Although low coherence microscopy (LCM) has been known for long time in the context of interference microscopy, coherence radar and white light interferometry, the whole subject has attracted a wide interest in the last two decades particularly accelerated by the entrance of OCT, as a noninvasive powerful technique for biomedical imaging. Today LCM can be classified into two types, both acts as three-dimensional imaging tool. The first is low temporal coherence microscopy; also known as optical coherence tomography (OCT), which is being used for medical diagnostics. The second is full field OCT in various modes and applied to various applications. FF-OCT uses low spatial and temporal coherence similar to the well-known coherence probe microscope (CPM) that have been in use for long time in optical metrology. The CPM has many advantages over conventional microscopy in its ability to discriminate between different transparent layers in a scattering medium thus allowing for precise noninvasive optical probing of dense tissue and other turbid media. In this paper the status of this technology in optical metrology applications will be discussed, on which we have been working to improve its performance, as well as its limitations and future prospective.

The interference fringe order of a transparent glass plate was determined using a three-surface wavelength-tuning Fizeau interferometer and an excess fraction method. We employed multiple-surface interferometry considering the potential for simultaneous measurement of the surface shape and geometric thickness. The optical thickness signal was separated from the three interference signals in the frequency space. A frequency selective phase-shifting algorithm and a discrete Fourier analysis detected the phase of the modulated interference fringes. The optical thickness obtained by wavelengthtuning Fizeau interferometry is related to the group refractive index. In contrast, the optical thickness deviation obtained by the phase-shifting technique is related to the ordinary refractive index. These two kinds of optical thicknesses were synthesized with the help of the dispersion relation of a fused-silica glass. Finally, the interference fringe order was determined using an excess fraction method that could eliminate the initial uncertainty of the refractive index.

We have demonstrated a full-field IR wavelength scanning interferometry system for the adhesive thickness measurement which in between the temporary bonded wafer and a carrier wafer. The illumination wavelength can be varied and selected by tilting the angle of interference filter along the main optical axis. The varying wavelength was calibrated by a commercial spectrometer. By combining the phase-shifting technique and the spectrum curve fitting method, the total thickness variation (TTV) of the adhesive layer and the adhesive thickness distribution map can be obtained. The experimental results showed that the TTV of the adhesive is 3.76 μm within the area of 110 mm diameter. The thickness variation is in a range from 16.47 μm to 20.23μm.

Interferometric inspection of optical surfaces and wavefronts requires permanently increasing accuracy. Therefore interferometric equipment is being improved and improved continuously. Point-diffraction interferometers (PDI) with an “inbuilt” reference wavefront originating from light diffraction by a pinhole aperture are potentially capable to produce the highest possible accuracy of a surface figure or wavefront characterization. The most mentioned configurations and their versions like Linnik-Smart and Sommargren schemes produce low-contrast spare-striped fringe patterns instead of full-contrast distinct interferograms, like e.g. produced by Fizeau interferometers, with clear phase shifting (PS) data flow. The concept of a PDI presented in this paper is to provide two perpendicularly outgoing wavefronts – test and reference ones – with mutual intensity regulation and arbitrary and stable phase shifts of one wavefront relative to the other. Such concept is also targeted to provide user-friendly measuring conditions similarly to interferometers which are in common use. Advantages of such arrangement of the PDI are: high numerical aperture (NA = 0.55), clear fringe patterns of high contrast, high accuracy of surface figure testing with wave-front RMS error 0.125 nm and wave-front RMS repeatability 0.05 nm. Performance of the PDI is illustrated by tables of repeatability and test surface profile plots for different azimuthal angles.

We propose a sparsity-based denoising algorithm for digital holography retrieved wrapped phase maps (WPMs) mod 2π by using a modified version of the SPADEDH (SPArsity DEnoising of Digital Holograms) algorithm, proposed in [1]. We test the proposed method on both simulated wrapped phase reconstructions and experimental wrapped phase maps obtained by digital holograms of living cells. Finally, we also show that the proposed algorithm can be used as a helper for the typical local phase unwrapping algorithms.

Thermo-elastic distortions of composite structures have been measured by a holographic camera using a BSO photorefractive crystal as the recording medium. The first test campaign (Phase 1) was performed on CFRP struts with titanium end-fittings glued to the tips of the strut. The samples were placed in a vacuum chamber. The holographic camera was located outside the chamber and configured with two illuminations to measure the relative out-of-plane and in-plane (in one direction) displacements. The second test campaign (Phase 2) was performed on a structure composed of a large Silicon Carbide base plate supported by 3 GFRP struts with glued Titanium end-fittings. Thermo-elastic distortions have been measured with the same holographic camera used in phase 1, but four illuminations, instead of two, have been used to provide the three components of displacement. This technique was specially developed and validated during the phase 2 in CSL laboratory. The system has been designed to measure an object size of typically 250x250 mm²; the measurement range is such that the sum of the largest relative displacements in the three measurement directions is maximum 20 μm. The validation of the four-illuminations technique led to measurement uncertainties of 120 nm for the relative in-plane and out-of-plane displacements, 230 nm for the absolute in-plane displacement and 400 nm for the absolute out-of-plane displacement. For both campaigns, the test results have been compared to the predictions obtained by finite element analyses and the correlation of these results was good.

Single Exposure Super Resolved Interferometric Microscopy (SESRIM) has been recently proposed as a way to achieve one dimensional super resolved imaging in digital holographic microscopy. SESRIM uses Red-Green-Blue (RGB) multiplexing for illuminating the sample having different propagation angles for each one of the three illumination wavelengths and it has been experimentally validated considering color (A. Calabuig, V. Mico, J. Garcia, Z. Zalevsky, and C. Ferreira, “Single-exposure super-resolved interferometric microscopy by red–green–blue multiplexing,” Opt. Lett. 36, 885-887, 2011) and monochrome (A. Calabuig, J. Garcia, C. Ferreira, Z. Zalevsky, and V. Mico, “Resolution improvement by single-exposure superresolved interferometric microscopy with a monochrome sensor,” J. Opt. Soc. Am. A 28, 2346-2358, 2011) digital sensors for holographic recording. In this contribution, we will first review some of the characteristics of the previously reported SESRIM approaches and second, we will present preliminary results for the extension of SESRIM to the field of lensless holographic microscopy. Experimental results are reported validating this new kind of superresolution imaging method named as lensless SESRIM (L-SESRIM).

In this paper we show how resolution enhancement and autofocusing in digital holographic microscopy (DHM) is obtained by using structured illumination. The structured illumination is generated by a spatial light modulator, and enables to project fringes of different orientations and phase shift without mechanical movement. The combination of the structured illumination and DHM improves the resolution of phase and amplitude imaging. Furthermore, the image plane is numerically determined by searching for the minimal deviation between the reconstructed images carried by different diffraction orders of the structured illuminations. The method can be applied to both amplitude and phase object.

The most suited techniques for quantitative and accurate determination of the phase distribution in a phase photonic microstructures are based on the interferometry, especially the digital holography (DH) in microscopic configuration. However there is well known limitation of the coherent full- field interferometric measurements: the phase difference between the neighboring samples cannot be larger than 2π, or objects shape have to generate light that can be collected by used optical system. This limitation might be overcame by use of a well-known technique called low-coherence interferometry (LCI) which allows for absolute shape measurements with a nanometer resolution and does not have 2π limitation of coherent interferometric techniques. In this work a dual channel measurement system for characterization of a high numerical aperture objects is presented. The system combines functionalities of the LCI system based on Twyman-Green configuration and the DHM system based on Mach-Zehnder configuration. The DHM allows to measure sample in transmission while LCI setup provides reflective measurement data and, therefore, provides a more complete tool for topography characterization. In presented paper we focus on the measurement of high gradient objects were both methods fail if applied independently: the LCI gives measurement only in the object area of low NA while the DHM cannot provide absolute shape characterization due to limited NA of imaging system. The dual channel system extends capabilities of both methods. In our paper we present experimental results for topography measurement of high NA microlenses. The accuracy of the development method is discussed and both simulation and experimental data are provided.

This paper proposes a robust method to compensate for the chromatic aberrations induced by the optical elements in digital color holography. It combines a zero-padding algorithm and a convolution approach with adjustable magnification, using a single recording of a reference rectangular grid. Experimental results confirm and validate the proposed approach.

Recently proposed, Lensless Object Scanning Holography (LOSH) is a fully lensless method, capable of improving image quality in digital Fourier holography applied to reflective objects, and involving a very simplified experimental setup. LOSH is based on the recording and digital post-processing of a set of digital lensless Fourier transform holograms which finally results in a synthetic image with improved resolution, field of view (FOV), signal-to-noise ratio (SNR), and depth of field (DOF). In this paper, LOSH is expanded to the case of diffuse-based objects. Now, the speckle can affect the resolution and it will not be a function of only the size of the aperture. The fact of increasing the aperture can produce the decrease of the size of the speckle. Moreover, there is an overlapping of speckles of the successive images. Different kinds of digital processing can be applied to obtain the final synthetic image. Among them, partial coherent processing, arising from the incoherent sum of several sets of images coherently added, provides the best improvement in the resolution and also in the SNR due to partial averaging of the speckles. Experimental results for a diffuse object are presented for different kinds of digital processing.

A vertical Long Trace Profiler (LTP) has been developed to characterize profile slope and figure error of grazing incidence aspherical X-ray mirrors with short radius of curvature (1 m - 5 m) and length up to 300 mm while achieving more than 100 mrad-level dynamical range and acceptable value of measurement accuracy (< 10 μrad). The increase of the dynamical range is obtained by separating the optical path delivering the probe beam to the test surface from the light path reflected by the sample, and by using a movable collecting mirror to redirect it towards the detector. Experimental data acquired through the developed prototype on X-ray optics are compared with the profiles measured on the same samples through a more complex profiler (called MPR700) based on a high resolution distance measuring sensor, laser interferometers and precise optical flats. The comparison between the two devices demonstrates the functionality of the proposed LTP scheme and shows the possibility to extend the field of applications of the LTPs avoiding the need of more expensive measuring devices based on distance measuring sensors and optical references.

We present several characterization techniques, which are suitable for small-size microlenses of lens diameters down to 5 μm. For an individual microlens, we apply full characterization for optical performance and surface characteristics. First, the optical performance is characterized by using a high-resolution interference microscope (HRIM). Second, a confocal microscope is applied to investigate the surface parameters. Third, the HRIM allows scanning the microlens array along the optical axis by using a piezo actuator. This leads to a measurement of the 3D intensity distribution near the focus of the lens. Such 3D intensity maps allow us to characterize the focal properties of each lens in an array. By studying those characterization techniques, we develop a new method to characterize a large number of microlenses, for instance, over one million lenses, which is already applied to wafer-based manufacturing in a cleanroom fab.

A new technique to measure depth based on dual wavelength digital holography and image correlation of speckle movements is demonstrated. By numerical refocusing of the complex optical field to different focus planes and by measuring the speckle movements caused by a wavelength shift both the object surface position and its local slope can be determined. It is shown how the speckle movement varies linearly with the surface slope, the wavelength shift and the distance of the numerical propagation. This gives a possibility to measure the slope with approximately the same precision as from the interferometric phase maps. In addition, when the object surface is in focus there is no speckle movement so by estimating in what plane the speckle movement is zero the absolute surface position can be measured.

Digital holographic profilometry using multiwavelength from laser diodes is applied to an inspection of inner surface of straight copper pipe and the detection of artificial defects such as a hole, rust and a scratch in its wall. To obtain the inner surface profile, a cone-shaped mirror attached to a rod having two acrylic spacers is inserted into the pipe and illuminated by the collimated laser beam from the other open end of the pipe. The measurement has been performed by shifting the mirror stepwise along the pipe. Distribution of an optical path length in the alignment is calculated and used to compensate for a distortion in the profile due to a positional misalignment of the mirror. The new algorithm to obtain the positional error is adopted for the compensation process and the shape and positions of defects in the inner wall can be investigated.

We show that imaging alive people through smoke and flames is possible by Digital Holography at far infrared. This capability is of crucial importance in the security field to provide a new tool for firefighters and first responders in fire accidents. So far, the existing thermographic infrared cameras allows to see people through dense smoke, sensing the radiation emitted by human body. However, these devices are often blinded due to the flame emission, which is collected by the zoom lenses employed for the scope, and the information of the targets beyond the flames is unavoidably lost. On the contrary, lensless Digital Holography at far infrared avoids the typical saturation of the camera detectors returning clear images of targets seen behind veils of smoke and curtains of flames. Moreover, we demonstrate that human-size holograms can be recorded, allowing to move this promising technology outside the lab for safety applications.

Shearography is an optical and nondestructive technique that has been largely used for damage detection in layered composite materials where delaminations and debondings are found among the most common flaws. Shearography is a relative measurement on which two images are recorded for different loading conditions of the sample. The applied loading induces some deformations into the sample generating a displacement field on its surface. The absolute difference between two phase maps recorded at two different loading instances produces an interference fringe pattern which is directly correlated to the displacements produced on the material surface. In some cases, depending on the loading level and mainly on the sample geometry, interference patterns will contain fringes resulting from geometry changes. This will mask those fringes correlated to flaws presented into the material, resulting in an image misinterpretation. This phenomenon takes place mainly when the sample has curved geometries, as for example pipe or vessel surfaces. This paper presents an algorithm which uses a mathematical processing to improve the visualization of flaws in shearographic images. The mathematical processing is based on divergent calculation. This algorithm highlights defected regions and eliminates fringes caused by geometry changes, providing an easier interpretation for complex shearographic images. This paper also shows the principle and the algorithm used for the processing. Results, advantages and difficulties of the method are presented and discussed by using simulated fringe maps as well as real ones.

