This PDF file contains the front matter associated with SPIE Proceedings Volume 6616, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Optical coherence tomography (OCT) originally started as an interferometric tool to investigate technical samples such as thin films with high precision. With the shift to biomedical applications OCT experienced a boost in detection performance. Novel methods such as Frequency domain OCT allow nowadays depth profile rates of more than 200 kHz. This trend is supported by new light source and detector technology. Fast 3D imaging in-vivo with resolution of a few micrometers is readily available as commercial instruments. Extensions of OCT such as polarization contrast, spectroscopic contrast, or Doppler measurements enrich the portfolio of applications in biology, medicine, and last but not least again in imaging and quality inspection of technical samples.

We present a white-light spectral interferometric technique for measuring the thickness of a thin film on a substrate. First, the channeled spectrum is expressed analytically for a setup of a slightly dispersive Michelson interferometer with a cube beam splitter of given effective thickness and a fiber-optic spectrometer of a Gaussian response function when one of the interferometer mirrors is replaced by the thin film on the substrate. Then we model the wavelength dependences of the reflectance, the visibility of the spectral interference fringes, the phase change on reflection and the so-called nonlinear phase function, respectively, for a SiO₂ thin film on a silicon wafer. In the modeling, the optical constants are known and multiple reflection within the thin-film structure is taken into account. Second, we perform interferometric experiments with a SiO thin film on aluminium and the SiO₂ thin film on the silicon wafer. Channeled spectra are recorded for determining the thin-film thickness, provided that the optical constants of the thin-film structure are known. We confirm very good agreement between theoretical and experimental channeled spectra and determine precisely the thicknesses for two cases including the SiO thin film on the aluminium and the SiO₂ thin film on the silicon wafer.

Particularly in optical industries and in micro systems technology white-light interferometry has become a standard tool for highly accurate topography measurement. Our work is based on a modified commercial white-light interferometer with a tube lens of a rather short focal length. This allows a compact design and a large field of view without influencing the numerical aperture of the objective. Furthermore, a LED illumination is used, which is a precondition for our approach. The short focal length of the tube lens requires a proper optical correction in order to avoid measuring errors caused by aberrations. Nevertheless, spherical surfaces with relatively large local surface tilts or MEMS with sharp edges often give rise to systematic measuring errors. These are caused by diffraction and dispersion effects, which finally lead to deviations between height values obtained from the envelope's maximum of a white-light interference signal and those values obtained from the signal's phase. For certain cases this may result in ghost steps in the measured topography. In order to identify these steps we use a second phase evaluation at a different center wavelength. During the depth scan images are taken for both center wavelengths. A special evaluation enables us to clearly identify the appearing phase steps and to correct the results in a second step. The main application of this technique is the measurement of curved or structured specular surfaces with high resolution, which until now is limited by the occurring effects. In addition, it might be possible to use low-cost optics in combination with the dual-wavelength technique in order to correct the measuring errors resulting from optical aberrations.

This article presents white light interferometry as a new application for the nanopositioning and nanomeasuring machine (NPMM). The NPMM was developed under the leadership of the Institute of Process Measurement and Sensor Technology at the Technische Universität Ilmenau (Germany) and allows highly exact dimensional and traceable positioning with a resolution of 0.1 nm within a volume of 25 mm x 25 mm x 5 mm. An application of white light interferometry was developed on the basis of these features which can utilize the device's very high precision and large effective range, which enables the stitching of partitioned results without overlapping measurements and expensive matching methods. In order to extract height data from the interferograms, a robust, precise and fast method using matched filters in the frequency domain has been put into practice. The filter templates are calculated according to a model function or are directly sampled from the light source power spectrum, which has been previously analyzed once. Thus, light sources with different spectral forms can be used.

Micro interferometers are powerful optical instruments for 3D-surface metrology that usually adopt one of two different concepts for the data acquisition: the Phase Shifting Interferometry (PSI) and the Vertical Scanning Interferometry (VSI). In our approach we generate an illumination with mixed coherence characteristics by superposition of light beams from a broadband incandescent lamp and from a laser source. With a novel data evaluation technique we are able to obtain with a single vertical scan a surface profile that has the resolution and the accuracy of PSI and the measurement range of VSI. As an example, we present a surface that has a step of about 1,3&mgr;m and a shallow hole of about 0.1&mgr;m depth that could be entirely surveyed in a single vertical scan.

The present work describes a new method to measure the contour position of plane reinforcement fabrics for the manufacturing of structural composite parts. The pursued approach uses optical metrology based on laser light-section technology. In detail, a laser line is projected over the edge of a fabric layer and acquired with a digital camera, which is located under an offset angle to the laser sensor. This leads to a distinctive displacement of the laser line in the acquired image, which is proportional to the distance between the sensor and the fabric layer. The distorted line can be described as a step profile, to which an analytical function is fitted to calculate the horizontal edge position with sub-pixel accuracy. To measure the whole layer position, the edges are scanned with the laser sensor to provide multiple contour points. This allows the interpolation of the object contour. The interpolated contour can be compared with the specified position and dimension of the textile layer. This enables a closed-loop control of the cutting and build-up process of the preform. Thus, an efficient production process of fibre-reinforced plastics through an automated inline measurement is possible.

The report describes a real-time pattern-projection system for measurement of 3D coordinates with simultaneous illumination and recording of four phase-shifted fringe patterns which are projected at four different wavelengths and captured by four synchronized CCD cameras. This technical solution overcomes the main drawback of the temporal phase-shifting profilometry in which the pattern acquisition is made successively in time. The work considers the use of a sinusoidal phase grating as a projection element which is made by analysis of the frequency content of the projected fringes in the Fresnel diffraction zone and by test measurements of relative 3D coordinates that are performed with interferometrically recorded sinusoidal phase gratings on holographic plates. Finally, operation of a four-wavelength profilometric system with four spatially phase-shifted at &pgr;/2 sinusoidal phase gratings illuminated with four diode lasers at wavelengths 790 nm, 810 nm, 850 nm and 910 nm is simulated and the systematical error of the profilometric measurement is evaluated.

Here we propose a method for 3D shape measurement by means of phase correlation based fringe projection in a stereo arrangement. The novelty in the approach is characterized by following features. Correlation between phase values of the images of two cameras is used for the co-ordinate calculation. This work stands in contrast to the sole usage of phase values (phasogrammetry) or classical triangulation (phase values and image co-ordinates - camera raster values) for the determination of the co-ordinates. The method's main advantage is the insensitivity of the 3D-coordinates from the absolute phase values. Thus it prevents errors in the determination of the co-ordinates and improves robustness in areas with interreflections artefacts and inhomogeneous regions of intensity. A technical advantage is the fact that the accuracy of the 3D co-ordinates does not depend on the projection resolution. Thus the achievable quality of the 3D co-ordinates can be selectively improved by the use of high quality camera lenses and can participate in improvements in modern camera technologies. The presented new solution of the stereo based fringe projection with phase correlation makes a flexible, errortolerant realization of measuring systems within different applications like quality control, rapid prototyping, design and CAD/CAM possible. In the paper the phase correlation method will be described in detail. Furthermore, different realizations will be shown, i.e. a mobile system for the measurement of large objects and an endoscopic like system for CAD/CAM in dental industry.

For various industrial applications contact-less optical 3D distance measurement systems with active illumination are suitable. A new approach for a pixel of such a 3D-camera chip for applications in displacement and 3D-shape measurement is presented here. The distance information is gained by measuring the Time-of-Flight (TOF) of photons transmitted by a modulated light source to a diffuse reflecting object and back to the receiver IC. The receiver is implemented as an opto-electronic integrated circuit (OEIC). It consists of a double-cathode photodetector performing an opto-electronic correlation, a decoupling network and an output low-pass filter on a single silicon chip. The correlation of the received optical signal and the electronic modulation signal enables the determination of the phase-shift between them. The phase-shift is directly proportional to the distance of the object. The measurement time for a single distance measurement is 20 ms for a range up to 6.2 m. The standard deviation up to 3.4 m is better than 1cm for a transmitted optical power of 1.2 mW at a wavelength of 650 nm. The OEIC was fabricated in a slightly modified 0.6 &mgr;m BiCMOS technology with a PIN-photodetector. The photosensitive area of the integrated PIN-photodetector is 120x115 &mgr;m². A fill factor of ~67% is reached.

Optical metrology methods are classified into three fundamental techniques: Triangulation makes use of different positions of cameras and/or light projectors; interferometry employs standing light wave patterns; time-of-flight uses temporal light modulation. Using the unifying framework of linear shift-invariant system theory, it is shown that in all three cases the phase delay of a harmonic function must be determined. Since the precision of such phase measurements is photon noise limited, the distance resolution and the dynamic range are governed by the same functional relationship for the three fundamental optical metrology methods. This equation is derived under the assumption of Gaussian noise in the photogenerated charges in the photodetector; this assumption is a very valid one for almost all light sources, optical elements and photosensors. The equation for the precision of all types of optical distance measurement techniques contains the method's experimental parameters in a single factor, from which the optimum distance range of each of the three fundamental techniques can be deduced. For interferometry this range is 1 nm - 1 &mgr;m, for triangulation it is 1 &mgr;m - 10 m, and for time-of-flight ranging it is > 0.1 m, if visible or near infrared light is used.

The combination of an atomic force microscope (AFM) and a Confocal Raman Microscope (CRM) has been used to study various surface coatings. The high spatial resolution of the AFM enables the morphological characterization of the top layer of the coating with molecular resolution. Raman spectroscopy provides additional information on the chemical composition of the coatings. In combination with a confocal microscope, the spatial distribution of the various phases can be determined with a resolution down to 200 nm. Therefore, the topographically different structures observed in AFM images can be associated to the chemical composition by using the Confocal Raman Microscope (CRM). In addition, the confocal setup of the CRM provides insight into the multi-layer structure of coatings without laborious sample preparation.

We propose a new point-diffraction interferometer (PDI) based on a pinhole filter made by a z-cut lithium niobate (LN) crystal. A thin aluminium layer with a circular opening is fabricated on the surface of the crystal by conventional photolithography and subsequent aluminium deposition and lift-off. This aluminium layer acts both as electrode and as pinhole filter on the exit face of the crystal, while a uniform planar aluminium layer is deposited on the opposite face. When a voltage is applied across the z-axis of the crystal, the refractive index changes everywhere in the crystal except in a small portion underneath the area of the pinhole. Therefore, the applied voltage causes an uniform phase shift over the aberrated wavefront while leaving unaffected the diffracted reference beam passing through the pinhole. The interference taking place behind the sample produces an interference fringe pattern containing the information on the aberrated wavefront. Four phase shifted images of the fringe pattern are acquired and processed by means of the Carre algorithm to retrieve the aberrated wavefront. The proposed PDI arrangement has several important advantages over the other PDI configurations. The technological processes are very simple, and the phase-shift operation can be applied at very high speed limited only by the minimum acquisition time of the camera device. In fact, the electro-optic effect can be induced onto LN with bandwidths up to several GHz. Moreover, LN is transparent in very wide spectral range from 400 nm to 5500 nm, thus being useful in numerous applications.

A super-heterodyne laser interferometer for sub-nanometer length measurement system is proposed. This interferometer has a possibility to realize high resolution by using the self-zooming method and high accuracy by using external cavity diode laser which is stabilized to femtosecond frequency comb(fs-comb) as an optical source. This length measurement system is going to be applied for linear-encoder calibration system for national standards.

The overlay control budget for the 32nm technology node will be 5.7nm according to the ITRS. The overlay metrology budget is typically 1/10 of the overlay control budget resulting in overlay metrology total measurement uncertainty (TMU) requirements of 0.57nm for the most challenging use cases of the 32nm node. The current state of the art imaging overlay metrology technology does not meet this strict requirement, and further technology development is required to bring it to this level. In this work we present results of a study of an alternative technology for overlay metrology - Differential signal scatterometry overlay (SCOL). Theoretical considerations show that overlay technology based on differential signal scatterometry has inherent advantages, which will allow it to achieve the 32nm technology node requirements and go beyond it. We present results of simulations of the expected accuracy associated with a variety of scatterometry overlay target designs. We also present our first experimental results of scatterometry overlay measurements, comparing this technology with the standard imaging overlay metrology technology. In particular, we present performance results (precision and tool induced shift) and address the issue of accuracy of scatterometry overlay. We show that with the appropriate target design and algorithms scatterometry overlay achieves the accuracy required for future technology nodes.

In this paper we present the improved interferometric tomography method for determination of 3D refractive index distribution. The improvement relies on numerical correction of experimental results obtained for strongly refractive objects based on the a priori, approximate knowledge about the refractive index distribution in the object under test. The complete correction methodology is presented and discussed. The applicability of the method is shown through the numerical simulations of the reconstruction process and the experiments including reconstruction of refractive index distribution in a grin lens.

Decades ago tomographic interferometry was successfully applied to the measurement of phase objects in a large scale. Recently the application field was extended to nearly micro scale, for example optical fibers. Nevertheless, the geometry of tested objects was usually relatively simple and the spatial resolution at the level of several microns was always a barrier. In this paper we investigate the possibility of tomographic reconstruction of complex phase objects by means of tomographic interferometry. The analyses have been performed on the photonic crystal fiber, which is not only a high-resolution object, but additionally contains periodic structures. The influences of the following factors are investigated: proper matching of the immersion liquid, mechanical imperfections of the rotation, geometry of the fiber, polarization of the illumination beam and type of reconstruction algorithm. In addition to experimental results, the numerical simulation of wavefront propagation through the fiber is performed. According to the results, the high - resolution reconstruction of the three-dimensional refractive index distribution in the object containing a periodic structure is possible, however limited by several conditions, as described in the paper.

The paper describes the basics of an active MEMS device that powers millions of business projector devices and consumer HDTV sets but offers much more for general optics. The structure and the operating principle of this MEMS spatial light modulator will be described. Addressing new emerging applications in optical engineering, specifications and features of the MEMS and the supporting chipset are presented.

Makyoh topography (MT) is an optical characterisation tool for flatness testing of mirror-like surfaces. In MT, the surface is illuminated by a collimated light beam, and the reflected image is detected on a screen placed some distance away from the sample. Because of the focussing/defocussing action of the surface undulaations, the image shows intensity variations related to the sample morphology. In its original form, MT is qualitative only. By inserting a structured mask (e.g., a grid) into the path of the illuminating beam, the surface topography can be calculated by the integration of the gradients obtained by the determination of the displacements of the grid node positions, compared to a reference flat, similarly to a wavefront sensor. A DMD provides an easy and verstile way of realisation of such a structured mask. In this paper, we report on a quantitative MT set-up using a programmed DMD. Possibilities of the realisation of different mask patterns are analysed. The results are compared to interferometry.

In future high intensity, high energy accelerators, beam losses have to be minimized to maximize performance and reduce activation of accelerator components. It is imperative to have a clear understanding of the mechanisms that can lead to halo formation and to have the possibility to test available theoretical models with an adequate experimental setup. Measurements based on optical transition radiation (OTR) provide an interesting opportunity for high resolution measurements of the transverse beam profile. An imaging system based on a beam core-suppression technique, in which the core of the beam is deflected by means of a micro mirror array, to allow for direct observation of the halo has been developed. In this contribution, a possible layout of a novel diagnostic system based on adaptive optics is presented and the results of first tests carried out in our optical lab are summarized.

