a FAWPZT sensor welded on the plate. Highly-curved surfaces scanning capability and adaptivity of the system for large laser incident angle up to 70° was demonstrated on a stainless steel cylinder with 2mm×1mm open-crack. The imaging results were presented in ultrasonic propagation movie which was a moving wavefield emerged from an installed ultrasonic sensor. Damages were localized by the scattering wavefields. The result images enabled easy detection and interpretation of structural defects as anomalies during ultrasonic wave propagation.

Today, typical polymer films consist of several functional layers, like printable surface or barrier layers. They are produced in coextrusion processes, in which the different materials are extruded through a single die and formed to a blown- or cast film with haul-off speeds up to 500 m/min. In the production of transparent multilayer films certain defects, called "interfacial instabilities", can occur. They emerge from shear stress and turbulences in the material flow during the process and result in a reduction of the mechanical properties and the optical quality of the product. Interfacial instabilities cannot be detected by conventional film inspection systems available on the market because the optical distortions they produce do not change the brightness of a pixel. In this paper, an approach for solving this problem is presented. The film is illuminated with a patterned line-light source in a backlight setting and a CCD line scan camera is used for recording the image lines. The defects can be detected using a 1D filter tuned to the spatial-frequency of the pattern. The distortion caused by the defects leads to a local extremum in the feature image generated by the filter, which can be easily detected by threshold segmentation. The system has been tested in an industrial setting and proved to be fast enough for inline-inspection. Further applications could be in the fast deflectometric inspection of high-gloss surfaces.

Optical tools offer a route to increasing throughput and efficiency in industrial inspection operations, one of the most time-consuming and labour-intensive aspects of modern manufacturing. One prominent example in the medical device industry is inspection of drilled holes, particularly in narrow-bore tubes (precision-flow devices, such as catheters for drug delivery, radio-opaque contrast agents, etc). The products in which these holes feature are increasing in complexity (reduced dimensions, increasing number of drilled features- in some products now reaching into the hundreds). These trends present a number of technical challenges, not least to ensure that holes are completed and that no damage to the part occurs as a result of over-drilling, for example. This paper will present a novel sensor based on back-side illumination of the drilled hole using side-glowing optical fibers to detect, qualify and quantify drilled holes. The concept is based on inserting a laser-coupled side-glowing optical fiber into the lumen of the tube to be drilled, and imaging the light emitted from this fiber through a drilled hole using a vision system mounted external to the tube. The light from the fiber allows rapid determination of hole completion, shape and size, as well as quantity in the case of products with multiple holes. If the fiber is mounted in the tube prior to drilling, the light emitted from the fiber can be used as a real-time hole breakthrough sensor, preventing under or overdrilling of the tube.

This paper presents a new optical system to measure internal cylindrical surfaces combining photogrammetry and fringe projection. The device uses two identical cameras, equipped with spherical and conical lenses, facing each other and aligned with the optical axis. A 360° helical fringe projector is used to project a sequence of phase shifted helical fringe pattern in the inner surface to be measured. The phase patterns are used to identify corresponding points and to reconstruct the surface in a regular cylindrical mesh using an alternative approach. A prototype was built, calibrated and tested. The paper presents the results of an application where two welded joints were measured in a 150 mm (6") diameter pipe. The goal was to inspect for defects in the internal part of the welding seams and to measure the transversal misalignment between the jointed parts.

Early surface defects inspection in hot steel products is a difficult task, but can help to reduce significantly production costs. This is the case of steel slabs when they are produced in the continuous casting line. Conoscopic holography phase-based long stand-off profilometers have shown to be a great tool for this kind of inspection, and a breakthrough system based on them is being used for more than 2 years in production conditions with high reliability and economical impact. This paper presents the results of this system and the challenges it has overcome: hot material up to 900°C, dust, scale over the inspected surface.

In this paper we present an optical measurement system approach for quality analysis of brakes which are used in high-speed trains. The brakes consist of the so called brake discs and pads. In a deceleration process the discs will be heated up to 500°C. The quality measure is based on the fact that the heated brake discs should not generate hot spots inside the brake material. Instead, the brake disc should be heated homogeneously by the deceleration. Therefore, it makes sense to analyze the number of hot spots and their relative gradients to create a quality measure for train brakes. In this contribution we present a new approach for a quality measurement system which is based on an image analysis and classification of infra-red based heat images. Brake images which are represented in pseudo-color are first transformed in a linear grayscale space by a hue-saturation-intensity (HSI) space. This transform is necessary for the following gradient analysis which is based on gray scale gradient filters. Furthermore, different features based on Haralick's measures are generated from the gray scale and gradient images. A following Fuzzy-Pattern-Classifier is used for the classification of good and bad brakes. It has to be pointed out that the classifier returns a score value for each brake which is between 0 and 100% good quality. This fact guarantees that not only good and bad bakes can be distinguished, but also their quality can be labeled. The results show that all critical thermal patterns of train brakes can be sensed and verified.

Strong demand exists for a non-contacting paper caliper measurement which can be used as an input to a paper thickness control system. Caliper sensors requiring sheet contact suffer from errors related to dirt or coating build up and from high maintenance costs related to wear. These sensors can also damage the product by picking holes and marking sheets. Details of an on-line measurement device which employs two opposed laser displacement sensors and an inductive displacement sensor are presented. The sheet is held perpendicularly to the sensors with a Coanda air clamp. Dust and temperature control features which enable the sensor to operate reliably in an industrial environment are discussed. Results of production trials of this sensor are presented. Sub-micron profile agreement to lab and contacting caliper measurements has been demonstrated on light sheets. Results are presented of measurements on a wide range of paper grades from coated and uncoated light sheets to coated board.

Online measurement of paper thickness profile is essential in paper production. For decades paper thickness has been measured online with sensors that are contacting the web on both sides. In 2005 a new optical online paper thickness gauge was introduced which only contacts the web on the other side. The sensor is based on a laser triangulation sensor and a magnetic sensor, and it determines the paper thickness from the difference of the two measurements. For calibration of the two sensors, a robust concept has been developed which utilizes the measured object and takes place in the measuring environment so that the calibration is automatically adjusted to the current measuring circumstances. More importantly, with the presented method the non-linearity of the laser sensor is cancelled enabling the measurement of the thickness profile shape with an accuracy much better than that of the laser sensor. Profile accuracy of 0.5 μm (2σ) has become normal while the measuring range is often several hundreds of microns and the measuring distance to the paper web 1.0-1.5 mm with a laser sensor having linearity of ±2 μm.

Reinforced plastic materials are widely used in high sophisticated applications. The length distribution of the fibres influences the mechanical properties of the final product. A method for automatic determination of this length distribution was developed. After separating the fibres out of the composite material without any damage, and preparing them for microscopical analysis, a mosaic of microscope pictures is taken. After image processing and analysis with mathematical methods, a complete statistic of the fibre length distribution could be determined. A correlation between fibre length distribution and mechanical properties, measured e.g. with material test methods, like tensile and impact tests, was found. This is a method to optimize the process and selection of material for the plastic parts. In result this enhances customer satisfaction and, maybe much more important, reduces costs for the manufacturer.

This paper describes non-invasive electro-optic sensors devoted to simultaneous electric field and temperature measurements. Based on Poeckel's effect, these sensors consist in non-centrosymmetric crystals for which an electricfield induces a modification of their refractive indices [1]. Such modification can also be induced by a drift of the crystal temperature [2]. After explanation of the principle, we will illustrate some applications (high power microwave characterization, bioelectromagnetism, electric field mapping of high voltage devices) for which electro-optic sensors give excellent performances. These sensors perform vectorial E-field measurement (modulus and phase of each E-field components) with both high spatial and temporal resolutions. As they are pigtailed, long distance remote sensing is then allowed. They are also non-invasive due to their fully dielectric design. However, their sensitivity remains quite low for electromagnetic compatibility and their size remains too important for bioelectromagnetism studies in Petry dishes for example. So, two ways of improvement are pursued. The first one consists in using Fabry-Perot microcavities based on LiNbO3 optical waveguide to dramatically reduce sensors size. The second one consists in an optical processing (optical carrier rejection) of the laser probe beam to increase the sensor sensitivity for high frequency measurements. We will present first results concerning these improvements and also results that have been performed in free space with a fully automated setup in both frequency and time domains.

Within this work, we describe our newly developed interrogation scheme for fiber optic sensing applications. This measurement system will be utilized in Ariane launchers for monitoring temperature and mechanical stress distribution during flight. The acquired sensing data can be used to control propulsion unit an thrusters and thereby adapt the flight path in a way that damage on the launcher is prevented. In order to detect the peak wavelength of e.g. fiber Bragg grating (FBG) sensors, a tunable laser source based on a modulated-grating laser diode is able to scan through a more than 40nm wide spectrum in the infrared region. Several sensors with different spectral answers can be placed inside one sensor fiber and then interrogated sequentially. The magnitudes of the reflected intensities depend on the actual sensor position that is determined by the measurand (e.g. temperature). One single sensor is scanned by a variable number of spectral sampling points and the spectral answer of the sensor is then calculated by centroid algorithms. Depending an the spectral width of one sensor, the number of sensors that shall be interrogated and the required sampling points per sensor, a maximum sampling frequency of 240kHz is achievable with our hardware. Contrary to comparable systems, our interrogator is capable of switching to any available wavelength of its spectrum within a couple of nanoseconds. Therefore standard continuous sweeping through the entire spectrum is not necessary. This results in a new measurement scheme, wherein spectral gaps between consecutive sensors do not need to be scanned and can be skipped. Since most of the spectrum consists of the gaps between the sensors, overall measurement time is thereby reduced significantly. One problem arises from this measurement scheme: Due to the fact that the sensor's spectral answers vary in time, a special algorithm for tracking the spectral movement has to be implemented. The scope of this work is the description, implementation and assessment of this new peak tracking procedure. After describing the measurement setup, we will therefore explain the algorithm behind the peak tracking measurement. Afterwards the simulation process is explained and results are shown. Performance obtained by peak tracking compared to standard continuous wavelength scanning is evaluated in detail and further development steps which are necessary to obtain a fully sophisticated interrogation systems are discussed.

There are many vibration damages happen in the world, such as Pipeline broken, Historical Relics stolen, even for the board destroy. With conventional vibration detection methods there is a gap between what you believe is occurring along area and what is actually happening. This information gap can result a delay in your discovering and locating broken. Based on the non-linear optical scattering theory, we have developed a new fiber grating vibration-monitoring system. This new system overcomes the limitations of measurement technologies available today, thus closing the monitoring gap and improving system integrity and safety.

Three-dimension coordinates measuring is the key technique in modern manufacturing, reverse engineering, automation, precision measurement and computer aided surgery. In recent years, the 3D vision coordinates measurement becomes a newly technique and has been developed rapidly. Some vision coordinates measurement machines (VCMM) were developed. But measuring accuracy of those VCMMs is susceptible to the mal-condition and external noise, i.e. index point brilliance and ambient light illumination. We developed a new 3D high-precise optical coordinate measuring system based on an infrared target and two CCD cameras. Both measuring principle and linear direct reconstruction method of binocular stereo vision based on cross optical axes are discussed. The detail design and geometric model of the infrared target is proposed. The position and direction of the infrared target and 3D coordinates of the tip can be directly computed according to rigid geometric transformation. Further results of calibration and measurement are verified experimentally. A high geometrical accuracy can be reached.