Speckle interferometry is one of important deformation measurement methods for an object with a rough surface. A novel fringe analysis method using a new optical system, which uses a plane wave as the reference beam of the speckle interferometer, is proposed. When the optical system is employed in the fringe analysis, the deformation information and the bias components of the speckle patterns clearly are separated in frequency domain. Therefore, the deformation information can be readily extracted by using Fourier transform. In the fringe analysis processing, when the deformation information is extracted by Fourier transform, a pair of a real-part and an imaginary-part components concerning the information are given. The specklegrams are calculated by using such real- and imaginary-parts of the information. Consequentially, the fringe image is given as specklegram, and is spatially filtered. Sequentially, the phase map is calculated by using spatial fringe analysis method from the filtered specklegram. From experimental results, it is confirmed that the new method can analyze a deformation process with a convex and/or concave phase distribution in a high resolution power. It is also confirmed that the resolution power of the measurement by this method is much higher than 1/250 of the light source of the optical system.

A relation between vectorial source structure and coherence-polarization of the fluctuating field is established. This relation connects the source structure to the degree of coherence by Fourier relation, and this is extension of the van Cittert-Zernike theorem to the vectorial regime. Experimental verification of the proposed theorem is presented by making use of space averages as replacement of ensemble averages for Gaussian stochastic field. Both experimental and analytical results are obtained for different polarized sources, and good agreements between two justify use of space average as replacement of ensemble average in the spatially fluctuating field.

The normal FSI system shows good performance about target objects with specular surface such as semiconductor dies or flat panel glasses. But, if there are transparent objects on test surfaces, their optical polarization characteristics usually make the observed interference fringes degraded. When illuminated light reflects or penetrates, the direction of polarization of light rotates depending on the polarization characteristic of objects. The rotation of direction of polarization causes difficulty in measurement. In this paper, a PFSI (Polarization-based Frequency Shifting Interferometer) system is proposed, which applies the polarization analysis method to the conventional FSI system. First, the PFSI system is proposed for robust measurement to object. Low contrast problem of interference fringe due to polarization rotation of acquired fringe image can be solved by using polarization adjustment. In addition, light distribution of object beam and reference beam can be controlled. So, reflected light intensities of the reference beam and object beam can be made similar for conspicuous interference signals. Second, using PFSI system, we can measure the transparent object. For example, the height of flux and the height of die of flux bottom side can be measured in the same system. In case of measuring the height of the flux, the multi-layer reflections are generated in the surface and bottom side of flux. Three interference signals are observed when transparent flux is deposited on the PCB surface. By controlling the polarization of the system, the height of flux and the height of bottom side of flux can be measured simultaneously. Third, the signal processing acceleration method for fast height calculation is proposed for the PFSI, based on parallel processing architecture, which consists of parallel processing hardware and software called GPU(Graphic Processing Unit) and CUDA(Compute Unified Device Architecture). As a result, the processing time reaches into tact time level of real-time processing. Finally, the proposed system is evaluated in terms of accuracy and processing speed through a series of experiment and the obtained results show the effectiveness of the proposed system and method.

White-light interferometry is a highly accurate technology for 3D measurements. The principle is widely utilized in surface metrology instruments but rarely adopted for in-line inspection systems. The main challenges for rolling out inspection systems based on white-light interferometry to the production floor are its sensitivity to environmental vibrations and relatively long measurement times: a large quantity of data needs to be acquired and processed in order to obtain a single topographic measurement. Heliotis developed a smart-pixel CMOS camera (lock-in camera) which is specially suited for white-light interferometry. The demodulation of the interference signal is treated at the level of the pixel which typically reduces the acquisition data by one orders of magnitude. Along with the high bandwidth of the dedicated lock-in camera, vertical scan-speeds of more than 40mm/s are reachable. The high scan speed allows for the realization of inspection systems that are rugged against external vibrations as present on the production floor. For many industrial applications such as the inspection of wafer-bumps, surface of mechanical parts and solar-panel, large areas need to be measured. In this case either the instrument or the sample are displaced laterally and several measurements are stitched together. The cycle time of such a system is mostly limited by the stepping time for multiple lateral displacements. A line-scanner based on white light interferometry would eliminate most of the stepping time while maintaining robustness and accuracy. A. Olszak proposed a simple geometry to realize such a lateral scanning interferometer. We demonstrate that such inclined interferometers can benefit significantly from the fast in-pixel demodulation capabilities of the lock-in camera. One drawback of an inclined observation perspective is that its application is limited to objects with scattering surfaces. We therefore propose an alternate geometry where the incident light is normal to the object surface and where an inclined grating is used as reference mirror.

For sub-micrometer measurements of large objects a setup is presented utilizing a line-scan camera for data acquisition with a Michelson interferometer. To extract height information a carrier fringe approach is used in combination with a linear axis moving the specimen. This technique provides the capability of quick measurements for large areas. For the estimation of the maximum acceptable scan speed the deviation of the linear axis from ideal movement is determined. Also a suitable choice for a light source is presented. Measurement capabilities are approved by reference measurements on a sinusoidal standard.

The probably best known chromatic sensor is the chromatic confocal point sensor, which is an optical displacement sensor (depicted in Fig. 1). It uses different wavelengths to encode the distance and has one measurement spot. Beside this prominent example, there are plenty of other realizations. E.g. Lee lists fiber optical sensors which measure temperature, displacement, current, strain and more. A variant of the chromatic confocal point sensor is used within this paper as example to apply the proposed method, referred to as CCT (chromatic confocal triangulation) sensor. In contrast to the point sensor the CCT sensor has many measurement spots next to each other (typically 2000 measurement spots in a row).

Confocal microscopy is a state of the art optical principle to measure the topography of technical surfaces. The output of the measuring process is an intensity curve for each scanned point on the topography. The maximum of the intensity curve correlates to the point height. However, the intensity function is influenced by the geometrical properties of the surface topography and its material. Simple peak picking of the intensity curve leads to insufficient results when calculating the point height. Therefore, the centre-of-gravity or fitting algorithms are preferred. Both have an integral behaviour and are able to suppress unwanted signal components. Today, the centre-of-gravity is often the state of the art method. Disadvantages are e.g.: the method is sensitive against vibrations of the instrument during the measuring process. In contrast to the centre-of-gravity calculation, fitting algorithms are numerically inefficient and slow. Moreover, the fitting process needs a priori information about the curve of the intensity function. We propose an alternative algorithm for the robust evaluation of intensity curves. The amplitude spectra of each intensity curve of a measured reference data set are analysed. The applied technique is based on the Cramér-Rao bound and leads to a threshold operator for calculating the centre-of-gravity in the frequency domain. A possible phase distortion (an asymmetrically shape of the intensity function) caused by diffraction or optical aberrations will also be significantly suppressed. The performance of the algorithm is shown and we compare the algorithm to the popular centre-of-gravity.

Confocal sensors are well established in optical surface metrology and their performance has been thoroughly studied both experimentally and theoretically. However most of the theoretical work has been based upon the assumption of locally flat or point like measurement objects. As confocal sensors have become increasingly popular in industrial inspection of rough surfaces in recent years, severe measurement artifacts have been observed in certain situations. The physical reason for these artifacts was not fully understood and therefore a systematic procedure to choose a set of sensor parameters, that minimizes the impact of these artifacts, has been missing. In fact planning measurements of rough surfaces has been a formidable task that even highly experienced experts approached on a trial and error basis. To make things even worse, different confocal measurement systems, e.g. from different manufacturers, and different sensor parameters, e.g. different numerical aperture objectives, typically give substantially differing results. A reliable interpretation of these results let alone a sound judgement of the remaining uncertainty in the measurement results is very difficult. Starting from a quick review of a recently developed signal model, we therefore present an attempt to systematically guide the user of confocal sensors through the planning of an inspection task. In order to support our proposal, we present measurements of two roughness calibration standards, that were conducted with varying numerical aperture objectives on a custom build confocal microscope with rotating micro lenses. The uncertainty in these measurements is then compared to the predictions of our assistance system.

In this paper we present chromatic confocal distance sensors for the parallelized evaluation at several lateral positions. The multi-point measurements are performed using either one- or two-dimensional detector arrays. The first sensor combines the concepts of confocal matrix sensing and snapshot hyperspectral imaging to image a two-dimensional array of laterally separated points with one single shot. In contrast to chromatic confocal matrix sensors which use an RGB detector our system works independently from the spectral reflectivity of the surface under test and requires no object-specific calibration. Our discussion of this sensor principle is supported by experimental results. The second sensor is a multipoint line sensor aimed at high speed applications with frame rates of several thousand frames per second. To reach this evaluation speed a one-dimensional detector is employed. We use spectral multiplexing to transfer the information from different measurement points through a single fiber and evaluate the spectral distribution with a conventional spectrometer. The working principle of the second sensor type is demonstrated for the example of a three-point sensor.

The hybrid measurement principle Chromatic Confocal Spectral Interferometry combines Spectral Interferometry with Chromatic Confocal Microscopy and therefore benefits from their respective advantages. Our actual demonstrator setup enables an axial measurement range up to 100 μm with resolution up to 5 nm depending on the employed evaluation method and the characteristics of the object’s surface. On structured surfaces, lateral features down to 1 μm can be measured. As the sensor raw signal consists of a Spectral Interferometry type wavelet modulated by a confocal envelope, two classes of evaluation methods working on the phasing or the position of the envelope are employed. Even though both of these information channels are subject to their respective problems, we show that a proper combination of the individual methods leads to a robust signal evaluation. In particular, we show that typical artifacts on curved surfaces, that are known from Chromatic Confocal Microscopy, are minimized or completely removed by taking the phasing of the Spectral Interferometry wavelet into consideration. At the same time the problem of determining the right fringe order of the Spectral Interferometry signal at surface discontinuities can be solved by evaluation of the confocal envelope. We present here a first approach using a contrast threshold on the signal and a median referencing for trusted sections of the analysed topography, which yields a reduction of artifacts in a submicron range on steep gradients, discontinuous specimen or curved mirror-like surfaces.

Nanopositioning and nanomeasuring machines (NPM machines) developed at the Ilmenau University of Technology allow the measurement of micro- and nanostructures with nanometer precision in a measurement volume of 25 mm × 25 mm × 5 mm (NMM-1) or 200 mm × 200 mm × 25 mm (NPMM-200). Various visual, tactile or atomic force sensors can all be used to measure specimens. Atomic force sensors have emerged as a powerful tool in nanotechnology. Large-scale AFM measurements are very time-consuming and in fact in a practical sense they are impossible over millimeter ranges due to low scanning speeds. A cascaded multi-sensor system can be used to implement a multi-scale measurement and testing strategy for nanopositioning and nanomeasuring machines. This approach involves capturing an overview image at the limit of optical resolution and automatically scanning the measured data for interesting test areas that are suitable for a higher-resolution measurement. These “fields of interest” can subsequently be measured in the same NPM machine using individual AFM sensor scans. The results involve extremely large data sets that cannot be handled by off-the-shelf software. Quickly navigating within terabyte-sized data files requires preprocessing to be done on the measured data to calculate intermediate images based on the principle of a visualization pyramid. This pyramid includes the measured data of the entire volume, prepared in the form of discrete measurement volumes (spatial tiles or cubes) with certain edge lengths at specific zoom levels. The functionality of the closed process chain is demonstrated using a blob analysis for automatically selecting regions of interest on the specimen. As expected, processing large amounts of data places particularly high demands on both computing power and the software architecture.

Considering modern manufacturing processes, there is an increasing demand for flexible, fast and precise inspection systems. Usually, the holistic inspection of technical components with a complex three-dimensional surface, like gears, needs to be separated into inspection steps. Different areas on the object need to be verified with respect to varying characteristic specifications, e.g. related to defects or roughness properties. Such manifold inspection tasks can for instance be realized using a multi-sensor measurement system which is also equipped with a multi-axis system to optimally move and rotate each sensor with respect to any desired position at the object’s surface. In order to generate an automatic inspection system, the entire process is defined with respect to a polygonal model of the measurement specimen, such that different sub-regions are connected with different specifications and parameterizations that this region must meet and hence needs to be verified by the inspection system. However, the data acquisition with respect to sub-regions on the model’s surface and the integration of obtained datasets in the model’s coordinate system is only feasible if the transformation of the real object to the model is determined before. Consequently, this needs to be determined in the initialization phase of the overall inspection process.

A low-cost optical fiber Bragg grating-based microphone is presented. The sensing system makes use of an intensitybased interrogation approach, with a fixed-wavelength laser source employed as optical source. The optical sensor is complemented by signal processing, consisting of adaptive filters and a Capon power spectral density estimator. System characterization has been carried out, showing maximum sensitivity in the 120-450 Hz range, with 0.45 Hz repeatability on single-tone detection. Application for condition-based maintenance of industrial plants, based on a simulated model, is discussed.