Modern spatial light modulators (SLM) enable the generation of more or less arbitrary light fields in three dimensions. Such light fields can be used for different future applications in the field of biomedical optics. One example is the processing/cutting of biological material on a microscopic scale. By displaying computer generated holograms by suitable SLMs it is possible to ablate complex structures into three-dimensional objects without scanning with very high accuracy on a microscopic scale. To effectively cut biological materials by light, pulsed ultraviolet light is preferable. We will present a combined setup of a holographic laser scalpel using a digital micromirror device (DMD) and holographic optical tweezers using a liquid crystal display (LCD). The setup enables to move and cut or process micro-scaled objects like biological cells or tissue in three dimensions with high accuracy and without any mechanical movements just by changing the hologram displayed by the SLMs. We will show that holograms can be used to compensate aberrations implemented by the DMD or other optical components of the setup. Also we can generate arbitrary light fields like stripes, circles or arbitrary curves. Additionally we will present results for the fast optimization of holograms for the system. In particular we will show results obtained by implementing iterative Fourier transform based algorithms on a standard consumer graphics board (Nvidia 8800GLX). By this approach we are able to compute more than 360 complex 2D FFTs (512 × 512 pixels) per second with floating point precision.

Light Beam-Induced Current (LBIC) imaging is a well-known characterization technique for solar cells, which allows to detect regions of low crystal quality. In this paper a fast, robust and reliable LBIC system is proposed by the use of digital micromirror device (DMD). The LBIC technique is usually performed by point-by-point mechanical sample scanning under a laser spot or by laser scanning, which leads to a measurement time of at least several minutes. In this proposed system with DMD, a new technique is introduced, in which a solar cell is scanned from different angles by a light-line instead of a light-spot. The obtained photocurrent data from these scans are used to reconstruct an LBIC image by using tomography principles. This leads to a lower number of measurements compared to any point scan method. This method helps in reducing measurement time and makes LBIC a fast characterization tool capable for inline investigations. Light-line scans over the cell from different angles are realized by a digital micromirror device (DMD) and its parallel interface controller. The DMD provides a fast solution for line-scanning the cell at speed up to 4 kHz, leading to a measure time of a few tens of seconds for a 256x256 pixel image. Since there are no moving parts involved in this setup, it is a robust and compact system, which will be ideal for the field environment and inline characterization.

We present an electronically tuneable external cavity diode laser that incorporates a digital micromirror device for spectral tuning. The design allows for high tuning speed of 0.85nm/ms over a typical tuning range of 47.4nm. The laser-system is characterized concerning spectral and time-related aspects. Application of the laser in a swept-source optical coherence tomography system is demonstrated.

Ferroelectric crystals, such as lithium niobate (LN) and lithium tantalate, find many photonic applications including the fabrication of periodically poled crystals for nonlinear frequency generation by quasi-phase-matching (QPM). All of the phenomena used in those devices depend on the existence and kinetics of the domain structure. As a consequence, the ability to micro-engineer ferroelectric domains is central to all of these applications and thus techniques for visualizing domain structure and dynamics are important. Recently a digital holography (DH) based technique has been proposed by the authors to visualize the free evolution of reversing domains in ferroelectric substrates during electric field poling. A fundamental step forward has been achieved in this work, where the technique has been applied to resist patterned samples under different voltage waveforms and resist conditions in order to characterize the dynamics of the periodic poling in presence of a resist grating. The results show that this technique can be used as a valid and reliable alternative tool to monitor online the periodic poling of ferroelectric crystals by a non-invasive in-situ procedure, avoiding both the critical control of the poling current and the post-poling etching process. The imaging of the resist grating and of the reversed domain regions can be discriminated accurately by using the qualitative and quantitative information provided by the amplitude and phase shift images, respectively. Moreover the technique allows to investigate systematically and, most important, in-situ the influence of different features on the poling behaviour, such as the poling waveform, the resist grating geometry, the patterned z face, the resist properties. The movies of the periodic poling dynamics are presented and discussed.

Emerging possibility of applying white-light interferometry to the area of thin-film metrology is addressed. Emphasis is given to explaining underlying spectrally-resolved interferometric principles of white-light interferometry for measuring the top surface profile as well as the thickness of thin-film layers, which enables one to reconstruct the complete 3-D tomographical view of the target surface coated with thin-film layers. Actual measurement results demonstrate that white-light interferometry in either scanning or dispersive scheme is found well suited for high speed 3-D inspection of dielectric thin-film layers deposited on semiconductor or glass substrates.

The application of fast 3D measuring methods is a fundamental venture in industrial measuring technology. This paper introduces the digital fringe projection technology based on the Digital Light Projection technology (DLP) from Texas Instruments as a measuring method for inline 3D measurement and inspection for industrial use. In this paper in the first part will be described the fundamental principles of the used 3D measuring method and the calibration of the measuring devices. In the second part will be described and/or represented the special needs of the hard and software components enabling the application of the digital fringe projection technology as a 3D inline measuring method for manufacturing systems. In a third part of the paper is described an inline system for 3D measurement and/or inspection of electronic components.

The paper presents the studies on correlation structure of biological tissues polarization images. The technique of polarization measurement of coordinate distribution of degree of mutual polarization has been proposed. The topological (singular) description of polarization inhomogeneous biological tissue images has been analyzed. It has been shown that average statistical size of S-contour agrees with half-width of autocorrelation function of degree of mutual polarization coordinate distribution.

A new technique for fluid mechanics measurement is proposed that makes use of pseudophase singularities in an analytic signal representation of a speckle-like pattern generated by a Laguerre-Gauss filter operation. Based on the formal analogy between the polarization of the vector wave and the gradient field for the complex analytic signal, a set of Stokes-like parameters have been applied for the description of the anisotropic core structure of the pseudophase singularities, which serves as unique fingerprints attached to the seeding particles moving with the flow. Experimental results for flow velocity and acceleration measurement are presented that demonstrate the validity of the proposed optical vortex metrology for fluid mechanics measurement.

Active image processing full field methods for 3D contactless profilometry are amongst the current methods of choice for obtaining point clouds from object surfaces. The fringe projection system plays a decisive role on the entire process, significantly impacting both quality and reliability of the final measurements. Moreover, most every phase measurement profilometer can only be used under laboratory controlled lighting environments. This note describes the ongoing LOME project for a coherent fringe projection system which will enable outdoor measurements by selectively band pass filtering the projected wavelength.

Free-space active W-band millimeter-wave imaging (75-110 GHz) makes possible imaging of phenomena, inaccessible to visible and infrared light. W-band supports the imaging of concealed objects, providing both enough spatial resolution and good penetration. An advantage of mm-wave radiation over X-ray is that it is non-ionizing, and there are no known hazards or risks to human health. When imaging an object with an mmwave coherent beam, this is accompanied with speckle phenomenon. Because mm-wave wavelength is closer to the surface roughness and to the object dimension as by optical imaging, spatial distribution of speckle gives us more information than the image itself. We will use a speckle contrast as a measure of the speckle. Speckle contrast contains useful information when it differs from unity, and has been utilized here to reveal surface roughness of concealed objects. The speckle contrast starts to be reduced from unity when an incoherent part compensates coherent light. A sequence of mm-wave images was acquired with a fixed angle interval. The speckle contrast of each pixel in the image was calculated and a new image was formed: a spatial speckle contrast image. It revealed areas, covered with interference. Comparing the two images together makes all features of the hidden object visible. We also present results, which illustrate mechanical speckle contrast reduction in full W-band by means of phase diversity Hadamard solution. Hadamard principle has been proven by experimental conversion of the coherent sum of the electrical millimeter wave amplitudes into an incoherent sum of intensities. The measured data give results on speckle contrast reduction that match accurately the theoretical statistical estimations. Industrial and medical imaging of concealed objects could benefit both from speckle contrast images and Hadamard speckle reduction.

The impact of a weak external magnetic field upon the conditions of optical bistability (OB) realization in the exciton absorption region of layer semiconductors has been investigated. With the 2H-polytype PbI₂ used as an example, the possibility of obtaining the OB realization region by changing the external magnetic field intensity has been shown. This effect can be used as a basic guideline in measuring the level of laser radiation signals, and can provide means for metrological maintenance of systems working in different active regime.

Both in industrial close-to-production quality control and in laboratory metrology, measuring optical components and systems with high precision and resolution (typically lambda/100 ptv) is currently achieved by phase-shifting interferometry devices. The main drawbacks of such devices compared to static fringes systems lie in a higher cost, and a greater the sensitivity to the environment, both vibration and air turbulence; the latter becomes unacceptable for large components and large cavity interferometers. Conversely, static fringes metrology usually lacks precision and resolution. Particularly, the lateral resolution is an issue, due to the sampling theorem. This paper shows how a linear prediction of a random function (with a Bayesian approach) makes it possible to tackle a lambda/100 resolution for the estimated wavefront, being the mathematical expectation of the prediction, i.e. the most probable form with respect to the fringe data. Incidentally, the prediction increases robustness by detecting and correcting aberrant fringe data with a high reliability. Furthermore, a Monte-Carlo simulation performed on the whole conditional probability density of the wavefront, provides a stochastic sub-fringe-spacing interpolation. As a result, confidence intervals for any parameter of interest (such as ptv, rms, ptv of slopes...) can be estimated over the whole aperture, which is novel worldwide. These algorithms have also been adapted to wavefront reconstruction from gradient data for Shack-Hartmann and for moiré devices. Examples of implementing these algorithms to industrial software will be shown.

A high resolution new fringe analysis method for ESPI with only one camera is proposed by using features of speckle interferometry in deformation process. The profile of intensity of each speckle of speckle patterns in the deformation process is analyzed by Hilbert transformation. A virtual speckle pattern for creating a carrier fringe image is produced artificially. The deformation map can be detected by the virtual speckle pattern in the operation based on spatial fringe analysis method. Experimental results show that the difference between the results by the new and the ordinary methods is less than 0.12 rad as standard deviation.

Digital holographic interferometry allows accurate measurements on a microscopic level. As the number and size of the recorded digital holograms increase so does their data volume. As a result the volume of holographic data can substantially constrain applications where storage or transmittance of such data is required. Compression of holographic data in order to reduce their storage requirements has been studied. The speckled nature of the interferograms makes their compression nontrivial; however image compression algorithms such as JPEG, JPEG2000 and Set Partitioning In Hierarchical Trees (SPIHT) have been shown to perform adequately. So far the compression effects of the holographic interferograms using such coding methods have mainly been studied in terms of errors at the reconstruction intensity. On the other hand, metrology applications usually rely on the holograms' reconstructed phase. In this paper we investigate hologram compression and how it affects the reconstructed phase. Holographic interferometry experiments are carried out to investigate measurement error due to interferograms compression using image compression methods. The results indicate that compression can be achieved while the measurement error due to compression is retained low.

Phase detection is an important issue when dealing with optical metrology techniques for which the magnitude to be measured is encoded through the phase of a given fringe pattern. Asynchronous phase detection techniques are employed when the rate of phase change (frequency) it is not known. These techniques always present a variable frequency response, in other words, their ability to recover properly the phase depends strongly on the local frequency. In many experiments, it is possible to have a rough knowledge about the range of frequencies involved. Therefore, it constitutes a great advantage to have a procedure to design an asynchronous demodulation method which is suited to a particular frequency response for a given experiment. In this way, we get a better behaviour against noise which leads to more accurate and reliable phase extraction. In this work we present a technique to design asynchronous demodulation algorithms with a desired frequency response using a Fourier-based technique. The method allows the design of algorithms with a limited algebraic error in the recovered phase which have better properties than standard asynchronous phase detection techniques as it is shown in numeric and real experiments.

A practical method is proposed for the wavefront measurement of arbitrary complex-valued fields. A mask having random phase is placed in the path between the object and the image sensor. Three or more diffraction patterns are collected, as the mask translated in the direction parallel to the sensor. Phase retrieval is performed by propagating the wave field back and forth between the sensor and the mask plane and making the following change on the calculated wavefront: at the sensor plane, the modulus of calculated wavefront is replaced with the square root of recorded intensity; while at the mask plane, the modulation phase is updated to the one corresponding to the next mask position for next iteration. This process starts from a random estimate of the object field falling on the mask and ends when the change of the amplitude of two successively retrieved object fields before the mask is below a given threshold. Further propagation of the retrieved field from mask to object plane yields the original object field. Results from both simulated data and experimental data show that this method works quite well in terms of its absence of stagnation, suitability for complex-valued field, and high immunity to the noise in recordings. The technique is believed to find wide applications, such as aspherical lens testing, and diffraction imaging of micro-objects.

We report on a method to achieve real-time dual-wavelength digital holographic microscopy with a single hologram acquisition. By recording both interferograms from two laser sources at different wavelengths in only one spatially-multiplexed digital hologram, we are able to independently propagate and apply numerical corrections on both wavefronts in order to obtain a beat-wavelength phase map of the specimen. This beat-wavelength being up to 10-100 times larger than the original wavelengths, we are in a situation where the 2&pgr; phase ambiguity of conventional DHM is removed and the phase measurement range of the technique is extended up to several tens of microns in height. The unique capability to perform such an operation with a single acquisition unables real-time dual-wavelength DHM measurements. Results on a moving micro-mirror are presented in this paper. We think that such a real-time dual-wavelength method represents a strong improvement to the current DHM state-of-the-art, and that it opens a whole new field of applications for this technique.

A new fast demodulation technique for a quasi-distributed temperature sensor based on the interrogation of identical concatenated fibre Bragg gratings is presented. The interrogation scheme is based on the optical time domain reflectometry technique, for which a commercial device has been extended to a wavelength-tuneable system, within an automated experimental set-up. Detection and localization of an important amount of sensing points along a unique optical fibre is demonstrated. The demodulation method is based on the optimization of the least square differences between reference and measured data. Repeatability measurements and associated accuracy of the sensor are presented.

The Traceable Multi Sensor (TMS) system is a scanning system for the measurement of the topography of large optical surfaces. The system uses a compact interferometer with an aperture of some millimetres to realize multiple distance sensors and an autocollimator for the angle measurement. In contrast to common stitching techniques, the systematic sensor errors are calculated in addition to the entire topography by the TMS algorithm. Additionally, piston and tilt at each position of the interferometer are determined by the algorithm. An essential requirement for the algorithm is the exact lateral positioning of the sensor at given locations. The goal of this paper is to investigate the influence of a class of error sources on the resulting topography estimation using computer simulations. The errors of this class result in inexact measurement positions of the distance sensors. Especially the lateral positioning errors of the scanning stage lead to increasing errors for short wavelengths. For topography wavelengths below 3mm with an amplitude of 100nm the resulting topography error increases to 3nm and more. For longer wavelengths the positioning errors are no longer the dominant error source and the root mean square error of the resulting topography is approximately 1 nm for positioning errors with a standard deviation of 5 &mgr;m. The pixel distance error and distortion of the interferometer strongly influence the topography measurement of specimens with large deviations from a plane. The simulations show that for a topography with a peak to valley of 50 &mgr;m the root mean square error of the reconstructed topography is below 10 nm. Furthermore, a possibility to compensate the lateral positioning error of the scanning stage is presented which makes the TMS method nearly independent of positioning errors of the scanning stage. As a consequence, it is possible to use systems of non equidistant distance sensors whose lateral distances are independent of the positioning interval.

Decorrelation in an interferometric set-up appears due to movements of the speckle pattern. In the case of rigid body movements the effect of decorrelation severely limits the performance of speckle interferometers. If the movement is larger than the speckle size the wanted phase information of the deformation is lost. Phase modulating spatial light modulators (SLMs) provide a new method to non-mechanically deflect and shape light. By using the SLM for scanning the field-of-view and focusing at different distances it is possible to measure intensity speckle patterns in a three-dimensional volume. These intensity images can then be cross correlated to give a three-dimensional correlation coefficient of the speckle pattern. If an SLM is utilized in an interferometric set-up it is possible to compensate for unwanted movements during an experiment. The measured correlation coefficient will then provide information regarding how large movements that are allowed with maintained performance of the interferometer. It is shown that for large movements the SLM can be used to retrieve phase maps.

3D profile measurement of an object is studied experimentally by using a standard fringe projection technique consisting of a CCD camera and a digital projector. The height profile of the object is calculated through the phase change distribution of the projected fringes with two dimensional fringe pattern by introducing the carrier frequencies in two spatial directions, x and y. The phase distribution is extracted from the optical fringe pattern by using S-transform gradient and S-transform phase methods. Experimental result for the Fourier transform profilometry algorithm is compared with the results of the S-transform analysis.

Fringe projection has been widely used for 3D geometry measurement in several classes of applications. The basic system is formed by a fringe projector and a camera. A triangulation algorithm is frequently used for retrieving 3D information from a scene. Alternatively, two cameras can be used in combination with one fringe projector. This configuration produces a significant measurement uncertainty improvement since only phase information encoded in the fringe pattern is used to locate homologue points in the triangulation algorithm and lack of linearity or imperfections of the fringe projector does not induce measurement errors. However, some parts with complex geometry can not easily been seen from both cameras in a convenient angle, what limits the applicability of this configuration. Frequently the clouds of points acquired from such systems are non-structured and, consequently, a non-regular mesh is obtained. This paper presents a very simple and effective procedure to combine data from multiple cameras to produce clouds of points in a regular mesh. The main idea starts by setting two independent coordinates for a node of a regular mesh. The third coordinate is found by scanning the dependent coordinate across the measurement volume until the phase values of the fringe patterns, acquired for the multiple cameras, reach the same common value. That approach naturally produces structured clouds of points independently of the number of cameras used. As an example, a 3D shape is acquired by an ordinary multimedia projector and a set of four low cost webcams. A calibration is necessary to reference the four webcams into the same coordinate system. For that, a reference object, composed by a set of small spheres in calibrated positions, is used.

In optics, optical elements are used to transform, to filter or to process physical wavefronts in order to magnify images, compensate for aberration or to suppress unwanted diffracted order for example. Because digital holography provides numerical wavefronts, we developed a digital optics, involving numerical elements such as numerical lenses and pinholes, to mimic numerically what is usually done physically, with the advantage to be able to define any shape for these elements and to place them everywhere without obstruction problems. We demonstrate that automatic and non-automatic procedures allow diffracted order or parasitic interferences filtering, compensation for aberration and image distortion, and control of position and magnification of reconstructed wavefront. We apply this digital optics to compensate for chromatic aberration in multi-wavelength holography in order to have perfect superposition between wavefronts reconstructed from digital hologram recorded with different wavelengths. This has a great importance for synthetic wavelength digital holography or tomographic digital holography that use multiple wavelengths.

We report a method to detect signed differences in two similar data sets representing 3-dimensional intensity profiles recorded by optical wide-field microscopes. The signed differences describe missing or unexpected intensity values, defined as defects. In technical applications like wafer and mask inspection, data sets often represent surfaces. The reported method is able to describe the size and position especially in relation to the neighboring surface and is called Three-Dimension-Aberration (TDA)-Technology. To increase the tool performance and to handle different sizes of defects a scaled bottom-up method is implemented and started with high reduced data sets for the search of large defects. Each analysis contains three steps. The first step is a correlation to calculate the displacement vector between the similar data sets. In the second step a new data set is created. The new data set consists of intensity differences. Extreme values in the data set represent the position of defects. By the use of linear and non-linear filters the stability of detection can be improved. If all differences are below a threshold the bottom-up method starts with the next larger scaled data set. In the other case it is assumed that the defect is detected and step three starts with the detection of the convex hull of the defect and the search of the neighboring surface. As a result the defect is described by a parameter set including the relative position. Because of the layered structure of the data set and the bottom-up technique the method is suitable for multi-core processor architectures.

This paper presents an algorithm based on Least Absolute Method to align and stitch multiple adjacent cylindrical clouds of points measured by white light interferometry using conical mirrors. The evaluation of the aligning and stitching algorithm was initially performed by using several numerically simulated clouds of points (COP) of cylindrical surfaces with small shape errors and quite rough surfaces. In order to evaluate the algorithm, each numerically generated COP was split into two parts but always keeping an overlapping area. Numerical translations and rotations were applied in one part to simulate real misalignments. After this, the algorithm was applied to align each adjacent COP pair and to obtain a stitched COP, and the result was compared with the original one. In this way, the performance of the presented algorithm was evaluated and analyzed for several overlapped areas. Excellent results were obtained with an overlapping area of 25% of the total measured length. The differences between the stitched and original cloud of points were always far below the roughness level of the measured surface. A brief description of a modified white light interferometer to measure in cylindrical coordinates as well as early applications of the algorithm in real measurements is also presented.

We present two di.erent white-light spectral interferometric techniques employing a low-resolution spectrometer for a direct measurement of the group dispersion of isotropic and anisotropic optical elements. First, the dispersion of the group refractive index for glass plate is measured in a Michelson interferometer with the plate of known thickness inserted in one of the interferometer arms. The technique utilizes the spectrometer to record a series of spectral interferograms for measuring the equalization wavelength as a function of the displacement of the interferometer mirror from the reference position, which corresponds to a balanced Michelson interferometer. The use of the technique is extended for measuring the dispersion of the group refractive indices for the ordinary and extraordinary polarizations in a quartz crystal. We con.rm that the measured group dispersions agree well with those resulting from the semiempirical dispersion equations. We also show that the measured mirror displacement depends, in accordance with the theory, linearly on the theoretical group refractive index and that the slope of the corresponding straight line gives precisely the thickness of the quartz crystal. Second, the group dispersion of the quartz crystal is measured in an unbalanced Mach-Zehnder interferometer with the adjustable path length when the crystal is inserted in the test arm. The use of the second technique is extended for measuring the di.erential group dispersion of a glass of a holey optical fiber.

The basic elements of the optical computer mouse (OCM) are; a light emitting diode (LED), image acquisition system (IAS) which acquires images via the lens and a digital signal processor (DSP) to implement the algorithm to determine direction and distance of motion. Here, we describe the light speckles produced from different colour LEDs to design and implement a new optical computer mouse. The speckle pattern will be used also to determine the velocity of the device relative to the surface it slides on it. The most important and critical property of speckles is their average diameter, which is independent of the type of the surface being illuminated by coherent (He-Ne laser and diode laser) or partially coherent light (LEDs). The average diameter of a speckle pattern is function of the diameter of the illuminated area of the surface, the distance between the surface and the detector, and the wavelength of the used light. In this work, we replaced the laser source by a small powerful white light lamp with different optical coloured filters and studying the resulting coloured speckle patterns to investigate the effect of different wavelengths on the velocity of the device relative to the surface it slides on it.

A flexible and real-time structure in hardware and software intended for driving a 320×240 detectors Infra-Red Focal Plan Array (IRFPA) is presented. The most critical case in the image detectors based on array elements is the Non-Uniformity Correction (NUC) between the sensitive elements due to the different characteristics of the materials in fabrication phase, especially for the IRFPAs with high elements and low cost ones which their non-uniformities are inherently more severe. Feasible NUC method of detectors and steps for implementation of an effective strategy for calibration of NUC factors by employment of the Least-Mean-Square method under a very compact hardware is discussed. A real-time method for contrast enhancement under a statistical approach by referring to Bi-Histogram Equalization which preserves the brightness of infrared images from theory to implementation on the Spartan family by arranging an adaptive Look-Up Table is manifested.

The resonance of saturated absorption in counterpropagating light fields is experimentally and theoretically studied. We focus on two cases: parallel and linearly polarized waves, driving an open dipole transition and the general case of elliptically polarized waves, driving closed dipole transition. The former reveals a new Doppler-free resonance as a peak within the saturated-absorption dip. The latter case reveals a new polarization effect, causing a shift and asymmetry of the saturated-absorption resonance. The results obtained can be found useful in metrology.

A proposed design of the multidirectional holographic interferometer (MHI) with diffusive illumination in 3D dodecagon geometry for optical tomography is presented. The beam from Nd-YAG laser is divided and transformed to six object beams that incident to diffusors and illuminate the cross section area. The optical axes of reference beams lie in six vertical planes that are turned 30 degrees to each other, which is the specific of our design. Next is discussed the constructional design of mechanical realization of filtering and collimating optics as well as the ways of traction of the rotationally embedded scanning system of CCD cameras. Finally, optical and mechanical properties of interferometer are digestedly summarized.

A new multi resolution self calibrating optical 3D measurement system using fringe projection technique named "kolibri FLEX multi" will be presented. It can be utilised to acquire the all around shape of small to medium objects, simultaneously. The basic measurement principle is the phasogrammetric approach /1,2,3/ in combination with the method of virtual landmarks for the merging of the 3D single views. The system consists in minimum of two fringe projection sensors. The sensors are mounted on a rotation stage illuminating the object from different directions. The measurement fields of the sensors can be chosen different, here as an example 40mm and 180mm in diameter. In the measurement the object can be scanned at the same time with these two resolutions. Using the method of virtual landmarks both point clouds are calculated within the same world coordinate system resulting in a common 3D-point cloud. The final point cloud includes the overview of the object with low point density (wide field) and a region with high point density (focussed view) at the same time. The advantage of the new method is the possibility to measure with different resolutions at the same object region without any mechanical changes in the system or data post processing. Typical parameters of the system are: the measurement time is 2min for 12 images and the measurement accuracy is below 3&mgr;m up to 10 &mgr;m. The flexibility makes the measurement system useful for a wide range of applications such as quality control, rapid prototyping, design and CAD/CAM which will be shown in the paper.

CCD cameras are widely used for different applications. Recently they are employed for imaging in industrial X-ray digital radiography or computed tomography inspections. Scientific grade CCD sensors are usually characterized for what concern defects (bad pixels), resolution capability, spectral sensitivity, dark current, pixel full well capacity and so on. In former times CCDs were mostly used in astronomy and dark current was one of the most important parameters to evaluate in this kind of applications because of the long exposure time needed to obtain a good image. Thus, most manufacturers still refer to noise of a CCD as the background (or dark current) noise. This might be in some cases misleading. When one wants to compute the effective dynamic range on the full scale of greylevels, in order to match with the correct number of bit required to quantize the information, and, most of all, to evaluate if the dynamics is adequate, a different analysis of noise is required. It is possible to find an experimental method to measure noise and to derive the effective intrinsic dynamic range of a CCD. A case study, carried out on a commercial CCD camera used in a prototype industrial CT system, is reported in this work and the experimental results are discussed.

This work reports on investigation of the sensitivity of a Fourier-transform spectrometer to noise sources based on Monte-Carlo simulation of measurement of a single spectrum. Flexibility of this approach permits easily to imitate various noise contaminations of the interferograms and to obtain statistically reliable results for widely varying noise characteristics. More specifically, we evaluate the accuracy of restoration of a single absorption peak for the cases of an additive detection noise and the noise which adds a fluctuating component to the carrier frequency in the source and the measurement channel of the interferometer. Comparison of spectra of an etalon He-Ne source calculated from more than 200 measured interferograms with the true spectrum supports a hypothesis that the latter fluctuations have characteristics of a coloured noise. Taking into account that the signal-to-noise ratio in the Fourier spectroscopy is constantly increasing, we focus on limitations on the achievable accuracy of spectrum restoration that are set by this type of noise which modifies the shape of the recorded interferograms. We present also results of the test measurements of the spectrum of a laser diode chosen as a test source using a three-channel Fourier spectroscopic system based on a white-sourced Michelson interferometer realized with the Twyman-Green scheme. The obtained results exhibit that fluctuations in the current displacement of the movable mirror of the interferometer should remain below 20 nm to restore the absorption spectrum with acceptable accuracy, especially at higher frequency bandwidth of the fluctuations.

An angular and displacement sensor that uses a polymer optical fiber and Moire patterns is demonstrated. Moire fringes are generated using two transparent superimposed planar gratings placed in front of an optical mirror. Moire patterns with periods ranging from 0.4 to 2 mm have been obtained in this way with 1mm-diameter plastic optical fibers for torsion angles ranging from 10° to 20° have been compared with theoretical calculations and a good agreement has been confirmed. Measuring the period length and the number of periods, both the relative angle between the gratings and the displacement of the fiber with respect to the mirror are obtained. With this technique very low angles can be measured with a very high resolution. The sensor principle has been successfully checked in the laboratory. Finally, the effect of employing different plastic fibers is also discussed. Besides, other possible applications of this measurement technique are presented and discussed.

Since its emergence in the early 1970s, Shack-Hartmann Wavefront Sensing technology has been investigated and explored world-widely by the researchers and engineers. However, there are few papers or reports to study the system performance and key factors to affect the performance of a Shack-Hartmann Wavefront Sensor (SHWS), in this paper, through experimental study of the system stability of a SHWS, it is found that the image sensor and detector, normally a CCD, should be placed exactly at the focal plane of the lenslet array, otherwise it will bring in significant wavefront measurement error. In order to improve the system performance, a special lenslet array with long focal range is designed, and it is functioned by a spatial light modulator for sampling wavefront in a SHWS. Diffractive lenses with long focal length range can provide pseudo-nondiffracting beams, and a long range of focusing plane. The performances and effects of the modified SHWS with such a special lenslet array generated by a programmable SLM, are investigated, and the experimental results show that the system stability and measurement repeatability are not sensitive to the sensing distance, and can keep at a good level in a long range.

The effects of linear birefringence (LB) upon Bulk Glass Optical Current Sensors (BGOCSs) with return-back optical path designs, such as the Orthoconjugate Reflection (OCR)-typed, the Direct Reflection (DR)-typed and the Roof-prism Reflection (RPR)-typed BGOCS design, are theoretically analyzed and compared with that of the BGOCS with a single-loop optical path in this paper. The results show that the return-back dual-loop current sensing designs with conventional signal processing scheme of "-/+" cannot eliminate the harmful effects of the LB thoroughly, if suitable signal processing schemes which can separate the LB from Faraday effect are not used.