A white-light spectral interferometric technique is used for measuring the thickness of a SiO₂ thin film grown by thermal oxidation on a Si substrate. The technique is based on recording of the spectral interferograms at the output of a Michelson interferometer with one of its mirrors replaced by a thin-film structure. From the spectral interferograms, the nonlinear-like phase function related to the phase change on reflection from the thin-film structure is retrieved. The function is fitted to the theoretical one to obtain the thin-film thickness provided that the optical constants of the thin-film structure are known. This procedure is used for measuring four different thicknesses of the SiO₂ thin film on the Si substrate. The results of the technique are compared with those obtained in the same setup by spectral reflectometry and good agreement is confirmed. To minimize the errors introduced by optical elements of the interferometer, the measurements are performed with the reference sample of the known phase change on reflection and reflectance.

Large aperture optics have been used more and more widely in modern optical system. But the testing of its surface quality is very difficult. The circular sub-aperture stitching (CSAS) testing method can effectively extend the interferometer's vertical dynamic range and enhance its lateral resolution, so it may be the best solution to the testing of large aperture optics. Actually, the CSAS method can be viewed as a special workpiece localization problem. If the pose data of all sub-apertures obtained are accurate enough, the sub-aperture data can be directly stitched together to create a map of the full aperture. In this paper, a CSAS system will be introduced. Its motion mechanism has seven degrees of freedom. This brings some trouble for obtaining the optics' accurate pose data along with the motion error's accumulation. So a stereovision system is added. By exploiting appropriate scheme and algorithm, it can directly give out the optics' accurate pose data. This provides an effective initial value for the stitching algorithm. Finally, a 150mm flat and a 100mm convex sphere is tested using this method, and the experimental results is given to show the effect of this method and the efficiency of the CSAS system.

Laser light scattering detection based on sheath flow technique are well established and routinely used in a variety of fields, ranging from ecology to medicine. Normally the width of sheath flow chamber is assumed as a constant, but the inaccuracy during manufacture changes the inter structure of sheath flow chamber. So the sheath flow width deviates its designed value. In our research, a novel method is applied to research sheath flow stability. The structure of sheath flow chamber in different positions is firstly imaged by CCD camera. The values of sheath flow width in different positions can be gotten by image processing technologies. According to chamber width values in different positions, principle sheath width can be calculated to be compared with the measured values. Hence sheath flow stability in different time and different positions can be detected. By this novel method, the real width of sheath flow forming with specific velocity rate in different positions can be measured. So the best measurement site for dynamic individual particles scattering can be selected.

A compact laser-induced-breakdown-spectroscopy (LIBS) system for surface elemental analysis using a low-energy, high-repetition rate Nd:YAG laser as excitation source has been developed. Elemental analyses were performed on various samples including non-metallic compounds and metal alloys. Fluorine and chlorine could be detected well qualitatively in different organic materials like Teflon FEP (fluorinated ethylene propylene) or PVC (polyvinyl chloride). Furthermore, low concentrations of silicon, magnesium and copper in aluminum have been measured and could be backed up by EDX and XPS analysis. Results were confirmed with a conventional LIBS system using a high-energy, low-repetition rate Nd:YAG SHG laser operating at 10 Hz with a pulse energy of 200 mJ. Especially the results with fluorine containing samples are very promising and show that LIBS measurements of non-metallic samples are possible even at very low pulse energies with a manageable trade-off in signal strength.

Several light incisions brought up when the large size workpiece was scanned along the cross-section by laser light structure sensors. Since discrete points of each light incision were fitted to elliptic curve, 3D coordinates of the center of the light incision plane could be attained. With the space line fitting and error examination algorithm, the large cross-section workpiece straightness was gained, and the geometry of cross-section could be calculated. This paper brought forward the method and mathematics model of straightness measurement of the large-size workpiece by laser vision, and experiment result was also given out.

Bidirectional ellipsometry has been developed as a technique for distinguishing among various scattering features near surfaces. The out-of-plane polarized light-scattering by metallic nanoparticles on wafer is calculated and measured. These calculations and measurements yield angular dependence of bidirectional ellipsometric parameters for out-ofplane scattering. The experimental data show good agreement with theoretical predictions for different diameter of gold spheres. The results suggest that improvements for accuracy are possible to perform measurements of scattering features from metallic nanoparticles. The polarization of light scattered by metallic nanoparticles can be used to determine the size of nano-particulate contaminants on silicon wafers.

Photonic crystals have many potential applications because of their ability to control light-wave propagation. In this paper, we have investigated PC-based optical waveguides implemented into wavelength division multiplexing (WDM) systems. The WDM splitters based on a PC waveguide coupler with square lattice are proposed. Their wavelength multiplexing properties are numerically investigated by using the finite-difference time-domain method. Rod-type photonic crystal structures were fabricated in silicon by electron beam lithography and dry-etching techniques. The WDM splitters were fabricated from two-dimensional photonic crystal waveguides. Transmission spectra were calculated by using finite-difference time-domain method. The WDM splitters can be used in infrared region. Such an approach to photonic element systems should enable new applications for designing components in photonic integrated circuits.

In this study, the optical activity of cholesteric liquid crystal and common-path heterodyne interferometry are used in a simple measurement technique that was developed to measure small wavelength differences. A circularly polarized heterodyne light passes through a cholesteric liquid crystal cell and an analyzer. Consequently, an interference signal is generated. When the cholesteric liquid crystal cell is properly chosen at circular regime, it owns strongly optical activity. Accordingly, the phase difference between the s- and p-polarized components of the interference signal depends strongly on the wavelength. As the wavelength changed, a variation of the phase difference can be accurately detected by heterodyne interferometry. Substituting the variation of phase difference into specially derived equations, the wavelength variations can be estimated accurately. The feasibility of this method was demonstrated and this method provides the advantages of a simple structure, easy operations, rapid measurement, high stability, and high sensitivity.

In this study a non-contact method for accurately measuring small concentration of solutions by surface plasmon resonance heterodyne interferometer is proposed. Firstly, a linearly polarized heterodyne light source is transmitted through a test box filled with pure water. The transmitted light is incident on the base of a hemi-spherical prism of a surface plasmon resonance apparatus. Then the reflected light passes through an analyzer and generates an interference signal on a photo-detector. Secondly, when the incident angle is chosen at resonant angle, a significant phase difference between the s- and p-polarized components occurs. This phase difference is a function of the incident angle at the base of the hemi-spherical prism. Finally, when the test box is filled with a test solution, the incident angle at the base of the hemi-spherical prism is changed. This causes a variation in the phase difference that can be detected by the heterodyne interferometry. Therefore, the concentration of the tested solution can be accurately determined with special derived equations. The validity of this method was demonstrated experimentally. The advantages of the propose method include a simple apparatus, rapid measurement, high stability, and high resolution. Due to the introduction of a common-path structure, the interference signal is not affected by surrounding fluctuations and can be captured easily.

A heterodyne speckle interferometry for measurement of in-plane displacement is proposed. The wavelength-modulated (WM) laser beam passing through an unequal-path-length optical configuration is used as a heterodyne light source. The scattering heterodyne speckle signal is received by letting the WM heterodyne light incidents on the in-plane moving rough surface. The object displacement would be determined by the speckle interferometry theorem with the measured phase variation of the heterodyne speckle signal. The experimental results demonstrate that the measurement range is up to 10 μm and resolution is about 10 nm.

We present a method of three dimensional shape measurement from the curvature data, which are obtained from the subaperture topography along the diagonal direction of artifact by using white-light scanning interferometry. The curvature is an intrinsic property of the artifact, which does not depend on the positioning errors of measuring sensor. Experimental results prove that the proposed method is useful, especially for large-scale optical surface profile measurement with nanometer accuracy. The current version of this paper has had a correction made to it at the request of the author. Please see the linked Errata for further details.

The optical speckle-displacement correlator based on hybrid optical-digital joint transform correlator architecture with digital first and optical second stage is used to determine correlation peak position with subpixel accuracy without usage of intricate interpolation algorithms. Experimental setup for realization of the optical speckle-displacement correlation technique was constructed on basis of a digital Fourier processor allowing joint power spectrum median and ring median binarization and an optical Fourier processor. Speckle patterns of steel beam specimen (steel 45) with different maximum spatial frequencies were recorded. As one of the joint transform correlator main parameters is distance between fringes at correlator frequency plane, comparison of optical speckle-displacement correlator performance for different values of speckle pattern maximum spatial frequency for the given joint power spectrum modulation was performed. Experimental results have shown that the signal-to-noise ratio (SNR) increases steadily while the maximum frequency of speckle pattern multiplied Fourier spectrum is reaching the Nyquist frequency fN. The analysis of the speckle pattern with frequencies higher than Nyquist frequency has shown that the SNR growth is continued to the some boundary frequency fB>fN after which the SNR is fallen sharply. Thus, the influence of aliasing on the correlator performance was studied and the best correspondence between value of speckle pattern maximum spatial frequency and distance between fringes at the correlator frequency plane was found.

In this paper we consider a new way for automated camera calibration and specification. The proposed setup is optimized for working with uncooled long wave infrared (thermal) cameras, while the concept itself is not restricted to those cameras. Every component of the setup like black body source, climate chamber, remote power switch, and the camera itself is connected to a network via Ethernet and a Windows XP workstation is controlling all components by the use of the TCL - script language. Beside the job of communicating with the components the script tool is also capable to run Matlab code via the matlab kernel. Data exchange during the measurement is possible and offers a variety of different advantages from drastically reduction of the amount of data to enormous speedup of the measuring procedure due to data analysis during measurement. A parameter based software framework is presented to create generic test cases, where modification to the test scenario does not require any programming skills. In the second part of the paper the measurement results of a self developed GigE-Vision thermal camera are presented and correction algorithms, providing high quality image output, are shown. These algorithms are fully implemented in the FPGA of the camera to provide real time processing while maintaining GigE-Vision as standard transmission protocol as an interface to arbitrary software tools. Artefacts taken into account are spatial noise, defective pixel and offset drift due to self heating after power on.

The work deals with the problem of non-contact measurement of the surface topography using chromatic (confocal) sensor. A detailed analysis of the influence of the refractive index of the plan-parallel plate material on the accuracy of measurement using chromatic sensor is performed. Relations which describe this phenomenon and enable to calculate an error due to material dispersion are derived. It can be seen from the performed analysis that the dispersion of plan parallel plate material causes measurement error that cannot by neglected for precise measurements.

The proper alignment of the individual elements is a crucial point in the final performance of an optical system. The alignment technique we present uses the image formation of a point sources array to detect the misalignments of an imaging system. We have displaced the analysis plane from the exit pupil plane to the image plane, where the PSFs functions are captured on a sensor. The PSFs are large enough to be sensitive to the misalignments and we are able to detect them using image analysis techniques. The proposed technique is a solution when more than one field position is necessary to obtain a well-balanced quality function over all the field of view. We have been studying this method on a particular collection of optical systems with decentering and rotation errors, achieving an accuracy of 0.1mm for decentering and 0.01° for rotation.

Makyoh topography is an optical tool for the flatness testing of specular surfaces, based on the defocused detection of a collimated light beam reflected from the tested surface. The reflection image is related somehow to the surface relief pattern of the surface due to the focusing/defocusing action of the surface irregularities. The main application of the method is the assessment of the polishing quality of wafers in semiconductor technology. In this contribution, the imaging properties of periodic and quasiperiodic surfaces is analysed through analytic calculations and ray-tracing simulations for surfaces of various spectral properties. General imaging properties are established. Practical implications in the semiquantitative inspection of surface morphology/texture are pointed out, and experimental results are shown to illustrate the main points of the presented analysis.

The paper presents a procedure for measuring laser radiation reflection and scattering coefficients of polished surface. A relation between the scattered light intensity and the polished surface roughness is studied. It is demonstrated that colorimetric characteristics of non-metallic materials can be determined from the light scattering and reflection coefficients. This work has demonstrated a possibility of and created prerequisites for the development of an express method for tentative assessment of polished surface roughness. Of interest is the use of the β(Rz) function for the purposes of quality inspection of polished surfaces of natural and synthetic stone and other non-metallic materials. It was established that the most relevant parameter of roughness, which can be defined by the light reflection is Rz. The Dependency of the reflection factor from parameter of roughness Rz was approximated by formula with inaccuracy 5-10%. Inaccuracy of the determination of roughness Rz has formed 1%. It was shown that method of the surface roughness control using the light reflection factor is the most efficient for surfaces with roughness Rz <0.3 microns, typical for finish diamond-abrasive machining.

In this work we present to methods to evaluate activity in low dynamic speckle patterns. The first one is based on the behavior analysis of the vortices associated to the pattern. The other one consists in binarizing the speckle image. The speckle grain areas, also called islands, experiment displacements and deformations. The variations of the island features were analyzed with the aim of finding a correlation with the activity of the speckle pattern. Both methods were evaluated in numerical simulations and controlled experiments. From the obtained results, it was possible to conclude that the developed methods can be very useful for the analysis of low activity speckle patterns with some advantages with other methods.

To estimate rock porosity in 2D and 3D, we used image technique to analyze rock fractures. We set up some models to characterize the rock fractures, based on the models, we used Best fit Ferret method to auto-determine fracture zone, then, analyze rock fracture porosities in 2-D and 3-D. In this study, rock sample is cut off into a number of slices of a certain thickness (18mm), then the fracture images are taken slice by slice both by using ultraviolet and visible lights, subsequently the fracture images are auto-thresholded into binary images, and fracture zones are determined by minimum circumscribed rectangles, finally the porosities are calculated in 2-D dimensional, and 3-D porosities are estimated based on 2-D porosity information.

The colony characteristics are used for evaluating the quality of water and food. Auto-detecting colony in an image is a hard task. This paper proposes a new multi-scale segmentation technique based on wavelet decompositions and watersheds. Firstly, we dispose the tiny colonies by using a wavelet domain median filter. Secondly, wavelet transform is used to create multi-resolution images. Then watershed segmentation algorithm is applied to segment the lowestresolution image and obtain the initial watershed segmentation result. Finally, we do segmentation on the high-resolution image based on the low-resolution image. Experiments results show that the colony images can be well segmented by using the new algorithm.

Recently, the industrial optical inspection has been a mainstream in measuring 2D images or 3D profiles of microstructures. For the 3D profiling, the scanning white-light interferometer has a high resolution, but due to the broadband light source, it has the low coherence length. Thus, it is very difficult to obtain the focused image with clear interfered fringes, and the traditional auto-focusing approaches usually determine the wrong focused position. This paper proposed a useful approach by the passive auto-focusing to determine the accurate focus for the scanning white-light interferometers. Some experimental results are presented to verify the feasibility of the proposed approach.

Distributed optical fiber sensors based on Brillouin scattering by measurement on time domain, due to its capability for strain and temperature measurement continuously for long range, are currently interesting. These sensors are based on spectral characteristics change of back scattered light at different places along the fiber. For this method Spatial resolution is limited by pulse length. We want to improve spatial resolution at time domain sensors by using of sinusoidal frequency modulation of pulse probe and continuous pump light. In this article, this method is simulated.

An instrument to attain surface topography is White Light Confocal Microscope (WLCM).WLCM utilizes a spectrometer to analyze the scattering wavelength from the surface of a specimen. In this paper we used a CCD and some image processing techniques instead of spectrometer to determine the scattered wavelength. Both simulation (By Zemax Optical Design Software) and experiment have been performed. To reach the longitudinal chromatic aberration, two biconvex lenses with longitudinal chromatic aberration were used in the simulation and the experiment. Also, the lateral resolution is provided by a 40X microscope objective lens. The white light source of the experiment setup is a Xenon lamp and the used wavelength ranges from 420 nm to 630 nm. Comparison of the results showed an acceptable conformity between the simulation and the experiment. Finally, the topography of the surface was achieved.

White-light scanning interferometry is a powerful technique for three-dimensional (3D) shape measurements of optical devices, industrial parts and microstructures. In order to obtain high performance out of this technique, many algorithms have been proposed such as phase-shifting, zero-crossing and Fourier-transform based methods. However, all of these algorithms require that the interferogram be sampled over a wide range. Unlike these conventional techniques, we here propose a weighted integral method that gives an estimate of the envelope peek position from only a fraction of the interferogram.

In order to study dropwise condensation on a metal plate, the method for controlling a tiny dew droplet deposited on a copper plate has been developed by using scattered laser light. The method employed the proportional control combined with shifting movement by an integrator to control the intensity of the scattered laser light constantly. Also, the control simulation of the method has been developed to confirm the usefulness of the method and the simulated three-dimensional shape of controlled dew droplet was obtained with the control action. A tiny thin dew droplet, of which the diameter was of handreds micrometers and the mass was about 10^-7 g, was controlled in the atmosphere at room temperature for 60 minutes at the preset level of the intensity of scattered laser light and the three-dimensional shape of the controlled dew droplet was shown from the interference fringes.

In this paper it is shown that temperature, refractive index and density and also convective heat transfer coefficient around a vertical axisymmetric cylindrical wire can be measured by the Michelson Interferometer. In experimental setup, a vertical wire has been put in one of the arms of the Michelson Interferometer. By applying voltage to the wire, temperature gradient is created around the wire. These phenomena curved the linear Michelson fringes. By measuring the fringes shift and applying the Abel transform, the distribution of refractive index can be evaluated. This distribution gives the density distribution. Minimum value for refractive index and density is found on the surface of the wire. For the far distance from the wire, density and refractive index approaches to the room values. Air density was evaluated experimentally, which is compatible with its reported value at definite weather conditions. Considering high reflectance of the wire, its thermal radiation is low and heat mostly transfers by convection. Convective heat transfer coefficient is measured experimentally which agrees with last results.

Displacement sensors with nanometer resolution used in precision engineering demand precise scale calibrations. Presented paper deals with the description of subsystems of a novel interferometric nanocomparator. High speed digital quadrature detector based on digital signal controller is used here for processing of the X-Y signals from the detection unit of the interferometer. Digital filtering increases signal to noise ratio and allows achievement of sub-nanometer resolution and accuracy of the laser interferometer. The refractive index of the air is computed continuously from the current atmospheric values using Edlen's formula. High dynamic range of the mirror displacement setting is achieved using a two stage positioning system formed of a linear guide way and piezoelectric actuators. The linear guide way is used for open-loop coarse positioning with 50 nm accuracy and up to 100 mm of displacement. Piezoelectric actuators in servo-loop linked to the interferometer value are used for fine positioning with better than 1 nm accuracy over a 5 μm range. Due to imperfections of the linear guide way with ball carrier bearings, random deviations of the mirror from the ideally perpendicular position to the laser beam may introduce uncertainties to the measurement. To compensate this, the position of the beam reflected from the mirror is measured by a 4-quadrant light detector. Using the piezoelectric actuators in servo-loop mode the control part of the system actively stabilizes the mirror in a position perpendicular to the laser beam.

Scanning white light interferometry (SWLI) allows dynamic full-field 3D profiling of MEMS devices. With stroboscopic illumination periodic out-of-plane oscillation can be characterized, but in-plane movement is unresolved. We combine stroboscopic SWLI with image processing to concurrently characterize periodic out-of-plane and in-plane displacement. A difference in frequency is induced between the sample excitation and stroboscopic illumination signals. The difference frequency is chosen to allow recording the surface movement at video rate. The stroboscopic image is thus no longer frozen in time, but moves at frequency equal to the difference in stroboscopic frequencies. This motion is captured with a CCD camera. The surface velocity is extracted from the apparent motion using optical flow algorithms. For concept validation we characterize the in-plane and out-of-plane movement of thermal microbridges fabricated on silicon-oninsulator by deep reactive ion etching. The microbridge geometry was designed for in-plane movement with minor outof plane deflection.

Fiber Bragg grating (FBG) sensors have proven to be adaptable for monitoring various physical quantitites like temperature, strain, or even vibrations and acoustic noise. Several interrogation methods, like spectroscopic evaluation, interferometric interrogation, active scanning or active filtering systems or passive filtering systems are capable of monitoring the wavelengths of the FBG sensors. Among the passive filtering systems, interrogators based on arrayed waveguide gratings (AWG) have shown to be promising candidates for sensing with FBGs, especially for high-frequency measurement tasks. Whereas the resolution- and the accuracy-dependency on light intensity of direct wavelength determining systems like spectrometers or scanning filter systems can be minimized by data processing algorithms, the performance of passive filtering based interrogators is more sensitive regarding uncertainties induced by electrical amplifier noise, FBG peak shape, light source intensity, etc.. The influence of different sources of uncertainties for AWGbased interrogators on the accuracy of the wavelength determination are investigated by an analytical model. The model is evaluated by a numerical simulation. It is shown how strongly the accuracy and the resolution of such an interrogator depend on the mentioned sources of uncertainties. Considering the obtained results, one can say that FBG interrogators based on arrayed waveguide gratings have, including the shown restrictions, the potential for rugged, compact and cost effective high accuracy wavelength interrogators.

Mono and polycrystalline Chemical Vapor Deposited (CVD) diamond is a promising material for several advanced topics: microchips substrate, biological applications, UV and particle detection. Commercial CVD diamonds are available in small square size, commonly 3-5 millimeters side and 0.5-1.5 millimeters thickness. To improve diamond reliability for described applications, it is important to have a quality control on diamond samples, not only for electrical constants but also for optical characteristics and surface roughness. In this paper we present an optical characterization method based on interferometric instruments, to measure surface structure and internal homogeneity of mono ad polycrystalline commercial CVD diamonds, with measurement examples.

Diffraction gratings have been successfully used in Optical Metrology for a long time. They can be found in scientific and industrial applications, such as optical encoders for determining the linear or angular displacement, spectrometers, robots, etc. Defects on the surface of the grating may occur due to the manufacturing process. Also dust particles, drops of liquids, etc. can be deposited on its surface the devices are placed in a dirty industrial environment. This separation from the ideal behaviour may produce a degradation of the self-images. In this work we analyze the effect produced by an irregular distribution of surface defects on the grating, with different distribution densities. In particular, we focus how the contrast of the self-images decreases when the defects density.

Need of precise definition of the calibrated length is of great importance in industrial application in these days. The Fabry-Perot interferometer or etalon with very high stable laser produces length etalon sensitive in nanometer scale with linear response to its change. Fabry-Perot interferometer (etalon) with length L represents a set of equidistant frequencies that could be transmitted through the length etalon. Each frequency could be described as multiple of free spectral range of Fabry-Perot etalon which depends inversely to the mirror spacing. Tuning DFB diode covering the tuning frequency range of hundreds of GHz is used as laser source for detection of transmitted light. Found DFB diode laser wavelength transmitted through the Fabry-Perot etalon is measured by wavelengthmeter. Train of femtosecond laser pulses produces an optical frequency spectrum (optical comb) of separate equidistant frequencies with an offset frequency. Stabilized optical comb generates a very precise frequency rule. Frequency beat between DFB laser source and the closest femtosecond laser line is detected to find the exact frequency. This procedure is done in whole DFB laser diode tuning range. Such method produce about hundred of reproductive and well defined measured points in DFB laser diode tuning range. Measured points are treated by computer algorithm. Moreover the Fabry-Perot mirror distance changes could be precisely analyzed by this method.

In this work, we consider the use of circular moments for invariant classification of images which have been blurred by motion. The test images of the objects under consideration have been acquired when they are vibrating. For this task an experimental setup is implemented to generate vibrations. A comparative analysis using several circular moment sets is presented; the studied sets are Zernike, Pseudo-Jacobi-Fourier, Orthogonal Mellin-Fourier, shifted Chebyshev-Fourier, and radial harmonic Fourier. The classification method is tested using images of mechanical parts which have intrinsically little differences between them, as screws with millimetric or standard threads. Experimental results and the optical setup used are presented.

In recent years there has been a considerable increase in the use of variable focal length lenses (VFLL), due to the fact that they are used as micro lenses in photographic cameras, endoscope, etc. The VFLL's come mainly in three types, one of them are formed of two transparent elastic membranes with a liquid medium between them, those made of an elastic material inside a mount which allow radial forces to be applied on its perimeter, and finally those which are made of a dielectric liquid medium. In these VFLL always have a mechanism that allows the shape of the lens and its geometrical parameters can be changed. In this study, we implement a mechanical mount to applied radial force, in the perimeter of a solid elastic lens. We measure the aberrations of wavefront present in deformable solid elastic lens (VFLL), when we change the radial forces applied on its borders. The wave sensor used were the Point Diffraction Interferometer (PDI) and null screen tests. Theoretical and experimental results are presented.

A double-cathode photodetector (DCP) featuring a buried-finger structure to achieve improved separation efficiency is presented. The interleaving comb-shaped cathodes are realized with n-buried implants and they are located in the p-epitaxial layer roughly 1μm below the surface. Based on MEDICI device simulations several layout variations have been realized in a slightly modified BiCMOS process. Best results are achieved with a finger distance of 12μm and a finger width of 1μm: separation efficiencies of 50, 67, and 54% and responsivities of 0.23, 0.47, and 0.38A/W were measured for the optical wavelengths 410nm, 660nm, and 850nm, respectively. All test structures occupy optical active areas of around 100×100μm². A maximum 3dB-modulation bandwidth of almost 300MHz was measured, while dark currents in the picoampere range are typical for these detectors up to a bias voltage of 5V at room temperature. In the application of a time-of-flight (TOF) distance measurement sensor, the DCP serves as optical detector and correlating device at the same time. Distance measurements up to 6.2m were performed with a 650nm laser source that emitted an average optical power of 1mW using rectangular modulation signals at 10MHz. The standard deviation is better than 1cm up to 3.4m for a total measurement time of 20ms per acquired distance point.

It has been demonstrated that non-destructive inspection of plates can be performed by using two-dimensional maps of instantaneous out-of-plane displacements obtained with a self-developed pulsed TV-holography system. Specifically, the interaction of guided elastic waves with defects produces scattering patterns that contain information about the defects (position, dimensions, orientation, etc.). For quantitative characterization on this basis, modeling of the wave propagation and interaction with the defects is necessary. In fact, the development of models for scattering of waves in plates is yet an active research field in which the most reliable approach is usually based on the rigorous formulation of elasticity theory. By contrast, in this work the capability of a simple two-dimensional scalar model for obtaining a quantitative description of the output two-dimensional maps associated to artificial defects in plates is studied. Some experiments recording the interaction of narrowband Rayleigh waves with artificial defects in aluminum plates are presented, in which the acoustic field is obtained from the TV-holography optical phase-change maps by means of a specially developed two-step spatio-temporal Fourier transform method. For the modeling, harmonic regime and free-stress boundary conditions are assumed. Comparisons between experimental and simulated maps are included for defects with different shapes.

This paper proposes the characterization of thermal lens by white light interferometry on the Methylene -blue/water solution. Thermal lens effect is determined by local phase, which is obtained by analyzing the thermal lens fringes with single sideband modulation method.

A Fizeau interferometer based system has been developed to measure the figure error of large synchrotron optics using single-pass, double-pass, and stitching geometries. The system, which uses a λ/100 reference flat, is designed to measure optics up to 1.5m in length, and is capable of nanometer level repeatability. Fizeau measurements, in single pass geometry, are conventionally limited to the diameter of the laser beam, typically 150mm or 300mm. Stitching adjacent fields of view together or using a double-pass geometry, allows much larger optics to be characterized. Results for the single-pass, double-pass, and stitching geometries are shown to give consistent figure error values. Data is also in good agreement with an autocollimator-based slope profiler. The Fizeau method is also advantageous since data can be acquired in less than 1 minute, particularly useful for characterizing the many degrees of freedom of active or adaptive optics. To obtain results consistent with alternative techniques, the importance of an a priori knowledge of the surface topography of the reference optics is also demonstrated.

The structural and material behaviour of parts of automobile seats must be known as extensively as possible. In order to assess deformation and failure in lightweight metallic tubular structural parts of auto seats a pseudo-dynamic procedure, to be briefly described herein, was devised. The deformation of circular section tubes subjected to centred transversal force can be assessed by measuring strain or the bending of the tubes. Most frequently contact gauges are used in this process. The authors employed optical noncontact microtopographic inspection using the MICROTOP.06.MFC microtopographer developed at the Microtopography' laboratory of the Physics Department of the University of the Minho. The system will be briefly described as well as the inspection methodology used. Bending radius can me directly measured. For stronger deformations however bending radius measures becomes unreliable and full topographic inspection must be performed. Roughness statistical parameters can also be calculated. If the surface of the tubes in the area where maximum deformation is expected to occur (located by finite elements simulation models) is textured to a certain level of roughness, changes in the roughness values after deformation were expected to be measurable. A direct correlation between the deformation state/tension, strain and stress, and surface' roughness, in particular the average roughness, was found. Results will be presented and discussed.

A new method, which combines the stereovision and phase shifting techniques, is proposed for more accurate 3-D shape measurement. This method uses two cameras and one projector and can eliminate errors caused by inaccurate phase measurement, for example, periodic errors due to the nonlinearity of the projector's gamma curve. The two cameras are set up for stereovision. The projector is used to project phase-shifted fringe patterns onto the object twice with the fringe patterns rotated by 90 degrees in the second time. Fringe images are taken by the two cameras from different directions simultaneously. The resulting phase maps are used to assist stereo matching at the pixel level. The coordinates of the object surface are calculated based on triangulation. Since the phase value at each pixel is used to assist stereo matching only, it does not have to be accurate. This means that the projector does not need to be calibrated, which simplifies the system calibration. Errors due to inaccurate phase measurement are significantly reduced because the two cameras produce phase maps with the same phase errors. This combined method is better than stereovision method alone because it provides higher resolution and easier stereo matching. It is better than the phase shifting method alone because it eliminates the need of accurate phase measurement in order to ensure high measurement accuracy. Experimental results and comparisons with the typical phase shifting method are presented to show the effectiveness and advantages of this newly proposed method.

Measuring system based on Photonic Bandgap Fiber (PBGF), which will be able to detect, distinguish and measure the concentration of various aliphatic hydrocarbons is proposed. Such a system can be applied on each stage of fuel evaluation, production, distribution and storage of petroleum products. Aliphatic hydrocarbons absorption spectra show several peaks around 1400-1600 nm wavelength. Thus, tunable lasers with 20 micron core photonic bandgap fiber matching above wavelengths were chosen for the optical measurement system. Measurements were performed at a low pressure to eliminate pressure broadening effect and to sharpen the absorption peaks. The sensitivity of measurement increases with increasing of the fiber's length. Length of fiber was adjusted using several methods. The best results were obtained using argon ion beam cutting. The angled cut was performed to improve signal to noise ratio.

In this contribution, we present a novel approach for three-dimensional (3D) mapping that is based in the coding provided by the coherence length of a laser source over the object depth. By using a classical temporal electronic speckle pattern interferometric (T-ESPI) setup, the object depth is encoded into the amplitude of the interference pattern instead of in the phase distribution. After performing phase-shifting method, the object shape is recovered by means of a range image obtained by computing the visibility of the image set of interferograms and where each gray level is representative of a given object depth. Experimental results validate the proposed approach for reflective diffuse objects at different measurement distances.

We describe a hybrid system for real-time, full-field vibrometry, incorporating features of high-speed electronic speckle pattern interferometry (ESPI) and laser Doppler vibrometry (LDV). Based on a 2D interferometric sensor array, comprising 16 × 16 parallel illumination and detection channels, the matrix laser vibrometer (MLV), captures full-field data instantaneously, without beam scanning. The instrument design draws on the advantages of scale offered by modern telecommunications fiber optic and digital electronics. The resulting architecture, comprising a compact measurement probe linked by fiber optic umbilical to a remote electronics unit, facilitates practical application of the system in fullfield measurement of transient vibrations and rapid non destructive testing of composite materials.

We present in this work a multifocus image fusion algorithm based on wavelet transforms applied to multifocus microscopy images acquired by the bright-field technique. The fusion scheme is based on the Daubechies family transforms. Experimental results are presented using metallic samples.

We propose to use a visibility-modulated fringe pattern to enable real-time image acquisition in the newly proposed combined stereovision and phase shifting method for 3-D shape measurement. The combined stereovision and phase shifting method uses two cameras and one projector and can eliminate errors caused by inaccurate phase measurement, such as periodic errors due to the nonlinearity of the projector's gamma curve. In order to achieve pixel-to-pixel matching between the two cameras, we previously used two phase-shifted fringe patterns, one with fringes in the vertical direction and the other in the horizontal direction. This means that the projected fringe pattern has to be switched during the image acquisition process, which slows down the process. As a result, measurement of dynamically changing objects is difficult. In this paper, we propose to use a visibility-modulated fringe pattern to eliminate the need of the second fringe pattern. This new fringe pattern is sinusoidal in the horizontal direction as in a conventional fringe pattern, but is visibility-modulated in the vertical direction. With this new pattern, we can obtain the phase information in one direction and fringe visibility information in the other direction simultaneously for stereo matching. Since no pattern changing is necessary during the image acquisition process, the image acquisition time can be reduced to less than half of the time previously required, thus making the measurement of dynamically changing objects possible. Experimental results are presented to demonstrate the effectiveness of the proposed method.

We discuss AFM (Atomic Force Microscopy) characterization in terms of critical dimension and depth for large area micro-optical elements. Results are shown and discussed in comparison with other techniques, such as SEM (Scanning Electron Microscopy) for CD measurements and FIB (Focused Ion Beam)-SEM characterization for the structure profile.

A new approach for quantifying the optical aberrations of aspherical lenses is presented. A measurement setup is developed which measures the local wavefront slopes using a motorized scanning system. The simulation results of the setup are presented in order to validate the potential of the measurement principle. Experimental results by the measurement of a commercial aspherical lens verify the theoretical investigations. Dynamic range of the measurable Zernike coefficients and Peak to Valley (P-V) wavefronts are quantified. Focal length of the aspheric lens under test is calculated from the Zernike coefficients which are determined by performing a nonlinear regression analysis for the measured slopes and the partial derivatives of the wavefront. Furthermore, 3rd order spherical aberration term of the wavefront is analyzed dependent on different wavelengths.

errata