In this paper measurement results of the fiber-optic interrogator module for telecommunication ‎satellite applications are presented. The sensor interrogator features from fiber ‎Bragg grating (FBG) based sensing. Benefits are intrinsic sensor distribution capability and the ‎possibility to embed optical fibers in composite structures like tanks and satellite panels. ‎ The fiber-optic interrogator module is based on a narrow-band monolithic laser diode where the ‎output wavelength is spectrally tuned by electric control signals. By evaluating the intensities of the ‎sensor response, the peak of the FBG can be monitored. The correct evaluation of the sensor ‎response is a challenging task, therefore different computational methods are presented, namely ‎centroid, finite impulse response filter and curve fitting algorithms. The algorithms shall met the ‎performance requirements in terms of measurement accuracy, robustness against laser degradation ‎and measurement rate. Furthermore the algorithms shall be implemented in an FPGA, which means ‎a detailed point of view to fixed-point arithmetic and necessary amount of hardware resources at ‎constant performance. ‎ Measurement results based on the different FBG evaluation algorithms are presented and traded ‎regarding accuracy robustness and their possible implementation in an FPGA.

A miniature optical fiber pressure sensor based on extrinsic Fabry-Perot interferometer (EFPI) is presented. The sensing probe has 0.2 mm outer diameter, and is based on an all-silica biocompatible structure, with a pressure sensitivity <1 nm/kPa. The probe is complemented by a fiber Bragg grating (FBG), in proximity of the EFPI tip, for temperature compensation. Interrogation is based on a low-cost white-light setup, whereas several pressure detection algorithms have been developed. Preliminary experimental validation and medical applications are discussed.

We present and experimentally analyze the applications of tilted fiber Bragg grating (TFBG) for the measurement of liquid parameters, including the concentration (or refractive index), liquid-level and dynamic concentration change. On the basis of analyzing the measurement principle of refractive index using TFBG, its spectral variations with the glycerol concentration and liquid-level are obtained. Meanwhile, a fast demodulation technique monitoring the small variation of TFBG transmission power in a strong background is employed to measure dynamic change in the liquid concentration. The results show that the method is easy to achieve fast, cost-effective measurement of the change process of liquid concentration.

Active triangulation systems are widely used for precise and fast measurements. Many different coding strategies have been invented to solve the correspondence problem. The quality of the measurement results depends on the accuracy of the pixel assignments. The most established method uses phase shifted-patterns projected on the scene. This is compared to a method using statistical patterns. In both coding strategies, the number and the spatial frequency of the projected patterns is varied. The measurements and calculations for all presented results were done with exactly the same measurement setup in a narrow time window to avoid any changes and to guarantee identical technical preconditions as well as comparability.

In an earlier paper we have described a concept for high speed 3D inspection using fringe projection techniques. We use a special CMOS camera with 300 x 300 px which can calculate the phase on board. The focus of the first step of development had been a fringe projector, which was able to modulate the projected fringes with up to 250 kHz. In the second step the image acquisition part of the system was developed. In case of 3D measurement with a matrix camera, the camera resp. the measuring object has to be moved stepwise in the lateral direction to cover multiple acquisition areas of the measurement object. Between each image the lateral movement has to correspond to the field of view of the camera. At the intended very high image acquisition rates the high acceleration of the system between each image will lead to inacceptable mechanical forces. In order to obtain a continuous scanning procedure and at the same time to use the performance of a matrix camera, a special lens system was developed. A measurement field 120 mm long and 3 mm wide is imaged onto the camera. The width of the measuring field is imaged onto the 300 rows of the camera, giving a lateral resolution of 10 μm. In the longitudinal direction the 120 mm object length is divided into 12’000 lines to reach the same resolution of 10 μm. Due to technical reasons that will be described later only 240 of the 300 pixel rows on the chip were used. Consequently, with each camera shot 240 separated lines are imaged onto the chip. Between each of these 240 lines there is a large empty space, which is not imaged by the camera. In principle, the camera is operating as 240 single line cameras. Therefore, if the camera is shifted in an inclined direction to the camera orientation over the object, the empty spaces can be recorded as well. In an optimum alignment, the complete measuring object can be scanned in a continuous movement, covering the total length of 120 mm. In this paper we will describe this image acquisition system and give first measuring results.

Measuring the three-dimensional (3D) surface shape of objects in real time has become an important task e.g. in industrial quality management or medical sciences. Stereo vision-based arrangements in connection with pattern projection offer high data acquisition speed and low computation time. However, these coded-light techniques are limited by the projection speed which is conventionally in the range of 200. . .250Hz. In this contribution, we present the concepts and a realized setup of a so-called 3D array projector. It is ultra-slim, but nonetheless able to project fixed patterns with high brightness and depth of focus. Furthermore, frame rates up to the 100 kHz range are achievable without any need of mechanically moving parts since the projection speed is limited mainly by the switching frequency of the used LEDs. According to the measurement requirements, type and structure of the patterns can be chosen almost freely: linear or sinusoidal fringes, binary codes such as the Gray code, square, hexagonal or random patterns and many more. First investigations on the functionality of such a 3D array projector were conducted using a prototype with a combination of Gray codes and phase-shifted sinusoidal fringes. Our contribution proves the high brightness of the proposed projector, its sharpness and the good Michelson contrast of the fringe patterns. We deal with the patterns’ homogeneity and the accuracy of the phase shift between the sinusoidal patterns. Furthermore, we present first measurement results and outline future research which is, inter alia, addressed to the use of other structured light techniques with the help of new purpose-built 3D array projector prototypes.

Stereophotogrammetric 3D shape measurement using structured illumination is an established class of methods for industrial inspection. One essential step in the measurement process for all stereophotogrammetric techniques is the assignment of corresponding points between the stereo views. As the purpose of the used structured illumination is to ease and improve the correspondence assignment, the choice of said sequence is of utmost importance. The precision of the correspondence assignment directly affects the noise of the final point cloud and therefore this assignment should be conducted with the highest precision possible. Depending on the chosen structured illumination sequence, different degrees of freedom for the pattern design exist and may affect the precision of the correspondence assignment and thus the noise of the 3d point cloud. In our contribution we want to discuss the influence of the frequency content of the structured illumination for a scheme employing bandlimited statistical patterns, which have been fruitfully used for highspeed applications in the past years. To evaluate the limits of the correspondence assignment accuracy we created a simple numerical signal-detector model. Using this model the correspondence assignment in dependence of the chosen structured illumination can be compared to ground truth-data. Furthermore, the noise of point clouds in real measurements is investigated to validate the results of the used simulation. Therefore, illumination sequences using different spatial frequency bands are created and projected onto a reference object. Afterwards, the noise of the resulting pointcloud is evaluated. The results indicate that it is advisable to optimize the pattern design depending on the used sensor and object properties.

The paper introduces a new fibrescopic micro fringe projector, showing the special requirements of micro fringe projection in combination with coupling to flexible image fibre bundles. So far performed example applications, such as measurements of deep drawing tools, will be shown and difficulties of certain geometries, such as internal gearing elements with steep flank gradients are discussed. Due to the miniaturization of the fringe pattern into a 2 mm diameter fibre bundle and the decrease of resolution in the bundle, a decrease of contrast has to be accepted. That leads to a fading of the sharp edges of black/white crossovers to sine like characteristics on the detection camera. Methods for the compensation of these artifacts in the beforehand made calibration and during the acquisition of the measurement data will be presented. Fitted applications of the conventional grey code technique will be as well introduced and compared as the developing method of encoded phase shift. In the current state the newly designed fringe projector is connected to a high resolution coordinate measurement machine (CMM). Measurement data and achievable resolutions of the connected systems will as well be presented, giving information about realizable measuring volumes.

The tilted wave interferometer is a non-null test interferometer for the measurement of aspheres and freeform surfaces without dedicated null-optics that uses an array of tilted waves to locally compensate the deviation of the surface from the spherical form. The concept allows for short measurement times of only a few minutes and high lateral resolutions at the same time. The calculation of the surface error is performed by perturbation of a polynomial representation of the surface. Since we are also interested in higher frequency errors of the surface which cannot be described by a polynomial of finite order these errors are evaluated in an additional step. Since every wavefront only covers a small area of the surface the challenge here is to reconstruct the surface from the information that is distributed over the different patches. We will present the method that was developed for the reconstruction of these high frequency errors as well as measurement results of aspheres and freeform surfaces without rotational symmetry that were obtained by this method.

Quality control in the fabrication of high precision optics these days needs nanometer accuracy. However, the fast growing number of optics with complex aspheric shapes demands an adapted measurement method as existing metrology systems more and more reach their limits. In this contribution the authors present a unique and highly flexible approach for measuring spheric and aspheric optics with diameters from 2mm up to 420mm and with almost unlimited spheric departures. Based on a scanning point interferometer the system combines the high precision and the speed of an optical interferometer with the high form flexibility of a classical tactile scanning system. This enables the measurement of objects with steep or strongly changing slopes such as “pancake” or “gull wing” objects. The high accuracy of ±50nm over the whole surface is achieved by using a full reference concept ensuring the position control even over long scanning paths. The core of the technology is a multiwavelength interferometer (MWLI); by use of several wavelengths this sensor system allows for the measurement of objects with polished as well as with ground surfaces. Furthermore, a large absolute measurement range facilitates measuring surfaces with steps or discontinuities like diffractive structures or even segmented objects. As all the measurements can be done using one and the same system, a direct comparison is possible during production and after finishing an object. The contribution gives an insight into the functionality of the MWLI-sensor as well as into the concept of the reference system of the scanning metrology system. Furthermore, samples of application are discussed.

Many aspheres and free-form optical surfaces are measured using a single line trace profilometer which is limiting because accurate 3D corrections are not possible with the single trace. We show a method to produce an accurate fully 2.5D surface height map when measuring a surface with a profilometer using only 6 traces and without expensive hardware. The 6 traces are taken at varying angular positions of the lens, rotating the part between each trace. The output height map contains low form error only, the first 36 Zernikes. The accuracy of the height map is ±10% of the actual Zernike values and within ±3% of the actual peak to valley number. The calculated Zernike values are affected by errors in the angular positioning, by the centering of the lens, and to a small effect, choices made in the processing algorithm. We have found that the angular positioning of the part should be better than 1, which is achievable with typical hardware. The centering of the lens is essential to achieving accurate measurements. The part must be centered to within 0.5% of the diameter to achieve accurate results. This value is achievable with care, with an indicator, but the part must be edged to a clean diameter.

Sub-aperture stitching (SAS) testing method is an effective way to extend the lateral and vertical dynamic range of a conventional interferometer. However, the center of each sub-aperture could be in error because of the complex motion of the mechanical platform. To eliminate the affection of lateral location error in the final stitching result, a lateral location error compensation algorithm is introduced and the ability of the algorithm to compensate the lateral location error is analyzed. Finally, a 152.4mm concave parabolic mirror is tested using SAS method with the compensation algorithm. The result showed that the algorithm can effectively compensate the lateral location error caused by the mechanical motion. The proposal of the algorithm can reduce high requirement of mechanical platform, which provides a feasible method for the practical application of the engineering.

Quantitative deflectometry is a new tool to measure specular surfaces. The spectrum of measurable surfaces ranges from flat to freeform surfaces with steep slopes, with a size ranging from millimeters to several meters. We illustrate this by several applications: eye glass measurements, measurements of big mirrors, and in-line measurements in ultra-precision manufacturing without unclamping of the sample. We describe important properties of deflectometry and compare its potentials and limitations with interferometry. We discuss which method is superior for which application and how the potential of deflectometry may be developing in the future.

The manufacturing of optical components more often requires grinding and polishing of non rotational symmetric aspheres or freeform surfaces. Although there are measurement techniques available for small diameters of some 10th of mm the measuring of larger surfaces is not or only by extreme efforts feasible. Based on the specification for a large mirror in semi professional and scientific astronomy with up to 1.2 m diameter and a relative aperture of F# < 1.5 a final measurement approach for the measurement of radius and shape deviation (parameters of code number 3 of DIN ISO 10110) is described. The combination and evaluation of different sensors and measurement methods for the measurement of high-precision optical surfaces with concave radii of 3.000 mm to infinity is examined and presented. A reproducibility and absolute accuracy of better l/12 (PV) and l/40 (rms) is to be achieved. The absolute maximum radius difference should be smaller than 0,1 %. Thus, also the measurement of aspheric surfaces and free-form surfaces are investigated. For the measurement of large surfaces, up to 100 individual sub apertures with up to 100 Million Points are recorded by deflectometric or interferometric measurement techniques and composed algorithmically to a total surface area. A precision granite portal with multifunctional device carrier will be presented as precise movements are crucial for all tests. The realization of the required accuracy in the portal-measurement device is verified, documented and compared with a simulation. Results on specimens of 200 and 430 mm diameter are evaluated. The measurements were taken by deflectometry and interferometry on the described test equipment. The validation of the samples with various interferometric procedures was performed. The obtained results are presented, analyzed and discussed.

Absolute measurement with SCOTS/deflectometry is a calibration problem. We use a laser tracker to calibrate the test geometry. The performance id demonstrated with the initial measurement results from the Large Synoptic Survey Telescope tertiary mirror. Systematic errors from the camera are carefully controlled. Camera pupil imaging aberration is removed with an external aperture stop. Imaging aberration and other inherent errors are suppressed with a rotation test. Results show that the SCOTS can act as a large dynamic range, high precision, non-null test method for precision aspheric optics. The SCOTS test can achieve measurement accuracy comparable with the traditional interferometric testing.

There are many optical metrological techniques to determine the profile of a surface or a wave-front. A group of them are based on the measurements of the profile slopes, like deflectometry or wave-front sensors. In both sensors, the profile is then obtained by integrating the gradient information provided by the measurements. The used integration method influences the quality of the obtained results. In this work we compare the performance of different bi-dimensional integration methods to obtain the profile from the slopes, and we propose some new methods. The first kind of methods is based on a path integral, in which the profile in a given point (x,y) is obtained by a 1D integral from (0,0) to (x,0) followed by a 1D integral from (x,0) to (x,y). The second kind of methods is based on finite differences, where the profile in a point is related with the profile in the neighbor points and the slopes of those points. On these methods different interpolations can be used. Finally, the third kind of methods is based on Fourier domain integration. Several simulation results are obtained to study the influence of several parameters: spatial frequency of the signal, local slope errors, random noise, and edge effects. Fourier domain methods could be considered as the gold standard, they suffer from edge effects because the signals are not periodic. Moreover they can only be applied when regular Cartesian sampling is used. Path integral methods create artifacts along the integration paths, when local errors are present. Finite difference methods are more versatile, and their accuracy depends on the used interpolation methods.

We present a novel method for measuring a curved specular surface profile, which is the moiré deflectometry under incoherent (white light) illumination. In our proposed system, moiré is produced by a superposition of two pairs of Ronchi gratings to obtain orthogonal components of a normal vector on a surface under test. The grating pair was moved along an axis perpendicular to the grating plane to modulate a spatial frequency of the moiré. The moiré is reflected by a specular object, then observed with a calibrated stereo camera. Normal vector distribution of the tested surface was measured by analysis of intensity oscillations captured by the stereo camera as a function of the position of the moved grating. A surface profile was reconstructed by an integration calculation. We successfully measured surface profiles of deeply curved mirrors with the curvature from -20 to 20 m^-1 by our system. Moreover, part of a miniature vehicle body, which has a complex curved specular surface, was also measured. Additionally, we theoretically and experimentally studied a measurable angle variation of the normal vector on the tested surface by our measurement system. We found that our system can allow to measure the angle deviation of 0.05 deg of the normal vector. This method has no ambiguity of slope and height measurements which is appeared in conventional deflectmetric metrologies. Furthermore, our proposed system only needs a single step calibration. Hence, the methodology we proposed has a potential to be developed into a 3D profiler for complex specular surfaces.

An axis-symmetrical optical laser triangulation system was developed by the authors to measure the inner geometry of long pipes used in the oil industry. It has a special optical configuration able to acquire shape information of the inner geometry of a section of a pipe from a single image frame. A collimated laser beam is pointed to the tip of a 45° conical mirror. The laser light is reflected in such a way that a radial light sheet is formed and intercepts the inner geometry and forms a bright laser line on a section of the inspected pipe. A camera acquires the image of the laser line through a wide angle lens. An odometer-based triggering system is used to shot the camera to acquire a set of equally spaced images at high speed while the device is moved along the pipe’s axis. Image processing is done in real-time (between images acquisitions) thanks to the use of parallel computing technology. The measured geometry is analyzed to identify corrosion damages. The measured geometry and results are graphically presented using virtual reality techniques and devices as 3D glasses and head-mounted displays. The paper describes the measurement principles, calibration strategies, laboratory evaluation of the developed device, as well as, a practical example of a corroded pipe used in an industrial gas production plant.

High precision optical non-contact position measurement is a key technology in modern engineering. Laser trackers (LT) can determine accurately x-y-z coordinates of passive retroreflectors. Next-generation systems answer the additional need to measure an object‘s rotational orientation (pitch, yaw, roll). These devices are based either on photogrammetry or on enhanced retroreflectors. However, photogrammetry relies on costly camera systems and time-consuming image processing. Enhanced retroreflectors analyze the LT‘s beam but are restricted in roll angle measurements. In the past we have presented a new method [1][2] to measure all six degrees of freedom in conjunction with a LT. Now we dramatically optimized the method and designed a new prototype, e.g. taking into consideration optical alignment, reduced power loss, highly optimized measuring signals and higher resolution. A method is described that allows compensating the influence of the LT’s beam offset during tracking the active retroreflector. We prove the functionality of the active retroreflector with the LT and, furthermore, demonstrate the capability of the system to characterize the tracking behavior of a LT. The measurement range for the incident laser beam is ±12° with a resolution of 0.6".

The modern robotic tacheometers equipped with digital cameras (called also imaging total stations) and capable to measure reflectorless offer new possibilities to gather 3d data. In this paper an automated approach for the tacheometer measurements needed in the dimensional control of industrial large scale objects is proposed. There are two new contributions in the approach: the automated extraction of the vital points (i.e. the points to be measured) and the automated fine aiming of the tacheometer. The proposed approach proceeds through the following steps: First the coordinates of the vital points are automatically extracted from the computer aided design (CAD) data. The extracted design coordinates are then used to aim the tacheometer to point out to the designed location of the points, one after another. However, due to the deviations between the designed and the actual location of the points, the aiming need to be adjusted. An automated dynamic image-based look-and-move type servoing architecture is proposed to be used for this task. After a successful fine aiming, the actual coordinates of the point in question can be automatically measured by using the measuring functionalities of the tacheometer. The approach was validated experimentally and noted to be feasible. On average 97 % of the points actually measured in four different shipbuilding measurement cases were indeed proposed to be vital points by the automated extraction algorithm. The accuracy of the results obtained with the automatic control method of the tachoemeter were comparable to the results obtained with the manual control, and also the reliability of the image processing step of the method was found to be high in the laboratory experiments.

The accuracy in the arrangement of grooved rolls for the finishing rolling mill is of large importance for the good roundness of the bar steel product supplied to the precision machinery components such as the bearing of the high speed motor. Combining telecentric optics, silhouette image processing techniques, and statistical data processing allowed the development of the quantitative alignment guidance technique of the grooved rolls. The developed system demonstrated a high measuring accuracy and was seen to have practical use.

Dimension measurement of hot large forgings is necessary for manufacturing process and quality control. Conventional non-contact optical measurement methods are not applicable, mainly because of high temperature and large dimensions. A novel approach to the axis staightness measurement of the cylindrical forging, based on the principle of photogrammetry and edge detection, is described in this paper. Proposed system is developing under laboratory conditions, but the actual conditions of steel production are also considered. Demands on the measurement system were set by our industrial partner, producer of cylindrical forgings with length of 4 to 20 m and diameter up to 1.4 m. The system should be able to detect axis straightness deviations higher than 5 mm (system accuracy has to be better than 5 mm). Cylindrical forgings are 4 to 20 m long with diameter up to 1.4 m. The approach is based on the assumption that the actual shape of the cylindrical forging axis can be determined (in the simplest case) using four boundary curves which lie in two mutually perpendicular planes. Four boundary curves can be obtained by detecting the forgings edges in two images. The article provides results of first validation of proposed method in laboratory conditions. Measurement repeatability was validated by carrying out ten measurements of a deformed rod. Each measurement was compared with a measurement performed by industrial fringe projection scanner Atos III Triple Scan in order to verify the accuracy of the proposed method.

The target size reduction for overlay metrology is driven by the optimization of the device area. Furthermore, for the future semiconductor nodes accurate metrology on the order of 0.2 nm is necessary locally in the device area, requiring small in-die targets that fit within the product structures on the wafer. In this, the diffraction-based overlay metrology using optical scatterometry is challenged to extreme limits. The small grating cannot be considered as an infinitely repeating line-space structure with a sharply peaked spectrum, however a continuous spectrum is observed. Also, metrology proximity effects due to the environment near the metrology target need to be taken into account. On the one hand, this sets strict design and assembly rules of the metrology sensor. On the other hand, the optical ray-based analysis is extended to wave-based analysis to capture the full extent of the overlay application and sensor. In this publication, the challenges of sub-nanometer in-die overlay metrology are addressed, including measurements and simulations.

We report on a fast and accurate shape metrology for nanoscale structures by analyzing the scattering pattern of visible light. The technique is based on model-based scatterometry which is inverse measurement technique comparing measured scattering data with numerical simulations of the scattering process using a physical model of the structures. We demonstrate the concept for an array of silicon nanopillars that are arranged in a twodimensional lattice and show that the proposed methodology provides a fast and reliable determination of the pillar dimensions with nanometer precision. Since the technique works contact-free and is applicable to large area samples, it can be readily implemented in an industrial environment for inline metrology applications.

Incoherent Optical Scatterometry (IOS) is widely used in semiconductor industry in applications related to optical metrology particularly in grating reconstruction. Recently, Coherent Fourier Scatterometry (CFS) has emerged as a strong alternative to the traditional IOS under suitable condition. When available, phase information is an added advantage in CFS to complement the intensity data. Phase information in the scattered far field is dependent on the structure and the composition of the grating. We derive and discuss the phase information accessible through the CFS. Phase difference between the diffracted orders is computed and the polarization dependent phase sensitivity of the grating parameters are discussed. The results are rigorously simulated and an experimental implementation of CFS demonstrates the functionality of the method.

A thorough knowledge of the angular distribution of light scattered by an illuminated surface under different angles is essential in numerous industrial and research applications. Traditionally, the angular distribution of a reflected or transmitted light flux as function of the illumination angle, described by the Bidirectional Scattering Distribution Function (BSDF), is measured with a point-by-point scanning goniophotometer yielding impractically long acquisition times. Significantly faster measurements can be achieved by a device capable of simultaneously imaging the far-field distribution of light scattered by a sample onto a two-dimensional sensor array. Such an angular-to-spatial mapping function can be realized with a parallel catadioptric mapping goniophotometer (CMG). In this contribution, we formally establish the design requirement for a reliable CMG. Based on heuristic considerations we show that, to avoid degrading the angular-to-spatial function, the acceptance angle of the lens system inherent to a CMG must be smaller than 60°. By means of a parametric study, we investigate the practical design limitations of a CMG caused by the constraints imposed by the properties of a real lens system. Our study reveals that the values of the key design parameters of a CMG fall within a relatively small range. This imposes the shape of the ellipsoidal reflector and drastically restricts the room for a design trade-off between the sample size and the angular resolution. We provide a quantitative analysis for the key parameters of a CMG for two relevant cases.

In this work, we report metrology solutions using scatterometry Optical Critical Dimension (OCD) characterization on two advanced CMOS devices: novel n-channel gate-last In_0.53Ga_0.47As FinFET with self-aligned Molybdenum (Mo) contacts and p-channel Ge FinFET formed on Germanium-on-Insulator (GOI) substrate. Key critical process steps during the fabrication of these advanced transistors were identified for process monitor using scatterometry OCD measurement to improve final yield. Excellent correlation with reference metrology and high measurement precision were achieved by using OCD characterization, confirming scatterometry OCD as a promising metrology technique for next generation device applications. In addition, we also further explore OCD characterization using normal incidence spectroscopic reflectometry (SR), oblique incidence spectroscopic ellipsometry (SE), and combined SR+SE technologies. The combined SR+SE approach was found to provide better precision.

Optical vision systems require both unidirectional and bidirectional measurements for the calibrations and the verification of the tool performance to enable accurate measurements traceable to the SI unit Metre. However, for bidirectional measurements up to now the national metrology institutes are unable to provide internationally recognized calibrations of suitable standards. Furthermore often users are not aware of the specific difficulties of these measurements. In this paper the current status and limitations of bidirectional optical measurements at the industrial level are summarised and compared to state-of-the-art optical linewidth measurements performed at PTB on measurement objects of semiconductor industry. It turns out, that for optical widths measurements at an uncertainty level below 1 μm edge localisation schemes are required, which are based on tool and sample dependent threshold values, which usually need to be determined by a rigorous simulation of the microscopic image. Furthermore the calibration samples and structures must have a sufficient quality, e. g. high edge angle and low edge roughness and the structure materials and their material parameters have to be known. The experience obtained within the accreditation process of industrial labs for width calibrations shows that, in order to be able to achieve a desired measurement uncertainties of about 100 nm, the imaging system needs to have a monochromatic Koehler illumination, numerical aperture larger than 0.5, a magnification greater than 50x and the ability to control the deviation of the focus position to better than 100 nm.

Shape measurement of moving, especially rotating objects is an important task in the field of process control. The Laser Doppler Distance Sensor was invented for this purpose. It is realized by two tilted interference fringe systems and enables the simultaneous measurement of the surface velocity and profile. The distance is coded in the phase difference between the generated interference signals of two photo detectors. In order to achieve a distance uncertainty of below 1μm a steep calibration function is necessary. This can be achieved by increasing the tilting angle. However, due to the speckle effect at rough surfaces, random envelopes and phase jumps occur disturbing the phase difference estimation with increasing tilting angle. This problem was overcome recently by employing a receiving optics matching reducing the distance uncertainty by about one magnitude. By evaluating the Doppler frequencies of the two fringe systems the surface velocity and thereby the objects mean diameter can be calculated as well as angular misalignment of the sensor can be detected.

Laser-Doppler vibrometry has become the state-of-the-art technique for broadband vibration analysis with picometer resolution in microelectromechanical systems (MEMS). Displacement or velocity is detected only in direction of the measurement beam and, thus, three impinging laser beams are necessary to investigate all components of a threedimensional (3D) motion. This requirement is not problematic for 3D-vibration measurements on macroscopic objects with scattering surfaces but for reflective microstructures. A general problem of measuring 3D vibrations with three laser beams is optical crosstalk. This problem is especially critical for MEMS applications because the three beams have to be positioned closely to achieve high lateral resolution. In this paper, we prove that it is possible to impinge the small laser focus of a single laser beam with 3.3 μm diameter on a proper edge, corner or etch hole of a MEMS device to obtain real-time, 3D-vibration measurements with picometer amplitude resolution without optical crosstalk. We present the first measurements of the 3D-vibrations in MEMS devices. We prove that our method can meet the requirement of the MEMS community for fast, full-3D, broad-bandwidth, vibration measurements with picometer amplitude resolution and micrometer spatial resolution.

Scanning laser-Doppler vibrometry is the standard optical, non-contact technology for vibration measurement applications in all areas of mechanical engineering. The vibration signals are measured from the different measurement points at different time points. This requires synchronization and the technology is limited to repeatable or periodic events. We have explored a new solution for the optical setup of the sensing system of a multi-channel vibrometer that we present in this paper. Our optical system is a 12-channel vibrometer and consists of a 12-channel interferometer unit which is connected with 12 optical fibers to a sensor head with 12 fiber-coupled objective lenses. Every objective lens can be focused manually and is placed in a sphere which can be tilted and fixed by a blocking screw. Thus it is possible to adjust a user defined measurement grid by hand. The user can define the geometry of the measurement grid in a camera image displayed in the software by just clicking on the laser foci. We use synchronous analog-digital conversion for the 12 heterodyne detector signals and a digital 12-channel-demodulator which is connected via USB to a computer. We can realize high deflection angles, good sensitivity, proper resolution, sufficient vibration bandwidth, and high maximum vibration amplitudes. In this paper, we demonstrate the optical and electrical setup of the manually adjustable 12-channel vibrometer, we present the experimentally evaluated performance of our device, and we present first measurements from real automotive applications.

In the paper we present implementation of 3D DIC method for in-situ diagnostic measurements of expansion bellows in heating chambers. The simultaneous measurements of a supply and a return pipeline were carried out in a heating chamber in Warsaw at the peak of the heating season in cooperation with Dalkia Warszawa. Results of the measurements enabled assessment of the risk of failure of expansion bellows. In-situ measurements were preceded by feasibility tests carried out in the Institute of Heat Engineering of Warsaw University of Technology. Potential implementations and a direction of future works are discussed in conclusions.

Residual stress measuring by optical methods has been proposed by several authors in the past years; nevertheless the technique is still confined to optical laboratories: indeed the large sensitivity of the optical methods allows measuring very low stress values with high reliability, but these advantages are counter-balanced by the high sensitivity to vibrations, which makes very difficult performing the measurements outside of optical laboratories. Digital Image Correlation (DIC) is a possible alternative: indeed this technique is much less affected by vibrations, but its sensitivity is quite low, thus negatively affecting the accuracy of results. This work proposes a variant of Digital Image Correlation, known as iDIC (integrated DIC), to perform residual stress measurement. Since this approach directly integrates in the formulation the hole drilling shape functions, it overcome most of the problem of standard DIC; in this way it is possible to obtain accurate results without using interferometric techniques.

Overlay metrology for stacked layers will be playing a key role in bringing 3D IC devices into manufacturing. However, such bonded wafer pairs present a metrology challenge for optical microscopy tools by the opaque nature of silicon. Using infrared microscopy, silicon wafers become transparent to the near-infrared (NIR) wavelengths of the electromagnetic spectrum, enabling metrology at the interface of bonded wafer pairs. Wafers can be bonded face to face (F2F) or face to back (F2B) which the stacking direction is dictated by how the stacks are carried in the process and functionality required. For example, Memory stacks tend to use F2B stacking enables a better managed design. Current commercial tools use single image technique for F2F bonding overlay measurement because depth of focus is sufficient to include both surfaces; and use multiple image techniques for F2B overlay measurement application for the depth of focus is no longer sufficient to include both stacked wafer surfaces. There is a need to specify the Z coordinate or stacking wafer number through the silicon when visiting measurement wafer sites. Two shown images are of the same (X, Y) but separate Z location acquired at focus position of each wafer surface containing overlay marks. Usually the top surface image is bright and clear; however, the bottom surface image is somewhat darker and noisier as an adhesive layer is used in between to bond the silicon wafers. Thus the top and bottom surface images are further processed to achieve similar brightness and noise level before merged for overlay measurement. This paper presents a special overlay measurement technique, using the infrared differential interference contrast (DIC) microscopy technique to measure the F2B wafer bonding overlay by a single shot image. A pair of thinned wafers at 50 and 150 μm thickness is bonded on top of a carrier wafer to evaluate the bonding overlay. It works on the principle of interferometry to gain information about the optical path length of the stacked wafers, to enhance the image contrast of overlay marks features even though they are locating in different Z plane. A two dimensional mirror-symmetric overlay marks for both top and bottom processing wafers is designed and printed in each die in order to know and realize the best achievable wafer to wafer bonding processing. A self-developed analysis algorithms is used to identify the overlay error between the stacking wafers and the interconnect structures. The experimental overlay results after wafer bonding including inter-die and intra-die analysis results will be report in the full paper. Correlation of overlay alignment offset data to electrical yield, provides an early indication of bonded wafer yield.

The Coarse Lateral Sensor (CLS) is a system able to measure the lateral position between two satellites. It bridges the gap between the coarse alignment accuracy achievable with radio frequency metrology or global positioning systems (GPS), and the alignment accuracy required to start higher-precision optical metrology systems based on interferometry. The system is a standalone unit. Once connected to an unregulated 28V power-supply, it delivers, the lateral position of a corner cube retro-reflector and tracks this position at a rate of 10 Hz. The system is operational with the sun in its field-of-view. The coarse lateral sensor has successfully undergone thermal qualification (40°C and -30 °C), and vibration test (highlevel sinus, random and shock test in the 3-axis).

This work presents a scanning deflectometric approach to solving a 3D surface reconstruction problem, which is based on measurements of a surface gradient of optically smooth surfaces. It is shown that a description of this problem leads to a nonlinear partial differential equation (PDE) of the first order, from which the surface shape can be reconstructed numerically. The method for effective finding of the solution of this differential equation is proposed, which is based on the transform of the problem of PDE solving to the optimization problem. We describe different types of surface description for the shape reconstruction and a numerical simulation of the presented method is performed. The reconstruction process is analyzed by computer simulations and presented on examples. The performed analysis confirms a robustness of the reconstruction method and a good possibility for measurements and reconstruction of the 3D shape of specular surfaces.

Trace gas measurements were performed by the eddy correlation technique. The time domain stability criterion for laminar and turbulent flows measured in the street canyon model was determined. The evaluation of the instrument performance was done by the concentration measurements (CH₃OH, C₂H₅OH). The Allan and Hadamard variance methods were used for stability analysis. The dependence of variances on different degrees of flow turbulence was evaluated. The influence of turbulence on the optimal averaging time for minimum detectable concentrations has been studied. The stability analysis of experimental set up consisting of the CO₂ laser photoacoustic detection and the simulated atmosphere in a wind tunnel was performed for different sample concentrations and flows. The sensitivity and stability analysis were determined by 1000 s, 2000 s and 10 000 s measurements.

Piston-cylinder assemblies are used in various actuator applications in all branches of industry, such as construction technology. It is often important for the operator to know the condition of the piston rod in the pressure-operated cylinder. A large number of operating cycles by this piston can lead to premature failure and breakage of the entire cylinder; this is conditioned by a high chance of splitting of the piston rod due to its elongation during the operating process. Therefore, it is necessary to know their operating lifetimes, for which purpose endurance tests are conducted. Since the pistons are located in hard-to-reach place, monitoring their operation via the contact method while there are in motion is not considered possible. In such situations, a non-contact method is used to monitor to moving parts, which is conducted on the basis of imaging sensors. The authors of this article have developed a new system for conducting endurance test on piston mechanism in a cylindrical valve. This system makes it possible to observe the shift of the reciprocating piston in real time, automate the process of recording data and promptly and accurately measure the parameters of the shift of the piston via a non-contact method and increase the reliability of the data received.

The analysis of complex spectra is an actual problem for modern science. The work is devoted to the creation of a software package, which analyzes spectrum in the different formats, possesses by dynamic knowledge database and self-study mechanism, performs automated analysis of the spectra compound based on knowledge database by application of certain algorithms. In the software package as searching systems, hyper-spherical random search algorithms, gradient algorithms and genetic searching algorithms were used. The analysis of Raman and IR spectrum of diamond-like carbon (DLC) samples were performed by elaborated program. After processing the data, the program immediately displays all the calculated parameters of DLC.

A fiber-optic interferometer to measure differences in temperature between two single-mode fiber arms is described. Temperature changes are observed as a motion of an optical interference fringe pattern. Values are calculated for the temperature dependence of the fringe motion. Temperature measurements are made with the interferometer, and the experimental results for sensitivity are in good agreement with the theoretical values.

The measurement and analysis of airflow field is very important in fluid dynamics. For airflow, smoke particles can be added to visually observe the turbulence phenomena by particle tracking technology, but the effect of smoke particles to follow the high speed airflow will reduce the measurement accuracy. In recent years, with the advantage of non-contact, nondestructive, fast and full-field measurement, digital holography has been widely applied in many fields, such as deformation and vibration analysis, particle characterization, refractive index measurement, and so on. In this paper, we present a method to measure the airflow field by use of digital holography. A small wind tunnel model made of acrylic glass is built to control the velocity and direction of airflow. Different shapes of samples such as aircraft wing and cylinder are placed in the wind tunnel model to produce different forms of flow field. With a Mach-Zehnder interferometer setup, a series of digital holograms carrying the information of airflow filed distributions in different states are recorded by CCD camera and corresponding holographic images are numerically reconstructed from the holograms by computer. Then we can conveniently obtain the velocity or pressure information of the airflow deduced from the quantitative phase information of holographic images and visually display the airflow filed and its evolution in the form of a movie. The theory and experiment results show that digital holography is a robust and feasible approach for real-time visualization and analysis of airflow field.

The measurement of temperature field distribution in transparent media is an attracting subject in many research fields. In transparent medium, the temperature change will induce a corresponding refractive index change and thus lead to the phase distribution and variation of the object wavefront passing through the medium. Different from the traditional optical holographic interferometry, the recently developed digital holographic interferometry allows recording the hologram using digitally imaging devices such as CCD, and reconstructing the holographic image by numerically simulating beam diffraction, so it can directly obtain the complex amplitude distribution of the object wavefront in different states by dynamically recording a series of holograms of the object field in different time. Then more detail information can be calculated, such as the refractive index distribution and variation in transparent media. In this paper, we introduce the principles and review some of the applications on dynamically measuring the temperature field distribution by using digital holographic interferometry with specially designed experimental setups, such as the temperature distributions and variations corresponding to Rayleigh-Benard convection, heat conduction process in glass samples, heating process of the oil in container, flame filed, cooling process of heat sink and so on.

This paper presents a misalignment aberrations calibration method for the interferometric testing of cylindrical surface. This approach is based on a simple polynomials function, which is deduced by analyzing the geometry of the misalignment aberrations and perfectly describes the relationship between the misalignment aberrations and the corresponding adjustment errors. A least-squares algorithm for calibration of the misalignment aberrations was implemented towards the measured phase data, and the adjustment errors can be estimated through the proposed mathematical model. Then by subtracting the fitting function from the measured phase data, the misalignment aberrations and the genuine deviation of the test cylindrical surface can be completely separated. By means of simulation and experimental results, the repeatability and accuracy of the technique are discussed.

Ways of refining autocollimation systems for the inspection of angular deformation of industrial objects are analyzed. Control elements based on tetrahedral reflectors with plane and cylinder reflecting sides are researched. Results of an analysis the action matrix of tetrahedral reflectors are considered. The features of tetrahedral reflector as the control elements for three-axis angular systems are discussed. Equations for static characteristics of the measuring system are shown.

The very large machine tools now available for applications ranging from aerospace to composite material castings present a new set of challenges when trying to match the traditional machining accuracies of the mechanical workshop. An optical system for the automatic recalibration of the machine during the machining process has been developed. While conventional linear and rotary optical encoders are used to control axes positioning, and their resolution is already more than compliant with the needed accuracies, our optical system provides a further error signal during operation in order to compensate for structural deformations of axis and sliding parts. Those signals are used in order to reach a global positioning error vector under 50 microns on a 3-axis translation stage. The system has been installed on a test machine, with a total range on the 3-axis of 3, 1.6 and 1.2 meters. The device increases ranging measurement accuracy by decreasing the dependence of the position to the temperature variation and other deformations. To achieve such results, collimated diode lasers and 2D position-sensing devices have been installed to the machine. In order to provide signals which are least affected by electrical noise, transimpedance amplifiers and analog to digital converters have been integrated close to the detectors. The tests performed on the prototype demonstrate the capability of mapping the actual distance from the ideal linear translation with an error of 25 um along the full axis travel for a tracing capability of ±3.5 mm in both directions on each of the three detectors. This result is within the requirements of the end users, manufactures of travelling column type boring and milling machines.

Surface profile control on solar concentrators is fundamental since the mirror can be imperfectly manufactured. Optical profilometric measurements are generally addressed to detect small localised irregularities. The paper presents an optical profilometer for linear solar collectors, which are typically employed in thermal plants and more recently in concentrating photovoltaic systems. The profilometer includes a source of parallel rays and a target placed at the collector focal distance. It was developed simulating profile measurements on linear parabolic mirrors; then the method was validated by tests on a practical realisation. The device examines the reflector surface operating on a plane transversal to the linear collector axis; then the detection is repeated displacing the optical profilometer along the collector axis. This experimentation allowed to deeply examine and reduce the errors of the measurement procedure.

The semiconductor industry is aggressively pushed to produce smaller and smaller feature size from their existing base of lithography system, wavefront aberration should be derived by comparing ideal and real wavefronts at the wafer plane of a high resolution lithography system. We propose the IIWS (Integrated Interferometer Wavefront Sensor) system. On the base of traditional lateral shearing interferometer, two-dimensional phase-shifting shearing interferometry and vectorial optical analysis are used in this paper. By adjusting polarization state and polarization distribution, the metrology accuracy of the wavefront aberration of the system, which is significant for the modern semiconductor industry, is greatly increased.

Scanning white-light interferometry (SWLI) provides the capability of fast and high-precision three-dimensional measurement of surface topography. Nevertheless, it is well-known that white-light interferometers more than imaging microscopes suffer from chromatic aberration caused by the influence of dispersion. In this paper several interferometric measurement systems are used for surface topography measurement. A Linnik interferometer and two Michelson interferometers of different aberration correction are compared. A correction system designed using the ray tracing software “Zemax” aims at an optimization the modulation transfer function (MTF). Although the MTF is optimized the resulting spot diagrams are blurred due to chromatic aberration. Finally, a doubly corrected Michelson interferometer will be presented. For this interferometer a nearly optimal MTF as well as minimized spot diagrams are achieved.

This work aims at showing the applicability of a scanning-stage bench-microscope in bright-field reflection mode for wirebonding inspection of integrated circuits (IC) as well as quality assurance of tracks in printed circuit boards (PCB). The main issues of our laboratorial prototype arise from the use of a linear image sensor taking advantage of its geometry to achieve lower acquisition time in comparison to traditional (pinhole) confocal approach. The use of a slit-detector is normally related to resolution degradation for details parallel to sensor. But an improvement will surely arise using light distribution along line pixels of the sensor which establishes a great advantage in comparison to (pure) slit detectors. The versatility of this bench-microscope affords excellent means to develop and test algorithms. Those to improve lateral resolution isotropy as well as image visualization and 3D mesh reconstruction under different setups namely illumination modes. Based on the results of these tests tests both wide-field illumination and parallel slit illumination and detection configurations were used in these two applications. Results from IC wire-bonding show the ability of the system to extract 3D information. A comparison of auto-focus images and 3D profiles obtained using different 3D reconstruction algorithms as well as a method for the determination of the diameter of the bond wire are presented. Measurements of PCB track width and thickness were performed and the comparison of these results from both longitudinal and transverse tracks stress the limitations of a lower spatial sampling rate induced by the resolution of object stage positioners.

For the optical resolution measurement, the Modulation Transfer Function (MTF) is widely applied. This paper presents the RD result of our developed optical resolution measurement system with the slanted slit method for small lenses. The MTF is built up by the Fourier's transformation of the Line-Spread Function (LSF) that is acquired by analyzing the projected dark-bright image of the measured lens. In order to obtain a smooth LSF, we propose a slanted slit method. And the slanted slit lets a part of the collimated light transmit through the measured lens, and a dark-bright slit-image is projected on the CCD-camera. Through a proper selection of the region of interest (ROI), a smooth LSF with dense sampled data can be formed by arranging pixels according to their distances to the slanted slit. And these sampled data of the LSF can effectively eliminate the aliasing effect and furthermore can accurately derive the MTF. The influences of the angle of the slanted slit and the ROI-selection on the performance of this optical resolution measurement system are thoroughly studied. The accuracy of its processing algorithm is experimentally verified by using the statistic factors GRR and STD-error. Based on a calibrated lens, the developed processing system and algorithm can achieve the industrial level with GRR of 27% and STDerror of 8%.

Now the design and manufacture of large aperture optical lens are increasing emphasis on the influence of the gravity deformation of optical system. A compensation method of large aperture optical lens for gravity deformation is presented in this paper. The method analyses in advance and predicts the gravity deformation to compensate it in the processing stage. Taking the difficulties of machining into consideration, the spherical compensation mode is adopted and the compensation accuracy is given. The wave aberrations caused by gravity deformation before and after the compensation are compared and it proves that this method can effectively reduce the influence of gravity deformation though advance compensation.

Flat surfaces and the determination of their surface characteristics are of major importance in industry. The absolute measurement of them is a great challenge however. A solution for the Three-Flat-Test was proposed by Kuechel. His solution relies on four normal measurements where the three flats are interferometrically measured in different permutations and one where the test-piece flat is rotated with respect to the reference flat. As the solution is not exact the quality of the result depends on the number of integration steps taken for the fifth measurement. Kuechel has shown that for a 640 x 480 pixel CCD array 20 rotations are sufficient. Using his algorithm a interferometric-measurement accuracy on the order of lambda/100 is likely. In the present work it could be shown that the algorithm works with both high and low frequency errors, here represented by fractal and Zernike surfaces respectively. In a first practical test the algorithm retrieved the wavefront errors of three ZYGO transmission flats. The three flats were given to have accuracies of A = lambda/15, B = lambda/15 and C= lambda/ 20. The application of the algorithm resulted in accuracies of Aa = lambda/ 39, Ba = lambda/ 42 and Ca = lambda/ 40. This implies that all surfaces could be more accurately determined than given by the manufacturer! A rotation stage which can be turned more precisely and transmission flats of known better quality are however expected to lead to the measurement of higher accuracies in the range of lambda/100. Hence this procedure is likely to allow for cheap and fast absolute calibration of transmission flats.

This paper provides a general description of main issues related to the design of an optical measurement system applied to continuous displacement monitoring of long-span suspension bridges. The proposed system’s architecture is presented and its main components - camera and active targets - are described in terms of geometrical and radiometric characteristics required for long distance measurement of the tridimensional displacement of the stiffness girder in the middle section of the bridge’s central span. The intrinsic and extrinsic camera parameterization processes, which support the adopted measurement approach, are explained in a specific section. Since the designed measurement system is intended to perform continuous displacement monitoring in long distance observation framework, particular attention is given to environmental effects, namely, refraction, turbulence and sensor saturation phenomena, which can influence the displacement measurement accuracy. Finally, a measurement uncertainty method is discussed in order to provide a suitable solution for the determination of the accuracy related to the proposed measurement approach.

The aim of the paper is to discuss the concept of a method for non-invasive, in situ characterization of a glass fibre diameter. The method involves the use of low-coherence radiation as a measurement tool. The essence of the method is to influence the spectral properties of the incident light in such a way to obtain the scattered field at a small angle easy to explain both, from the physical as well as mathematical point of view. Some numerical examples demonstrate the properties of the scattered field. To obtain the fibre diameter, direct and reverse mathematical analysis will be introduced with the aid of a solution to the Huygens-Fresnel integral. An empirical research will be aimed to demonstrate some achievements in the formation and analysis of the filed scattered on an optical fibre.

Computer generated holograms (CGHs) are widely used in aspheric surface testing and metrology. The primary role of the CGHs is to generate any desired wavefronts to realize phase compensation. In order to eliminate alignment errors of CGH and the tested aspheric, this paper designs a new layout of CGH that has the advantages of high alignment accuracy and simple experimental operation. And further the influence of the location deviation of CGH and the tested aspheric mirror to the entire system is discussed; it shows that the error introduced by the CGH and the tested aspheric mirror tilting around the x-axis or y-axis as well as the tested aspheric mirror moving along the x-axis or y-axis direction is large. Then the CGH design principle and design process are reviewed. Finally, a CGH is designed for measurement of an aspheric mirror (diameter=226mm, F-number =2.2). Interferometric test results of an aspheric mirror show that the whole test system obtains the demanded high accuracy.

Deep penetration welding is a typical industrial application of high power lasers, where plasma can be generated above the keyhole. Thanks to the plasma plume presence welding process can be controlled on-line by means of the plasma intensity measurements. Various on-line monitoring methods have been developed in research centers all over the world. Goal of them is to enable promptly operator action to avoid enormous economical looses if un-expected defect is detected. Our laboratory was participated in project CLET - “Closed loop control of the laser welding process through the measurement of plasma” as a responsible partner for developed system testing both in the laboratory with pulsed Nd:YAG laser and in the real welding facility with high power continual CO₂ laser. Control system is based on the electron temperature computation from the relative intensities of couple of emission lines belong to certain metal ion present in plasma plume. Our experiment was realized using Ocean Optics HR2000+ spectrometer within the stainless steel tube longitudinal welding. Several couples of emission lines were tested to acquire a good signal at actual welding conditions. Then power calibration was made to obtain the electron temperature dependence on increasing power. Samples were prepared for microanalysis and measured by laser confocal scanning microscope to find optimal power range for full penetrations achieving without thermal distortion of the tube or weld humping. Numerical model of the remelted area cross section was made to display temperature distribution dependence on increasing power.

Optical vision systems have been developed gradually from wide field of view to all directional field of view for the purpose of security, surveillance, and teleconferencing. An omnidirectional image of optical vision systems is an image with 360 degrees field of view in the horizontal plane and wide field in the vertical plane. The fish-eye lens and the multiple cameras are typically used to get the omnidirectional image. In this paper, we designed and fabricated an omnidirectional camera lens system (OCLS) with a catadioptic system, which have as following several advantages; wide vertical field of view (+53 deg ~ -17 deg.), small size, low cost, ease of fabrication, and high resolution images.

X-ray inspection technique for foreign objects in food products can determine and mark the presence of contaminants within the product by using image processing and pattern recognition technique on the X-ray transmission images. This paper presents the dual view X-ray inspection technique for foreign objects in food jar via analyzing the weak points of the traditional single view X-ray inspection technique. In addition, a prototype with the new technique is developed in accordance with glass splinters detection within the food jar (glass jar especially) which is a typical tickler. Some algorithms such as: adaptive image segmentation based on contour tracking, nonlinear arctan function transform and etc., are applied to improve image quality and achieve effective inspection results. The false recognition rate is effectively reduced and the detection sensitivity is highly enhanced. Finally the actual test results of this prototype are given.

In this report, we propose a zero-method interferometer by means of dynamic generation of reference wave front using liquid crystal type spatial light modulator (LCoS-SLM). This interferometer was developed to aim to measure the shape of complex plane, such as aspherical plane. It is difficult for interferometer to measure such a surface which include large inclination, because of the problem of saturation of interference fringe. To overcome this problem, and to enlarge the dynamic range of interferometer, we attempted to combine interferometer and zero-method. Zero-method is characterized by its wide dynamic range. To apply zero-method to interferometer, SLM is adopted to configure variable reference surface. The basic configuration of the developed interferometer is Twyman-Green interferometer. A SLM is placed instead of reference mirror. In this interferometer, the shape of a target is measured using interference between object wave front and reference wave front that is generated using SLM. At first, the SLM generates flat wave front. And the detected phase map is fed back to the SLM. Then the difference between object wave front and detected phase map in the first turn. The operation is recursively repeated until the phase range of detected phase map becomes under the threshold. Then the generated wave front should become equal to the target shape. In this report, the basic idea of zeromethod interferometer using LCoS-SLM is verified through several numbers of simulative experiments.

Study is devoted to experimental research and development of absolute imaging position encoder based on standard calibrated scale of invar alloy with 1 mm spacing. The encoder uses designed imaging system as a vernier and absolute magnetic encoder as a rough indication. The features of optical design, choice and use of imaging system as long as indexes images processing algorithm are described. A shadow method was implemented: indexes images on a CCD array are formed by the lens focused at the scale surface; the laser module lights up the scale through a beam-splitting prism by a parallel beam. Further dark indexes images on a light scale background are detected and analyzed to estimate the encoder position. Full range of experimental tests was set to calibrate the encoder and to estimate the accuracy. As a result, accuracy close to 1 μm at 1 m was achieved.

In this paper we present a method for the characterization of (semi-transparent) thin film growth during PACVD processes (plasma assisted chemical vapour deposition), based on analysis of thermal radiation by means of nearinfrared imaging. Due to interference effects during thin film growth, characteristic emissivity signal variations can be observed which allow very detailed spatio-temporal analysis of growth characteristics (e.g. relative growth rates). We use a standard CCD camera with a near-infrared band-pass filter (center wavelength 1030 nm, FWHM 10nm) as a thermal imaging device. The spectral sensitivity of a Si-CCD sensor at 1μm is sufficient to allow the imaging of thermal radiation at temperatures above approx. 400°C, whereas light emissions from plasma discharges (which mainly occur in the visible range of the electromagnetic spectrum) barely affect the image formation.

In this paper we report on the progress in building the superresolution microscope using optical vortices. The outline of the general idea is presented. Some of the specific problems are discussed in more details. Specifically, the scanning method by vortex lens movement is discussed.

We present an image quality improvement using the speckle method in an in-line digital holography by means of a multi-mode fiber. In the proposed method, we use the speckle field emitted from the multi-mode fiber as both the reference wave and the wavefront illuminating the object. To capture multiple holograms, the speckle fields are changed by vibrating the multi-mode fiber using a vibrator. This method has an advantage in that the alignment of an optical setup becomes ease due to the introduction of an optical fiber and the speckle method can be readily performed by means of a vibrator.

This paper shows a portable device to measure mainly residual stress fields outside the optical bench. This system combines the traditional hole drilling technique with Digital Speckle Pattern Interferometry. The novel feature of this device is the high degree of compaction since only one base supports simultaneously the measurement module and the hole-drilling device. The portable device allows the measurement of non-uniform residual stresses in accordance with the ASTM standard. In oil and gas offshore industries, alternative welding procedures among them, the friction hydro pillar processing (FHPP) is highlighted and nowadays is an important maintenance tool since it has the capability to produce structure repairs without risk of explosions. In this process a hole is drilled and filled with a consumable rod of the same material. The rod, which could be cylindrical or conical, is rotated and pressed against the hole, leading to frictional heating. In order to assess features about the residual stress distribution generated by the weld into the rod as well as into the base material around the rod, welded samples were evaluated by neutron diffraction and by the hole drilling technique having a comparison between them. For the hole drilling technique some layers were removed by using electrical discharge machining (EDM) after diffraction measurements in order to assess the bulk stress distribution. Results have shown a good agreement between techniques.

The Large Millimeter Telescope (LMT) is a 50m diameter millimetre-wave radio telescope situated on the summit of Sierra Negra, Puebla, at an altitude of 4600 meters. The reflector surface of the LMT currently employs84 segments arranged in three annular rings. Each segment is comprised of 8 precision composite subpanels located on five threaded adjusters. During the current primary surface refurbishment, individual segments are aligned in the telescope basement using a laser tracker. This allows increased spatial resolution in shorter timescales, resulting in the opportunity for improved logistics and increased alignment precision. To perform segment alignment an iterative process is carried out whereby the surface is measured and subpanel deformations are corrected with the goal of 40 microns RMS. In practice we have been able to achieve RMS errors of almost 20 microns, with 35 microns typical. The number of iterations varies from around ten to over 20, depending mainly on the behaviour of the mechanical adjusters that support the individual subpanels. Cross marks scribed on the reflector surface are used as fiducials, because their positions on the paraboloid are well known. Measurement data is processed using a robust curve fitting algorithm which provides a map of the surface showing the subpanel deviations. From this map the required subpanel adjuster movements are calculated allowing surface improvement in a stepwise manner.

Limited depth of field (DOF) is one of the main shortage for many optical imaging systems. This is a limitation that precludes to get in focus, in a single plane, objects that are located at different distances, but that fall in the same field of view. Furthermore, the depth of field is reduced as much as greater is the requirement for a high magnification and to obtain an extended focus image (EFI) of these objects remains one of the major challenges. In this work we propose and compare two different approaches to build the EFI of holograms recorded on a tilted plane. In the first case, a simplified three-dimensional (3D) formulation of the angular spectrum method (ASM) is proposed. It allows to generate the entire stack of propagated images in a single shot. In the second approach, a numerical cubic phase plate (CPP) is included into the reconstruction process of digital holograms with the aim to enhancing DOF of optical imaging system. Theoretical formulations of the two approaches are supported by experimental evidences. The obtained results show that the proposed strategies allow to reconstruct effectively an EFI from holograms recorded on an inclined plane.

Images from coherent laser sources are severely degraded by a mixture of speckle and incoherent additive noise. In digital holography, Bayesian approaches reduce the incoherent noise, but prior information are needed about the noise statistics. On the other hand, non-Bayesian techniques presents the shortcomings of resolution loss or very complex acquisition systems, required to record multiple uncorrelated holograms to be averaged. Here we propose a fast non- Bayesian method which performs a numerical synthesis of a moving diffuser in order to reduce the noise. The method does not depend on prior knowledge of the noise statistics and the proposed technique is one-shot, as only one single hologram capture is required. Indeed, starting from a single acquisition multiple uncorrelated reconstructions are provided by random sparse resampling masks, which can be incoherently averaged. Experiments show a significant improvement, close to the theoretical bound. Noteworthy, this is achieved while preserving the resolution of the unprocessed image.

Characteristics of the system were studied in laboratory conditions. The research confirmed effectiveness of the considered angular deformation measurement system for large-size objects such as the primary mirror of a radio telescope.

To test an off-axis aspheric surface in high precision, a multiple combined computer generated hologram (CGH) is designed and fabrication. Multiple combined CGH which is a hologram including different areas with different purposes can not only measure off-axis aspheric surface, but also align every element in test system. The design methods of test CGH and alignment CGH were deduced in detail. Ray trace and B-spline were used to devise test CGH, reflection CGH was used to align interferometer and CGH, and hologram alignment mark was used to align CGH and off-axis aspheric surface. A design example was given to test an off-axis paraboloid with 50mm aperture and 35mm off-axis distance. Meanwhile, this CGH was fabricated and this paraboloid was measured by it. The test result (PV=0.305λ，RMS=0.042λ) is matched well with the outcome verified by autocollimation (PV=0.320λ，RMS=0.043λ). At last, we analyzed and solved the noise in the CGH test result. It proves that these designs are correct and this method can test off-axis aspheric surface in high precision.

The combination of fossil-derived fuels with ethanol and methanol has acquired relevance and attention in several countries in recent years. This trend is strongly affected by market prices, constant geopolitical events, new sustainability policies, new laws and regulations, etc. Besides bio-fuels these materials also include different additives as anti-shock agents and as octane enhancer. Some of the chemical compounds in these additives may have harmful properties for both environment and public health (besides the inherent properties, like volatility). We present detailed Raman spectral information from toluene (C₇H₈) and ethanol (C₂H₆O) contained in samples of ElO gasoline-ethanol blends. The spectral information has been extracted by using a robust, high resolution Fourier-Transform Raman spectrometer (FT-Raman) prototype. This spectral information has been also compared with Raman spectra from pure additives and with standard Raman lines in order to validate its accuracy in frequency. The spectral information is presented in the range of 0 cm^-1 to 3500 cm^-1 with a resolution of 1.66cm^-1. This allows resolving tight adjacent Raman lines like the ones observed around 1003cm^-1 and 1030cm^-1 (characteristic lines of toluene). The Raman spectra obtained show a reduced frequency deviation when compared to standard Raman spectra from different calibration materials. The FT-Raman spectrometer prototype used for the analysis consist basically of a Michelson interferometer and a self-designed photon counter cooled down on a Peltier element arrangement. The light coupling is achieved with conventional62.5/125μm multi-mode fibers. This FT-Raman setup is able to extract high resolution and frequency precise Raman spectra from the additives in the fuels analyzed. The proposed prototype has no additional complex hardware components or costly software modules. The mechanical and thermal disturbances affecting the FT-Raman system are mathematically compensated by accurately extracting the optical path information of the Michelson interferometer. This is accomplished by generating an additional interference pattern with a λ = 632.8 nm Helium-Neon laser (HeNe laser). It enables the FT-Raman system to perform reliable and clean spectral measurements from the materials under observation.

Over the past century there has been a dramatic increase in the demand for float glass in many fields of industry. Usually, 10 to 30% of produced float glass is coated with various coatings for different purposes. As a consequence quality control of the coatings is one of the most current issues during the process of float glass manufacturing. In this work we describe a system designed for the online control of reflectivity, transmittance and color coordinates of the coatings during the glass production process. The working principle of the system is based on the measurement of the spectral characteristics of reflectivity and transmittance of coatings within the 400-700 nm spectrophotometer spectral range during the online coating process. The measurement unit consists of two microspectrometers (one for the measurements of the spectral characteristics of the reference source, and the other for the measurements of the reflectance spectrum), illumination head (consisting of one white 1W LED and collimating lenses), stabilized power supply, microprocessor and 18 bits precision ADC. The use of the reference channel allows us to stabilize the intensity of the incident light up to 10-4 level. The repeatability of the measurement of reflectivity coefficient in laboratory conditions was in range of ± 0.001. However, in the measurements in the factory environment, due to the vibration of the glass ribbon on the conveyer, the measurement reproducibility was about ± 0.005.

Energetic sensitivity of a system with optical equisignal zone is considered in the paper. Energetic sensitivity is a criterion for choosing components of such a system and determines its potential accuracy. In calculation of this term only monochromatic radiation of sources in previous studies. As we are going to use dispersion method for air refraction influence attenuation, light sources of different wavelengths must be used. Because of dispersion in lenses of the objective the distribution of energetic sensitivity along the distance is different for wavelengths used, and the response of the receiver depends on the wavelength, too. Thus the term of energetic sensitivity is revised for a spectrum and spectral response of the sensor is taken into account. The suggestion of using of effective energetic sensitivity in preliminary assessment of system sensitivity is confirmed by experimental results.

In scanning probe microscopy laser interferometers are usually used for measuring the position of the probe tip with a metrological traceability. As the most of the AFM setups are designed to work under standard atmospheric conditions the changes of the refractive index of air have an influence to measured values of the length with 1.0exp(-4) relatively. In order to achieve better accuracies the refractive index of air has to be monitored continuously and its instantaneous value has to be used for compensating the lengths measured by all of the interferometric axes. In the presented work we developed a new concept of an electronic unit which is able to monitor the refractive index of air on basis of measurement of ambient atmospheric conditions: temperature, humidity, pressure of the air and the CO₂ concentration. The data processing is based on Ciddor equation for calculating the refractive index of air. The important advantage of the unit is a very low power consumption of the electronics so the unit causes only negligible temperature effects to the measured environment. The accuracy of the indirect measuring method employed by the unit was verified. We tested the accuracy in comparison with a direct method of measuring refractive index of air based on an evacuatable cell placed at the measuring arm of a laser interferometer. An experimental setup used for verification is presented together with a set of measurements describing the performance. The resulting accuracy of the electronic unit falls to the 4.1 exp(-7) relatively.

The Large Millimeter Telescope (LMT) currently employs a 32.5m diameter primary reflector composed of 84 surface segments. Global alignment of the surface is carried out using the best-fit parabola. Surface alignment follows an iterative procedure that consists of measuring the surface with a laser tracker to determine the deviations from the theoretical surface, followed by surface adjustments at the segment level. Global alignment of the primary surface presents many unusual problems related to the measurement of a large object in a non-metrology environment. The LMT antenna is located at high altitude (4700m, 15000ft) in a rural setting, where mean temperatures oscillate around zero degrees centigrade, thus presenting a challenge for traditional sensitive metrology equipment such as the laser tracker. Measurement of the antenna surface with the laser tracker requires the use of fiducial points that can be used to tie the measurement of each segment position to a common reference. Several approaches to the allocation of fiducial markers on and around the antenna are discussed in this paper. In-house data analysis provides a surface error and detailed output for the iterative adjustment of individual segments in order to reduce the global surface error. In this paper we discuss many aspects of the global alignment process with particular emphasis on making optimum use of laser tracker metrology.

This paper describes an iterative process of surface improvements made to the central 1.7m zone of a 2.5 metre hyperbolic reflector constructed of cast and machined aluminium. Throughout all stages of the process, the mirror surface was measured using a laser tracker, with initial maps taken by scanning the tracker target over the surface at low spatial resolution. While the overall RMS of the full surface was in excess of 200 microns, the central area of interest was in excess of 60 microns. The final goal of the program was to achieve 40 microns or better in this central area. Surface maps showed a major low area on the mirror surface covering many tens of square centimeters, plus several smaller high spots. The high spots were removed progressively by sanding with an orbital sander. Frequent pauses were made to take repeat surface measurements with the tracker. A total of 22 grinding iterations were interspersed with tracker measurements at differing spatial resolutions, allowing the RMS surface error to be reduced from 63 to 35 microns best measurement. Sanding periods lasted from 15 seconds to 4 minutes at each sanding spot, while tracker measurements took approximately 15-20 minutes to acquire from 600 data points (low spatial frequency) to 6800 points at high resolution. We present details of the surface improvement program with emphasis on the assurance of metrology integrity. We discuss data fitting to the desired hyperbolic shape, sampling strategies, identification of sanding zones, and tracker performance outside of operating environment specifications.

Multiscale parallel imaging--based on a monocentric optical design--promises revolutionary advances in diverse imaging applications by enabling high resolution, real-time image capture over a wide field-of-view (FOV), including sport broadcast, wide-field microscopy, astronomy, and security surveillance. Recently demonstrated AWARE-2 is a gigapixel camera consisting of an objective lens and 98 microcameras spherically arranged to capture an image over FOV of 120° by 50°, using computational image processing to form a composite image of 0.96 gigapixels. Since microcameras are capable of individually adjusting exposure, gain, and focus, true parallel imaging is achieved with a high dynamic range. From the integration perspective, manufacturing and verifying consistent quality of microcameras is a key to successful realization of AWARE cameras. We have developed an efficient testing methodology that utilizes a precisely fabricated dot grid chart as a calibration target to extract critical optical properties such as optical distortion, veiling glare index, and modulation transfer function to validate imaging performance of microcameras. This approach utilizes an AWARE objective lens simulator which mimics the actual objective lens but operates with a short object distance, suitable for a laboratory environment. Here we describe the principles of the methodologies developed for AWARE microcameras and discuss the experimental results with our prototype microcameras. Reference Brady, D. J., Gehm, M. E., Stack, R. A., Marks, D. L., Kittle, D. S., Golish, D. R., Vera, E. M., and Feller, S. D., “Multiscale gigapixel photography,” Nature 486, 386--389 (2012).

Although the laser interferometry represents the most precise class of techniques in the field of precise measurement of geometrical quantities, its wide use in measurement systems is still accompanied by many unresolved challenges. One of these challenges is the complexity of underlying optical systems. We present a novel approach to the interference phase detection - fringe subdivision - in the homodyne laser interferometry that aims at reduction of the optical complexity while the resolution is preserved. Our method employs a series of computational steps to infer a pair of signals in quadrature that allows to determine the interference phase with a sub-nanometre resolution from an interference signal from a non-polarising interferometer sampled by a single photodetector. The complexity trade-off is the use of laser beam with frequency modulation capability. The method was experimentally evaluated on a Michelson interferometer-based free-space setup and its performance has been compared to a traditional homodyne detection method. The results indicate the method is a feasible al­ ternative for the traditional homodyne detection since it performs with comparable accuracy (< 0.5nm standard deviation), especially where the optical setup complexity is principal issue and the modulation of laser beam is not a heavy burden, for instance in multi-axis measurement systems or laser diode based systems.

The goal of this work was to implement a low-cost machine vision system to help the roller operator to estimate the amount of strip camber during the rolling process. The machine vision system composing of a single camera, a standard PC-computer and a LabVIEW written program using straightforward image analysis determines the magnitude and direction of camber and presents the results both in numerical and graphical form on the computer screen. The system was calibrated with LED set-up which was also used to validate the accuracy of the system by mimicking the strip curvatures. The validation showed that the maximum difference between the true and measured values was less than ±4 mm (k=0.95) within the 22 meter long test pattern.

We present a non-contact low-cost displacement sensor based on plastic optical fiber (POF), designed for industrial applications. The proposed system is based on bifurcated fiber bundle (BFB) approach. The bundle is composed by a transmission fiber, used both to illuminate the target and collect backreflected power, and an additional receiving fiber that allows implementing target reflectivity and input power compensation. A Monte Carlo ray-tracing technique has been developed in order to evaluate system performance and tolerances to geometrical misalignments and target surface alteration. Experimental results show an accuracy of 0.04 mm on displacement readout, on the 0-1.2 mm range, assessing reflectivity compensation.

The advantages of digital holographic microscopy to record not only the intensity but also the optical phase are employed. The experimental arrangement comprises a Mach-Zehnder type interferometer with a microscopic objective of magnification 100x. The used camera is a 5 Mpixels Allied Vision Guppy Pro F-503 with a pixel pitch of 2.2 μm. The lateral magnification is set to about 200x based on the standard MIL-STD-150A 1951 USAF resolution test target. The dimensions of the aggregated natural cellulose nanowhisker fibers used are in the range of some hundreds of nanometers, which are positioned in the front of the microscopic objective using a 3D translation stage in the object arm of the holographic setup. The recorded off-axis holograms are refocused using the angular spectrum method. The reconstructed complex field is used to calculate optical phase and intensity distributions of the object at different reconstructions depths. The dimensions and orientation of the fibers can be evaluated from the optical field at different depths. Then, the shape and textures along the aggregated natural cellulose nanowhisker fiber can be presented in 3D space. The nano fiber found to have the dimensions of mean width 223 nm, depth 308 nm and length of 8.1 μm. Further, the mean local refractive index of the nano fibers can be calculated (n=1.501).

Coherence scanning interferometry (CSI) is an optical profilometry technique that uses the scanning of white light interference fringes over the depth of the surface of a sample to measure the surface roughness. Many different types of algorithms have been proposed to determine the fringe envelope, such as peak fringe intensity detection, demodulation, centroid detection, FFT, wavelets and signal correlation. In this paper we present a very compact and efficient algorithm based on the measurement of the signal modulation using a second-order nonlinear filter derived from Teager-Kaiser methods and known as the five-sample adaptive (FSA) algorithm. We describe its implementation in a measuring system for static surface roughness measurement. Two envelope peak detection techniques are demonstrated. The first one, using second order spline fitting results in an axial sensitivity of 25 nm and is better adapted to rough samples. The second one, using local phase correction, gives nanometric axial sensitivity and is more appropriate for smooth samples. The choice of technique is important to minimize artifacts. Surface measurement results are given on a silicon wafer and a metallic contact on poly-Si and the results are compared with those from a commercial interferometer and AFM, demonstrating the robustness of the FSA algorithm.

Traditional limitations of capacitive, inductive or discharging probe sensor for tip timing and tip clearance measurements are overcome by reflective intensity modulated optical fiber sensors. This paper presents the signals and results corresponding to a one stage turbine rig which rotor has 146 blades, obtained from a transonic wind-tunnel test. The probe is based on a trifurcated bundle of optical fibers that is mounted on turbine casing. It is composed of a central illuminating fiber that guides the light from a laser to the turbine blade, and two concentric rings of receiving fibers that collect the reflected light. Two photodetectors turn this reflected light signal from the receiving rings into voltage. The electrical signals are acquired and saved by a high-sample-rate oscilloscope. In tip clearance calculations the ratio of the signals provided by each ring of receiving fibers is evaluated and translated into distance. In the case of tip timing measurements, only one of the signals is considered to get the arrival time of the blade. The differences between the real and theoretical arrival times of the blades are used to obtain the deflections amplitude. The system provides the travelling wave spectrum, which presents the average vibration amplitude of the blades at a certain nodal diameter. The reliability of the results in the turbine rig testing facilities suggests the possibility of performing these measurements in real turbines under real working conditions.

We present an interferometric technique based on differential interferometry setup for measurement in the subnanometer scale in atmospheric conditions. One of the important limiting factors in any optical measurement are fluctuations of the refractive index of air representing a source of uncertainty traditionally compensated when the index is evaluated indirectly from the physical parameters of the atmosphere. Our proposal is based on the concept of overdetermined interferometric setup where a reference length is derived from a mechanical frame made from a material with very low thermal coefficient on the 1*E-8 level. The technique allows to track the variations of the refractive index of air on-line directly in the line of the measuring beam and to compensate for the fluctuations. The optical setup consists of three interferometers sharing the same beam path where two measure differentially the displacement while the third evaluates the changes in the measuring range acting as a tracking refractometer. The principle is demonstrated on an experimental setup and a set of measurements describing the performance is presented.

A scanning white light interferometer can characterize out of plane features and motion in M(N)EMS devices. Like any other form and displacement measuring instrument, the scanning interferometer results should be linked to the metre definition to be comparable and unambiguous. Traceability is built up by careful error characterization and calibration of the interferometer. The main challenge in this calibration is to have a reference device producing accurate and reproducible dynamic out-of-plane displacement when submitted to standard loads. We use a flat mirror attached to a piezoelectric transducer for static and (quasi)dynamic calibration of a stroboscopic scanning light interferometer. First we calibrated the piezo-scanned flexure guided transducer stage using a symmetric differential heterodyne laser interferometer developed at the Centre for Metrology and Accreditation (MIKES). The standard uncertainty of the piezo stage motion calibration was 3.0 nm. Then we used the piezo-stage as a transfer standard to calibrate our stroboscopic interferometer whose light source was pulsed at 200 Hz and 400 Hz with 0.5% duty cycle. We measured the static position and (quasi)dynamic motion of the attached mirror relative to a reference surface. This methodology permits calibrating the vertical scale of the stroboscopic scanning white light interferometer.

Digital holographic tomography, a computed tomography by use of digital holography, has a huge potential for three-dimensional imaging of weakly-diffracting phase objects. But the need of multiple angles of illumination weakened imaging capability of dynamic objects. For cylindrically symmetric object, we can use complex amplitude data of single hologram under zero incidence angles to replace the other complex amplitude data under different incidence angles. Therefore, it is possible to achieve the dynamic imaging of cylindrically symmetric objects. The digital holographic tomography can provide a way for the dynamic imaging of phase-type objects having a cylindrically symmetric structure. We report an experimental example of the capillary tube having a cylindrically symmetric structure. Tomography of the capillary tube is performed by filtered back-projection algorithm and Fourier diffraction algorithm respectively to reconstruct the 3-D map of refractive index. Experimental results show that, comparing with the filtered back-projection reconstruction, diffraction tomography based on the Rytov approximation better respects the dimensions of the capillary tube.

A frequency tripled Q-switched Nd-YAG laser (wavelength 355 nm, pulse duration 12 ns) has been used to pump Coumarin 153 dye solved in ethanol. The laser induced fluorescence (LIF) spectrum has been recorded using a spectrometer at different dye concentrations. The frequency doubled 532 nm beam from the same laser is used as a probe beam to pass through the excited volume of the dye. Because of stimulated emission an increase of the probe (532 nm) beam energy is recorded and a reduction of the spontaneous fluorescence spectrum intensity is observed. A model was developed that approaches the trend of the gain as a function of the probe beam energy at low dye concentrations (less than 0.08 g/L). The stimulated LIF is further recorded using digital holography. Digital holograms were recorded for different dye concentrations using collimated laser light (532 nm) passed through the dye volume. Two holograms without and with the UV laser beam were recorded. Intensity maps were calculated from the recorded digital holograms and are used to calculate the gain of the green laser beam due to the stimulated fluorescence emission which is coupled to the dye concentration. The gain of the coherent 532 nm beam is seen in the intensity maps and its value is about 40% for a dye concentration of 0.32 g/L and decreases with the decrease of the dye concentration. The results show that pulsed digital holography can be coupled to the stimulated LIF effect for imaging fluorescent species.

These days there are many real-time 3D measurement systems. Those method has finite exposure time, therefore the motion blur is inevitable in principle. We developed a motion deblurring technique in surface orientation images using a correlation image sensor for 1D movement by belt conveyor. This imaging system consists of two components; one is ring-shaped modulation illumination for encoding surface orientation into the amplitude and phase of the reflected light intensity, and the other is the three-phase correlation image sensor (3PCIS) for demodulating the amplitude and phase of reflected light. The higher spatial frequency components which is lost by motion are captured by modulation imaging using correlation image sensor. The reconstruction algorithm is proposed for modulation imaging picture which is complex value image representing surface orientation. We applied wiener filtering method, and then still normal vector image is successfully reconstructed.

We have designed and constructed the calibration system of line standards such as tape and rule for the secondary calibration laboratories. The system consists of the main body with linear stage and linear encoder, the optical microscope with digital camera, and the computer. The base of the system is a aluminum profile with 2.9 m length, 0.09 m height and 0.18 m width. The linear stage and the linear encoder are fixed on the aluminum profile. The micro-stage driven by micrometer is fixed on the carriage of the long linear stage, and the optical microscope with digital camera and the tablet PC are on the this stage. The linear encoder counts the moving distance of the linear stage with resolution of 1 μm and its counting value is transferred to the tablet PC. The image of the scale mark of the tape is captured by the CCD camera of optical microscope and transferred to the PC through USB interface. The computer automatically determines the center of the scale mark by image processing technique and at the same time reads the moving distance of the linear stage. As a result, the computer can calculate the interval between the scale marks of the tape. In order to achieve the high accuracy, the linear encoder should be calibrated using the laser interferometer or the rigid steel rule. This calibration data of the linear encoder is stored at the computer and the computer corrects the reading value of the linear encoder. In order to determine the center of the scale mark, we use three different algorithms. First, the image profile over specified threshold level is fitted in even order polynomial and the axis of the polynomial is used as the center of the line. Second, the left side and right side areas at the center of the image profile are calculated so that two areas are same. Third, the left and right edges of the image profile are determined at every intensity level of the image and the center of the graduation is calculated as an average of the centers of the left and right edges at all intensity levels. The system can measure the line standards up to 2.5 m. The expanded uncertainty for the tape calibration is U = [(0.04)²+ (0.015•L)²]^1/2 mm, where L is measured length of the tape or rule in meters. At this system, the long distance measuring instruments such as ultrasonic distance meter or laser displacement sensor can be also calibrated.

For today the development in lighting technologies, in particular the creation of powerful extended and multicomponent sources, occupies a leading position in the field of innovation. The development of mentioned lighting devices is not possible without providing of careful control for parameters and characteristics both of the each source’s emitting element and of the entire lighting device as a whole. There are many various devices and measuring complexes, intended for verification and evaluation of extended and multicomponent light sources parameters and characteristics. However, none of them enables the simultaneous analysis of the spatial distribution of illuminance, color and spectral characteristics as well as power settings parameters of extended or multicomponent light sources. This problem can be solved by using of automated hardware and software complex for extended light sources verification, developed by the employees of the chair of optical-electronic devices and systems of St.-Petersburg national research university of information technologies, mechanics and optics in Russia. The paper presents the theoretical and practical aspects of the extended and multicomponent light sources spectral and color characteristics analysis as well as the results of illuminance distribution investigation in three-dimensional space for some kinds of light sources. In addition, we present the experimental results of several types of extended and multicomponent light sources with different shape, order and quantity of the emitting elements, spectral and energy characteristics of the radiation.