This PDF file contains the front matter associated with SPIE Proceedings Volume 10329 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

This publication presents a novel interferometric method for the simultaneous measurement of the phase and state of polarization of a light wave with arbitrary, in particular locally varying elliptical polarization. The mea- surement strategy is based on variations of the reference wave concerning phase and polarization and processing the interference patterns so obtained. With this method, that is very similar to the classical phase shifting interferometry, a complete analysis of spatially variant states of polarization and their phase fronts can be done in one measurement cycle. Furthermore, a direct analysis of specimens under test regarding birefringence and the impact on the phase of the incoming light can be realized. The theoretical description of the investigated methods and their experimental implementation are presented.

This work investigates methods to eliminate calibration errors as one of the limiting factors to reduce measurement uncertainty in Tilted-Wave-Interferometry. The correlations between errors in the model parameters and in the measurement result are investigated, taking into account the symmetry of the surface under test. Two schemes for the elimination of such errors are introduced: Rotations around the z-axis allow the removal on non-rotationally symmetric error components. Measurements in lateral shears allow the elimination of calibration errors with higher spatial frequency. The corresponding algorithms and underlying models are explained for both approaches and examples for their application are presented.

High precision measurement of optical elements with long focal length is affected by vibration, airflow and other environmental factors due to the long cavity length, which has been difficulty and hot issue in optical machining and detection. In order to overcome the difficulties of high precision measurement of optical elements with long focal length, the paper proposes a full-field heterodyne interferometric measurement technique that could effectively suppress the environmental interference. In the early related research, a series of Hertz-level high-stability, low-differential frequency acousto-optic frequency shifters were successfully developed, which could be applied to heterodyne interferometry, instead of traditional phase-shifting intererometry. On this basis, a full-field heterodyne interference measurement system is developed, using array detector with conventional frame rate for full-field detection, to solve the problem of different optical paths of reference light and measuring light in dynamic interferometers. It could effectively suppress the vibration, noise, airflow and other factors, and thus significantly improve measurement accuracy and environmental adaptability. In typical environment with vibration and airflow, our measurement system can achieve technical indicators as follows: surface measurement accuracy is better than λ/1000 and repeated measurement accuracy is better than 5λ/10000. Thereby the new full-field heterodyne interferometry could be applied to dynamic measurement of large-diameter optical components and systems quality inspection, system installation correction, on-line measurement and other areas.

We demonstrate the voltage induced switching of single defect centers between its charge states. The individual charge states do show different emission wavelengths and are identified by their ground state spin properties.

We demonstrate a phase imaging method based on a single-pixel camera based on a complex-amplitude representation to measure a surface profile of objects. The use of the complex-amplitude representation of the input signal and the phaseshifting technique enables us to perform the phase imaging of an object, that is, the profilometry. The complex-amplitude mask can directly represent the Hadamard patterns that have the positive and negative values. The complex-amplitude masks are displayed on phase modulation mode liquid crystal on silicon spatial light modulator (LCOS-SLM). Furthermore, the residual area is used for the reference beam with the phase shifting. Therefore, the phase imaging system with the coaxial structure has high stability for external disturbances.

A spatial-temporal phase shifting interferometry is proposed to suppress the phase errors in dynamic Fizeau interferometer. The process of phase errors suppression in this interferometry includes three steps: (1) utilizing the spatial phase shifting interferometry to calculate the initial phase; (2) viewing all the effects of the error sources as a complex; (3) utilizing the temporal phase shifting interferometry to obtain multiple different initial phases and calculate the average phase. Experimentally, the phase errors are suppressed effectively and the measurement results are in good agreement with those obtained by Zygo GPI interferometer, which verifies that the proposed interferometry is a powerful tool for phase errors suppression in dynamic interferometer.

A common way to test high-quality aspherical lenses is to use a measurement system based on a set of null corrector and a laser interferometer. The null corrector can either be a combination of spherical lenses or be a computer generated hologram (CGH), which compensates the aspheric wave-front being tested. However, the null optics can’t be repeatedly used once the shape of tested optics changes. Alternative active null correctors have been proposed based on dynamic phase modulator devices. A typical dynamic phase modulator is liquid crystal spatial light modulator (LCSLM), which can spatially change the refractive index of the liquid crystal and thus modify the phase of the input wave-front. Even though the measurement method based on LCSLM and laser interferometer has been proposed and demonstrated for optical testing several years ago, it still can’t be used in the high quality measurement process due to its limited accuracy. In this paper, we systematically study the factors such as LCSLM structure parameters, encoding error and laser interferometer performance, which significantly affect the measurement accuracy. Some solutions will be proposed in order to improve the measurement accuracy based on LCSLM and laser interferometer.

This paper proposes a quality assessment of focusing criteria for imaging in digital off-axis holography. In literature, several refocus criteria have been proposed in the past to get the best refocus distance in digital holography. As a general rule, the best focusing plane is determined by the reconstruction distance for which the criterion function presents a maximum or a minimum. To evaluate the robustness of these criteria, a set of thirteen criteria is compared with application on both amplitude and phase images from off-axis holographic data. Experimental results lead to define general rule and to exhibit the most robust criteria for accurate and rapid refocusing in digital holography.

In this contribution, we propose a method of digital holographic microscopy (DHM) that enables measurement of high numerical aperture spherical and aspherical microstructures of both concave and convex shapes. The proposed method utilizes reflection of the spherical illumination beam from the object surface and the interference with a spherical reference beam of the similar curvature. In this case, the NA of DHM is fully utilized for illumination and imaging of the reflected object beam. Thus, the system allows capturing the phase coming from larger areas of the quasi-spherical object and, therefore, offers possibility of high accuracy characterization of its surface even in the areas of high inclination. The proposed measurement procedure allows determining all parameters required for the accurate shape recovery: the location of the object focus point and the positions of the illumination and reference point sources. The utility of the method is demonstrated with characterization of surface of high NA focusing objects. The accuracy is firstly verified by characterization of a known reference sphere with low error of sphericity. Then, the method is applied for shape measurement of spherical and aspheric microlenses. The results provide a full-field reconstruction of high NA topography with resolution in the nanometer range. The surface sphericity is evaluated by the deviation from the best fitted sphere or asphere, and the important parameters of the measured microlens: e.g.: radius of curvature and conic constant.

Multiwavelength digital holography on moving objects enables fast and precise inline-measurements of surface pro files. Due to the use of multiple wavelengths, optically rough surfaces with structure heights in the micrometer range can be mapped unambiguously. In this work we explore the influence of the object velocity on height measurements on inclined surfaces. We show measurements using spatial-phase-shifting holography employing two wavelengths and object velocities of up to 90 mm/s with eye-safe cw-lasers with less than 1 mW of laser light. Despite motion blur exceeding the mean speckle size, reliable height measurements can be conducted at these velocities. The height map of a metal cone with two different slope angles (1° , 10° ) is measured at an exposure time of 2 ms. Using line shaped illumination, each frame yields a height map of approximately 2 x 17 mm². The overlap between the frames allows averaging as the image is put together, improving data quality. The mean repeatability of the height information in the investigated setup is better than 4.5 µm at a synthetic wavelength of 214 µm.

In digital holography (DH), the coherent nature of the employed light sources severely degrades the holographic reconstructions due to a mixture of speckle and incoherent additive noise. These can affect both the visual quality in holographic imaging and display, and the accuracy of quantitative phase-contrast reconstructions. Typically, the noise problem is tackled by reducing the illumination coherence, thus the most intuitive way involves the recording of multiple uncorrelated holograms to be incoherently combined. This framework is known as Multi-Look DH (MLDH). However, single shot recordings are highly desirable in DH, and numerical methods are required to go beyond the improvement bound of ML techniques. Among the existing image processing methods, the 3D Block Matching filtering (BM3D) has shown the best performance. Here we present the MLDH-BM3D, a method specifically suitable to filter DH images that combines the two aforementioned strategies to overcome their respective limitations. We demonstrate the effectiveness of this framework in three different experimental situations, i.e. reconstructions of single wavelength holograms and color holograms in the visible region and the challenging case of the Infrared Radiation Digital Holography (IRDH) reconstructions, where a very severe noise degradation occurs.

In this paper we present a miniaturized digital holographic sensor (HoloCut) for operation inside a machine tool.
With state-of-the-art 3D measurement systems, short-range structures such as tool marks cannot be resolved inside a machine tool chamber. Up to now, measurements had to be conducted outside the machine tool and thus processing data are generated offline.
The sensor presented here uses digital multiwavelength holography to get 3D-shape-information of the machined sample. By using three wavelengths, we get a large artificial wavelength with a large unambiguous measurement range of 0.5mm and achieve micron repeatability even in the presence of laser speckles on rough surfaces. In addition, a digital refocusing algorithm based on phase noise is implemented to extend the measurement range beyond the limits of the artificial wavelength and geometrical depth-of-focus. With complex wave field propagation, the focus plane can be shifted after the camera images have been taken and a sharp image with extended depth of focus is constructed consequently.
With 20mm x 20mm field of view the sensor enables measurement of both macro- and micro-structure (such as tool marks) with an axial resolution of 1 µm, lateral resolution of 7 µm and consequently allows processing data to be generated online which in turn qualifies it as a machine tool control.
To make HoloCut compact enough for operation inside a machining center, the beams are arranged in two planes: The beams are split into reference beam and object beam in the bottom plane and combined onto the camera in the top plane later on. Using a mechanical standard interface according to DIN 69893 and having a very compact size of 235mm x 140mm x 215mm (WxHxD) and a weight of 7.5 kg, HoloCut can be easily integrated into different machine tools and extends no more in height than a typical processing tool.

A single-shot technique to measure areal profiles on optically smooth and rough surfaces and for applications in noncooperative environments is presented. It is based on hyperspectral interferometry (HSI), a technique in which the output of a white-light interferometer provides the input to a hyperspectral imaging system. Previous HSI implementations suffered from inefficient utilisation of the available pixels which limited the number of measured coordinates and/or unambiguous depth range. In this paper a >20-fold increase in pixel utilization is achieved through the use of a 2-D microlens array as proposed for integral field units in astronomy applications. This leads to a 35×35 channel system with an unambiguous depth range of 0.88 mm.

Process control of laser processes still encounters many obstacles. Although these processes are stable, a narrow process parameter window during the process or process deviations have led to an increase on the requirements for the process itself and on monitoring devices.

Laser transmission welding as a contactless and locally limited joining technique is well-established in a variety of demanding production areas. For example, sensitive parts demand a particle-free joining technique which does not affect the inner components.

Inline integrated non-destructive optical measurement systems capable of providing non-invasive tomographical images of the transparent material, the weld seam and its surrounding areas with micron resolution would improve the overall process. Obtained measurement data enable qualitative feedback into the system to adapt parameters for a more robust process.

Within this paper we present the inline monitoring device based on Fourier-domain optical coherence tomography developed within the European-funded research project “Manunet Weldable”. This device, after adaptation to the laser transmission welding process is optically and mechanically integrated into the existing laser system. The main target lies within the inline process control destined to extract tomographical geometrical measurement data from the weld seam forming process. Usage of this technology makes offline destructive testing of produced parts obsolete. ^1,2,3,4

Within the last decade, 3D printing has moved from a costly approach of building mechanical items to the present state-of-the-art phase where access to 3D printers is now common, both in industry and in private places. The plastic printers are the most common type of 3D printers providing prints that are light, robust and of lower cost.

The robustness of the structure printed is only maintained if each layer printed is properly fused to its previously printed layers. In situations where the printed component has to accomplish a key mechanical role there is a need to characterize its mechanical strength. This may only be revealed by in-depth testing in order to discover unwanted air-gaps in the structure.

Optical coherence tomography (OCT) is an in-depth imaging method, that is sensitive to variations in the refractive index and therefore can resolve with high resolution translucid samples.

We report on volume imaging of a 3D printed block made with 100% PLA fill. By employing ultrahigh resolution OCT (UHR-OCT) we show that some parts of the PLA volume reveal highly scattering interfaces which likely correspond to transitions from one layer to another. In doing so, we document that UHR-OCT can act as a powerful tool that can be used in detecting fractures between layers stemming from insufficient fusion between printed structure layers. UHR-OCT can therefore serve as an useful assessment method of quality of 3D prints.

The multiple layer paint systems on modern cars serve two end purposes, they firstly protect against corrosion and secondly give the desired visual appearance. To ensure consistent corrosion protection and appearance, suitable Quality Assurance (QA) measures on the final product are required. Various (layer thickness and consistency, layer composition, flake statistics, surface profile and layer dryness) parameters are of importance, each with specific techniques that can measure one or some of them but no technique that can measure all or most of them. Optical Coherence Tomography (OCT) is a 3D imaging technique with micrometre resolution. Since 2016, OCT measurements of layer thickness and consistency, layer composition fingerprint and flake statistics have been reported. In this paper we demonstrate two more novel applications of OCT to automotive paints. Firstly, we use OCT to quantify unwanted surface texture, which leads to an “orange peel” visual defect. This was done by measuring the surface profiles of automotive paints, with an unoptimised precision of 37 nm over lateral range of 7 mm, to quantify texture of less than 500 nm. Secondly, we demonstrate that OCT can measure how dry a coating layer is by measuring how fast it is still shrinking quasiinstantaneously, using Fourier phase sensitivity.

We propose Chromatic Confocal Coherence Tomography as a new system able to achieve corrected topography measurements of multi-layered specimens by measuring position, thickness and refractive index of each layer simultaneously at each measurement point. This feature is achieved by a combination of a chromatic confocal scheme and an interferometric one. The numerical aperture of the used microscope objective has a significant effect on the measurement uncertainty. Hence, its contribution to uncertainty is discussed in more detail.

Although coherence scanning interferometry (CSI) commonly achieves a sub-nanometre noise level in surface topography measurement, the absolute accuracy is difficult to determine when measuring a surface that contains varying local slope angles and curvatures. Recent research has shown that it is possible to use a single sphere with a radius much greater than the source wavelength to calibrate the three-dimensional transfer function of a CSI system. A major requirement is the accurate knowledge of the sphere radius, but the three-dimensional measurement of a sphere with nanometre level uncertainty is a highly challenging metrology problem, and is not currently feasible. Perfect spheres do not exist and every measurement has uncertainty. Without having a quantitative understanding of the tolerance of the sphere radius, the calibration method cannot be used confidently for calibration of the transfer function of a CSI system that may be used in research laboratories or industry. In this paper, the effects of the tolerance of the radius of the calibration sphere on surface topography measurements are quantitatively analysed through a computational approach. CSI measurements of spherical, sinusoidal and rough surfaces are investigated in the presence of various degrees of radius error. A lookup table that relates the surface height error as a function of the radius error and surface slope angle is provided. The users may estimate the required tolerances of the sphere radius for their specific surface measurements if this calibration approach is used. The output of this paper provides a feasibility analysis for this calibration method for further development and applications.

This paper gives an approach for the application of the principle of GOBO projection for underwater 3D measurement systems based on optical 3D scanners using stereo cameras. The GOBO projection principle is explained and the special challenges of underwater structured light projection using GOBO projection are discussed. The new principle was realized in a laboratory setup where camera and projection unit were placed outside a water tank. Several experiments were performed in order to estimate the necessary measurement conditions and parameters such as exposure time, camera lens apertures, measurement field size, and object distance. Additionally, selected different fringe patterns were applied and analyzed. First measurements were performed using a mobile 3D scanner and a GOBO projection unit.

Inline three-dimensional measurements are a growing part of optical inspection. Considering increasing production capacities and economic aspects, dynamic measurements under motion are inescapable. Using a sequence of different pattern, like it is generally done in fringe projection systems, relative movements of the measurement object with respect to the 3d sensor between the images of one pattern sequence have to be compensated.

Based on the application of fully automated optical inspection of circuit boards at an assembly line, the knowledge of the relative speed of movement between the measurement object and the 3d sensor system should be used inside the algorithms of motion compensation. Optimally, this relative speed is constant over the whole measurement process and consists of only one motion direction to avoid sensor vibrations. The quantified evaluation of this two assumptions and the error impact on the 3d accuracy are content of the research project described by this paper.

For our experiments we use a glass etalon with non-transparent circles and transmitted light. Focused on the circle borders, this is one of the most reliable methods to determine subpixel positions using a couple of searching rays. The intersection point of all rays characterize the center of each circle. Based on these circle centers determined with a precision of approximately 1=50 pixel, the motion vector between two images could be calculated and compared with the input motion vector. Overall, the results are used to optimize the weight distribution of the 3d sensor head and reduce non-uniformly vibrations. Finally, there exists a dynamic 3d measurement system with an error of motion vectors about 4 micrometer. Based on this outcome, simulations result in a 3d standard deviation at planar object regions of 6 micrometers. The same system yields a 3d standard deviation of 9 µm without the optimization of weight distribution.

The use of Digital Image Correlation has been generally limited to the estimation of mechanical properties and fracture behaviour at low to moderate strain rates. High speed cameras dedicated to ballistic testing are often used to measure the initial and residual velocities of the projectile but rarely for damage assessment. The evaluation of impact damage is frequently achieved post-impact using visual inspection, ultrasonic C-scan or other NDI methods. Ultra-high speed cameras and developments in image processing have made possible the measurement of surface deformations and stresses in real time during dynamic cracking. In this paper, a method is presented to correlate the force- displacement data from the sensors to the slow motion tracking of the transient failure cracks using real-time high speed imaging. Natural fibre reinforced composites made of flax fibres and polypropylene matrix was chosen for the study. The creation of macro-cracks during the impact results in the loss of stiffness and a corresponding drop in the force history. However, optical instrumentation shows that the initiation of damage is not always evident and so the assessment of damage requires the use of a local approach. Digital Image Correlation is used to study the strain history of the composite and to identify the initiation and progression of damage. The effect of fly-speckled texture on strain measurement by image correlation is also studied. The developed method can be used for the evaluation of impact damage for different composite materials.

Based on progress in the field of additive manufacturing optical components can now be printed with rapid prototyping technologies. In this contribution the possibilities of rapid prototyping for optical metrology are exemplified by the fabrication of miniaturized reflectors and the construction of a miniaturized metrology system designed for an industrial metrology application.

Focusing on the manufacturing and post processing steps the process chain to fabricate the miniaturized mirror is described. This includes an evaluation of the mirror based on roughness measurements. The reflectors are later utilized in a miniaturized sensor system to scan the interior of small pipes. The additively manufactured mirror is used in the metrology system to create a defined sampling signal within the cavity. Thereby the sensor system generates a point cloud of the internal surfaces using a 3D acquisition algorithm based on the laser triangulation principle. Part of this contribution will be the setup, the 3D acquisition and calibration principle as well as an evaluation of the metrology system. To optimize the point cloud acquisition three different hardware setups were designed using different cameras and calibration algorithms. These three approaches are evaluated and compared.

3D - Inline - Process - Control is getting more attention in any fields of manufacturing processes to increase productivity and quality. Sensor systems are necessary to capture the currently process status and are basement for Inline-Process- Control. The presented work is a possibility to get inline information’s about the additive manufacturing process Fused Filament Fabrication. The requirement is the ability to manipulate the machine code to get free field of view to the topside of the object after every manufactured layer. The adaptable platform layout makes possible to create different approaches for inline process control. One approach is the single camera layout from bird view to get 2,5D information’s about the manufactured object and the other one is the active stereoscopic camera layout with pattern projection. Both approaches are showing a possibility to get information’s of the manufactured object in process. Additional this cases allow a view inside the manufactured object and defects can be located. Deviations in the manufacturing process can be corrected and relevant parameters can be adapted during slicing process to increase the manufacturing quality.

In many application areas such as object reconstruction or quality assurance, it is required to completely or partly measure the shape of an object or at least the cross section of the required object region. For complex geometries, therefore, multiple views are needed to bypass undercuts respectively occlusions. Hence, a multi-sensor measuring system for complex geometries has to consist of multiple light-stripe sensors that are surrounding the measuring object in order to complete the measurements in a prescribed time. The number of sensors depends on the object geometry and dimensions. In order to create a uniform 3D data set from the data of individual sensors, a registration of each individual data set into a common global coordinate system has to be performed. Stateof- the-art registration methods for light-stripe sensors use only data from object intersection with the respective laser plane of each sensor. At the same time the assumption is met that all laser planes are coplanar and that there are corresponding points in two data sets. However, this assumption does not represent the real case, because it is nearly impossible to align multiple laser planes in the same plane. For this reason, sensor misalignments are neglected by this assumption. In this work a new registration method for light-stripe sensors is presented that considers sensor misalignments as well as intended sensor displacements and tiltings. The developed method combines 3D pose estimation and triangulated data to properly register the real sensor pose in 3D space.

Optical metrology using phase measurements has benefited significantly from the introduction of phase-shifting methods, first in interferometry, then also in fringe projection and fringe reflection. As opposed to interferometry, the latter two techniques generally use a spatiotemporal phase-shifting approach: A sequence of fringe patterns with varying spacing is used, and a phase map of each is generated by temporal phase shifting, to allow unique assignments of projector or screen pixels to camera pixels. One ubiquitous problem with phase-shifting structured-light techniques is that phase artefacts appear near regions of the image where the modulation amplitude of the projected or reflected fringes changes abruptly, e.g. near dirt/dust particles on the surface in deflectometry or bright-dark object colour transitions in fringe projection. Near the bright-dark boundaries, responses in the phase maps appear that are not plausible as actual surface features. The phenomenon has been known for a long time but is usually ignored because it does not compromise the overall reliability of results. In deflectometry, however, often the objective is to find and classify small defects, and of course it is then important to distinguish between bogus phase responses caused by fringe modulation changes, and actual surface defects. We present, for what we believe is the first time, an analytical derivation of the error terms, study the parameters influencing the phase artefacts (in particular the fringe period), and suggest some simple algorithms to minimise them.

We present a fringe projection system to measure glowing hot hybrid components in between production processes. For this a high power green light projector, based on TI DLP technology, is used to create the highest possible contrast between fringes on the red glowing specimen. It has a resolution of 1140 x 912 pixels with a maximum frame rate of 120 images per second for fast measurement. We use a green bandpass filter (525 nm) on the camera lens to block unwanted incoming radiation from the specimen caused by self-emission. Commercial measurement standards are not calibrated for temperatures other than 20° C, so they cannot be used to validate measurement data at the required temperatures of up to 1000°C since thermal expansion invalidates the geometry specification from the calibration data sheet. In our first development we use a uniformly heated pipe made of stainless steel as a dummy specimen to examine the measured geometry data. A pyrometer measures the temperature of the pipe so the expansion can be easily calculated using the thermal expansion coefficient. Different impact and triangulation angles are investigated to identify the effects of hot ambient air on the measurement. The impact of the induced refractive index gradient is examined to check the need for pre-processing steps in the measurement routine.

Recent digital technology allows binary patterns to be projected with a very high speed, which shows great potential for high-speed 3D measurement. However, how to retrieve an accurate phase with an even faster speed is still challenging. In this paper, an accurate and efficient phase retrieval technique is presented, which combines a Hilbert three-step phaseshifting algorithm with a ternary Gray code-based phase unwrapping method. The Hilbert three-step algorithm uses three squared binary patterns, which can calculate an accurate phase even under a slight defocusing level. The ternary Gray code-based method uses four binary patterns, which can unwrap a phase with a large number of fringe periods. Both simulations and experiments have validated its accuracy and efficiency.

In this paper we show that, by using a photogrammetry system with and without laser speckle, a large range of additive manufacturing (AM) parts with different geometries, materials and post-processing textures can be measured to high accuracy. AM test artefacts have been produced in three materials: polymer powder bed fusion (nylon-12), metal powder bed fusion (Ti-6Al-4V) and polymer material extrusion (ABS plastic). Each test artefact was then measured with the photogrammetry system in both normal and laser speckle projection modes and the resulting point clouds compared with the artefact CAD model. The results show that laser speckle projection can result in a reduction of the point cloud standard deviation from the CAD data of up to 101 μm. A complex relationship with surface texture, artefact geometry and the laser speckle projection is also observed and discussed.

Precise astronomical spectroscopy with the forthcoming E-ELT and its high resolution spectrograph HIRES will address a number of important science cases,1 e.g. detection of atmospheres of exoplanets. Challenging technical requirements have been identified to achieve these cases, principal among which is the goal to achieve a radial velocity precision on the order of 10 cms-1. HIRES will experience systematic errors like intrapixel variations and random variations like fiber noise, caused by the non-uniform illumination of the coupling fibers, with these and other systematic errors affecting the performance of the spectrograph. Here, we describe the requirements for the calibration sources which may be used for mitigating such systematic errors in HIRES. Precise wavelength calibration with wide-mode-spacing laser frequency combs (LFCs), so called astrocombs, has been demonstrated with different astronomical spectrographs. Here we present a comparison of currently used astrocombs and outline a possible solution to meet the requirements of HIRES with a single broadband astrocomb.

We present the design, architecture and results of the End-to-End simulator model of the high resolution spectrograph HIRES for the European Extremely Large Telescope (E-ELT). This system can be used as a tool to characterize the spectrograph both by engineers and scientists. The model allows to simulate the behavior of photons starting from the scientific object (modeled bearing in mind the main science drivers) to the detector, considering also calibration light sources, and allowing to perform evaluation of the different parameters of the spectrograph design. In this paper, we will detail the architecture of the simulator and the computational model which are strongly characterized by modularity and flexibility that will be crucial in the next generation astronomical observation projects like E-ELT due to of the high complexity and long-time design and development. Finally, we present synthetic images obtained with the current version of the End-to-End simulator based on the E-ELT HIRES requirements (especially high radial velocity accuracy). Once ingested in the Data reduction Software (DRS), they will allow to verify that the instrument design can achieve the radial velocity accuracy needed by the HIRES science cases.

Reflectance anisotropy spectroscopy (RAS) allows for in-situ monitoring of reactive ion etching (RIE) of monocrystalline III-V semiconductor surfaces. Upon use of RAS the sample to be etched is illuminated with broad-band linearly polarized light under nearly normal incidence. Commonly the spectral range is between 1.5 and 5.5 eV. Typically the spectrally resolved difference in reflectivity for light of two orthogonal linear polarizations of light is measured with respect to time - for example for cubic lattices (like the zinc blende structures of most III-V semiconductors) polarizations along the [110] and the [-110] direction. Local anisotropies on the etch front cause elliptical polarization of the reflected light resulting in the RAS signal. The time and photon energy resolved spectra of RAS include reflectometric as well as interferometric information. Light with wavelengths well above 100 nm (even inside the material) can be successfully used to monitor surface abrasion with a resolution of some tens of nanometers. The layers being thinned out act as optical interferometers resulting in Fabry-Perot oscillations of the RAS-signal. Here we report on RAS measurements assessing the surface deconstruction during dry etching. For low etch rates our experimental data show even better resolution than that of the (slow) Fabry-Perot oscillations. For certain photon energies we detect monolayer-etch-related oscillations in the mean reflectivity, which give the best possible resolution in etch depth monitoring and control, i.e. the atomic scale.

Photoacoustic/photothermal spectroscopy is an established technique for detection of chemicals and explosives. However, prior sample preparation is required and the analysis is conducted in a sealed space with a high-sensitivity sensor coupled with a lock-in amplifier, limiting the technique to applications in a controllable laboratory environment. Hence, this technique may not be suitable for defense and security applications where the detection of explosives or hazardous chemicals is required in an open environment at a safe standoff distance. In this study, chemicals in various forms were excited by an intensity-modulated quantum cascade laser (QCL), while a laser Doppler vibrometer (LDV) was applied to detect the vibration signal resulting from the photocoustic/photothermal effect. The photo-vibrational spectrum obtained by scanning the QCL’s wavelength in MIR range, coincides well with the corresponding spectrum obtained using typical FTIR equipment. The experiment in short and long standoff distances demonstrated that the LDV is a capable sensor for chemical detection in an open environment.

Three-dimensional (3D) Dammann confocal microscopy is proposed based on introducing 3D Dammann gratings into traditional confocal microscopy. The conventional confocal microscopy usually has a single focal point. Using threedimensional Dammann gratings, it shows a new confocal microscopy which could obtain three-dimensional information of object, therefore, novel Dammann-based microscopy should be developed for practical applications.

Micro-electro-mechanical system's (MEMS) applications have greatly expanded over the recent years, and the MEMS industry has grown almost exponentially. One of the strongest drivers are the automotive and consumer markets. A 100% test is necessary especially in the production of automotive MEMS sensors since they are subject to safety relevant functions. This inspection should be carried out before dicing and packaging since more than 90% of the production costs are incurred during these steps. An electrical test is currently being carried out with each MEMS component. In the case of a malfunction, the defect can not be located on the wafer because the MEMS are no longer optically accessible due to the encapsulation. This paper presents a low coherence interferometer for the topography measurement of MEMS structures located within the wafer stack. Here, a high axial and lateral resolution is necessary to identify defects such as stuck or bent MEMS fingers. First, the boundary conditions for an optical inspection system will be discussed. The setup is then shown with some exemplary measurements.

Confocal microscopes are widely used for areal measurements thanks to its good height resolution and the capability to measure high local slopes. For the measurement of large areas while keeping few nm of system noise, it is needed to use high numerical aperture objectives, move the sample in the XY plane and stitch several fields together to cover the required surface. On cylindrical surfaces a rotational stage is used to measure fields along the round surface and stitch them in order to obtain a complete 3D measurement. The required amount of fields depends on the microscope’s magnification, as well as on the cylinder diameter. However, for small diameters, if the local shape reaches slopes not suitable for the objective under use, the active field of the camera has to be reduced, leading to an increase of the required number of fields to be measured and stitched. In this paper we show a new approach for areal measurements of cylindrical surfaces that uses a rotational stage in combination with a slit projection confocal arrangement and a highspeed camera. An unrolled confocal image of the cylinder surface is built by rotating the sample and calculating the confocal intensity in the centre of the slit using a gradient algorithm. A set of 360º confocal images can be obtained at different heights of the sample relative to the sensor and used to calculate an unrolled areal measure of the cylinder. This method has several advantages over the conventional one such as no stitching required, or reduced measurement time. In addition, the result shows less residual flatness error since the surface lies flat in the measurement direction in comparison to field measures where the highest slope regions will show field distortion and non-constant sampling. We have also studied the influence on the areal measurements of wobble and run-out introduced by the clamping mechanism and the rotational axis.

Optical profilers are mature instruments used in research and industry to study surface topography features. Although the corresponding standards are based on simple step height measurements, in practical applications these instruments are often used to study the fidelity of surface topography.

In this context it is well-known that in certain situations a surface profile obtained by an optical profiler will differ from the real profile. With respect to practical applications such deviations often occur in the vicinity of steep walls and in cases of high aspect ratio.

In this contribution we compare the transfer characteristics of different 3D optical profiler principles, namely white-light interferometry, focus sensing, and confocal microscopy. Experimental results demonstrate that the transfer characteristics do not only depend on the parameters of the optical measurement system (e. g. wavelength and coherence of light, numerical aperture, evaluated signal feature, polarization) but also on the properties of the measuring object such as step height, aspect ratio, material properties and homogeneity, rounding and steepness of the edges, surface roughness. As a result, typical artefacts such as batwings occur for certain parameter combinations, particularly at certain height-to-wavelength ratio (HWR) values. Understanding of the mechanisms behind these phenomena enables to reduce them by an appropriate parameter adaption. However, it is not only the edge artefacts, but also the position of an edge that may be changed due to the properties of the measuring object.

In order to investigate the relevant effects theoretically, several models are introduced. These are based on either an extension of Richards-Wolf modeling or rigorous coupled wave analysis (RCWA). Although these models explain the experimental effects quite well they suffer from different limitations, so that a quantitative correspondence of theoretical modeling and experimental results is hard to achieve.

Nevertheless, these models are used to study the characteristics of the measured signals occurring at edges of different step height compared to signals occurring at plateaus. Moreover, a special calibration sample with continuous step height variation was developed to reduce the impact of unknown sample properties. We analyzed the signals in both, the spatial and the spatial frequency domain, and found systematic signal changes that will be discussed. As a consequence, these simulations will help to interpret measurement results appropriately and to improve them by proper parameter settings and calibration and finally to increase the edge detection accuracy.

Spatial bandwidth limitations frequently introduce large biases into the estimated values of RMS roughness and autocorrelation length that are extracted from topography data on random rough surfaces. The biases can be particularly severe for focus-variation microscopy data because of the technique’s spatial bandwidth limitations (limited lateral resolution and field-of-view). We recently developed a measurement protocol that greatly reduces the bias due to limited resolution[1]. In the present paper, we describe an extension of the protocol to correct for limited field-of-view, and present measurements on a series of commercial surface roughness comparator samples to validate the protocol. The protocol strictly applies to the case of surfaces that are isotropic, and whose topography displays an autocovariance function that is exponential, with a single autocorrelation length. However, we find that applying the protocol yields extracted values of roughness and autocorrelation length for each surface that are accurate and consistent among datasets obtained at different magnifications (i.e. among datasets obtained with different spatial bandpass limits), even for samples that are not in any way selected to conform to the model’s assumptions.

Microscopic surface topography measurement is an important aspect of industrial inspection. Optical and near field scanning techniques are increasingly replacing the use of the traditional mechanical stylus since they provide better lateral resolutions and higher measurement speeds. The main far field optical techniques used are interference microscopy and confocal microscopy, with the advantages of having larger fields of view and higher measurement speeds. Interference microscopy is now widely used, mainly because of its nanometric axial measurement sensitivity and its ease of use but suffers from a limitation in lateral resolution of about /2 due to diffraction. A new technique for high resolution 2D imaging using a microsphere placed on the sample has been recently combined with interferometry by several groups to greatly improve the lateral resolution. In this paper we present some of our own first results using glass microspheres with a white light Linnik interferometer and demonstrate a lateral resolution of /4 and an axial measurement sensitivity of several nm. Results are shown on calibrated square profile gratings with periods down to 400 nm, with a minimum feature size of 200 nm and a height of 148 nm and a field of view of several μm. While these features are not visible directly with the microscope objective, they become observable and measurable through the microsphere. An analysis using rigorous electromagnetic simulations is also given to help better understand the imaging properties of the technique. These first experimental and simulation results clearly indicate that this is an important new technique that opens new possibilities for surface metrology with a lateral resolution well beyond the diffraction limit.

Calibration, adjustment and verification of surface topography measuring instruments are important tasks, often facilitated by precision step-height specimens that have been calibrated using traceable metrology such as interferometry. Although standardized procedures for calculating parameters of the step-height are available for line profiling contact stylus systems, there is inconsistent guidance as to how to interpret step height data for 3D, areal surface topography instruments, such as confocal and interference microscopes. Here we provide definitions for the reference and measurement areas of step-height specimens as well as practical measurement protocols for processing the surface topography map.

The white-light scanning interferometer (WLSI) and confocal microscope (CM) are the two major optical inspection systems for measuring three-dimensional (3D) surface profile (SP) of micro specimens. Nevertheless, in practical applications, WLSI is more suitable for measuring smooth and low-slope surfaces. On the other hand, CM is more suitable for measuring uneven-reflective and low-reflective surfaces. As for aspect of surface profiles to be measured, the characteristics of WLSI and CM are also different. WLSI is generally used in semiconductor industry while CM is more popular in printed circuit board industry. In this paper, a self-assembled multi-function optical system was integrated to perform Linnik white-light scanning interferometer (Linnik WLSI) and CM. A connecting part composed of tubes, lenses and interferometer was used to conjunct finite and infinite optical systems for Linnik WLSI and CM in the self-assembled optical system. By adopting the flexibility of tubes and lenses, switching to perform two different optical measurements can be easily achieved. Furthermore, based on the shape from focus method with energy of Laplacian filter, the CM was developed to enhance the on focal information of each pixel so that the CM can provide all-in-focus image for performing the 3D SP measurement and analysis simultaneously. As for Linnik WLSI, eleven-step phase shifting algorithm was used to analyze vertical scanning signals and determine the 3D SP.

Super-resolution photonic nanojet interferometry is a new modality for 3D label-free super-resolution imaging. We present a comparative study of the photonic nanojet interaction with a polymer sample. We use numerical modelling to understand the interaction between a microsphere-induced photonic nanojet and the polymer sample. The numerical model employs the same set of input parameters (melamine formaldehyde microsphere with a diameter of 11 μm and a refractive index of 1.68), as in our experiments. The interaction is described using the Finite-Difference Time-Domain method applied on a finely discretized mesh. The knowledge gained using the verified and validated model, will be used to conduct numerical simulations in a wider parameter space. This enables optimizing the design of 3D-interferometric super-resolution microscopes.

By means of an interferometric line sensor system, the form of a specimen can be measured by stitching several overlapping circular subapertures to form one 3D topography. This concept is very flexible and can be adapted to many different specimen geometries. The sensor is based on a Michelson interferometer configuration that consists of a rapidly oscillating reference mirror in combination with a high-speed line-scan camera. Due to the overlapping areas, movement errors of the scan axes can be corrected.

In order to automatically adjust the line sensor in such a way that it is perpendicular to the measurement surface at a fixed working distance, a white-light interferometer was included in the line-based form-measuring system. By means of a fast white-light scan, the optimum angle of the sensor (with respect to the surface of the specimen) is determined in advance, before scanning the specimen using the line-based sinusoidal phase shifting interferometer. This produces accurate measurement results and makes it possible to also measure non-rotational specimens.

In this paper, the setup of the line-based form-measuring system is introduced and the measurement strategy of the sensor adjustment using an additional white-light interferometer is presented. Furthermore, the traceability chain of the system and the main error influences are discussed. Examples of form measurement results are shown.

State of the art optical systems become more complex. There are more lenses required in the optical design and optical coatings have more layers. These complex designs are prone to induce more thermal stress into the optical system which causes birefringence. In addition, there is a certain degree of freedom required to meet optical specifications during the assembly process. The mechanical fixation of these degrees of freedom can also lead to mechanical stress in the optical system and therefore to birefringence. To be able to distinguish those two types of stress a method to image the birefringence in the optical system is required. In the proposed setup light is polarized by a circular polarization filter and then is transmitted through a rotatable linear retarder and the tested optical system. The light then is reflected on the same path by a mirror. After the light passes the circular polarization filter on the way back, the intensity is recorded. When the rotatable retarder is rotated, the recorded intensity is modulated depending on the birefringence of the tested optical system. This modulation can be analyzed in Fourier domain and the linear retardance angle between the slow and the fast axis as well as the angle of the fast axis can be calculated. The retardance distribution over the pupil of the optical system then can be analyzed using Zernike decomposition. From the Zernike decomposition, the origin of the birefringence can be identified. Since it is required to quantify small amounts of retardance well below 10nm, the birefringence of the measurement system must be characterized before the measurement and considered in the calculation of the resulting birefringence. Temperature change of the measurement system still can produce measurement artifacts in the calculated result, which must also be compensated for.

Over the last two decades the use of single-frame interferometric techniques, known as Dynamic Interferometry, has become widely available in commercial interferometer systems and they have been used extensively in the production of state-of-the-art space-based optical systems. This paper presents an overview of the techniques and configurations used to build dynamic interferometers and measurement results for a variety of space-based optical components as well as the structures that hold them under simulated space-flight conditions. These techniques and configurations have applicability for many non-space applications as well.

Optical glasses with certain inner quality e.g. low striae content are essential for good optical systems. A stria is a small local change in the refractive index inside the glass resulting in a wave front distortion that can cause blurring of the image. During the production process of optical glass, striae are observed by measuring it with the so-called shadow graph method. This simple measurement displays a stria as a shadow on an observation screen. A human operator evaluates the contrast by comparing it with references. The new proposed approach uses a digital camera and image processing to measure human independent the stria level. A first repeatability measurement shows wave front deviation (maximum deviation, peak-topeak) of less than +/- 8 nm.

The increased range of manufacturable freeform surfaces offered by the new fabrication techniques is giving opportunities to incorporate them in the optical systems. However, the success of these fabrication techniques depends on the capabilities of metrology procedures and a feedback mechanism to CNC machines for optimizing the manufacturing process. Therefore, a precise and in-situ metrology technique for freeform optics is in demand. Though all the techniques available for aspheres have been extended for the freeform surfaces by the researchers, but none of the techniques has yet been incorporated into the manufacturing machine for in-situ measurement. The most obvious reason is the complexity involved in the optical setups to be integrated in the manufacturing platforms. The Shack-Hartmann sensor offers the potential to be incorporated into the machine environment due to its vibration insensitivity, compactness and 3D shape measurement capability from slope data. In the present work, a measurement scheme is reported in which a scanning Shack-Hartmann Sensor has been employed and used as a metrology tool for measurement of freeform surface in reflection mode. Simulation studies are conducted for analyzing the stitching accuracy in presence of various misalignment errors. The proposed scheme is experimentally verified on a freeform surface of cubic phase profile.

The manufacture of mirrors for space application is expensive and the requirements on the optical performance increase over years. To achieve higher performance, larger mirrors are manufactured but the larger the mirror the higher the sensitivity to temperature variation and therefore the higher the degradation of optical performances. To avoid the use of an expensive thermal regulation, we need to develop tools able to predict how optics behaves with thermal constraints. This paper presents the comparison between experimental surface mirror deformation and theoretical results from a multiphysics model. The local displacements of the mirror surface have been measured with the use of electronic speckle pattern interferometry (ESPI) and the deformation itself has been calculated by subtracting the rigid body motion. After validation of the mechanical model, experimental and numerical wave front errors are compared.

Speckle interferometry is an optical metrology technique for characterizing rough surfaces. In one application, the deformation of a specimen under a load may be determined by comparing measurements before and after the load is applied. Owing to the surface roughness, however, the results are impaired by phase singularities, leading to a strong noise in the measurement results. Usually, filtering and smoothing operations are performed to reduce the noise. However, these procedures also affect the underlying systematic phase and are therefore disadvantageous. Instead, we examine incoherent averaging, a physical procedure, to reduce the number of phase singularities in the first place. We tailor the spatial coherence of the light using extended light sources of continuous or multipoint shape, achieving smoother phase distributions. The mechanism behind the reduction process involves subtle effects like enhancing phase singularity correlations in the fields before and after the deformation takes place.

The analysis of materials and geometries in tensile tests and the extraction of mechanic parameters is an important field in solid mechanics. Especially the measurement of thickness changes is important to obtain accurate strain information of specimens under tensile loads. Current optical measurement methods comprising 3D digital image correlation enable thickness-change measurement only with nm-resolution. We present a phase-shifting electronic speckle-pattern interferometer in combination with speckle-correlation technique to measure the 3D deformation. The phase-shift for the interferometer is introduced by fast wavelength tuning of a visible diode laser by injection current. In a post-processing step, both measurements can be combined to reconstruct the 3D deformation. In this contribution, results of a 3Ddeformation measurement for a polymer membrane are presented. These measurements show sufficient resolution for the detection of 3D deformations of thin specimen in tensile test. In future work we address the thickness changes of thin specimen under tensile loads.

Surface micro topography measurement (e.g., form, waviness, roughness) is a precondition to assess the surface quality of technical components with regard to their applications. Well defined, standardized measuring devices measure and specify geometrical surface textures only under laboratory conditions. Laser speckle-based roughness measurement is a parametric optical scattered light measuring technique that overcomes this confinement. Field of view dimensions of some square millimeters and measuring frequencies in the kHz domain enable in-process roughness characterization of even moving part surfaces. However, camera exposure times of microseconds or less and a high detector pixel density mean less light energy per pixel due to the limited laser power. This affects the achievable measurement uncertainty according to the Heisenberg uncertainty principle. The influence of fundamental, inevitable noise sources such as the laser shot noise and the detector noise is not quantified yet. Therefore, the uncertainty for speckle roughness measurements is analytically estimated. The result confirms the expected inverse proportionality of the measurement uncertainty to the square root of the illuminating light power and the direct proportionality to the detector readout noise, quantization noise and dark current noise, respectively. For the first time it is possible to quantify the achievable measurement uncertainty u(Sa) < 1 nm for the scattered light measuring system. The low uncertainty offers ideal preconditions for in-process roughness measurements in an industrial environment with an aspired resolution of 1 nm.

The deformation measurement method by using only two speckle patterns has been proposed in ESPI (electronic speckle pattern interferometry) by using Fourier transform. Furthermore, three-dimensional deformation of the object was able to be measured with the same sensitivities in each direction of three-dimensional axis. However, the measurement results of a complex shape deformation are not always a smooth distribution of phase map. It can be thought that this trouble is caused from the effect of speckle noise which is included in speckle pattern. In this paper, the solution of the problem concerning the speckle noise is investigated. The degradation of measurement accuracy in speckle interferometry is caused by some speckle noise. The speckle noise influences the bias component and the amplitude of the speckle pattern. Furthermore, the spatial movement of speckles of speckle-pattern during the deformation process also influences into the measurement accuracy. In this paper, the pre-treatment for the speckle interferometry is proposed in order to reduce such influence by speckle noise. In the experimental results, it is confirmed that the influence of speckle noise can be reduced by using the features of the reference and the object beams’ intensity distributions in interference measurement process. The proposed method can reduce the influence of speckle noise to 1/1000 in comparing with the results of conventional method. The validity of the proposed method in the practical operation is confirmed from the experiments.

The residual stress of the glass substrate might be one of causes to produce the non-uniform light distribution defect, i.e. Mura, in thin film transistor-liquid crystal display (TFT-LCD) panels. Glass is a birefringent material with very low birefringence. Furthermore, the thinner and thinner thickness request from the market makes the traditional photoelasticity almost impossible to measure the residual stresses produced in thin glass plates. Recently, a low-level stress measurement method called transmissivity extremities theory of photoelasticity (TEToP) was successfully developed to measure the residual stress in glass plate. Besides, to measure the stress of the glass plate in the TFT-LCD panel whose rear surface may has different kinds of coatings, an advanced reflection photoelasticity was also developed. In this paper, three commercially available glass plates with 0.33mm nominal thickness and three glass circular disks with different coatings were inspected to verify the feasibility of the TEToP and the advanced reflection photoelasticity, respectively.

The precision of measurements as well as the need for precise measurements are increasing more and more. Thus, the importance of a good calibration of a setup is increasing, too. In the world of topography measurement a huge variety of techniques are available. Some of these techniques are using known shadow patterns reflected by the device under test (DUT). The reflected patterns are recorded using a camera with imaging optics. From the changes of the patterns, the topography can be resolved. Other measurement techniques are using a tactile sensing head, which is in contact with the surface to determine its topography. However, these techniques need a reference surface to calibrate movements. If this reference surface presents deviations from its expected form, errors are introduced.
We have developed a calibration method for reflective surface measurements based on experimental ray tracing (ERT) without the need of a reference surface. In our measurement setup, a narrow laser beam introduced in the measurement under a certain angle is reflected by the device under test. After the reflection the position and the direction of the ray in terms of the coordinate system of the camera is detected. Thus, no errors are introduced by using an additional imaging optic. To calibrate position and direction of the incident ray in respect to the coordinate system of the camera, the reflected rays from the measurement are used only. From these rays, the incident ray is determined by detecting the line, all reflected rays are intersecting with. This leads to two major advantages. First, there is no calibration run needed, since the measurement data can be used directly for the calibration. Second, for the calibration no well-known reference surface is needed. However, some regulations have to be considered for a stable process of this calibration method. In terms of peak-to-valley values of the sag of the surface as well as of the change of the surface slope, the surface has to show values deviating from zero. If a surface like this is measured, a separate measurement run can be performed using another surface fulfilling these requirements. Since the DUT is scanned by moving the DUT itself, the position and the direction of the incident ray is not changed from one measurement to another and can be reused. We describe the newly introduced calibration method for the incident ray in detail and present the necessary boundary conditions. The calibration has been tested using simulations and has been implemented in a measurement setup. Within this measurement setup, the expected performance resulting from the simulations has been examined.

A shearing interferometer combined with an LED multispot illumination provides a high flexibility form characterization of optical surfaces as it is needed for aspheres and freeforms. Core element of the setup is the spatial light modulator as shearing element (SLM). Error influences due to the used blazed grating of the SLM need to be investigated. We show results of wavefront measurements with a Shack-Hartmann sensor which demonstrate residual structures of the grating at the wavefront under test. Additionally, simulated data are compared to the measurements to get a better understanding of the expected effects. These investigations help to correct the wavefront under test for this static error and improve the accuracy of the form characterisation.

This work presents the development of a special shearography system with radial sensitivity and explores its applicability for detecting adhesion flaws on internal surfaces of joints of composite material pipes. The system uses two conical mirrors to achieve radial sensitivity. A primary 45° conical mirror is responsible for promoting the inspection of the internal surface all way around 360°. A special Michelson-like interferometer is formed replacing one of the plane mirrors by a conical mirror. The image reflected by this conical mirror is shifted away from the image center in a radial way and a radial shear is produced on the images. The concept was developed and tested. Two tubular steel specimens internally coated with composite materials and having known artificial defects were analyzed to test the ability of the system to detect the flaws. The system presented very good results on all inspected specimens. The experimental results obtained in this work are promising and open a new front for inspections of inner surfaces of composite pipes with shearography.

We demonstrate an alternative approach to determination of the third order elastic moduli of materials based on registration of nonlinear bulk strain waves in three basic structural waveguides (rod, plate and shell) and further calculation of the Murnaghan moduli from the recorded wave parameters via simple algebra. These elastic moduli are available in literature for a limited number of materials and are measured with considerable errors, that evidences a demand in novel approaches to their determination.

Over the last few years, fiber optic sensors (FOS) have seen an increased acceptance and widespread use in industrial sensing and in structural monitoring in civil, aerospace, marine, oil & gas, composites and other applications. One of the most prevalent types in use today are fiber Bragg grating (FBG) sensors. Historically, FOS have been an attractive solution because of their EM immunity and suitability for use in harsh environments and rugged applications with extreme temperatures, radiation exposure, EM fields, high voltages, water contact, flammable atmospheres, or other hazards.

FBG sensors have demonstrated that can operate reliably in many different harsh environment applications but proper type and fabrication process are needed, along with suitable packaging and installation procedure. In this paper, we review the impact that external factors and environmental conditions play on FBG’s performance and reliability, and describe the appropriate sensor types and protection requirements suitable for a variety of harsh environment applications in industrial furnaces, cryogenic coolers, nuclear plants, maritime vessels, oil & gas wells, aerospace crafts, automobiles, and others.

Flow rate measurements are a common topic for process monitoring in chemical engineering and food industry. To achieve the requested low uncertainties of 0:1% for flow rate measurements, a precise measurement of the shear layers of such flows is necessary. The Laser Doppler Velocimeter (LDV) is an established method for measuring local flow velocities. For exact estimation of the flow rate, the flow profile in the shear layer is of importance. For standard LDV the axial resolution and therefore the number of measurement points in the shear layer is defined by the length of the measurement volume. A decrease of this length is accompanied by a larger fringe distance variation along the measurement axis which results in a rise of the measurement uncertainty for the flow velocity (uncertainty relation between spatial resolution and velocity uncertainty). As a unique advantage, the laser Doppler profile sensor (LDV-PS) overcomes this problem by using two fan-like fringe systems to obtain the position of the measured particles along the measurement axis and therefore achieve a high spatial resolution while it still offers a low velocity uncertainty. With this technique, the flow rate can be estimated with one order of magnitude lower uncertainty, down to 0:05% statistical uncertainty.¹ And flow profiles especially in film flows can be measured more accurately. The problem for this technique is, in contrast to laboratory setups where the system is quite stable, that for industrial applications the sensor needs a reliable and robust traceability to the SI units, meter and second. Small deviations in the calibration can, because of the highly position depending calibration function, cause large systematic errors in the measurement result. Therefore, a simple, stable and accurate tool is needed, that can easily be used in industrial surroundings to check or recalibrate the sensor. In this work, different calibration methods are presented and their influences to the measurement uncertainty budget of the sensor is discussed. Finally, generated measurement results for the film flow of an impinging jet cleaning experiment are presented.

A non-contact speckle correlation sensor for the measurement of robotic tool speed is presented for use in robotic manufacturing and is capable of measuring the in-plane relative velocities between a robot end-effector and the workpiece or other surface. The sensor performance was assessed in the laboratory with the sensor accuracies found to be better than 0:01 mm/s over a 70 mm/s velocity range. Finally an example of the sensors application to robotic manufacturing is presented where the sensor was applied to tool speed measurement for path planning in the wire and arc additive manufacturing process using a KUKA KR150 L110/2 industrial robot.

The characterization of modern jet engines or stationary gas turbines running with lean combustion by means of swirl-stabilized flames necessitates seedingless optical field measurements of the flame transfer function, i.e. the ratio of the fluctuating heat release rate inside the flame volume, the instationary flow velocity at the combustor outlet and the time average of both quantities. For this reason, a high-speed camera-based laser interferometric vibrometer is proposed for spatio-temporally resolved measurements of the flame transfer function inside a swirl-stabilized technically premixed flame. Each pixel provides line-of-sight measurements of the heat release rate due to the linear coupling to fluctuations of the refractive index along the laser beam, which are based on density fluctuations inside the flame volume. Additionally, field measurements of the instationary flow velocity are possible due to correlation of simultaneously measured pixel signals and the known distance between the measurement positions. Thus, the new system enables the spatially resolved detection of the flame transfer function and instationary flow behavior with a single measurement for the first time. The presented setup offers single pixel resolution with measurement rates up to 40 kHz at an maximum image resolution of 256 px x 128 px. Based on a comparison with reference measurements using a standard pointwise laser interferometric vibrometer, the new system is validated and a discussion of the measurement uncertainty is presented. Finally, the measurement of refractive index fluctuations inside a flame volume is demonstrated.

In nowadays industry, complex surfaces with material contrasts or surface coatings are present and represent a challenge for optical topography measuring instruments. The reason is that varying optical properties lead to phase jumps and to topography deviations when the surface height is evaluated. Thus, Ellipso-Height-Topometry as a measurement technique which can measure both topography and material properties of technical surfaces was proposed in order to achieve a correction of the occurring topographic artefacts. The height correction value can be obtained for the compensation of material-induced height deviations and the thickness of surface layers can be evaluated. Currently, it is possible to calculate the surface characteristics from ellipsometric parameters for at most two layers. However, the described height corrections are only possible when well-defined and realistic models of surface layers can be utilized, e.g. a given set of homogeneous oxide layers. Oxidation effects however describe statistical processes which can be predicted with underlying material distribution models. This leads to an uncertainty in ellipsometry, which is considered with a new approach that will be discussed in this publication. Therefore, an extended multi-layer approach which is capable of handling additional layers based on a parallelized algorithm using graphic processing units and the commonly known CUDA technology is proposed. This algorithm can also be used to consider material proportions which result from oxidation effects in z direction. The new approach for the Ellipso-Height-topometry measurement technique is compared with the current procedures which often neglect the existence of an oxide layer for the basic material. To experimentally verify the approach and according algorithm, it is applied for the evaluation of actual surfaces with multiple plane layers and different materials. Test samples with different materials are used in order to evaluate the complex refractive index, the distribution of identified materials and the layer thicknesses with actual Ellipso-Height- Topometry measurements. The results of the measurements are compared to the predicted theoretical results.

In-situ 3-D shape measurements with submicron shape uncertainty of fast rotating objects in a cutting lathe are expected, which can be achieved by simultaneous distance and velocity measurements. Conventional tactile methods, coordinate measurement machines, only support ex-situ measurements. Optical measurement techniques such as triangulation and conoscopic holography offer only the distance, so that the absolute diameter cannot be retrieved directly. In comparison, laser Doppler distance sensors (P-LDD sensor) enable simultaneous and in-situ distance and velocity measurements for monitoring the cutting process in a lathe. In order to achieve shape measurement uncertainties below 1 μm, a P-LDD sensor with a dual camera based scattered light detection has been investigated. Coherent fiber bundles (CFB) are employed to forward the scattered light towards cameras. This enables a compact and passive sensor head in the future. Compared with a photo detector based sensor, the dual camera based sensor allows to decrease the measurement uncertainty by the order of one magnitude. As a result, the total shape uncertainty of absolute 3-D shape measurements can be reduced to about 100 nm.

Dynamic fibre-optic curvature sensing using fibre segment interferometry is demonstrated using a cost-effective rangeresolved interferometry interrogation system. Differential strain measurements from four fibre strings, each containing four fibre segments of gauge length 20 cm, allow the inference of lateral vibrations as well as the direction of the vibration of a cantilever test object. Dynamic tip displacement resolutions in the micrometre range over a 21 kHz interferometric bandwidth demonstrate the suitability of this approach for highly sensitive fibre-optic directional vibration measurements, complementing existing laser vibrometry techniques by removing the need for side access to the structure under test.

A new method for precise subpixel edge estimation is presented. The principle of the method is the iterative image approximation in 2D with subpixel accuracy until the appropriate simulated is found, matching the simulated and acquired images. A numerical image model is presented consisting of three parts: an edge model, object and background brightness distribution model, lens aberrations model including diffraction. The optimal values of model parameters are determined by means of conjugate-gradient numerical optimization of a merit function corresponding to the L2 distance between acquired and simulated images. Computationally-effective procedure for the merit function calculation along with sufficient gradient approximation is described. Subpixel-accuracy image simulation is performed in a Fourier domain with theoretically unlimited precision of edge points location. The method is capable of compensating lens aberrations and obtaining the edge information with increased resolution. Experimental method verification with digital micromirror device applied to physically simulate an object with known edge geometry is shown. Experimental results for various high-temperature materials within the temperature range of 1000°C..2400°C are presented.

Smaller and lighter optical systems with better performance can be built by the use of freeform optics. However, most optical systems were constrained to traditional surfaces for the accurate metrology of freeform surface is a challenge so far unsolved. One high-precision approach to measure freeform surface with less time and expense is using tilted wave interferometer. A lens array is placed in the test path of the interferometer, which can generate light source array that locally compensate the gradient of test surface. But each source generated by lens array is not ideal spherical wave which contains aberrations. In addition, the sources cannot be activated individually during the measurement, so that it is impossible to perform an irregular source array according to the gradient variation of each test surface. Thus, a novel technique based on fiber array is proposed for generating irregular source array. Whereas, the position deviation of each fiber and phase difference produced by the length of each fiber affect the measurement result. In this paper, the consequences of above errors are analyzed. A calibration method can obtain the exact spatial coordinates of each fiber is suggested to calculate the position deviation of each fiber. Meanwhile, a method based on Mach-Zehnder interference system is presented, which can get phase difference produced by the length of each fiber accurately. Afterwards, the data obtained by the two calibration methods are introduced into the mathematical model of system error for eliminating the measurement error introduced by the use of fiber array. An elliptical mirror is measured by our tilted wave interferometer based on fiber array showing the feasibility of the proposed methods.

The conjugate differential method has been applied to the absolute test of flat, cylindrical, and axicon surfaces. In the previous work, simulations and correspond experiments have been carried out to verify the feasibility of the method. To analyze the influences of different factors upon the measurement result, the conjugate differential method is discussed in detail. Considering the characteristics of the test surface such as surface types and surface profiles, the application ranges of the conjugate differential method are discussed into three parts. According to the three surface types using the conjugate differential method, the method can be extended to the absolute test of the spherical surfaces based on spherical coordinate system. The reconstructed errors caused by different aberrations expressed as Zernike polynomial terms show that they are more sensitive to high order aberration terms of the surface under test. And for surfaces with different frequency distributions, the surface with less mid-spatial frequency information is less sensitive to the sampling frequency. The influence from the other factors in interferometric test are also discussed into three parts. The influences from the uncertainty of shifts are correlated with the increased aperture diameters, since the integration error caused by the shift error increases gradually with the expanding of the integration path. The integration error changes by the influences from the coherent noise and pixel noise related to pixel deviations. The reconstructed deviations get increased while the peak pixel deviation is increasing. For the balance of the differential deviation and integration error, the optimization of sampling resolution should take considered for accuracy improvement.

We present a new optical setup, which uses scanning mirrors in combination with laser induced fluorescence to monitor the spatial distribution of lubricant on metal sheets.

Current trends in metal processing industry require forming procedures with increasing deformations. Thus a welldefined amount of lubricant is necessary to prevent the material from rupture, to reduce the wearing of the manufacturing tool as well as to prevent problems in post-deforming procedures. Therefore spatial resolved analysis of the thickness of lubricant layers is required. Current systems capture the lubricant distribution by moving sensor heads over the object along a linear axis. However the spatial resolution of these systems is insufficient at high strip speeds, e.g. at press plants.

The presented technology uses fast rotating scanner mirrors to deflect a laser beam on the surface. This 405 nm laser light excites the autofluorescence of the investigated lubricants. A coaxial optic collects the fluorescence signal which is then spectrally filtered and recorded using a photomultiplier. From the acquired signal a two dimensional image is reconstructed in real time. This paper presents the sensor setup as well as its characterization. For the calibration of the system reference targets were prepared using an ink jet printer.

The presented technology for the first time allows a spatial resolution in the millimetre range at production speed. The presented test system analyses an area of 300 x 300 mm² at a spatial resolution of 1.1 mm in less than 20 seconds. Despite this high speed of the measurement the limit of detection of the system described in this paper is better than 0.05 g/m² for the certified lubricant BAM K-009.

With continued advances in cylindrical optics manufacturing capability, interferometric testing of such optics is difficult. This is due to the lack of a well characterized cylindrical reference surface. In this paper, the Random Fiber Test (RFT) is used to experimentally quantify the quality of fiber surface as a cylindrical reference. The basic idea of the experiment is to take measurements at different rotations about, and translations along the fiber axis. From these measurements the quality of the fiber surface in both directions can be determined.

Forensic in situ investigations, for example for aviation, maritime, road, or rail accidents would benefit from a method that may allow to distinguish ductile from brittle fractures of metals - as material defects are one of the potential causes of such accidents. Currently, the gold standard in material studies is represented by scanning electron microscopy (SEM). However, SEM are large, lab-based systems, therefore in situ measurements are excluded. In addition, they are expensive and time-consuming. We have approached this problem and propose the use of Optical Coherence Tomography (OCT) in such investigations in order to overcome these disadvantages of SEM. In this respect, we demonstrate the capability to perform such fracture analysis by obtaining the topography of metallic surfaces using OCT. