The paper describes analgorithm of photoelastic tomography and its application for residual stress measurement in glass articles of complicated shape. The algorithm is based on a linearized solution of the equations of integrated photoelasticity. The problem of tensor field tomography is decomposed into several problems of scalar field tomography for normal stress components of the stress tensor. The method is implemented with an automated polariscope with a rotary stage. Several examples illustrateapplication of the method.

A novel principle for absolute position measurements of rough surfaces is presented. A measurement object with a rough surface acts as an external reflector for an antireflection coated laser diode. Determining the longitudinal mode spacing yields the distance from the laser diode to the measurement object. Synchronous pumping of the laser diode results in locking of the modes of the built-up Fabry-Perot resonator. Due to resonance enhancement the mode locked external cavity laser sensor allows highly resolved displacement measurements of rough surfaces. The influence of the object as well as the active gain medium on the accuracy of the measurements is investigated by experiments and simulations.

We present experimental results achieved by a method of direct conversion of the relative changes of the measurement optical path of Michelson interferometer to relative changes of the resonant optical-frequency of Fabry-Perot (F.-P.) resonator. We developed the method as a testing process for verification of scale-linearity of Michelson interferometer with total resolution 0,3 nm. The method consists of a mechanical coupled shift of the corner cube mirror of the interferometer measurement arm with one of the mirrors of F.-P. resonator. A piezoelectric transducer (PZT) with approximately 10 microns elongation drives that mechanical shift. An external tunable laser source at 633 nm wavelength provides identification of one of the resonant optical frequency of F.-P. resonator by the frequency locking mechanism with synchronous detection technique in the servo loop feedback. Because definition of the meter unit is based on iodine stabilized He-Ne laser, then the optical frequency of the locked tunable laser is frequency compared with HeNeI₂ laser by the heterodyne optical mixing. A fast high-resolution counter counts the resultant radio-frequency signal as a product of the optical mixing. Measured frequency values and values of interference phase acquired by the interferometer are simultaneously sampled step by step for each elongation position of PZT element. The experimental data achieved by F.-P. resonator shows uncertainty of the relative distance change better than 0,01 nm. We verified the scale-linearity of Michelson interferometer to ±1,0 nm limit.

A theoretical model of the optical system of an interference microscope includes both geometrical and spectral contributions to fringe contrast localization. An incoherent superposition of interference patterns over a range of wavelengths and pupil-plane coordinates predicts the frequency-domain portrait of the interference phenomenon. An inverse Fourier transform then provides simulated signals that correlate very closely to experimental data. The model is particularly useful for signal prediction, algorithm testing, uncertainty analysis and system characterization, including modern applications in thin film analysis and stroboscopic interferometry.

Inspection and linewidths measurements of subwavelength structures using optical microscopy are severely confined both by the limited resolution and by a manifold of light-structure interactions affecting the optical image. A straightforward way to improve the resolution is the reduction of the wavelength of the imaging radiation to the UV or DUV spectral range. But changing the wavelength will be accomplished by a modification also of the interaction between the light and the specimen. This modification also affects the contrast mechanism and therewith also the signal to noise ratio for various microscopy methods in a different way. Additionally the quality of the structure edge localisation may be affected due to changing field displacement effects in the field structure interaction. We investigated theoretically the changes of the contrast mechanisms for different microscopy methods between visible, UV and DUV microscopy for different materials like Chrome, SiO₂ or Silicon. The investigated methods are bright field reflection microscopy, confocal microscopy and a newly developed dark field method using alternating grazing incidence illumination. The calculations are based on rigorous diffraction calculation.

As an alternative to the intensity correlation technique used in conventional speckle metrology, we propose a new technique of displacement measurement based on spatial signal-domain phase-only correlation that makes use of the pseudo phase of the complex analytic signal generated from a Hilbert-filtered speckle pattern. Experimental results are presented that demonstrate the validity and the advantage of the proposed signal-domain phase-only correlation technique over the conventional intensity correlation technique.

The use of computer generated sinusoidal fringe patterns has found wide acceptance in optical metrology. There are corresponding software solutions that reconstruct the phase field coded in the fringe pattern in order to get 3D-shape data via triangulation and deflection measuring setups, respectively. Short recording time is a common issue of high importance for all tasks on the factory shop floor as well as in applications for life sciences and for security locks. Recent high-speed implementations take advantage of MEMS based spatial light modulators and the digital micromirror chipset DMD Discovery is the fastest mature component currently available for this aim. Being an on-off-state system, the sinusoidal gray level pictures recorded by a time averaging analog detector are produced using the DMD pulse-width modulation (PWM). This digital generation of “intensities” provides outstanding precision and long-term stability. However, there is no corresponding counterpart on the detector side up to now. The recording of light fields by CCD or CMOS cameras is always an analog process despite the fact that the camera output may be digital (CameraLink or FireWire). A new proposal is discussed in this paper that could be suited to overcome this limitation. After a brief classification of state-of-the-art systems, the author describes what he envisages being the way to future digital phase-code readings at extremely high speed and precision.

In the following, optical 3D-measurement systems based on fringe projection techniques according to the principle of phasogrammetry are introduced. These self-calibrating measuring systems allow the automated measurement of complex objects. In combination with adequate software tools to evaluate the data, a variety of different tasks can be performed in a productive environment.

Optical, glass ceramics and crystals are used for various specialized applications in telecommunication, biomedical, optical, and micro lithography technology. In order to qualify and control the material quality during the research and production processes several specialized ultra trace analytisis methods have to be appliedcs Schott Glas is applied. One focus of our the activities is the determination of impurities ranging in the sub ppb-regime, because such kind of impurity level is required e.g. for pure materials used for microlithography for example. Common analytical techniques for these impurity levels areSuch impurities are determined using analytical methods like LA ICP-MS and or Neutron Activation Analysis for example. On the other hand direct and non-destructive optical analysistic becomes is attractive because it visualizes the requirement of the optical applications additionally. Typical eExamples are absorption and laser resistivity measurements of optical material with optical methods like precision spectral photometers and or in-situ transmission measurements by means ofusing lamps and or UV lasers. Analytical methods have the drawback that they are time consuming and rather expensive, whereas the sensitivity for the absorption method will not be sufficient to characterize the future needs (coefficient much below 10^-3 cm^-1). For a non-destructive qualification for the current and future quality requirements a Jobin Yvon FLUOROLOG 3.22 fluorescence spectrometery is employed to enable fast and precise qualification and analysis. The main advantage of this setup is the combination of highest sensitivity (more than one order of magnitude higher sensitivity than state of the art UV absorption spectroscopy), fast measurement and evaluation cycles (several minutes compared to several hours necessary for chemical analystics). An overview is given for spectral characteristics using specified standards, which are necessary to establish the analytical system. The elementary fluorescence and absorption of rare earth element impurities as well as crystal defects induced luminescence originated by impurities was investigated. Quantitative numbers are given for the relative quantum yield as well as for the excitation cross section for doped glass and calcium fluoride.

Semiconductor technology progresses at a relentless pace, making it possible to provide image sensors and each pixel with an increasing amount of custom analog and digital functionality. As experience with such photosensor functionality grows, an increasing variety of modular building blocks become available for smart pixels, single-chip digital cameras and functional image sensors. Examples include a non-linear pixel response circuit for high-dynamic range imaging with a dynamic range exceeding 180 dB, low-noise amplifiers and avalanche-effect pixels for high-sensitivity detection performance approaching single-photoelectron resolution, lock-in pixels for optical time-of-flight range cameras with sub-centimeter distance resolution and in-pixel demodulation circuits for optical coherence tomography imaging. The future is seen in system-on-a-chip machine vision cameras (“seeing chips”), post-processing with non-silicon materials for the extension of the detection range to the X-ray, ultraviolet and infrared spectrum, the use of organic semiconductors for low-cost large-area photonic microsystems, as well as imaging of fields other than electromagnetic radiation.

The compact class of excimer lasers has been developed originally for the ophthalmology (vision correction). These table-top excimer lasers have output energies below 50 mJ, typically up to 20 mJ depending on the emitted wavelength. Due to the continual development in the recent years these laser systems are now available with lifetimes of some billion pulses and repetition rates up to two kHz. All commercially used wavelengths between 351 nm and 157 nm are realized in this laser class. For generating the high voltage pulses to initiate the laser emission a solid state pulsed power module (SSPPM) is installed. This module has a nearly unlimited lifetime. Further work is done to enlarge the life time of all sub-modules especially of the laser tube and the resonator optics. These laser systems can be applied as light sources in metrology and inspection systems especially for the lithography. The state of the art of compact excimer lasers will be presented and especially the results at 193 nm and 157 nm will be discussed. An outlook of the future trends of development of compact excimer lasers will be given, too.

For a long time the confocal imaging technique was known to be a high precision imaging method in the field of microscopy providing unique depth discrimination properties, but suffering from slow response in connection with pointwise height detecting sensors. At the same time, it is obvious for triangulation systems to be unable to cope with the huge variety of shapes and specular surfaces in the continuous trend towards miniaturisation in electronics and micro machining. It is commonly understood that confocal height profiling usually requires a time consuming readjustment of the distance between the object and the sensor whilst scanning across a surface. Moreover, height steps on surfaces give rise to artefacts at the edges in many cases. In order to overcome these drawbacks we developed a high speed confocal sensor head, featuring a pixel data rate of 8000 Hz independent of surface steps and surface reflectivity. An essential feature is a fast focus scan in Z direction perpendicular to the object at a preset height measuring range. The focus adjustment is realised by scanning an image with a punctiform light source in conjunction with a punctiform detector utilizing a mirror which is attached to a high frequency mechanic oscillator. Both, the light source and the detector coincide at the end of a fibre. By moving the small sensor head relative to a surface a profile scan is taken. The time needed to determine the height value of one pixel and to measure its brightness is less than 125 microseconds. This high speed true confocal height detection technology opens up a new range of applications, e.g. in-line roughness, profile, displacement and coating thickness measurement as well as the profiling of holes where shading effects inhibit the use of triangulation based sensors.

A complete framework for automatic calibration of camera systems with an arbitrary number of image sensors is presented. This new approach is superior to other methods in that it obtains both the internal and external parameters of camera systems with arbitrary resolutions, focal lengths, pixel sizes, positions and orientations from calibration rigs printed on paper. The only requirement on the placement of the cameras is an overlapping field of view. Although the basic algorithms are suitable for a very wide range of camera models (including OmniView and fish eye lenses) we concentrate on the camera model by Bouguet (http://www.vision.caltech.edu/bouguetj/). The most important part of the calibration process is the search for the calibration rig, a checkerboard. Our approach is based on the topological analysis of the corner candidates. It is suitable for a wide range of sensors, including OmniView cameras, which is demonstrated by finding the rig in images of such a camera. The internal calibration of each camera is performed as proposed by Bouguet, although this may be replaced with a different model. The calibration of all cameras into a common coordinate system is an optimization process on the spatial coordinates of the calibration rig. This approach shows significant advantages compared to the method of Bouguet, esp. for cameras with a large field of view. A comparison of our automatic system with the camera calibration toolbox for MATLAB, which contains an implementation of the Bouguet calibration, shows its increased accuracy compared to the manual approach.

In this paper a novel framework for surface quality inspection of industrial parts based on three-dimensional surface reconstruction by self-consistent fusion of shading and shadow features is presented. Relying on the analysis of at least two pixel-synchronous greyscale images of the scene acquired under very different illumination conditions, this framework combines a shadow analysis of the first image of the scene, allowing for a determination of large-scale altitude differences on the surface at high accuracy, with a variational shape from shading scheme applied to the second image (and eventually to further images), estimating the surface gradients and altitude profile. In a first step, the result of shadow analysis is used for selecting a solution of the variational shape from shading scheme which is consistent with the average altitude difference derived by shadow analysis. In a second step, the detailed shadow structure is taken into account. An error term that aims at adjusting the altitude differences extracted from the reconstructed surface profile to those derived from shadow analysis is incorporated into the error function to be minimized by the variational shape from shading scheme. The second reconstruction step is initialized with the result of the first step. In contrast to existing shape from shading or photometric stereo approaches, our algorithm shows the advantage that it neither requires a very accurate knowledge of the reflectance function of the surface to be reconstructed, nor does it critically depend on the initialization. The described framework is applied to the three-dimensional reconstruction of metal sheet and raw cast iron surfaces in the context of industrial quality inspection.

The mathematical fundamentals of some black box calibration procedures for fringe projection system are introduced. These calibration procedures are based upon a direct mathematical transformation between the measuring volume and the image data obtained with a camera. Aided by a mathematical model of a fringe projection system various calibration procedures are compared to each other in numerical simulations. The numerical simulations facilitate statements about the attainable measuring error depending on the calibration procedure and system parameters.

A novel compact sensor head combining optical interference and scanning probe microscopy in a single instrument has been developed. The instrument is able to perform complementary quantitative measurements, combining fast non-destructive three-dimensional surface analysis with high lateral resolution imaging. The sensor head has been integrated within the architecture of a commercial interference microscope. The combined instrument makes available both the acquisition software and the hardware interface of the commercial microscope. Furthermore, the use of an optical fiber to transmit light from an external laser removes a major heat source from the measurement environment and its small diameter makes aperture correction unnecessary. Lateral resolution is extended by the attachment of a specially designed scanning probe microscope (SPM) module to the microscope objective. The SPM unit is based upon piezo-resistive cantilever technology and is self-sensing to ensure a compact design that satisfies working distance criteria defined by the optics. A major benefit of the system, in terms of a quantitative nano-metrology, is the possibility to perform a traceable and direct calibration of the SPM module. Ellipsometry has been used to quantify the impact of material differences upon interference height data. Corrected values show excellent agreement with SPM height data.

New material applications and novel manufacturing processes are driving a systematic rise in market demands concerning surface inspection methods and the performance of non-contact profilers. However, analysis of the specifications and application notes of commercial optical profilers shows that no single system is able to offer all the features a general purpose user would like simultaneously. Whereas white light interferometers can achieve very fast measurements on the micro and nano-scale without any range limitation, they can not easily deal with steep smooth surfaces or structured samples containing dissimilar materials. PSI techniques allow the user to perform shape and texture measurements even below the 0.1 nm scale, but they have an extremely short measurement range. Imaging confocal profilers overcome most of these difficulties. They provide the best lateral resolution achievable with an optical profiler, but they have a resolution limit, which is dependent on the NA and cannot achieve the 0.1 nm vertical resolution. In this paper we introduce a new dual-technology (confocal & interferometer) illumination hardware setup. With this new sensor head it is possible to choose between standard microscope imaging, confocal imaging, confocal profiling, PSI and white light interferometry, by simply placing the right objective on the revolving nosepiece.

A novel interferometer based on sampling the maxima and minima of intensity of an optical standing wave has been developed. The photoelectric detection of the standing wave is performed by using a partially transparent thin-film photodiode. The automatic bidirectional fringe counting is provided by a partially transparent and phase-sensitive detector which is realized by the integration of two stacked transparent photodiodes along the optical axis of the standing wave. To obtain the ideal sine and cosine signals, the transparent phase-sensitive detector has to be optimized by adjusting the thickness of the single layers. Some features of optimization will be presented and explained. Length measurements have been demonstrated by displacing the plane mirror and bidirectional fringe counting within the standing wave.

Fulfilling the recent needs of visualization of variable in time 3D objects in virtual reality environment requires development of new approach towards combining rapid 3D shape measurement with data filtering, coding and streaming. These operations have to enable performing real-time transmission and visualization of 3D data in virtual reality. In the paper the novel system based on digital structure light projection applied to gather 3D data representing variable in time objects and extended numerical procedures coupled with virtual camera concept for interactive object visualization is presented. The proposed measurement and data processing methodology has been verified successfully at computer generated models of moving and morphing 3D objects. Both types of data have been visualized with the average frequency of 10 frames per second in virtual reality environment.

For the production of aspheres and free-form surfaces, high-accuracy and flexible measurement techniques are necessary. The Large Area Curvature Scanning (LACS) method can be used to measure the surface form of arbitrary smooth surfaces with high accuracy. The curvature values of the surface elements along a scan line are captured by a curvature sensor and from these values the form is calculated. The curvature sensor typically is a small interferometer with an aperture of some millimeter. From a model fit to the measured interferogram, the local surface patch and the local curvature value are extracted. Determining the curvature values from the captured interferograms with high accuracy is a challenging task and requires some kind of intelligent procedures for defect recognition and for the choice of matched surface models. Several aspects of these problems are discussed. Examples of measured surfaces are shown. Special emphasis is laid on the measuring speed of the LACS system, which is mainly determined by the speed of the curvature evaluation procedure, as this is important for the use as an in-situ measurement system integrated into production systems.

A new kind of electronic speckle pattern interferometer was developed by the authors' group using conical mirrors to measure the radial in-plane displacement component. True radial in-plane sensitivity is achieved by double illumination ESPI. A compact version of this interferometer was designed and built and successfully tested outside of an optical table. This paper presents a measurement evaluation of a second generation of this interferometer applied to residual stresses measurement. An ultra high-speed drilling unit was added to the device to drill a small blind hole in the region of interest. Due to the drilling process residual stresses are released in the neighborhood of the hole. The resulting radial displacement field is conveniently measured by the radial in-plane interferometer and fitted to a mathematical model. The principal residual stresses and principal stresses directions are then determined. One main difficulty dealing with evaluation of a residual stresses measurement device is to obtain a standard with a well known reference value. Two mechanical devices where built to provide a reference residual stresses value. The first one is a long specimen under a known uniform stresses field. The second one is a long pipe with known internal pressure. Both were designed, built and calibrated to provide a reference residual stresses value to calibrate the built residual stresses measurement device. Results of the evaluation of this device are also presented in detail in this paper. Both devices where used to check the measurement performance of the developed residual stresses measurement system and the results are presented and discussed in this paper.

Temperature and transverse load sensitivities of fibre Bragg gratings (FBGs) fabricated in a range of commercially available high birefringent (HiBi) fibre were measured and compared for the 1550 nm wavelength region. The highest transverse load sensitivity, of 0.23 ± 0.02 nm/(N/mm), and temperature sensitivity, of 16.5 ± 0.1 pm/⁰C, were obtained with FBGs fabricated in elliptically clad and Panda fibres respectively. The greatest differential transverse load and temperature sensitivities were measured between the eigen axes of the bow tie and elliptical clad fibres respectively. The FBGs fabricated in bow tie fibre were successfully used to monitor the transverse strain development during the cure process of glass fibre/epoxy composites and of unreinforced resins. It was observed that the development of transverse strain was sensitive to the degree of cure of the resin. A FBG fabricated in single mode fibre was also used to monitor the predominantly axial strain development, during the cure of a glass fibre composite, for comparison with transverse strain measurements.

In this work we propose to extend the Grating Interferometry scheme by Digital Holography. The main advantages of this complementary approach are that no imaging lens is needed and that the reconstruction is not limited to the image plane as it is using a lens. Additionally, this technique provides sensitivity to both directions, normal and parallel to the surface under test. Because the grating is directly integrated into the surface, this allows measuring the displacement of that surface under long term conditions within the magnitude of the used wavelength. Good qualitative results are obtained using a single illumination direction. Quantitative results are obtained using multiple illumination directions and the in-plane sensitivity of the presented technique is shown to be equivalent to that of the Grating Interferometry.

The temperature-mapping system presented is based on a grayscale CCD camera, rotating near infrared filters and an image processing software which is used for thermal imaging of heated metal parts in heat treatment processes (plasma nitriding). Due to relatively low process temperatures of about 300°C - 500°C the received light intensity of the glowing metal parts is very weak. The quality of these images can be improved by applying modern image processing filter methods. A precondition for a correct application of these denoising filters is an exact noise characterisation of the imaging system. A camera characterisation procedure based on the photon transfer technique and the system transfer function is presented. Based on these results, examples for density and intensity estimations of Poisson noise images with multiresolution methods (Platelets) are presented. The results are used to improve image quality and measurement accuracy of CCD based thermal images.

We present a design of a stabilized laser system, an etalon of the optical frequency at the 1.5 μm band following the demands of the telecommunication industry in the Czech Republic. Our laser system employs a DFB laser diode in a two stage fully digital stabilizing scheme. The linear absorption arrangement with an acetylene filled absorption cell of a pressure about 1 kPa is used to lock the laser to the Doppler-broadened lines. To achieve a reliable and robust stabilization of the laser frequency we arranged a two-loop digital servo-system overcoming the problem of a narrow locking range of the detected transition. The wavelength of the laser is modulated by current and the servo-control and tuning is performed by a fast and precise thermal control. To achieve the resolution of the weak sub-Doppler transitions we assembled a locking scheme via frequency-modulation spectroscopy to the high finesse cavity. The system is assembled using predominantly fibre-optic components. A technology of acetylene absorption cells with AR coated windows is presented as well.

Depth-scanning is an established technique in macroscopic and microscopic 3-D metrology. Representative in this context are the confocal technique and the white-light interferometry. A new fast depth-scanning technique has been applied to a confocal point sensor to be used in a laser-welding application for in-process measurement. The depth measurement range can be extended to about +/-1 mm at about 1500 measurement cycles per second. The possibilities and the potential of these techniques are described. Another principle of depth-scanning is the chromatic confocal technique. In connection with a new approach, an innovative confocal setup enables the parallelization of the complete depth-scan for the complete measurement of a line cut of moved objects. In the macroscopic scale, the new measurement techniques of depth-scanning fringe projection (DSFP) was introduced recently. In the microscopic scale, it has been implemented successfully in a stereo microscope.

We present a measurement setup for the acquisition of topographic and 3-D point cloud data using the depth-scanning fringe projection technique (DSFP). We describe the signal generation, its processing using techniques known from short coherence interferometry and discuss a direct 3-D calibration method. Our measurement system delivers an absolute phase map of the scene under measurement. Calibration procedures for macroscopic measurement methods like fringe projection and / or photogrammetry consider the principal distance (that is to say the distance between the center of projection and the image plane) as a constant. This is feasible as long as no focusing and zooming are performed during measurement. Consequently the depth of the measurement volume is limited by the depth of sharpness of the imaging system. By focusing through the whole depth of the measurement volume, our system overcomes this problem, and offers a virtually unlimited measurement depth. However, we have to take the issue of focusing into consideration in order to calibrate our system. The well-known direct calibration method has been adapted to our DSFP setup in order to deal with the problem of geometrical aberrations and to provide a 3-D point cloud. It has been completed to a set of three polynomial transformations, which allow to include the depth-scanning principle in the calibration of the system.

We present a new way to obtain a precise and rapid characterization of the BRDF of a surface using Fourier optics. A special optical setup with Fourier optics allows us to measure the entire scattering pattern of the sample very rapidly with a large angular aperture both in incidence (0 to 80°) and azimuth (0 to 360°) using a CCD camera. The sample is illuminated true the same optics at fixed wavelength or with white light. The illumination angles can be controlled easily using the Fourier optics. The measurement spot size can be adapted from 100µm to 2mm. Anti blooming detector and multi exposures allow measurements with good signal/noise ratios very rapidly. The instrument is described and results on unprinted and printed paper are presented in relation with other more standard characterizations.

Visible spectroscopic ellipsometry is applied to monitor in-situ the behaviour of metal and metal oxides in various aqueous solutions. Ellipsometry measures the change in polarisation state upon reflection on a sample and is widely used for the determination of the optical properties of surfaces and thin films. The technique has the advantage that no reference measurements are needed. The use of in-situ ellipsometry in the fields of electrochemistry and corrosion is illustrated by means of three cases. These show the possibilities to obtain film thickness, film refractive index, and the surface roughness of the metal. The first case is related to oxide films on aluminium. For the native oxide (several nm thick) on the metal the roughening of the substrate as well as the changes in oxide film thickness can be observed independently. On thicker oxides (> 100 nm), it is possible to independently determine in-situ the refractive index and thickness of the oxide, as well as the interface roughness. This was shown in a study of the effect of aggressive solution son aluminium/aluminium oxide surface. The second case concerns the electrochemical polishing process of copper. A good coincidence is achieved between the interface roughness and layer thickness from ellipsometry and the expected surface structure for the different electrochemical conditions. A last example shows the possibility of ellipsometry to study the copper corrosion in an aggressive solution. For this case, the thickness and the refractive index of the corrosion film can only be obtained in that part of the spectrum where the oxide is transparent. The degree of corrosion protection was characterised by monitoring the protective film thickness.

We present a new method to measure specular free-form surfaces within seconds. We call the measuring principle `Phase Measuring Deflectometry' (PMD). With a stereo based enhancement of PMD we are able to measure both the height and the slope of the surface. The basic principle is to project sinusoidal fringe patterns onto a screen located remotely from the surface under test and to observe the fringe patterns reflected via the surface. Any slope variations of the surface lead to distortions of the patterns. Using well-known phase-shift algorithms, we can precisely measure these distortions and thus calculate the surface normal in each pixel. We will deduce the method's diffraction-theoretical limits and explain how to reach them. A major challenge is the necessary calibration. We solved this task by combining various photogrammetric methods. We reach a repeatability of the local slope down to a few arc seconds and an absolute accuracy of a few arc minutes. One important field of application is the measurement of the local curvature of progressive eyeglass lenses. We will present experimental results and compare these results with the theoretical limits.