The joint effects of reciprocal optical parameters of a bulk glass current sensing head upon the polarization state of the output optical beam of a Faraday Mirror-typed Optical Current Transformer (FMOCT) are theoretically analyzed, digitally simulated and compared with that of an optical current transformer with polarization-preserving total reflection coatings in this paper. The results show that the FMOCT design can effectively suppress the polarization state fading of the output optical beam induced by the joint effects of reciprocal optical parameters of the bulk glass current sensing head. The work reported here might have some reference significance to the performance improvement and development of bulk glass optical current transformers for practical applications.

A new design of optical current sensor using a Faraday Mirror directly as the current sensing element is proposed, the optical setup is shown, the mathematical expression of the working principle is derived, the experimental result is given, the advantages and shortcomings of the design are discussed in this paper. This design may be used as the primary current sensing element of an electrical current transformer for high voltages applications.

Preliminary results of the tests performed by using a modular fiber-optic sensor for hydrostatic pressure/temperature and also rotation measurements envisaged for refinery applications are presented. The prototype fiber optic sensor for rotation measurements has been successfully installed and tested in the ORLEN Refinery in Plock, Poland. During the initial tests, we used a rotating machine to measure its rotor velocity whereas the sensor head was connected to a pigtailed laser diode (&lgr;=635 nm) and to a detector by a 100-meters-long loop of multimode optical fibers. The output signals of the optical sensor were transferred into a refinery automatic control system (-2 or -20 V). During tests in the ORLEN Refinery we obtained very good agreement of output signals from standard magnetic sensor and the proposed optical sensor. In addition, the proposed optical fiber rotation sensor was immune to electromagnetic noise that disturbs output signals of the magnetic sensors.

The paper presents a new method of optical axis determination in uniaxial crystals by use of light depolarization measurements. Partially temporary coherent light may be depolarized during propagation through birefringent media. Degree of polarization fading depends on coherency of light, birefringence of the medium as well as direction of the optical axis of the medium. Hence a light beam passing through the crystal for three perpendicular directions may change degree of polarization in different way and it allows to calculate azimuth of the optical axis. In the test experiments we applied a laser diode lasing at 670 nm and a cube made with lithium niobate (&Dgr;n= 0.086, 1=5mm) as a tested crystal. Degree of polarization of light outgoing from the crystal was measured by use of high quality Glann-Thomson polarizer and a quarter wave plate. The optical axis orientation determined in the crystal was in good agreement with axis azimuth found by use a standard microscopic method.

The paper deals with a common problem in measuring surface flatness of transparent quasi-parallel plates in a Fizeau interferometer. The beam reflected from the rear surface leads to a complicated interferogram intensity distribution. The application of phase shifting for the plate front surface flatness determination becomes ineffective. We propose a new computation approach to suppress spurious modulations. First we find a two-beam-like interference pattern relevant to plate thickness variations using either temporal or spatial phase shifting. Its distribution is calculated using the Hilbert transform. The residual spherical aberration of the illuminating beam and the shape of the reference flat (determined by an absolute flatness testing conducted with the same interferometer) are subtracted from the plate thickness distribution. In this way the shape of the front surface is obtained. Numerical studies are complemented by experimental results.

This paper reports the optimization possibilities of some non-linear sources of limitations in the resolution and accuracy of an Absolute Distance Interferometry setup using an External Cavity Laser Diode for wavelength scanning and a fibered Mach-Zehnder interferometer as a reference. The system is able to measure one or two simultaneous targets with a relative uncertainty of some 10^-6 for distances of 1 to 20m. In order to achieve better performances, the experimental non-linearities in the wavelength sweep are isolated and compared to different simulated sweeping models. This study leads to the conclusion that accuracy and resolution could be improved by an optimal modulation of the wavelength sweep. Another sensible point is the drift of the reference Optical Path Difference of the Mach-Zehnder with temperature variations. This drift can be minimized by using an acrylate-coated fiber and a copper-coated fiber of different lengths, adjusted by experimental measurements in a climatic chamber for a 10 to 40°C range.

An innovative instrument for fast and accurate surface profiling of three dimensional patterned microstructures and insitu plasma etching depth control is proposed. Several advantages of the design make it promising for in-situ metrology. First, the system constitutes a common-path interferometer with the spatial phase shift between the reference and the object beams, thus the vibration and improper positioning of an object have a minor impact on the system performance. Second, no mechanical translation of either object or sensor is required; instead, a digital micromirror array is used for scanning the surface. It results in a higher processing rate, better measuring reproducibility, and easy adaptation of the method to specifics of the fabrication technology or object under test. Third, recording a full fringe for a particular pair of object's pixels is done within a single frame of a CCD camera. Also, multiple fringes for the whole line of object pixels can be captured at once. Then only 1-D scan is required to recover the depth profile of a 2-D object area. The experimental setup has been constructed to verify major principles of the method and measurement of test samples have been realized and compared to alternative measuring methods.

Optical profiling techniques, mainly confocal and white light interferometry, have demonstrated to be suitable techniques for characterization of transparent thick films. Measurements are carried out by vertically scanning the upper and lower film interfaces. Thickness of the layer is determined from the two peaks in the confocal axial response or from the two sets of interference fringes developed during the vertical scan. The 3D topographies of the upper and lower interfaces of the film can also be obtained. Measurements of photoresists or oxide coatings are typical examples of thick film characterization. On the other hand, measurement of thin films is considered to be a very difficult application to carry out with most optical imaging profilers. A film should be considered as thin when the two peaks obtained along the vertical scan become unresolved. We introduce new methods based on confocal techniques, which make it possible to measure sub-micrometric layers on structured samples. These techniques are based on the comparison between the axial responses obtained in areas where the film is present and those in other areas where only the substrate is present. This method has been successfully used for thickness assessment of several samples, such as a set of calibrated Si-SiO₂ layers.

Interferometry is now an established technique for the measurement of surface topography. It has the capability of combining sub-nanometre resolution. A very useful extension to its capability is the ability to measure thick and thin films on a local scale. For films with thicknesses in excess of 1-2μm (depending on refractive index), the SWLI interaction with the film leads simply the formation of two localised fringes, each corresponding to a surface interface. It is relatively trivial to locate the positions of these two envelope maxima and therefore determine the film thickness, assuming the refractive index is known. For thin films (with thicknesses ~20nm to ~2μm, again depending on the index), the SWLI interaction leads to the formation of a single interference maxima. In this context, it is appropriate to describe the thin film structure in terms of optical admittances; it is this regime that is addressed through the introduction of a new function, the 'helical conjugate field' (HCF) function. This function may be considered as providing a 'signature' of the multilayer measured so that through optimization, the thin film multilayer may be determined on a local scale.

Precision mechatronics is defined in the paper as the science and engineering of a new generation of high precision systems and machines. Nanomeasuring and nanopositioning engineering represents important fields of precision mechatronics. The nanometrology is described as the today's limit of the precision engineering. The problem, how to design nanopositioning machines with uncertainties as small as possible will be discussed. The integration of several optical and tactile nanoprobes makes the 3D-nanopositioning machine suitable for various tasks, such as long range scanning probe microscopy, mask and wafer inspection, nanotribology, nanoindentation, free form surface measurement as well as measurement of microoptics, precision molds, microgears, ring gauges and small holes.

Quickly developing nanotechnology drives the industrial need for fast but sensitive nano-scale feature detection and evaluation. In this work we bypass the diffraction limit for achieving nanoscale sensitivity by introducing optical singularities into the illuminating beam for a modified laser scanning microscopic architecture. A good correspondence was obtained between laboratory experiments and corresponding simulations that indicated a theoretical potential of 1nm sensitivity under a practical signal to noise ratio of 30dB. For analysis of the experimental and simulation results, two simple but effective algorithms were developed. A significant improvement of signal to noise ratio in the optical system with coherent light illumination can be achieved by utilization a highly redundant data collected during experiments. Our experimental results validate achievable sensitivity down to 20nm. The unique combination of nano-scale sensitivity together with implementation simplicity and on-line, real-time analysis capability make Singular Beam Microscopy a valuable industrial analytic method.

A new type of microscope: the Laser-Scanning Confocal Vibrometer Microscope has been proven to be an ideal tool for out-of-plane vibration measurements in microsystems. This system measures vibrations with heterodyne laser-Doppler technique. The phase demodulation of the carrier of the heterodyne-interferometer detector signal reveals the instantaneous displacement signal. In addition to this well-known property of the heterodyne detector signal, the power of the carrier is proportional to the instantaneous light intensity. We show in this paper that this intensity measurement can be used for an auto-focus control with the vibrometer-laser beam when the microscope objective is moved precisely with a piezoelectric z-positioning stage. The deflection of the z-positioning stage is measured at the maximum signal strength and corresponds to the height information. We demonstrate that the geometry data obtained with the auto-focus routine implemented in our laser-scanning confocal vibrometer microscope matches automatically to the measurement points of the vibration measurements. Our measurements demonstrate that the full-width-half-maximum (FWHM) diameter of the depth response is less than 1 &mgr;m. This enables height measurements with resolutions of a few ten nanometers. Our demonstration system can measure up to 1.5 points in 1 second if the full z-range of 250 &mgr;m is examined.

This paper presents measurements of calibrated step height and pitch standards using a homodyne interferometer-based metrological scanning probe microscope (SPM) and a nanopositioning and nanomeasuring machine (NPM machine). These devices were developed at the Institute of Process Measurement and Sensor Technology of the Technische Universität Ilmenau. Together these devices are capable of highly exact dimensional and traceable long-range positioning and measurement with a resolution of 0.1 nm over the positioning and measurement range of 25 mm × 25 mm × 5 mm. Measurements of different calibrated step height and pitch standards were completed in order to test the repeatability and accuracy of the metrological SPM. The deviations between the calibrated and measured values were smaller than the uncertainty values determined by the Physikalisch-Technische Bundesanstalt (PTB) calibration. The extended uncertainty of the measurement results (step height or mean pitch value) was less than 1 nm.

In today's manufacturing of PCBs (Printed Circuit Boards), there is an increasing demand on 3-D inspection of mesoscale objects for quality assurance. Two representative examples are the solder pastes on printed circuit board and bumps on FC-BGA (Flip Chip - Ball Grid Array) substrates, of which heights and volumes are precisely controlled to avoid defects in direct surface mounting of semiconductor chips. Despite the demand, no suitable 3-D inspection techniques are available yet, especially for high speed real time quality control of FC-BGA bump heights. Well-established monochromatic or white light interferometry is not easy to produce large measuring ranges up to a few millimeters and become robust to the vibrations on factory floor, while widely-used optical triangulation techniques with structured light illumination fail to provide the measurement precision usually required down to a few micrometers. Moire interferometry may be considered as a hybrid approach that combines the two distinct principles of the monochromatic light interferometry and optical triangulation. Thus, when appropriately configured, moire interferometry is capable of filling the gap between the two principles in terms of measurement range and precision. In this paper we propose a new method of 3-D inspection of meso-scale objects, which is in fact based upon the principle of grating projection moiré interferometry. This method projects a series of line patterns with predetermined phase shifts onto the target object and detects phase information leading to construction of 3-D profiles. Making the most of modern computer vision and digital signal processing technology allows for high speed measurement of 0.6 sec per 15mm×15mm field of view, with a resolution of 1μm for all three (x,y,z) axis.

Optical microsensors are used to carry out a great variety of coordinate metrology tasks on micro-parts. For the testing of such sensors calibrated artefacts are needed. The existing micro-artefacts have smooth surfaces and can therefore only be used for white-light interferometry and tactile probing. For sensors based on triangulation (structured light, autofocus, confocal...), artefacts with optically rough surfaces are needed. Consequently artefact surfaces with a small mechanical roughness but diffuse optical scattering (high optical roughness) are required. For this purpose, different production techniques to roughen smooth surfaces and to form parts having rough surfaces are tested successfully at the Physikalisch-Technische Bundesanstalt (PTB). The roughness Ra is about 0.3 &mgr;m. A suitable artefact set is currently being developed in compliance with the existing standards. A first micro-artefact (micro-contour artefact) is already commercially available. By means of the developed artefacts it also becomes possible to analyze for different optical sensors the dependence between the uncertainty and the measured surface as well as the surface slope.

Interferometric profilometers make use of two-beam interferometers with spectral broad band or more general polychromatic illumination either simultaneously or successively on the time axis. Since the criterion for a position of an object point on the z-axis is commonly the condition OPD = 0, the two-beam interferometer should allow for such an adjustment being a typical feature of Michelson- or Mirau-type instruments. However, the very simple Fizeau interferometer does not allow for this adjustment since it is a real wedge instrument. But it is well known that the superposition fringes between two interferometers in a series arrangement enable such an adjustment. In case of two two-beam interferometers in series arrangement a loss in contrast by a factor of at least 2 has to be tolerated. The combination of a multi-beam interferometer as a Fabry-Perot resonator with a Fizeau interferometer will deliver a fringe pattern which has a contrast of R^m where R is the reflectivity of the Fabry-Perot(FP)-plates and m is the ratio of the resonator lengths of the two interferometers in series. The disadvantage of the FP-solution is an intensity loss of the order (1-R)². Here the occurrence of bright broad-band sources with transversal mono-mode character as superlum-diodes or fs-lasers opens up new perspectives. Fine tuning could be obtained either by mirror shifts or tilt of a FP-etalon.

LIL and LMJ are two French high power laser facilities dedicated to laser-plasma interaction experiments. In order to control the flatness requirements of their optics in a wide spatial periods bandwidth, the CEA has several Fizeau interferometers of different diameters. We use special phase objects to qualify their spatial resolutions. A few papers already dealt with the determination of a Fizeau interferometer transfer function. This was achieved by using either a phase step object or a "virtual" sinusoidal phase object (made of the superposition of two wavefronts with different amplitudes and a small tilt). For practical reasons, we chose to use true sinusoidal phase objects to qualify our instruments. Sinusoidal profiles were then eroded in silica plates. Three different periods are available: 10 mm, 2.5 mm and 1 mm, with two different amplitudes for each period. These phase plates are used to qualify the interferometers performance in terms of spatial resolution in the different configurations (wide or narrow field of view, reflection or transmission) used for LIL/LMJ optics inspection. A comparison to the transfer functions obtained using steps of different widths is also proposed. An experimental verification of the Talbot effect is achieved with the 1-mm plate to investigate propagation effects, as well as contribution of the depth of field.

A new interferometric technique for the measurement of aspheric elements based on multiple test beams is presented. By means of an array of sources (Point Source Array) an aspheric surface is illuminated under different angles which allow the measurement of the zones where the local gradient of the test piece is compensated. One of the main advantages of the system is that the measurement process is performed in parallel (many sources are used at the same time) thus requiring extremely short measurement time in comparison with other available subaperture testing techniques. Another important aspect is that the asphere stays in the same position during the whole process; there are no mechanical movements of the test part involved. The technique allows the measurement of strong aspheric elements with departures from the best fit sphere up to ±10°. The method was developed to obtain accuracies of up to λ/30 and better. Simulations and first experimental results are presented.

In this article, a stitching Shack-Hartmann profilometric head is presented. This instrument has been developed to answer improved needs for surface metrology in the domain of short-wavelength optics (X/EUV). It is composed of a highaccuracy Shack-Hartmann wavefront sensor and an illumination platform. This profilometric head is mounted on a translation stage to perform bidimensional mappings by stitching together successive sub-aperture acquisitions. This method ensures the submicroradian accuracy of the system and allows the user to measure large surfaces with a submillimetric spatial resolution. We particularly emphasize on the calibration method of the head; this method is validated by characterizing a super-flat reference mirror. Cross-checked tests with the Soleil's long-trace profiler are also performed. The high precision of profilometric head has been validated with the characterization of a spherical mirror. We also emphasize on the large curvature dynamic range of the instrument with the measurement of an X-ray toric mirror. The instrument, which performs a complete diagnostic of the surface or wavefront under test, finds its main applications in metrology (measurement of large optics/wafers, post-polishing control and local surface finishing for the industry, spatial quality control of laser beam).

The application of optical techniques to the measurement of shape and deformation of structures in the aerospace industry poses unique challenges resulting from the large length scales involved, which are typically in the 1-10 m range. For example, the relative immobility of large samples requires a network of sensors to be linked into a common global coordinate system; traceable calibration requires the development of new types of calibration artefact; and traditional interferometric techniques for displacement field mapping are frequently too sensitive to observe the physical effect of interest. We describe a system designed to address some of these problems based on the projected fringe technique combined with temporal phase unwrapping. Multiple cameras and projectors are linked into a common coordinate system using calibration concepts borrowed from the photogrammetry field. Traceable calibration is achieved through the use of reference spheres separated by a bar of known length. Traditional two-dimensional image processing techniques for recognizing circles (Hough transforms) have been extended to the automatic detection of spheres within the measured 3-D point clouds. Bundle adjustment software has been developed to refine the camera and projector calibration parameters as well as the rigid body translation and rotation coordinates defining the poses of the calibration artefact. An overview of all these aspects of the developed techniques is given in the paper. Typical results from a compression test on a large scale aluminium structure, performed on-site at Airbus UK using the developed system, are also presented.

The paper presents the analysis of metrologic performance and measurement uncertainty of an optical scanner for the measurement of surface profile of large size panels designed to operate on-line in real time on moving panels in a noisy industrial environment. After a brief discussion of standards relevant to this type of sensor and of sensor specifications, an analytical model developed for the sensor design and for the uncertainty budget estimation is described. In addition, rather than presenting the common analysis of uncertainty of laser scanners based on the modelling of the image formation and processing, this paper addresses this question through a black-box approach, analysing the whole system as a sensor and therefore performing an experimental evaluation of uncertainty which embodies all possible sources of uncertainty, according to type A and type B approaches of the ISO-Guide to The Expression of Uncertainty in Measurement, which is an uncommon approach in the field of laser scanners calibration and represents the main novelty of this paper.

White-light interferometry is an absolute 3D-measurement technique, used for the inspection of structured silicon and other materials with high quality surfaces. In this technique, each pixel of the camera detects a separate interference signal, which correlates with the height of the corresponding object point. Different signal processing algorithms are used, which extract the height from the interference signal by using the coherence or the phase information of the signal. However, measurement errors can occur if there are chromatic aberrations in the interferometer system. Then the phase information correlates with the height information in an unexpected manner and there are often disturbing 2&pgr; phase jumps in the numerical evaluation process, although the topography of the object is continuous and a light source with a short coherence length is used. We examined a Mirau type white-light interferometer with chromatic aberrations and explain how mirrorlike, tilted objects cause a correlation of the phase and the height information in each interference signal. We also show that this measurement error depends on both the slope of the object point and its field position. A comparison of measurements and a simulation, which shows the described correlation effect, is given.

This paper presents a new photogrammetric approach to automatically reconstruct and measure the imprecision or deformations of metallic parts composed of curved edges. This approach uses images provided by a CCD camera moving around the part. The main purpose of the approach is to reconstruct curved edges automatically and accurately. For that, the solution uses data from the computer aided design model (CAD) and information extracted from the images. Experimental results on several parts present the precision and robustness of the process. They show that the proposed approach has a promising potential in automatic 3D control of industrial parts.

The feasibilities for optical correlation diagnostics of a rough surface with large surface inhjmogeneities by determining the transformations of the longitudinal coherence function of the field scattered by such surface are substantiated and implemented.

The paper presents a study to detect the three-dimensional profile of an object using a technique based on the projection of colour-coded lines. The accessibility at low-cost of projectors and digital photographic cameras has approved the employment and the development of these techniques. They provide information concerning the profile through the acquisition of a couple of images. The first one concerns a reference plane and it is captured only once, while the second one refers to the object image. The proposed methodology simplifies the individuation of homologous lines within the two images, when grating projection techniques are employed. Even though these methods are conceptually very simple, they are rarely applied because of this difficulty in stating the correspondence between observed deformation and projected line. The attribution of a different colour to every single line, or to a set of them, introduces an element useful for their selection. After the image acquisition, the data pertaining to the profile are extracted examining the image by means of an algorithm developed in Matlab language for this application. The research work is in progress beyond the results presented in this paper, which already represent a excellent starting point for further studies and evolutions of the technique.

Digital fringe projection profilometry employs a digital video projector as a structured light source and thus gains great flexibility. However, the luminance nonlinearity of the video projector may decrease measurement accuracy and resolution. To overcome this problem, we propose a nonlinearity correction technique for digital fringe projection profilometry. This technique allows determining the response curve of a digital video projector by matching the histogram of the fringe images with that of a standard sinusoid signal. By iterating the two steps, histogram matching and phase evaluation, the phase distribution of the fringe pattern is finally solved with higher accuracy. In so doing, neither photometric calibration nor knowledge about the device is required. Both computer simulation and experiment are carried out to demonstrate the validity of this technique.

Deflectometry is an optical metrological technique to determine the shape of test surfaces. This technique is based on the measure of the deviation that the light suffers when impinges the test surface and is reflected. The information of the surface slopes is contained in the reflection angle. Then, the integration of the slopes is necessary to obtain the final profile of the surfaces. In this work, we present a brief review of two dimensional integration methods and we propose a new two dimensional integration method. A comparison of the integration methods is presented in term of the mean quadratic error between the original profile and the profile obtained by integration.

A method is proposed for smooth surface roughness measurement. Two standard reference surfaces and two polaroids are employed to realize the measurement. The reversibility of the optical beam is overcome by using two quarter-wave plates. Measuring optical set-up is shown. The mathematical expression of the working principle of the method is derived. The uncertainty of the method is theoretically calculated and digitally simulated. Finally, the feasibility of this method is verified by measuring a standard roughness sample. The measurement result is in accordance with the standard value of the sample roughness provided by the manufacturer.

In the last years the investigations in the area of optics of Bessel and their associated conical beams are being shifted from the domain of scientific research to the one of practical applications. This is appreciably due to new potentialities of the practical use of these light fields, which are not realizable in the framework of traditional optics of Gaussian beams. The spatio-angular properties of conical light beams are optimal to control the form and quality of surfaces close to cylindrical and conical ones. This is related to the fact that a conical light beam enables one to realize the longitudinally uniform illumination at a certain angle. The grazing-incidence geometry of illumination permits one to significantly reduce the speckle noise in the field reflected and to extract, thereby, information on the macroscopic shape of the surfaces. In this work we develop two optical profilometers intended for non-destructive testing of objects having the form close to the cylindrical one. In particular, a new scheme of vibration-proof laser profilometer based on using the superposition of two conical beams is proposed. A laboratory optical setup of the profilometer is designed. The developed device includes two ring diaphragm as a basic element for crating two conical light beams. One of these beams serves as a reference beam and the second - as an object one. As a result, the independent reference arm has been removed and a single-arm scheme has been realized. The conical beams are spatially separated so that one beam illuminates the cylindrical surface and another beam is freely propagates. Due to a single-arm configuration, this profilometer is noted for a high mechanical stability. The experimental testing of the laboratory setup has confirmed this property of the device. The methods of eliminating the systematic errors and the misalignment aberrations are developed. The conical beam - based profilometer applies to controlling various cylindrical and conical samples including the roller bearings. It is shown that the single-arm profilometer is suitable for testing the roller bearings, because it is vibration-proof and also provides an enough measuring accuracy. Besides, this type of profilometers is not time consuming, which allows the online control of bearings.

Our work describes a method for testing a shape of optical surfaces (i.e. flat, spherical or aspherical surfaces) using correlation analysis of interference patterns and optimization techniques. The aim of this work is to propose a diverse evaluation method for industrial control of optical surfaces that makes possible to speed up the testing process of optical surfaces in special cases. The proposed method does not require an implementation of a detail analysis of the detected interference field as it is necessary with existing interferometric methods. The deviation of the tested optical surface from its nominal shape can be characterized by the correlation coefficient between the tested wave field and reference wave field that corresponds to the nominal shape of surface. The shape of the tested optical surface and the deviation from its nominal shape can be calculated by optimization of the correlation coefficient.

A method to measure basic lens parameters of intraocular lenses is described in detail. Most of the work is performed using interferometry methods, for contactless and high-accuracy measurements of radius of curvature, thickness and particularly wave aberrations; we perform also measurement of the focal length through magnification method, and we compute the refractive index by formulas. The method is reported, together with experimental results for two different intraocular lens types.

Industrial inspection requires very fast and reliable measurements. One of the techniques, recently widely used for monitoring of engineering objects, is digital holographic interferometry (DHI). In the paper we present novel digital holographic cameras (DHC). Their configuration allows to provide high accuracy information about shape, out-of-plane and in-plane displacement distributions, through capture of digital hologram by CCD, numerical reconstruction of phases and their proper manipulation. Digital holographic systems presented have compact design, fibre optics light delivery system and automatic data acquisition and processing. The cameras capture data in real-time and have low sensitivity to environmental changes. In the paper several examples of engineering application of these cameras are presented.

Demonstration of electronic speckle pattern interferometry of opaque scattering objects at 10 &mgr;m wavelength using a commercial thermal-camera is presented for the first time to our knowledge. The idea of using a wavelength longer than the usual visible ones is to render such holographic displacement measurement techniques less sensitive to external perturbations. We discuss some particular aspects of the increase in wavelength to the 10 &mgr;m thermal range. We then show results of in-plane measurement of the rotation of a metallic plate. We applied the phase-shifting technique for quantitative measurements and the results are correlated to countermeasurements with a theodolite.

In this study, behavior of ball grid arrays (BGA) under external cycling loading was studied. A loading system for inducing cycling stress to BGA was successfully built. Dynamic electronic speckle pattern interferometry (DESPI) with in-plane sensitivity and Hilbert transform for phase analysis was applied. The cycling deformation of one solder ball was measured continuously. Temporal, whole-field deformation on one solder ball was demonstrated.

Quantitative surface strain measurement using shearography requires the calculation of six components of displacement gradient. This is done using shearography instrumentation with at least three measurement channels combined with two orthogonal shear directions. These channels take the form of either multiple illumination or observation directions. The system presented here is based on the illumination of the object of interest using a pulsed Nd:YAG laser and the observation of the object from four separate positions arranged in a square around the illuminating beam. Images from the four observation positions are transported to a shearing interferometer using coherent fibre-optic imaging bundles, where they are spatially multiplexed onto the sensor of a single CCD camera. Displacement gradient measurements from a static test object are presented and compared to the results of a computational model. Phase analysis is carried out using two approaches, temporal phase stepping and the carrier fringe technique, with the aim of extending the application of the instrument to the monitoring of dynamic loading events.

Residual stresses determination in thin-walled structures by combining the hole drilling method and reflection hologram interferometry is considered as a tool with some unique properties in the field of industrial inspection. The relations used for converting experimentally derived parameters into stress values of interest are presented. Required input data are obtained by simultaneous measurements of probe hole distortions in two principal strain directions on opposite sides of thin plane specimen. Emphasis is made on obtaining high-quality interferograms with high fringe density around small probe hole drilled in residual stress field. Such fringe patterns are capable of describing residual stress components of high level in a presence considerable stress gradients. It is shown that a resolution of ten fringes can be achieved over a hole of 1.5 mm diameter. Practical implementing developed technique is illustrated in the course of residual stresses characterisation near different welded joints of thin aluminium plates.

Liquid nematic crystals are nowadays more often used to change the polarization and/or phase and amplitude of impinging light wave. Nematic liquid crystals valves (LCLV) are also called SLM (Spatial Light Modulator) or LCVR (Liquid Crystal Variable Retarder). This paper will show the different steps required to get a procedure (optical mounting and computing software) enabling the use of LCLV in the output beam of the laser coupled with a 3D speckle interferometry set-up. This LCLV generates the phase shifts between the reference and object beams. The calibration setup is made of a Mach Zender interferometer with the LCLV in one arm. Interference fringes are obtained and recorded with a CCD camera as LCLV voltage is increased. The fringe processing is achieved with a slice analysis in the Fourier domain. Required phase shifts are then implemented in the phase shifting software. The existing set-up already uses a phase shifter composed by a moving mirror driven by a piezoelectric transducer (PZT). Results of the calibration are compared between piezoelectric device and LCVR. The phase shifting rate and resulting phase error shows the main advantages of the LCVR.

Advances in emerging technologies of microelectromechanical systems (MEMS) and nanotechnology, especially relating to the applications, constitute one of the most challenging tasks in today's micromechanics and nanomechanics. In addition to design, analysis, and fabrication capabilities, this task also requires advanced test methodologies for determination of functional characteristics of devises produced to enable verification of their operation as well as refinement and optimization of specific designs. In particular, development of miniscule devices requires sophisticated design, analysis, fabrication, testing, and characterization tools. These tools can be categorized as analytical, computational, and experimental. Solutions using the tools from any one category alone do not usually provide necessary information on MEMS and extensive merging, or hybridization, of the tools from different categories is used. One of the approaches employed in this development of structures of contemporary interest, is based on a combined use of the analytical, computational, and experimental solutions (ACES) methodology. Development of this methodology was made possible by recent advances in optoelectronic methodology, which was coupled with the state-of-the-art computational methods, to offer a considerable promise for effective development of various designs. This approach facilitates characterization of dynamic and thermomechanical behavior of the individual components, their packages, and other complex material structures. In this paper, recent advances in optoelectronic methodology for micro-and nanoscale measurements are described and their use is illustrated with representative examples.

This paper reports on a sub-pixel resolution vision approach for the characterization of in-plane rigid-body vibration. It is based on digital processing of stroboscopic images of the moving part. The method involves a sample preparation step, in order to pattern a periodic microstructure on the vibrating device, for instance by focused ion beam milling. An image processing has then been developed to perform the optimum reconstruction of this a priori known object feature. In-plane displacement and rotation are deduced simultaneously with a high resolution (better than 0.01 pixel and 0.0005 rad. respectively). The measurement principle combines phase measurements - that provide the high resolution - with correlation - that unwraps the phase with the proper phase constants. The vibration modes of a tuning fork were fully characterized for the demonstration of the method capabilities. Then the tuning fork was loaded with a tungsten wire sharpened in a sub-micrometer tip for use in shear-force microscopy. The vibrations of the scanning probe were also characterized furnishing representative data on its actual vibration amplitude. The technique could however be applied to many kinds of micro-devices, for instance comb driven electrostatic actuators. For applications allowing the sample preparation, the proposed methodology is more convenient than common interference methods or image processing techniques for the characterization of the vibration modes, even for amplitudes in the nanometer range.

The demand for rapidly increasing data communication speed between spacecraft and ground stations leads to the development of highly stable parabolic satellite antenna structures. Besides the requirement for a very accurate overall shape precision, one of the main design challenges for these antennas is their shape stability under varying thermal conditions (in-flight operation). Although accurate mathematical models (FEM), already established during the design phase of the antennas, allow predictions of their behavior under varying operational conditions, even minute variations of the introduced material property constants can lead to significantly varying simulation results. For the validation of the mathematical model, a Pulse ESPI system has been used to measure the thermal distortion in a space simulation chamber. ESPI measurements have been recorded during two consecutive cooling down cycles under vacuum condition (less than 10^-4 hpa remaining pressure), each cycle covering a temperature range from approx. +110°C to approx. - 110°C. The evaluated data sets allowed determination of the overall distortion of the antenna and its deformation in temperature intervals of approximately 0.3°C at any time of each cycle. After evaluation of the interferometric data, a comparison with the deformation predictions from the FEM simulation has been carried out.

For the new generation aircraft families, the use of fibre-reinforced plastics is considered for the leading edge of the wings. However, this leading edge is very prone to bird strike impact. This paper presents the use of the projection moire technique to measure the out-of-plane deflections of composite plates subject to bird strike. Very strict constraints with regard to: (i) high speed image acquisition, (ii) vibrations of the impact chamber, and (iii) projection and observation angles - complicated substantially the development of the set-up. Moreover, the high frame rates (12000 fps) required a very intensive illumination. In the optimized configuration, a specially designed grating with gradually changing period is projected by means of special Metal Hydride lamps through one of the side windows of the impact chamber onto the composite plate riveted in a steel frame. The digital high speed camera is mounted on the roof of the impact chamber and records through a mirror the object surface with the projected fringe pattern on it. Numerical routines based on Local Fourier Transform were developed to process the digital images, to extract the phase and the out-of-plane displacements. The phase evaluation is possible due to the carrier frequency nature of the projected moire pattern. This carrier frequency allows separation of the unwanted additive and multiplicative fringe pattern components in the frequency domain via the application of a proper mask. The numerical calculations were calibrated for the bird strike of an aluminium plate, where the plastic deformation could be checked after the test.

Theory, analysis and applications of digital in-line holography are presented for metrological applications. Particularly time averaged in-line digital holography is explored for dynamic characterization of membranes and MEMS diaphragms. The analysis and capability of numerically reconstructed amplitude and phase information from time averaged holograms is presented. Reconstructed amplitude provides the vibration mode shapes by showing the time average fringes that are modulated by zero-order Bessel function, same as in conventional time-averaged holography. However the numerical phase information divided in two parts, the first part represents the surface roughness information of object and is a source of noise for single exposure, and the second part called the time average phase. By using a novel double exposure method, the reconstructed phase information from time averaged holograms can be used for mean static deformation as well for better visualization of time averaged fringes. In case of the vibrating objects with simultaneous mean static deformation, the phase information mixes together and used for precise analysis of vibration behaviors. The use of double exposure method also suppress the noise from the real image wave, caused by overlapping of zero-order term and twin image wave because of in-line geometry. The experimental results are presented for vibrations of aluminum membrane with 10mm in size, and also for a MEMS diaphragm with 6mm in size.

One of the most interesting points when evaluating the response of an implanted prosthesis is the knowledge of how biomaterials behave under a certain deforming stress. Obviously, the greater the stress on a particular moment, the higher possibility of the failure implant. But in many cases, the most important fact regarding the implant failure is due to a lesser stress that is continuously applied. Therefore it is helpful to know how biomaterials respond to this lesser stress. Digital speckle interferometry (DSPI) is suitable for this type of determination because of it is a highly sensitive and non-invasive optical technique. The aim of the presented work is determining the elasticity of biomaterials such as osseous structures and implants used to replace bones and to fix fractures between them. In particular, preliminary results were obtained applied to macerated human radius and a titanium screw used to treat the fractures of this bone. The analysis shows high correlation ratios in determining Young's modulus via DSPI technique in comparison with than that obtained by creation of the bone computer aided design (CAD) model using finite element method (FEM) in ANSYS software. The high degree of concordance between the results of both methods makes it possible to continue studying osseous samples with a fixed implant, and also other implants made of different alloys.

The heterodyne interferometer (vibrometer) is a well established technique for measuring all kinds of mechanical vibrations in a broad range of applications. The non-contact measurement principle relies upon the Doppler (or phase-) shift that laser light experiences when it is reflected by the vibrating surface. The speckle nature of the reflected light imposes problems and creates additional measurement noise if the object is moving transversely through the laser spot or is rotating around an axis perpendicular to the laser direction. Another implication that can arise is cross coupling from in-plane vibrations into the out-of-plane measurement direction when small in-plane vibrations are present. A model is presented in this paper that describes the origin of these disturbances. Using this model it is possible to quantify the amplitude spectrum of the noise in displacement and velocity measurements. This enables the user to calculate the limits of resolvable vibration amplitudes when transverse motion is present. The results of the model have been confirmed well by measurements. In addition, the influence of the surface roughness and beam inclination on the out-of-plane vibration measurements at a tilted surface is investigated. The conditions for the measurability of the profile of a transversely moving surface are derived in this work. It is discussed that the R_q-roughness parameter has to be less than &lgr;/4 to obtain the slope information in the speckle-perturbed interferometer signal.

White light scanning interference microscopy is used for measuring the surface morphology of materials and devices more and more widely in many areas of research and industry. However, a limiting requirement is that the surface to be analysed be kept static during measurement, which can typically take from several seconds to several minutes. As industries such as MEMS manufacturing mature and create more complex dynamic devices, it becomes increasingly important to be able to characterize structures that undergo periodic or transitory motion. In this paper we present the architecture of a 4D (3D + time) interference microscopy system that is being developed based on continuous fringe scanning over the depth of the sample. The simulation of results using real time detection of the peak fringe intensity (PFSM, Peak Fringe Scanning Microscopy) or the maximum of the fringe visibility (FSA, Five Sample Adaptative non linear algorithm) is discussed. During scanning, a high speed CMOS camera provides images at a rate of 500 i/s (1280x1024 pixels) that are processed using a FPGA (Field Programmable Gate Array) to extract the 4D measurements. At a bit stream rate of 625 Mbyte/second, it is reasonable to expect a measurement rate of nearly 1 i/s at full frame size over a 20 &mgr;m depth and 9 i/s over a depth of 2 &mgr;m. By reducing the image size to 128x128 pixels, the rate is increased to 16 i/s over a 20 &mgr;m depth and 600 i/s over 2 &mgr;m. These values could be increased further using under sampling or by means of higher speed reference mirror scanning.

Capacitor Micromachined Ultrasonic Transducers (CMUTs) are being developed and fabricated to be integrated in a 1 mm diameter catheter, aiming to detect vulnerable plaques in the coronary arteries. The structure is built up of an array of 72x104 CMUTs, where two linear arrays of CMUT cells are bonded together. The CMUTs have resonance frequencies of about 30MHz. The radius of each CMUT is 5.7 &mgr;m and the vibration amplitude is in the range 20pm-12nm. A heterodyne interferometer has been built for characterizing the CMUTs. It offers the possibility of both phase and high resolution absolute amplitude vibration measurements. The setup can measure vibrations from 0 to 1.2GHz. In this work we present interferometric measurements on the CMUTs and compare them with electrical measurements performed by using a network analyzer. Using the interferometer we are able to investigate individual CMUT cells, whereas the electrical measurements are based on a sum of all currents in the CMUTs bonded together. In addition to a RF voltage at the operating frequency, the CMUT is supplied with a bias voltage to vibrate. The CMUT resonance frequency can be tuned by varying this DC voltage. In this article we have investigated the predicted linear relationship between applied AC voltage and vibration amplitude. Other parameters investigated are the effects of temperature increase in addition to traveling charges on the CMUT membrane. The interferometric setup can be used to characterize various devices with small surface movements, such as MEMS- and SAW-devices.

Optimum performance from advanced composites requires careful control of the resin matrix during cure. This is to ensure there are no cure induced voids and to minimise the build up of internal stresses. Careful control of the process is also necessary to reduce wastage. Traditional resin inspection techniques are bulk or sample oriented and thus cannot provide data about critical component parts. Optical fibre based sensors however, allow for in-situ monitoring techniques to be deployed in components without effecting their structural integrity. In this work, two fibre optic grating techniques are demonstrated as process monitoring sensors and are compared with a Fresnel refractometric method. The change in refractive index of a resin has previously been used as a means for assessing the degree of cure. The central wavelength of an attenuation band of a long period grating (LPG) was monitored during the cure of a resin. In parallel the spectral resonances of a tilted fibre Bragg grating (FBG) are also monitored. The two techniques are shown to correlate well with the Fresnel based method in both detecting the resin and monitoring the state of cure, indicating the potential of the techniques for online production monitoring.

Shearography is a recognized interferometric technique in non-destructive testing to detect defects. Defects are detectable in wrapped phase maps because they are characterized in their neighborhood by singular fringes. They are detectable in unwrapped phase maps, because they induce unexpected phase values. By analyzing the length of unexpected phase values area in shearing direction, and by taking into consideration shearing amount, defect size can be locally estimated. To examine this length, we propose to locally determine borders of unexpected phase values region by analyzing wavelet transform of unwrapped phase map profiles. The borders of defect area are found by examining the convergence at fine scales of lines of wavelet modulus maxima. To have a physical interpretation of this convergence, second derivate of a Gaussian is employed as mother wavelet: estimated borders of defect region are some maximal curvature points of unwrapped phase map profile. To finish, we show that shearing amount does not affect estimated defect size with our methodology. So, shearography is adapted to quantify defects in shearing direction. Currently, in any other direction, an ambiguity exists on the position where the local estimation of defect width is performed. The methodoly cannot be employed.

For the interpretation of optical Pump-Probe Measurements on microstructures the wave propagation in anisotropic 3-D structures with arbitrary geometries is numerically calculated. The laser acoustic Pump-Probe technique generates bulk waves in structures in a thermo-elastic way. This method is well established for non-destructive measurements of thin films with an indepth resolution in the order of 10 nm. The Pump-Probe technique can also be used for measurements, e.g. for quality inspection of three-dimensional structures with arbitrary geometries, like MEMS components. For the interpretation of the measurements it is necessary that the wave propagation in the specimen to be inspected can be calculated. Here, the wave propagation for various geometries and materials is investigated. In the first part, the wave propagation in isotropic axisymmetric structures is simulated with a 2-D finite difference formulation. The numerical results are verified with measurements of macroscopic specimens. In a second step, the simulations are extended to 3-D structures with orthotopic material properties. The implemented code allows the calculation of the wave propagation for different orientations of the material axes (orientation of the orthotropic axes relative to the geometry of the structure). Limits of the presented algorithm are discussed and future directions of the on-going research project are presented.

Image processing and thermography for its own are very versatile and established measurement techniques for many years. However, the combination of these two measurement technologies opens a new field of applications. The online monitoring of the laser-brazing of titanium overlap joints is such a new application. The laser brazing process for overlap joining of formed titanium sheets for the production of heat exchangers is presently being investigated at the Fraunhofer IPT. In comparison to conventional furnace brazing the laser brazing technology decreases substantially the heat impact and thus reduces the thermal material damage in the parts due to local selective heating in a laser beam focal spot. Even though the process is stable, errors in the brazing seam such as pores or unacceptable material oxidation can occur. To ensure a high quality an online process monitoring or even process control is necessary. But since the surface remains unchanged during this brazing process no geometrical inspection of the surface can be conducted. Therefore today's quality assurance performs x-ray or destructive testing. This paper demonstrates how the use of thermography in combination with image processing allows a machine integrated online monitoring of the laser brazing process. First the basic principals are presented which cover the fields of heat coupling, heat transmission and heat distribution as well as the temperature emission of light and the spectral properties of the laser beam shaping optic and so lead to the optical set-up. Then analysis algorithms are derived which characterize the process, detect process failures and make a seam tracking possible.

Monitoring machines during operation is an important issue in measurement engineering. The usual approach to monitoring specific machine components is using strain gauges. Strain gauges, however, may sometimes not be used if conditions are harsh or installation space is limited. Fiber optic sensors seem to be an alternative here, but dynamic health monitoring has been dificult so far. The focus of this field study is to measure vibration characteristics of machine parts during operation using fiber optic sensors with the objective of early damage detection. If that was possible, downtime and maintenance costs could be minimized. Therefore a field test for dynamic fiber optic strain measurement on a roller bearing was carried out. The test setup consisted of the bearing built into a gear test stand and equipped with an array of fiber Bragg grating sensors. Fifteen fiber sensors were interrogated with a sample rate of 1 kHz and the vibration pattern was extracted. The radial load distribution was measured with high spatial resolution and a high degree of compliance with simulation data was found. The findings suggest that fiber optic health monitoring for machine components is feasible and reasonable. Especially with the help of distributed sensing on various components extensive health monitoring on complex technical systems is possible.

Interference microscopes remain one of the most accurate, repeatable, and versatile metrology systems for precision surface measurements. Such systems successfully measure material in both research labs and production lines in micro-optics, MEMS, data storage, medical device, and precision machining industries to sub-nanometer vertical resolution. Increasingly, however, these systems are finding uses outside of traditional surface-measurement applications, including film thickness determination, environmental responses of material, and determination of behavior under actuation. Most recently, these systems are enabling users to examine behavior of materials over varying time-scales as they are used in cutting or grinding operations or where the material is merely in continual contact with another such as in medical implants. In particular, quantification of wear of surfaces with varying coatings and under different conditions is of increasing value as tolerances decrease and consistency in final products is more valuable. Also, response of materials in corrosive environments allows users to quantify the gains of varying surface treatments against the cost of those treatments. Such quantification requires novel hardware and software for the system to ensure results are fast, accurate, and relevant. In this paper we explore three typical applications in tribology and corrosion. Deterioration of the cutting surfaces on a multi-blade razor is explored, with quantification of key surface features. Next, wear of several differently coated drill bits under similar use conditions is examined. Thirdly, in situ measurement of corrosion of several metal surfaces in harsh environmental conditions is performed. These case studies highlight how standard interference microscopes are evolving to serve novel industrial applications.

There are a lot of factors that call into question the integrity, safety and reliability of concrete macrostructures such as bridges, buildings, tunnels and dikes. Examples of such factors are humidity variations, in-excess load supported during years, vibrations and pH variations, which can damage the concrete structure after extended periods. In order to test the real state of such structures, we present the design and development of fiber optic based sensors that permit the measurement of loads and tensions applied to the structure, just as both the humidity and pH of the concrete at the measurement point. The load of the structure can be measured by means of fiber Bragg grating techniques, which involves wavelength multiplexing and optical spectrum analysis, and the humidity and pH measurements are achieved by incorporating different types of hydrogels to the nearness of the fiber Bragg grating. The change in humidity and pH produces volume changes in these hydrogels that modify the spectral response provided by the fiber Bragg grating. Thus, it is possible to place multiple sensors along the macrostructure to visualize the on-line status during its life time.

The optical speckle-displacement correlation technique was developed to increase the reliability of surface displacement field recovery near stress concentrators. The performance of optical speckle correlators based on joint transform correlator (JTC) architecture and a joint power spectrum nonlinear filtering (median thresholding, adaptive median thresholding, ring median thresholding) is studied by using computer models of these correlators. The design of hybrid joint transform speckle correlator is detailed. Example results of correlation signal using computer models of digital speckle correlation and optical speckle-displacement correlation techniques and created hybrid joint transform speckle correlator setup are described.

The active Twyman-Green laser interferometer for MEMS measurement equipped with Spatial Light Modulator (SLM) as a reference element is reported. The SLM is electrically addressed, reflective (made in Liquid Crystal on Silicone technology) and phase-only device which allows to actively shape of the reference beam wavefront in the interferometer. The proper use of the SLM in interferometric MEMS measurement is possible after opto-mechanical modification of the interferometer, performed calibration procedures and special interferogram processing. All these aspects are described. The use of such device benefits extension of measurement range and simplification testing procedures. Usefulness of the SLM is shown at the examples of active microelements testing. Advantages and disadvantages of SLM application are described and potential of this device for interferometry is discussed.

When a mechanical stress pulse, which is propagating in an elastic medium, encounters a material- or phase interface, which generally represents a change of the acoustic impedance, it is split up into a part, which propagates further into the new material and another part, which is reflected. The amplitude ratio of the reflected and the transmitted part is governed by the normalized difference of the acoustic impedance only, provided that the impedance change is a pure step function in space. If the acoustic impedance change is broadened spatially, the ratio of the transmitted and reflected part becomes frequency dependent and the effect can therefore be used for filter-, damping-, acoustic isolation-, and/or spectrum analysis purpose or for quantitative analysis of interface. The effect is of growing importance for micro- and nanostructures since the relative size of the interface layers is generally larger than in macroscopic structures. In this work, a pulse propagating in a linear elastic graded material is described with analytical solutions and one dimensional simulations. The numerical scheme is based on the Finite-Difference Time-Domain method (FDTD). The validation of the numerical model occurs by comparing the simulated pulse propagation-history with an analytical solution based on.¹ On-coming research is also given at the end of this study.

In the present work we present the results of our latest research into an implementation of optical fiber sensors for flaw tolerance test application on high pressure composite hydrogen vessels. For monitoring influence of flaws on composite parameters, as point measurement heads permanently installed on tank's surface, fiber Bragg gratings (FBG) were used. The aim of our experiments was to examine structural behavior of the composite hydrogen vessels and test appropriate topologies of sensors to detect the damages.

We have developed a scanning laser system based on the optical triangulation principle for the shape measurement of fusion weld surfaces. The system integrates a triangulation module consisting of a laser line projector and a digital video camera with a mechanical scanning stage and an industrial computer. The system is small and rugged, suitable for application in industrial environment. The system can sample a weld surface at a rate of up to 30 profiles per second achieving 0.1mm accuracy. Software was developed which analyses the captured weld surface shape in real time determining the characteristic shape parameters (length, width, height, cross section, volume, starting position,...) which are then used for automated classification of the welds into acceptable and unacceptable. The software also detects surface defects such as undercutting, holes or melt splash, etc. The system has been tested in a robotized welding cell for automotive parts in an industrial production facility. Weld classification obtained by the system was compared to an independent classification determined by a trained weld inspector on the basis of visual inspection and to another one determined on the basis of metallographic analysis of the weld. Using the metallographic based classification as the reference we find that the developed weld inspection system can achieve better classification reliability than a trained visual weld inspector.

Numerous fiber optic measurement systems making use of sensors such as Fabry-Perot or fiber Bragg gratings incorporate superluminescent or other edge emitting light sources. These sources often have a high degree of polarization. The combination with birefringence in fibers results in measurement errors. A possibility to overcome these errors is to depolarize the light source. Low coherence lengths make passive means of depolarization suitable. A common solution is the fiber Lyot depolarizer, which works especially well with very low coherence lengths. For coherence lengths corresponding to for example the reflection spectrum of narrow band fiber Bragg grating, long fiber lengths are required. A second way is offered by fiber ring depolarizers, where the coherence length is of minor concern. To estimate the performance of the fiber ring depolarizer in a practical measurement system, we employ both concepts. The measurement system is a CCD based spectrometric interrogation unit, with a superluminescent diode as light source. The source itself is well polarized. We observe the effect of birefringence in a transversally loaded fiber Bragg grating array consisting of eight sensors, when the polarization on the path to the sensor is rotated. The improvement in polarization dependency when using the two depolarization methods is compared.

Modern production processes use more and more components made of new materials like carbon fiber reinforced plastics (CFRP). These components have different sizes, functionalities, high assembly complexity and high security requirements. In addition optimized joining processes, especially during welding are implemented in manufacturing processes. The increasing requirements during the manufacturing of complex products like cars and aircrafts demand new solutions for the quality assurance. The main focus is to find a measurement strategy that is cost effective, flexible and adaptive. The extension of the conventional ultrasound technique for non destructive testing with the laser ultrasound method brings new possibilities into the production processes for example for the inspection of small complex CFRP-parts like clips and the online observation during seam welding. In this paper we describe the principle of laser ultrasound, especially the adaptation of a laser ultrasound system to the requirements of non destructive testing of CFRP-components. An important point is the generation of the ultrasound wave in the surface of the component under investigation. We will show experimental results of different components with complex shape and different defects under the surface. In addition we will present our results for the detection of defects in metals. Because the online inspection of welded seams is of high interest experiments for the investigation of welded seams are demonstrated.

MEMS characterisation is an important application area for interferometry. In this paper a Mach-Zehnder interferometer configuration is presented that combines both coherent and low coherent techniques in one setup. It incorporates the application of classical Laser Interferometry (LI) and Electronic Speckle Pattern Interferometry as well as classical Low Coherence Interferometry (LCI), full-field Optical Coherence Tomography and Low Coherence Speckle Interferometry. Digital Holography can be applied by minor modifications of the setup. The setup, working principle, and applications of the interferometer will be described. Measurements on a MEMS-based pressure sensor are presented. The sensor consists of a glass wafer attached to a silicon membrane. A cavity is etched into the glass wafer. The wafers are bonded and form a vacuum cavity. Membrane deformations are measured through the window using LI and LCI. LCI provides information about the shape of the glass window. Results from speckle techniques are compared with similar results from plane wave techniques. The influence of the glass window and the illumination of the object are investigated.

Terahertz (THz) imaging technology is now becoming a very important technology for the applications of the THz electromagnetic wave. The good imaging method can provide more information about the object to be investigated. A new terahertz phase imaging method with multi-wavelengths is proposed in this presentation. This novel approach can image object with larger optical length compared to the largest wavelength in the terahertz spectrum and does not involve the usual phase unwrapping in the detection of phase discontinuity. Furthermore, this technique can also effectively reduce the noise background. Two examples are presented to demonstrate the validity of this new method. It was shown that the multi-wavelengths phase imaging is a straightforward and efficient phase data processing method in terahertz imaging application.

We present a compact, robust, and transportable fiber-coupled THz system for inline monitoring of polymeric compounding processes in an industrial environment. The system is built on a 90cm x 90cm large shock absorbing optical bench. A sealed metal box protects the system against dust and mechanical disturbances. A closed loop controller unit is used to ensure optimum coupling of the laser beam into the fiber. In order to build efficient and stable fiber-coupled antennas we glue the fibers directly onto photoconductive switches. Thus, the antenna performance is very stable and it is secured from dust or misalignment by vibrations. We discuss fabrication details and antenna performance. First spectroscopic data obtained with this system is presented.

Polymers cover the whole range from commodities to high-tech applications. Plastic products have also gained in importance for construction purposes. This draws the attention to joining techniques like welding. Common evaluation of the weld quality is mostly mechanical and destructive. Existing non-destructive techniques are mostly not entirely reliable or economically inefficient. Here, we demonstrate the potential of terahertz time-domain spectroscopy imaging as a non-destructive testing tool for the inspection of plastic weld joints. High-density polyethylene sheets welded in a lap joint with varying quality serve as samples for terahertz transmission measurements. Imperfections within the weld contact area can clearly be detected by displaying the transmitted intensity in a limited frequency range. Contaminations such as metal or sand are identified since they differ significantly from the polymer in the terahertz image. Furthermore, this new and promising technique is capable of detecting the boundaries of a weld contact area. Aside from revealing a contrast between a proper weld joint and no material connection, the size of an air gap between two plastic sheets can be determined by considering the characteristic frequency-dependent transmission through the structure: The spectral positions of the maxima and minima allow for the calculation of the air layer thickness.

This paper presents the fibre-optics low coherence interferometric sensor LISE and its applications in the optics manufacturing industry. The sensor works as a comparator of optical group delays. The group delay along the optical axis of the probe interferometer arm containing an object, for example a lens assembly, is compared with the group delay of the reference arm containing a movable delay line. The light source is a super luminescent diode (SLD) emitting at 1.31 &mgr;m with a coherence length of typically 25 &mgr;m. Thanks to the limited temporal coherence of the source, multiple surfaces of the object can be detected during a single scan of the delay line. Measurement ranges are between a few mm up to 600 mm (optical thickness). The measurement range can be placed at a working distance of up to several meters away from the instrument's exit. Two classes of accuracy exist. While the standard system has an absolute accuracy of ±1 &mgr;m for position and distance measurements, the second generation, high-accuracy system reaches an accuracy of better than ±200 nm for distance measurements while maintaining the ±1 &mgr;m accuracy for position measurements. The paper starts by explaining the measurement principle in Section 1. The following Section 2 describes the system design and the individual system components. The definition and validation of the absolute accuracy are discussed in Section 3, followed by a description of the complete detection procedure for the high accuracy system in Section 4. In its final Section 5 the paper gives examples of applications in the optics manufacturing industry. This description ranges from the centre thickness measurement of lenses to the "global" on-axis metrology of completely mounted optical systems such as objectives where all lens thicknesses and airgaps are measured without touching or disassembling the optical system. Practical considerations concerning alignment, focusing of the measurement beam, model-based signal identification, dispersion and longitudinal resolution are discussed.

In this paper a new segmentation method for highly precise inclusion detection in 3D X-ray computed tomography (CT), based on multiresolution denoising methods, is presented. The aim of this work is the automatic 3D-segmentation of small graphite inclusions in cast iron samples. Industrial X-ray computed tomography of metallic samples often suffers from imaging artifacts (e.g. cupping effects) which result in unwanted background image structures, making automated segmentation a difficult task. Additionally, small spatial structures (inclusions and voids) are generally difficult to detect e.g. by standard region based methods like watershed segmentation. Finally, image noise (assuming a Poisson noise characteristic) and the large amount of 3D data have to be considered to obtain good results. The approach presented is based on image subtraction of two different representations of the image under consideration. The first image represents the low spatial frequency content derived by means of wavelet filtering based on the 'a trous' algorithm (i.e. the 'background' content) assuming standard Gaussian noise. The second image is derived by applying a multiresolution denoising scheme based on 'platelet'-filtering, which can produce highly accurate intensity and density estimates assuming Poisson noise. It is shown that the resulting arithmetic difference between these two images can give highly accurate segmentation results with respect to finding small spatial structures in heavily cluttered background structures. Experimental results of industrial CT measurements are presented showing the practicability and reliability of this approach for the proposed task.

The interrelation between the state of polarization of local zones of object field and the value of inclination angle of skin epidermis plates has been found in the single scattering approximation. The technique of polarization reconstruction of coordinate distribution of inclination angles of surface micro-irregularities of skin epidermis has been suggested. Statistics of the 1st-4th orders of optical-geometric properties of rough surface of physiologically normal and pathologically changed skin has been analyzed. It was shown that microrelief of the sound skin surface has fractal angular structure. Pathological changes cause random distribution of inclination angles of micro-irregularities of the skin surface.

This contribution presents novel laser Doppler techniques, which allow simultaneous measurement of radial position and tangential velocity and, thus, determination of the shape of rotating objects with one single sensor. Conventional laser Doppler velocimeters measure only velocities. A concurrent position measurement can be realized by generating two fan-like interference fringe systems with contrary fringe spacing gradients and evaluating the quotient of the two resulting Doppler frequencies. Alternatively, two tilted fringe systems in combination with phase evaluation can be employed. It is shown that the position uncertainty of this sensor is not only independent of the surface roughness but, most notably, that it is in principle independent of the object velocity. Thus, in contrast to conventional distance sensors, the novel laser Doppler position sensor offers high temporal resolution below 3 &mgr;s and high position resolution in the micrometer range simultaneously. The sensor was applied to automatic 3D shape measurements of turning parts and to monitoring rotor unbalance and dynamic deformations. Furthermore, in situ measurements of tip clearance and rotor vibrations at turbo machines for up to 600 m/s blade tip velocity are reported. The results are in excellent agreement with those of triangulation and capacitive probes, respectively.

Recent and future needs for high spatial resolution lead to increase the pupil diameters and the focal lengths of space telescopes. In parallel, considerable efforts have been realised in the field of image processing by developing techniques which require high levels of performances characterization. The main consequences are the increase of the size of the Ground Support Equipments and facilities but also the mastering of the influence of the environment which becomes more and more fundamental. Wavefront and contrast measurements are two conventional but key tests which require constant evolution to be adapted to new needs.

The degree of cure of the coatings should be known for quality control and design of the curing system. Often the radiation part of the curing installation is oversized, because the spectral irradiances needed for a certain conversion of carbon double bonds were not determined beforehand. The usual testing methods for the quality of a coating, as for instance ATR spectroscopy, are only sensitive to the attributes of the surface. In our investigations, we measured the degree of conversion locally at different depths of the layer by means of confocal Raman spectroscopy with a spatial resolution of approximately 1&mgr;m. For the kinetic studies, we measured the change of Raman scattering of 532 nm Laser radiation. Which induces a transition on a vibration level of the carbon double bond corresponding to a wavenumber of 1620 cm^-1. The change was normalized with respect to the CH₂ deformation mode. Furthermore, we investigated the effect of different spectral distributions of radiation on the local conversion at different depths. By this it could be shown that most of the radiation power is needed to harden the surface. This is caused by the inhibiting effect of oxygen which hinders the generation of radicals. The measured depth profile of conversion reveals that oxygen is effective up to depths of 30 &mgr;m. The results of confocal Raman spectroscopy could also be used to optimize a curing system with inertization so that the radiation power could by reduced by 91%.

XtremeFringe is a new library for fringe pattern processing which incorporates modern methods for automatic analysis including fringe pattern demodulation, fringe pattern filtering and phase unwrapping methods. XtremeFringe is written in C# and is usable as an assembly from any .NET language (C#, C++ .NET, J#) and additionally as a Matlab toolbox, which ensures an easy adaptation in custom applications, providing the user with a versatile and powerful tool for fringe pattern analysis in a flexible way. The functions of XtremeFringe are suitable to be employed in metrological applications such interferometry, photoelasticity, Moire techniques, holography, etc. supplying the user with up-to-date fringe analysis tools. In this work, we demonstrate the capabilities of the XtremeFringe library, processing different examples showing the ability of the library to analyze complex fringe patterns in a fast, reliable and automatic way.

Laser beam of the infrared pulsed Nd:YAG laser was used to re-melting PVD coatings on the steel substrates. Chemical composition of these layers contains carbide Cr₃C₂ with alloy NiCr or nitrides TiN, TiAlN, TiAlSiN and CrAlSiN. First coatings were prepared by method of high velocity oxygen fuel (HVOF) that protects the machine component surfaces from abrasion, corrosion or ensures thermal isolation, nitrides by PVD (Physical Vapor Deposition). Processing parameters such as pulse energy, pulse length and frequency were optimized in many experiments to achieve the sufficient surface energy density to melting without vaporization of the material. Multimode beam diameters about some millimetres were computed and adjusted in the suitable distance from focus plane. High laser power re-melting decreases their porosity, increases adhesion to basic material. In case of high laser energy gas vapours escape from basic material and cause fissures, re-melted surfaces have to be carefully controlled. New approach to evaluation of the quality surface structure was realized by laser confocal microscopy. Direct measuring or 3D surface model is possible with resolution less than hundred nanometres, depressions along laser beam path or rises on the laser spot edges were determined. Particles and grains with dimensions about one micron in re-melting structures can be observed better then by optical microscopy. Parallel measurements of the surface roughness were realized by the contact inductive profilometer Talysurf, collected data were displayed by software tool Talymap in a plane or spatial pictures.

The paper deals with the investigation of formation mechanisms of laser radiation polarization structure scattered by human skin in two registration zones: a boundary field and a far zone of Fraunhofer's diffraction. There has been defined the interrelation of optical and geometrical parameters of skin architectonics and formation conditions of polarization singularities of scattered radiation field as well. There has been studied statistical and fractal polarization structure of object fields of physiologically normal and pathologically changed skin. It has been shown that polarization singularities of radiation scattered by sound skin samples have fractal coordinate structure. It is characteristic for fields of pathologically changed skin to have statistical coordinate structure of polarization singularities in all diffraction zones.

The paper presents the studies on correlation structure of biological tissues polarization images. The technique of polarization measurement of coordinate distribution of degree of mutual polarization has been proposed. The topological (singular) description of polarization inhomogeneous biological tissue images has been analyzed. It has been shown that average statistical size of S-contour agrees with half-width of autocorrelation function of degree of mutual polarization coordinate distribution.

Measurement and monitoring of diffusion process is important in many areas of physical, chemical and biological sciences. Usually interferometric methods are used for this. Even though very accurate, they require controlled environments (especially to be isolated from external noise) and should adhere to stringent optical considerations. Single beam optical techniques are more suitable in noisy environments. Since a diffusing medium has a non-uniform refractive index distribution, a ray passing through such a medium will deflect towards regions of higher refractive index. If this deflection can be measured somehow, it can be used for finding the refractive index gradient and hence the refractive index distribution inside the medium. Here a method is proposed to measure these deflections and hence the diffusion coefficient using active optical elements, by converting the incident light into a spatially varying polarization pattern.

Shack-Hartmann Wavefront Sensor (SHWS) recently has been extensively researched for optical surface metrology due to its extendable dynamic range compared with the interferometry technique. In our institute, we have developed a digital SHWS by adopting a programmable Spatial Light Modulator (SLM) to function as a microlens array and replace the physical one in the traditional configuration of this sensing system. In this paper, we proposed to use the developed system for the relative measurement of toroidal surfaces, which are widely used in many optical systems due to their unique optical features of different curvatures in X and Y directions. An innovative idea to design the diffractive microlens array implemented by SLM was presented to tackle the measurement challenge. This unconventional design approach has a great advantage to provide different optical powers in X and Y directions so that focusing spots can be formed and captured on the detector plane for accurate centroid finding and precise wavefront evaluation for 3D shape reconstruction of the toroidal surface. A digital Shack-Hartmann Wavefront Sensing system with this unique microlens array was built to verify the design concept, and the experimental results were presented and analyzed.

High power laser systems such as the LMJ laser or the LIL laser, its prototype, require large optical components with very strict and various specifications. Technologies used for the fabrication of these components are now usually compatible of such specifications, but need the implementation at the providers' sites of different kind of metrology like interferometry, photometry, surface inspection, etc., systematically performed on the components. So, during the production for the LIL and now for the LMJ, CEA has also equipped itself with a wide range of specific metrology devices used to verify the effective quality of these large optics. These various systems are now used to characterize and validate the LMJ vendors' processes or to perform specific controls dedicated to analyzes which are going further than the simple "quality control" of the component (mechanical mount effect, environment effect, ageing effect,...). After a short introduction on the LMJ laser and corresponding optical specifications for components, we will focus on different metrology devices concerning interferometry and photometry measurements or surface inspection. These systems are individually illustrated here by the mean of different results obtained during controls done in the last few years.

We present an improved technique for detection of trace impurities in iodine-filled absorption cells for laser frequency stabilization. The results of purity investigation are compared to frequency shifts measured with a set of two iodine stabilized Nd:YAG lasers. The setup for direct fluorescence measurement with an Argon-ion laser operating at 502 nm wavelength is equipped with compensation for laser power and spectral instabilities.

Xe excimer lamps are used as VUV source for industrial application like surface cleaning. To determine the VUV efficiency of the lamp the radiant flux need to be known. Due to the difficulties of VUV measurements, it is often determined by interpolation from a value of a fixed angle, which results in large uncertainties. Here a goniometric setup is presented to measure the radiant flux of VUV sources like Xe excimer lamps which emit a narrow spectral band in the VUV range between &lgr; = 147 nm and 200 nm with a peak at 172 nm and spectral lines in NIR. By the use of two monochromators, we measure the spectral resolved radiant flux from 120 nm to 1000 nm. The measurement uncertainty of 9.7 % is rather low for the VUV spectral range and depends mainly on the uncertainty of the used deuterium calibration standard from PTB (7%). Due to the strong temperature dependence of the transmission edge of silica used for the lamp vessel, the measurements are done in nitrogen atmosphere to ensure the convection cooling of the lamp. We measured the radiance distribution curve and radiant flux of Xe excimer lamps and could show the angle dependence of the spectrum. The measured correlation between the VUV band and the NIR lines gives us a better understanding of the plasma kinetics, which is used to optimize the pulsed excitation of the lamp.

Illumination engineering is a field that spans many topics and the number industries that actively work in the field is expanding. In this field the efficiency of the design is only a part of the design. Of nearly the same importance is the distribution of the light at the target. Many times the factors that are necessary to develop an illumination system will contradict one another, thus making the design of illumination systems complex and demanding. Optical modeling plays a basic role in obtaining new models. In general, the LED optical model obtains its parameters as a mathematical transformation or the average of a large set of measured experimental data. The main goal of this paper is to measure directly the parameters of the LED optical model. We use the typical LED spatial distribution model based on ray distribution. The basic parameters of this model are: the slope of the ray and the energy of each ray. The measurement system incorporates the slope measuring method used in deflectometry into an energy measurement technique. The method was tested using the measured data of two LEDs to analyze the illumination distribution provided at the image screen of standard Köhler illumination system.

The laser interferometer space antenna (LISA) mission utilizes as current baseline a high sensitivity optical readout for measuring the relative position and tilt of a free flying proof mass with respect to the satellite housing. The required sensitivities are ~5pm/&sqrt; Hz for the translation measurement and ~20 nrad/&sqrt;Hz for the tilt measurement. For this purpose, EADS Astrium GmbH - in collaboration with the Humboldt-University Berlin and the University of Applied Sciences Konstanz - develops a fiber-coupled heterodyne interferometer including differential wavefront sensing for the tilt measurement. The interferometer is based on a highly symmetric design where both, measurement and reference beam have the same optical pathlength, frequency and polarization. We realized a mechanically highly stable and compact setup which is located in a temperature stabilized vacuum chamber and utilizes frequency stabilization of the laser and intensity stabilization of the heterodyne frequencies at the fibre outputs. Noise levels below 5 pm/&sqrt; Hz in translation movement and below 10 nrad/&sqrt;Hz in tilt movement (both for frequencies above 10^-2 Hz) were measured. While this setup is developed with respect to the requirements of the LISA space mission, it also has potential applications beyond: In industry, high precision position measurements - with ever increasing sensitivity - are needed e.g. for guaranteeing very small tolerances for automobile industry components. While current systems developed for this purpose use for instance whitelight-interferometry with resulting sensitivities in the nm-range, our interferometer opens the possibility to further improve the sensitivity. Here, we discuss possible implementations of our interferometer for industrial applications.

When the thickness and the refractive index of a thin film (around 1000nm) growing onto a substrate is measured, two experimental data have to be measured. In the Experimental Astrophysics Laboratory of the "Universidad Politécnica de Valencia", we use an experimental setup that allows us to obtain both, thickness and refractive index of thin films grown onto a substrate, from the values of reflectance at two different angles. The experiments are performed in a vacuum chamber operating at a pressure of 10^-7 mbar and a temperature which can be set between 17 and 300 K. When initial conditions are established, the substances that will form the film are prepared in gas form in a prechamber and goes trough a needle valve to the chamber. The proportions of a particular composition are controlled by their partial pressures. To monitor the thickness of the film during the accretion, two He-Ne laser beam (632.8 nm) are reflected at two different incidence angles. From the interferometric patterns we can obtain the refractive index from the quotient between the periods corresponding to each pattern. This arrangement makes up the double laser interferometric technique and it is argued on the basis as the grown rate is always the same so the quotient of periods is constant and it only depends on incidence angles (its values were chosen to optimize the measure process) and refractive index of the film, whose value can be obtained from experimental data.

Conventional techniques applied to three dimensional (3D) acquisition of information has significant limitations depending on the features of the piece under test. Thus, complex curvatures, deeper concavities and higher volumes are some examples of critical factors in which contact digitising systems are not suitable to undertake such kind of task. In these cases, the usage of optical 3D digitization systems implies a more appropriate way to obtain 3D information about the sample. In particular, structured illumination by means of white light provides point-to-point object acquisition with accuracy and resolution that are always below the manufactured tolerances. Moreover, when the object under test is too large, structured illumination can be mixed with photogrammetrical techniques in order to avoid errors by means of the delimitation of the overall working volume. This proceeding presents several real cases applied to mould industry in which 3D shape measurement using white light structured illumination is combined with finite element method (FEM) and laser cladding techniques to allow the repair of the mould.

Laser interferometers are even more precise distance measurement devices with resolution up to sub-nanometer region. If the measurements are carry out under atmospheric conditions (usual situation in an industry), the interferometers measure optical path length of an unknown distance instead of its true geometrical value. It is caused by an index of refraction of air that introduces a multiplicative constant to measured results. If we want correct values of the distance measurement the knowledge of the instantaneous value of the index is necessary. In the work, we present design and the first experimental results of method of the direct measurement of the index, where a Fabry-Perot (F.-P) interferometer is used as a detection system. The method employs a differential setup of two F.-P interferometers, where the cavity of the first is permanently evacuated and the other is on the air. The ultimate resolution of the measurement and the operating regime without need of a vacuum pump stay the method very advantage. The work includes comparison of the method with conventional refractometer where evacuatable cell is inserted into the measuring arm of Michelson interferometer. The comparison of the method with indirect measurement of the index with using Edlen formula is presented too.

This paper presents a force plate specially designed for measuring ground reaction forces in small animals. Digital Speckle Pattern Interferometry (DSPI) is used to measure the plate deformation produced by the animal. Elasticity theory is used to obtain force magnitude and application position from the vertical displacement field measured with DSPI. The force plate has been tested with static weights of 5g and 10g at various locations on the plate. Some experiments with 20g body weight transgenic mice are also reported.

This paper describes the design, realization and testing of an optical scanner for real time on-line detection of the shape of wood-panels entering a sanding machine on a transport belt. The paper describes the options considered for the design of the triangulation sensor, taking into account target performance specifications and geometrical constraints. Final design is a folded optical system which employs two laser line projectors and one CMOS camera, operated over a limited Region of Interest. Sensor calibration is outlined and examples of on-line measurements on moving panels are presented.

The measurement of the size distribution of a particles mixture is utilised in industrial and biomedical fields. In the current method, the laser (or monochromatic) light scattered by the sample at various scattering angles is measured; then, a simplified analysis uses the diffraction theory in order to calculate the distribution of the particle size. In particular, a set of n equations is generated: n is the number of measurements that differ by the scattering angle (it acts as control parameter), and the unknown quantities are the ratios between the number of particles that fall in a specified size range and the total number of particles (obviously n must be not less than the number of the predefined size ranges). That requires the use of a dedicated setup and accurate angular measurements. Our method requires only two measurements on the sample, carried out by a spectrophotometer equipped with an integrating sphere. The diffuse spectral transmittance (or reflectance) and the total spectral transmittance (or reflectance) are measured and their ratio is calculated, then it is generated an equations set similar to the previous, but integrated on the angular range of the diffuse spectral transmittance measurement: now we utilise as control parameter the wavelength (then, each equation has a different value of wavelength), while the unknown quantities are the same of the previous method. Due to the fact that both methods use the same equations set, they have the same applicability limits, but our method has the advantage that we can use a standard commercial spectrophotometer.

LIL and LMJ are two french high power laser facilities dedicated to laser-plasma interaction experiments. In order to control the flatness requirements of their optics, the CEA has an 800 mm diameter Fizeau interferometer. We decided to qualify our cavity flats with absolute calibrations. To achieve three-flat methods, a third 600 mm diameter silica transmission flat with a custom design mount that enables an easy rotation around the optical axis with low distortion of the flat is being fabricated. Over the past two decades, many papers have been published explaining how the traditional three-flat method can be improved to obtain two-dimensional data of a reference flat with various precisions. After a quick overview of these different methods (mostly using translations and rotations of at least one of the flats), we shall present several two-flat methods to get absolute flatness measurements over a wide spatial period bandwidth that we will use during the fabrication of our flat. For low frequencies, translations of the flat provide absolute slopes that are then integrated. For high frequencies, averaging of a few measurements taken with specific positions of the flat under test enables to separate the contributions of the reference and the test optics. Simulation results show the efficiency of the flat reconstruction and put forward the loss of information due to the method.

Determination of lens parameters is important from their application point of view. These parameters include focal length, radius of curvature and refractive index of the lens material. Of these the refractive index data will shed light on the reflectance and transmittance of the material with which the lens is made. Digital holography can be used for the parameter determination as well as for the test of collimation of waves emanating from lenses. Digital holograms are recorded for various positions of the test lens from a point source and the focal length is the position of the test lens where a single fringe results. Radius of curvature is determined by focusing a collimated beam on to the surface of the test lens. Using the lens equation the refractive index of the material of the lens can be determined. Simulations for the method in the case of a thin bi-convex lens are presented in the paper.