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.