A new technique to measure shapes and deformation with a high resolution is proposed. It combines the conventional Schlieren technique principle with the phase-shifting approach generally used in interferometry. By an adequate Schlieren filter and an adapted set-up, some Schlieren Fringes are generated. After the application of the phase shift technique, the Schlieren phase is calculated and converted into beam deviation values, which are integrated to deduce the object's shape. Both theoretical and experimental demonstrations are given. The technique is first validated on a reference target. With a setup working in reflection, we have measured the curvature radius of a lens surface with accuracy better than 1%. Then an application in a fluid physics experiment is given. The shape of a liquid-gas interface in a conventional Marangoni-Benard experiment has been measured with a resolution of 30nm and amplitudes up to 50μm. The shape of MEMS has also been measured in a PSS microscope with a nanometric resolution. Finally, we propose an adaptation of the setup to make it possible the measurement of fast phenomena at video frame rate.

For the purpose of online process control and quality assurance robot based inline metrology systems are used more often nowadays. With the application of this systems new so far not realizable concepts like a 100% inspection of all manufactured parts can be used. In this article an easy way of improving the programming of close range inspections with robots is presented. Therefore robots can be used even more flexible and effective in the production metrology. The resulting visual robot control relays on the depth of focus effect. The visual control concept and calibration method are presented.

This work is intended to show the results of a few architectural and archaeological surveys realized by means of a 3D scanning device, based on TOF (Time-Of-Flight) technology. The instrument was set up by the Art Diagnostic Group of the National Institute for Applied Optics (INOA) and it is composed by a high precision scanning system equipped with a commercial low-cost distance-meter. This device was projected in order to provide the following characteristics: reliability, good accuracy and compatibility with other systems and it is devoted to applications in Cultural Heritage field.

We present a novel deflectometric method for the ultra-precise 2D topography measurement of large optical surfaces. The approach is a 2D extension of the established Extended Shear Angle Difference (ESAD) technique, which has previously been limited to the 1D form measurement of plane or slightly curved surfaces. We report in detail on the new 2D ESAD scanning facility capable of measuring large (up to 600 mm in diameter) optical surfaces and present first measurement results. Information on the mathematical algorithms involved in the data acquisition and analysis are given and the mathematics used in the reconstruction of 2D topography maps from a set of angle difference data are described. The intricacies of 2D angle measurement with a modified autocollimator and calibration issues are discussed.

Accurate 3D shape measurement is of big importance for industrial inspection. Because of the robustness, accuracy and ease of use optical measurement techniques are gaining importance in industry. For fast 3D measurements on big surfaces fringe projection is commonly used: A projector projects fringes onto the object under investigation and the scattered light is recorded by a camera from a triangulation angle. Thus, it is possible reaching a depth resolution of about one by 10.000 of the measurement field size (e.g. 100 μm for a 1 m sized field). For non- or low scattering objects it is common to put scattering material like particle spray onto the object under investigation. Objects where this is not allowed are often regarded as problematic objects for full field non-coherent optical measurement techniques. The solution is to switch from fringe projection to fringe reflection. The fringe reflection technique needs a simple setup to evaluate a fringe pattern that is reflected from the surface under investigation. Like for fringe projection the evaluated absolute phase identifies the location of the originating fringe. This allows identifying the reflection angles on the object for every camera pixel. The results are high resolution local gradients on the object which can be integrated to get the 3D shape. The achievable depth resolution compared to fringe projection is much better and reaches to a depth resolution down to 1 nm for smooth surfaces. We have proven the ability, robustness and accuracy of the technique for various technical objects and also fluids. A parallel paper of this conference 'Evaluation Methods for Gradient Measurement Techniques' picks up further processing of the evaluated data and explains in more detail the performed calculations. This paper mainly concentrates on the fringe reflection principle, reachable resolution and possible applications.

Digital holograms recorded with a charge coupled device camera array are numerically reconstructed in amplitude and phase through calculation of the Fresnel-Kirchhoff integral. The flexibility offered by the reconstruction process in digital holography allows exploitation of new possibilities of application in microscopy. Through the reconstruction process we will show that it is possible to control image parameters as focus distance, image size and image resolution. We report on recent developments obtained in the numerical reconstruction process of holograms. Novel prospective of application of digital holography in single and multi-wavelengths operation either for display and metrological applications can be explored by those recent achievements. Examples of applications of digital holographic microscopy for characterizing silicon MEMS structures by adopting new procedures are illustrated and discussed.

Digital holography is a powerful tool in NDT. Different measuring methods have been developed to perform more flexible measurements and to alleviate the drawbacks of this technique. The rapid development of spatial light modulators in the past few years opened an exciting new area in coherent optical metrology. Commercially available liquid crystal spatial light modulators (SLM's) are capable to optically reconstruct digital holograms in good quality, so the reconstructed real image of an object can be used as a coherent illuminating mask in optical measurement methods like digital holography. Combination of digital holography and TV holography (ESPI) is also possible. In the present work five methods of digital holography are investigated which are able to implement comparative measurement. Both the experimental arrangements and measuring results are presented.

We report on a method called Digital Holographic Microscopy (DHM) for the numerical reconstruction of digital holograms taken with a microscope. It allows for simultaneous amplitude and quantitative phase contrast imaging. The reconstruction method computes the propagation of the complex optical wavefront diffracted by the object and is used to determine the refractive index and/or shape of the object with an accuracy in the nanometer range along the optical axis. A single hologram is needed for reconstruction. The method requires the adjustment of several reconstruction parameters. The adjustment is performed automatically by using a suitable algorithm. The method has been applied to the measurement of several integrated optics devices, MOEMS, and integrated micro-optical components: microlenses.

Digital holographic interferometry (DHI) provides full-field, non-invasive access to object and allows high sensitivity and accuracy of measurement of interference phase with high spatial resolution. Nowadays CCD and CMOS detectors and microlasers allow building miniaturized and compact digital holographic interferometers. In the paper a modular DHI system consisting of opto-electro-mechanical head and digital processing/analysis module is proposed. In order to achieve compactness and insensitivity to vibration a novel solution of interferometer head which employs two diffraction gratings is analyzed. Microlaser illuminates the first grating which acts as reference and object illumination beams generator. The first minus and plus diffraction orders form adequately reference and object beam. The second grating serves as reference and object beam recombiner providing interference pattern at the CCD matrix plane. To get off axis configuration the spatial frequencies of both gratings should differ slightly. The phase shifting version of DHI may be introduced by moving the second grating in the direction perpendicular to its lines. The usefulness of this design is proven by exemplary 3D object reconstruction and out-of-plane displacement measurement of an active silicon membrane.

Optical measurement methods based on digital holography are highly effective for shape and deformation investigation of microcomponents. One of the most commonly discussed methods is digital holographic contouring connected with digital holographic interferometry. Unfortunately, this approach requires much time and it is difficult to apply to real time measurements. In the paper a novel, simple and inexpensive setup for shape and deformation measurements is proposed. The method uses fringe projection combined with digital holography. First a fringe image projected onto the surface under the test is registered using digital holography without any optical system. Next, the fringe image is reconstructed from the hologram what allows the determination of the surface shape. Small displacements are measured with digital holographic interferometry and larger ones by comparing the shapes for two object states. Because only one hologram for the shape and two for the displacement investigation are needed, quite fast measurements are possible. However, the CCD camera used in the arrangement restricts the measurement time. The comparison of both methods, particularly related to the measurement precision, will be given. The results obtained by experimental means are presented together with a discussion of the limitations and further possibilities of this method.

An optical system based on short-coherence digital holography suitable for three-dimensional microscopic investigations is described. An in-line arrangement is used, in which the light source is a short-coherence laser and the holograms are recorded on a CCD sensor. The interference (hologram) occurs only when the path lengths of the reference and the object beam are matched within the coherence length of the laser. The phase of the object wave front in the plane of the CCD detector is determined by phase shifting. The image of the part of the sample that matches the reference beam is reconstructed by numerical evaluation of the hologram. The three-dimensional scanning of the sample is easily obtained by shifting the position of a mirror in the reference arm of the interferometer. Reconstruction of different layers of the sample is possible up to a depth of several hundred micrometers. However, in tissues and other biological samples, while the surface of the sample is properly reconstructed, the multiple scattering and the inhomogeneties in the refractive index reduce the imaging quality of the deepest layers. The possibility to correct numerically this sample-induced aberrations has been studied. Simulations and experimental results are presented.

The first two-wavelength contouring method of difference holographic interferometry (DiffHI) has been developed - as a more sensitive and more user-friendly alternative to the already existing two-refractive-index contouring method of DiffHI. It is built on "compensation-friendly" two-wavelength contouring method and on its tilt compensation version, developed specially for this purpose. Experimental verification is presented for the numerically correct functioning of the two-wavelength contouring method of DiffHI - although it is limited temporarily to mirror objects, only, because of intensity problems of the available laser. However, we hope to get the same results on diffuse objects, too - just in the near future. Two ideas seem to be applicable in the digital holographic version of the two-wavelength contouring method of DiffHI and subsequently in the Distant Shape Control project (DISCO), too. The first one is the application of the extra adjustment-monitoring mirror surface to control alignment accuracies in holographic illuminations and in remote duplication of the optical arrangement. The second one is the tilt compensation process which can correct the previous inaccuracies. The first one, on the other hand, can be used for the control of the accuracy of the calculated reference direction change, as well - at contouring with non-holographic illumination, too.

Shearography is a full-field interferometric optical technique that is usually used for the qualitative investigation of defects in non-destructive testing applications. The optical configuration is sensitive directly to displacement gradient, a parameter closely related to the surface strain. The component of the displacement gradient that is measured is determined by the illumination and viewing directions and by the direction of the applied shear. The sensitivity is governed by the magnitude of applied shear and by the optical wavelength. Full characterisation of the surface strain requires a measurement of six-components of displacement gradient; this is achieved in shearography by forming a number of distinct measurement channels using multiple illumination, or viewing, directions. In this paper the authors discuss the quantitative measurement of the strain field around a fatigue crack, using a time-division-multiplexed diode laser shearography instrument. To investigate moving objects, a pulsed laser provides a method of freezing the object position at two points in the loading cycle. A shearography instrument incorporating two frequency doubled pulsed Nd:YAG lasers, with a common injection seeder is described. The measurement channels are spatially-multiplexed by viewing from four directions using an optical fibre imaging bundle, with optical processing at a remotely located interferometer head. Preliminary experimental measurements are presented.

Two different measurement techniques based on tandem interferometry are used to measure the dispersion of group and phase modal birefringence in elliptical-core optical fibers. The first technique is based on time-domain tandem interferometry and uses processing of a series of interferograms at different wavelengths recorded in a tandem interferometer placed at the output of the optical fiber under test. The second technique is based on spectral-domain tandem interferometry and employs a low-resolution spectrometer. It uses a series of the spectral interferograms recorded at the output of a tandem configuration of a Michelson interferometer and the optical fiber under test to resolve the so-called equalization wavelengths, at which the overall group optical path difference is equal to zero. This technique enables the direct dispersion measurements of the group modal birefringence over a wide spectral range. The results obtained by both measurement methods are compared each other and good agreement is confirmed. We also modeled the dispersion of phase and group modal birefringence in the optical fibers using the modified perturbation approach first proposed by Kumar.

A light beam is incident on the boundary surface between the thin metal film of a surface-plasmon-resonance (SPR) apparatus and the test medium. If the incident angle is equal or very near to the resonant angle, then the phase difference between p- and s- polarizations of the reflected light is related to the associated physical parameter. The phase difference can be measured accurately by the heterodyne interferometry. If the relation between the phase difference and the associated physical parameter is specified, the associated physical parameter can be estimated with the data of the phase difference. This method has the advantages of both common-path interferometry and heterodyne interferometry.

This paper presents a positioning control system based on an optical heterodyne interferometric technique associated to a home-made high frequency electronic board. This system aims to control the translation of a mechanical stage with a quantified step as low as 0.258 574 970 5 (5) nm. Intrinsic relative uncertainty is very low. Hence the method is suitable for long displacement range, even millimeters long. Experimental results show the reliability of the method.

Holographic interferometric metrology allows a fast, non destructive and quantitative high resolution full field detection of optical path length changes. Furthermore, by utilization of modern CCD sensor technology and digital image process-ing algorithms an on-line application of these methods even on biological specimens is possible. In combination with a microscopic resolution this offers new possibilities for the detection of variations of shape, micro movements or refractive index changes e. g. for the marker free analysis of cellular samples. Three holographic interferometric systems for microscopy applications based on digital holography, (speckle) interferometry and photorefractive crystals as holographic recording medium are introduced. Results of investigations on test charts and biological samples to characterize and optimize the lateral resolution as well as the resolution of the detected phase difference changes are presented and discussed. Finally, the applicability of the developed measurement techniques on living cells is demonstrated.

In VanderLugt type correlators, the input scene and the filter could be implemented onto twisted liquid crystal displays (LCD's). The modulator used to display the scene and the elements placed before the filter usually introduce phase aberrations. These aberrations have an important influence in the final correlation plane. We propose a new method to evaluate and correct in situ these aberrations by using the correlator as a point diffraction interferometer. In this work, the wave front phase distribution evaluation is performed by means of the phase shift interferometry (PSI) technique. We present the theory on which the method is based and the experimental results obtained by applying it in a convergent correlator.

The comparison of two objects is of great importance in the industrial production process. Especially comparing the shape is of particular interest for maintaining calibration tools or controlling the tolerance in the deviation between a sample and a master. Outsourcing and globalization of production places can result in large distances between co-operating partners and might cause problems for maintaining quality standards. Consequently new challenges arise for optical measurement techniques especially in the field of industrial shape control. In this paper we describe the progress of implementing a novel technique for comparing directly two objects with different microstructure. The technique is based on the combination of comparative holography and digital holography. Comparing the objects can be done in two ways. One is the digital comparison in the computer and the other way is by using the analogue reconstruction of a master hologram with a spatial light modulator (SLM) as coherent mask for illuminating the test object. Since this mask is stored digitally it can be transmitted via telecommunication networks and this enables the access to the full optical information of the master object at any place wanted. Beside the basic principle of comparative digital holography (CDH), we will show in this paper the set-up for doing the analogue comparison of two objects with increased sensitivity in comparison to former measurements and the calibration of the SLM that is used for the experiments. We will give examples for the digital and the analogue comparison of objects including a verification of our results by another optical measurement technique.

The paper summarizes main researches done at the Department of Physics for DISCO project - Distant Shape Control. The main contribution to the project is the comparative technique - difference holographic interferometry (DHI) - elaborated earlier and developed continuously at the Department. Applications of digital holography are presented which include direct and comparative displacement measurement with both digital and analogue reconstructions. A special attention is taken to the increasing practical upper measuring limit of both analogue and digital holographic interferometry that is well below its theoretical value and is determined by evaluation system used and by peculiarities of the actual interference pattern. Because of the space and time limitations the main ranges of the work are presented here; for further details the reader is kindly referred to papers of F. Gyimesi at al., ("Two wavelength contouring in difference holographic interferometry and DISCO") and J . Kornis at al. ("Comparative displacement measurement by digital holographic interferometry") in this volume.

Fiber laser systems have the potential to represent an interesting alternative to more conventional laser sources emitting in the visible spectral range. In this contribution we present new results based on fluoride Pr/Yb-doped fiber systems. This Pr/Yb-doped fiber system with emission wavelengths in the red, orange, green and blue spectral range can be operated as a tunable laser source with a tuning range (around 605 nm) of almost 8 nm and as a mode-locked laser system with a pulse duration below 100 ps. The laser system was realized using Pr/Yb-doped fluoride fibers as an active media and fiber Bragg gratings in silica fibers as the basic element for the realization of the reflective and tuning components.

Approaching the ideal high resolution phase addressable modulator is a main task for current SLM (Spatial Light Modulator) development. Different technologies, such as optically addressed, modal and electrically addressed spatial light modulators compete in performance and applicability. The requested high Space-Bandwidth-Product (SBWP) can be served by the actual micro-structuring technology used to fabricate LCoS (Liquid Crystal on Silicon) micro-displays. Liquid crystal displays in different modes are suitable due to their birefringence properties and wide transmission range.

Electronically addressed spatial light modulators (SLMs) are key elements for the reconstruction of digital holograms. Reflective liquid-crystal-on-silicon displays (LCOS) have great potential to fulfill this task due to their high fill factors of over 90% and their small pixel sizes of less than 15 μm. In order to obtain maximum diffraction efficiency of the holographic reconstruction, analog phase holograms have to be implemented making a maximum phase shift of 2π in each LCOS pixel necessary. Therefore, each LCOS display has to be thoroughly characterized prior to its use as a holographic element. In this publication, we report on a specially designed LCOS test bench. Here, displays can be characterized with respect to their phase and amplitude modulation (i.e. the complex transmittance) under a varying angle of the incident linearly polarized light. Additionally, the Jones matrix of the displays can be measured, which allows computation of the response of the displays to light of arbitrary polarization. The measurement of panel flatness is also possible which is necessary to compensate wave front aberrations. Results of measurements of two LCOS dis-plays are presented and a comparison to other measurement methods is given.

Ultra thin hard films such as diamond like carbon, carbon nitride or cubic boron nitride are instrumental for many high-tech products, e.g. to extend the useful life of tools or to protect the magnetic layers in hard disk drives. In the last years the development went to thinner protection layers. Especially carbon films with a thickness down to 2 nm were investigated using ellipsometry and x-ray reflectometry. Their thickness and optical constants were determined and correlations to other film parameters such as hardness, hydrogen or nitrogen content were found. The main problem of the optical characterization of these thin hard films on real functional layers is caused by the unknown optical constants of these underlayers. Thus these have to be measured simultaneously, which increases the number of unknown parameters significantly. As a consequence the development work for optical metrology of these products need more sophisticated methods like spectroscopic ellipsometry, Raman spectroscopy, x-ray reflectometry, and atomic force microscopy. With the data from these investigations in the development lab the real mass production can be controlled by simpler optical instrumentation such as single wavelength ellipsometry and FT-IR spectroscopy.

Nowadays production systems of fancy yarns for knits allow the creation of extremely complex products in which many effects are obtained by means of color alteration. Current production technique consists in defining type and quantity of fibers by making preliminary samples. This samples are then compared with a reference one. This comparison is based on operator experience. Many samples are required in order to achieve a sample similar to the reference one. This work requires time and then additional costs for a textile manufacturer. In addition, the methodology is subjective. Nowadays, spectrophotometers are the only devices that seem to be able to provide objective indications. They are based on a spectral analysis of the light reflected by the knit material. In this paper the study of a new method for color evaluation of a mix of wool fibers with different colors is presented. First of all fiber characterization were carried out through scattering and absorption coefficients using the Kubelka-Munk theory. Then the estimated color was compared with a reference item, in order to define conformity by means of objective parameters. Finally, theoretical characterization was compared with the measured quantity. This allowed estimation of prediction quality.

For industry and research there is an interest in increasing large master surfaces and other unique optics. Even for meter-scale objects, an uncertainty of form measurement in the range of nanometers has to be fulfilled. The deviation in the radius of curvature should reach 1000 kilometers and more. We present a robust optical profiler that allows the measurement of absolute topographic profiles of flat and slightly curved surfaces up to one meter in length. It is based on simultaneous multiple angle measurement, actually carried out with a common electronic autocollimator and a specially designed front aperture. By implementation of the Extended Shear Angle Difference (ESAD) algorithm - developed at the PTB - the complete angular topography can be reconstructed from two data sets of angle difference. At last, integration leads to the height topography. The uncertainty of measurement of the parabolic form contribution is close to the one claimed above and is referenced to a smaller diameter flatness transfer standard. All other form components are measured absolutely. Measurements on an excellent optical flat standard of 60 cm in length show a reproducibility of about 0.2 nm rms. The systematic errors contributing to the uncertainty budget are listed and investigated experimentally. Starting from this, suggestions will be made how advancement can be reached, and it is proposed, that the limit is clearly over 1000 kilometer in radius of curvature.

The laser induced deflection technique (LID) is introduced for measuring small absorption coefficients of highly transparent DUV/VUV optical materials with high sensitivity and accuracy. The measuring principle, the calibration and the developed experimental realization are explained. At 193 nm in situ absorption and fluorescence measurements of fused silica give evidence that a commonly observed absorption decrease at the onset of laser irradiation is a bulk effect and due to a diminution of oxygen deficient centers ODC II. This decline is caused by a single photon absorption process and terminates after a dose of 4-5 kJ/cm². Fluence dependent bulk absorption measurements of fused silica are presented which indicate the presence of a nonlinear dependence between the absorption coefficient α and the fluence H. For calcium fluoride a very good agreement between direct absorption and conventional transmission measurements is obtained. At 157 nm, a modified compact experimental setup is introduced which exhibits a significantly higher sensitivity than that applied for 193 nm experiments. First measurements of high quality calcium fluoride show that the obtained absorption is independent on the laser repetition rate. The investigation of equivalent CaF₂ samples of different thickness (10 mm and 20 mm) indicates that the measured absorption coefficient is virtually free of contributions from the irradiated surfaces. Finally, a very good agreement is obtained by comparing LID data with transmission measurements of 100 mm long samples.

Deutsche Bahn (German Railways) requires its suppliers to deliver concrete sleepers with high precision dimensions for critical sections. To meet these demands suppliers have to continuously monitor the production process. Critical dimensions are the track width and the widths of both rail supporting planes. Also their orientation must not exceed given tolerances. That demands measurements with a precision of 0.2 mm or better. The contactless measurement system developed uses the triangulation approach based on laser plane projection. It consists of two CCD-cameras and four lasers projecting planes under 45° each. A third camera serves for the recognition of the mould numbers. Software detects if a sleeper is in a measuring position, the camera images are frozen and the measurements are done using line approximation and subpixel accuracy. Additionally the measurement of the positions of peg holes is integrated, these data serve for the control of a screw-in robot. The system is added to the running production line in a harsh industrial environment. It works fully automatically. All measured data are transferred to the production monitoring for evaluation and archiving. The system has been working now for two years, more than half a million sleepers have been reliably monitored.

The aim of this work is to show how 3D techniques can be used to integrate standard diagnostic ones, adding useful and powerful tools for the restorers. A 3D model allows both to monitor restoration processes and to keep trace of any significant modification of an artwork. We present 3D measurements carried out on different kind of samples: a statue, a painting, a xylography board and two ancient coins. These surveys were carried out by means of a high-resolution laser micro-profilometer developed by the Art Diagnostic Group of the National Institute of Applied Optics. It is composed of a commercial distance meter mounted on a scanning device and allows dense data sampling with high quota resolution and accuracy.

The symmetry concerning the fabric pattern is not always suitable for the quality that we expected from fabric textile. The moire effects produced by a periodic structure may be caused by various and diverse factors as folds, lines, etc. The defect that we are concern is bright and dark fringes appearing in the Nylon Fabric are viewed with necked eye, from a particular angle using white light. To prevent these annoying effects, one should be focusing the research basically on geometrical fabric structure, physical, optical and dyeing. We start this work by an exhaustive study made to obtain enough information in order to identify and analyze the problem in order to identify, explain and prevent it appearance. To realize that we may define the factors that causes the phenomena. Concerning the experimental results, we begin with a conventional experiment called "Flat table examination" using Fluorescent white light bulb as types of illumination. We have used as well a microscope examination. It is useful to inspect the fiber and yarns which may have different characteristics of size and form. The light interaction with the fiber will produce especially kind of reflection and absorption. We finish the work by designing and developing an optical system able not only for detecting those kinds of fringes. As well to allow some defects inspection. We believe that some measurements are necessary during some process of fabrication (dyeing, spinning and knitting), at least to reduce this types of defects.

One of the most interesting and useful applications of shearographic interferometry is the detection, visualisation and measurement of the mechanical vibration of opaque objects. Until now the time-average shearography is a qualitative interferometric method for determining the oscillating loadings. The detected gradient of the deformation can be determined by changing the shearing distance. The fringes of the moving object are often faded and become clearer by filtering with FFT and against an uniform background intensity. The fringes formed in time-average shearography of sinusoidal motions have an irradiance described by the Bessel function J_o². Quantitative interpretation of the shearogram requires a more precise analysis. Such a technique for extending or decreasing the sensitivity of vibration measurements and for determining the relative phase of vibration across the object surface is the stroboscopic illumination. Stroboscopic shearographic interferometry is a technique which compensates the deficiencies of time-average shearography at the expense of some increase in experimental complexity. However more complex is the recording of stroboscopic shearograms by using two pulses from a double-pulse laser.

The compensation of distortion in manufacturing processes is important for quality assurance in component production and product accuracy. Researches at the University of Bremen show that the main distortion effects for metal components take place during the quenching process. To measure and finally control these deformations a measurement principle which has no influence to the quenching process is necessary. Any measurement principles contacting the object are therefore inappropriate. Capacitive measurement principles drop out because the sensors have to be placed close to the object, disturbing the volume flow of the quenching gas. However, in this presentation optical metrology is shown to be suitable. As a fast, contactless measurement technique Digital Holography was used to measure surface deformation during the quenching process with interferometric accuracy. The results of these measurements shall give input to control processes in the gas quenching stand. Observing an axle of about 25 cm height, having a diameter of 2 cm and a quenching process starting at temperatures of the axis of about 800 °C, several problems had to be faced: The glow of the observed axis could be compensated by application of an interference filter. Vibrations of the axis and the setup due to the gas streaming and subsonic noise had been suspended by application of a Nd-YAG-Pulselaser with 8 ns pulse duration and 10 Hz repetition rate. Because of the high volume flow of the quenching gas nitrogen, smear effects can be neglected. Surface microstructure decorrelations are shown to be of minor interest. An interferometric correlation of two timely neighboured holograms in a series of holograms taken with a time gap of 0,5 s was possible. Difference phase maps of an area of 1 x 5 cm² showing out-of-plane deformation of a few micrometers show the Digital Holography to be a suitable measurement technique for the gas quenching process.

One of the most challenging applications of optical metrology is measuring the shape of the inner surfaces of nozzles such as those of fuel injectors, wiring dies and printheads. A current non-contact solution is confocal laser scanning microscopy (CLSM). However, the inner urfaces of the nozzles behave as though they were optically polished, which gives rise to very weak, backscattered light signals. Therefore, measuring with CLSM is a very slow process and the uncertainty of the results is very high. Moreover, new nozzle designs are moving towards even steeper walls, which means that CLSM may well become useless in the near future. In this paper, we introduce a new method based on a proprietary unfolded confocal arrangement, which uses the light that is reflected onto the inner surfaces and that passes through the nozzle instead of the backscattering signal. The setup and implementation of this new method and the attendant profiling algorithms are explained. With regard to real applications, we focus on measuring the 3D topography of conical nozzles drilled into organic polymer films with excimer lasers. These films are used in the manufacture of the orifice plates, which are attached to the printheads of thermal inkjet cartridges. Fast measurements and accurate results obtained for nozzles of 25 micrometers in diameter and wall angles close to 17º are demonstrated.

The temporal resolution of a synchroscan streak camera is mainly limited by the intrinsic tube resolution, the laser pulse width and the synchronization jitter between the camera and the laser source. Studies show that laser phase noise is localised principally at low frequency. A previous system was designed in order to eliminate the very low frequency jitter. The system allows the streak camera to accumulate a signal during over a long period (several hours) without significant temporal resolution degradation. In order to work properly, this system use a laser reference directly coupled to the streak camera on the top of the photocathode. The localisation of this laser reference spot is locked at a predefined position and then, the temporal axis of the streak camera image is locked. To allow this control, the software changes the phase between the deflection plate voltage and the synchroscan signal. The resolution obtained was about 2 ps Full Width at Half Maximum (FWHM) which is the best resolution available in the accumulation mode and this can be achieved whatever the accumulation time. In this paper, we describe an upgrade of this system which uses the laser reference information to accumulate the different frames after a retiming. It calculates the centre of gravity (COG) of the laser reference, shifts the image on the temporal axis with a sub-pixel resolution to place this COG to a predefined position. Then the frames are accumulated. By this way, the inter frame jitter is reduced. This system benefits from the very high temporal resolution of the streak camera to make to correction so that it can be very efficient. In photon counting, the temporal resolution with this system is improved to a value of 1,5 ps FWHM. With a signal to noise ratio of about 1000 the acquisition time is 35 minutes.

Short owerwiev of the development of a virtual optical laboratory for coherent optical metrology is presented. Based on TV holographic applications, results in simulation of deformation and shape measurement are shown. Examples for visualization of the defined optical arrangement are also presented. Application of a real optical setup or a real deformation pattern in virtual optical laboratory is also possible.

New construction of instrument for measurement and luminance analyse of the surrounding visual field has been presented. We used three special shaped optical guides for analyse each of visual field zone. Computer program analyse all signals and makes calculations.

As is shown the thickness of thin membranes and MEMS can be measured using a transmission short coherence interference technique and choosing a suitable wavelength range in the infrared. The method evaluates the phase difference between the object and reference beam and the actual instrument can accommodate a wide thickness measurement range.

We designed a camera based on a fast CMOS APS imager for high speed optical detection which produces images simi-larly as a streak camera. This imager produces the intensity information I as function of one spatial dimension and time (I=f(x,t)) from one frame with two spatial dimensions. The time sweeping is obtained by delaying successively the integration phase for each pixel of the same row. For the first FAMOSI (Fast MOs Imager) prototype the start of in-tegration is given by the camera itself. This signal is injected to a laser trigger. This laser emits a 10 nanoseconds light pulse onto the sensor. The temporal evolution of the light pulse is then resolved by the camera with a resolution of 800 ps. In single shot, the maximum dynamic of the camera is estimated to 64 dB and is limited by the readout noise. We decide to work in accumulation mode in order to increase the signal to noise ratio of the camera. But the high laser trigger (about 20 ns rms) does not allow accumulation of several optical events without a large spreading. The camera has been modified in order to be triggered by an external signal delivered by a trigger unit. In this new configuration the laser emit pulses at a repetition rate of 50 Hz. A photodiode detect a part of the laser pulse and generate the trigger signal for FAMOSI. The laser pulse is delayed with an optical fibre before being directed to the camera. The trigger jitter obtained is then less than 100 ps and allows accumulation without significant loss of the temporal resolution. With accumulation the readout noise is attenuated by a √N factor. Then with N = 1000 accumulations, the dynamics approach 93 dB. This allows the camera to work similarly as a synchroscan streak camera and then to observe weak signal.

It was proposed technique for modeling of adaptive diffractive elements in holographic system that based on a new method of wave equation solution analysis of the aperture diffraction problem. The method is based on new integral approach to modeling of laser beam diffraction on an arbitrary aperture by investigation of the singular wave component derived from a rigorous Sommerfeld's solution. Developed on the basis of proposed integral representation the effective algorithm is useful for providing analytical studying and numerical modeling the aperture diffracted field without paraxial approximation and the specific form of the convolution kernel that describes the diffraction with taking into account the size of cell allows alternative reconstruction procedure of diffraction pattern. The structure of the diffraction field not only in far zone but also in near and middle diffraction zone depending on profile of the amplitude-phase diffractive grating can be analysed. The extension of new method of modeling diffraction on amplitude-phase mask and possibilities of its practical application such as computer modeling of diffraction on a spatial light modulator (SLM), which consists of squared cells, for a wavefront reconstruction are considered. Conclusions regarding the possibilities the representation the arbitrary fields by using the discrete matrix of elementary diffractive aperture cell for enhancement of iteration algorithm of hologram synthesis and phase retrieval are arrived at. Proposed method for reconstructed images of computer-generated holograms (CGH) enables one to synthesize CGH's and simulate digital image processing techniques for 3D image reconstruction by kinoform. The result of computer simulations and optical experiments are presented.

The theory and method for design of the optical systems for realization of the Fourier transform in systems for optical data processing is described. There are given relations for initial design of these optical systems using the third order theory of aberrations. As an example, the parameters of the four element optical system are given, which enables to obtain a suitable image quality required in systems for optical image processing.

A theory of deformation of the thin flat mirror, which vibrates harmonically in the direction of the normal to its surface, is shortly introduced in our work. Vibrating thin flat mirrors are used in various areas of science and engineering, e.g. in optical measurement systems. These mirrors can be generally deformed with respect to environmental conditions during measurements. The mirror deformation is closely related to the dynamic wave aberration of the wave-front, reflected from the mirror. The consequence of the wave aberration is a spatially inhomogeneous frequency shift of the light reflected from the vibrating mirror. The influence of the wave aberration on the frequency shift is studied theoretically and examples are given.

Many optical metrology methods deliver 2D fields of gradients, such as shearography, Shack-Hartmann sensors and the fringe reflection technique that produce gradients for deformation, wave-front shape and object shape, respectively. The evaluation for gradient data usually includes data processing, feature extraction and data visualization. The matters of this talk are optimized and robust processing methods to handle and prepare the measured gradients. Special attention was directed to the fact that optical measurements typically produce data far from ideal behavior and that parts of the measured area are usually absent or invalid. A robust evaluation must be capable to deliver reliable results with non perfect data and the evaluation speed should be sufficient high for industrial applications. Possible data analysis methods for gradients are differentiation and further integration as well as vector processing when orthogonal gradients are measured. Evaluation techniques were investigated and optimized (e.g. for effective bump and dent analysis). Key point of the talk will be the optimized data integration that delivers the potential of measured gradients. I.e. for the above mentioned examples: the deformation, wave-front and object shape are delivered by successful data integration. Local and global existing integration methods have been compared and the optimum techniques were combined and improved for an accelerated and robust integration technique that is able to deal with complicated data validity masks and noisy data with remaining vector rotation which normally defeats a successful integration. The evaluation techniques are compared, optimized and results are shown for data from shearography and the fringe reflection technique (, which is demonstrated in talk “High Resolution 3D Shape Measurement on Specular Surfaces by Fringe Reflection”).

The capacity of holographic memory can be made higher than that of the conventional optical disks because it can use 3D memory storing area. This paper discusses ROM type holographic memory that uses CGH for data storing. High speed calculation method for creation of CGH is studied. By the experiment and simulation to create the Lohmann type CGH pattern by the optical disc cutting system, it was shown that the creation of CGH pattern that can generate high quality reconstructed 2D image is feasible by this method.

In order to tap the full potential of optical metrology, a comprehensive knowledge of the measuring system properties is of particular importance. The surface characteristics, the sensor's orientation towards the device under test and even the measuring frequency affect the result. Understanding the function of particular components of the device under test must also be seen as a basic prerequisite for the definition of the inspection features which will make up the inspection plan. The problems arising from the complex application of optical metrology, mainly in machine integration and embedment into existing quality management, will be the central theme of two research projects. An emphases of the technical development will be on the integration of optical metrology into machine tools and production-related coordinate measuring machines while ensuring consistency of data and on the conceptual design of software interfaces for user-friendly application of optical metrology. For that purpose, database-supported automatic generation of measurement and digitization procedures from CAD data will be implemented. This work will centre around the definition of variable sensor parameters and the allocation and configuration of these parameters according to the measurement task at hand. The technological basis for these studies are a conoscopic sensor mounted on a coordinate measuring machine and a scanning triangulation sensor integrated into a five axis machine tool.

We present a new method for the measurement of the absolute distance of a remote target based on the laser diode self-mixing interferometry technique, assisted by an electronic feedback loop capable of increasing the measurement accuracy. In this method, we use an electronic feedback loop to generate a wavelength change that exactly corresponds to one single interferometric fringe. This allows to measure the target distance with a higher accuracy, in principle limited only by detection shot-noise, and not by the fringe quantization error typical of conventional fringe counting approaches. The target distance can be measured with 0.3 mm accuracy, in the 0.2-3 m range.

Time-averaged holographic interferometry is a known technique frequently used for analyzing vibration properties of objects. The development of array photo-detectors allowing long integration times enabled the capture of time-averaged holograms. A new technique called 'subtraction digital holography' has been recently developed for suppressing the zero-order disturbance in off-axis digital holography. In this work, we combine the time-averaged principle with subtraction digital holography technique. Results for a torsional micro-electro-mechanical systems (MEMS) and an oscillating membrane demonstrate clear hologram reconstructions covered with high-contrast fringes that describe the vibration modes.

The accuracy and precision of the thin wires still requiring special attention. Both theoretical and experimental studies together may give closest approximation to the "real" value. Concerning the optical technique of measurement, perhaps one may analyze more in detail the interaction between light and matter (wire) which can lead to a simple mathematical approach. Besides this, a calibrating system and robust technique of measurement is required both in the industrial sector and laboratories. Measuring the wires depends especially on how much accuracy and precision we want to achieve, we have static or dynamic measurement, which kind of wire we need to measure...etc. This report shows some work about the diffraction models and some measurement of the thin wire (30-500 μm). Statistical technique of measurement is provided as well.

One of the most important problems to address when applying interferometric techniques to industrial applications is the high presence of noise which results in poor fringe patterns and thus poor measurements. One of the techniques that suffers most with this problem is conoscopic holography. Even if this interferometric technique is ideal for industrial inspection, the poor quality of fringe patterns obtained in adverse environments may even make measurement impossible. Classical filtering techniques based on one-dimensional filters or general speckle removal filters such as Frost or Gamma may not suffice in adverse conditions, therefore a new approach based on the nature of the fringe pattern information itself must be looked into. In this paper we propose the use of orientational filters to develop a filtering method, that not only removes noise of any nature, but also enhances the fringe pattern information. Several approaches to these algorithms are implemented and evaluated using synthetic conoscopic fringe patterns under different noise conditions, showing how they clearly outperform classical filters with a negligible distortion even in the worst conditions. Examples with real data acquired with the latest prototype of conoscopic long-standoff profilometer are also provided.

Automatic 3D-reconstruction from an image sequence of an object is described. The construction is based on multiple views from a free-mobile camera and the object is placed on a novel calibration pattern consisting of two concentric circles connected by radial line segments. Compared to other methods of 3D-reconstruction, the approach reduces the restriction of the measurement environment and increases the flexibility of the user. In the first step, the images of each view are calibrated individually to obtain camera information. The calibration pattern is separated from the input image with the erosion-dilation algorithm and the calibration points can be extracted from the pattern image accurately after estimations of two ellipses and lines. Tsai’s two-stage technique is used in calibration process. In the second step, the 3D reconstruction of real object can be subdivided into two parts: the shape reconstruction and texture mapping. With the principle of “shape from silhouettes (SFS)”, a bounding cone is constructed from one image using the calibration information and silhouette. The intersection of all bounding cones defines an approximate geometric representation. The experimental results with real object are performed, the reconstruction error <1%, which validate this method’s high efficiency and feasibility.

Traditional backlighting vision systems are unable to measure the height dimensions of an object. It can then be more convenient to use a 3D scanner, based for example on the projection of structured light. Despite the high potential of this technique and the growing demand of the industry for performing quality vision control, 3D measurement systems are still often considered as unusual solutions. This proceeding presents our 3D measurement laboratory setup based on the projection of structured light by means of a LCD beamer. This system is intended to be used in automated assembly line. The height information comes from a phase map obtained through temporal phase unwrapping. This phase always contain noise. Part of this noise brings a random phase error. A simple estimator of the random phase error is presented. It gives two parameters to which it is necessary to pay attention in order to predict measurement repeatability and thus to improve it. The estimator is experimentally validated on our setup.

In some specific applications the electronic speckle pattern interferometry (ESPI) is superior to other optical surface metrology methods. The two-wavelength ESPI for surface contouring can achieve both high accuracy of height resolution in the micron range and short measurement times far below a second. A further advantage of this method is that compared to e.g. triangulation, illumination axis and observation axis can be identical. A problem of interferometric methods in general are phase ambiguities originating from discontinuous measurement object surfaces. A common idea to decrease the range of ambiguity is the fusion of several interferograms recorded at different wavelengths. This paper presents a concept for a loss free sequential superposition of several spatially separated laser beams as well as algorithms for the determination of measured surface discontinuities. Also a solution of a stability control for fast wavelength tuning of laser diodes is presented.

We present here the observation of the Talbot effect in digital holography (DH). A self-imaging phenomena is observed by reconstructing the amplitude of the object wavefield by using different distances and different illumination wavelengths. The numerical reconstruction allows to determine the complex field amplitude at different wavelengths while maintaining constant the reconstruction distance. We investigate on the possibility to build a spectrometer based on the Talbot effect. In particular, the spectrometer proposed in this work can cover the whole visible spectrum ranging from 350nm to 750nm and, from the FWHM of the spectrograms with a resolution of about 20nm

Two different spectral-domain techniques based on reflectometry and white-light interferometry are used to measure spectral characteristics of thin-film systems. A technique of spectral reflectometry uses a standard configuration with a halogen lamp, a reflection probe and a thin-film system under test to record the reflection spectrum over a wide range of wavelengths. A new white-light spectral interferometric technique uses a slightly dispersive Michelson interferometer with a cube beamsplitter to measure the phase spectra of reflective or transparent thin-film systems over a wide range of wavelengths. This technique is based on a Fourier transform method in processing the recorded spectral interferograms to obtain the ambiguous spectral fringe phase function. Then, using a simple procedure based on the linear dependence of the optical path difference between beams of the interferometer on the refractive index of the beamsplitter material, the ambiguity of the spectral fringe phase function is removed and the beamsplitter effective thickness and the phase spectrum of the thin-film system are determined.

Continuous Paul Wavelet is a suitable tool for direct phase distribution evaluation in the case of digital interferograms. The method is based on the correlation in the Fourier domain between the digitized ineterferogram and the optical Paul wavelet filter spectrums. This correlation can be made directly with a computer or in optical set-up using an addressable liquid crystals display. We present the technique and the obtained results on simulated interferograms.

Ellipsometry is a technique of surfaces analysis, founded on the measure of light polarization state after reflection on a plane surface. Work consists in characterizing the surface quality of polished optical glass by ellipsometry. The measured ellipsometric parameters enabled us to lead to a correlation with roughness while being based on the theory of Maxwell-Garnett to determine the optical properties of the effective milieu.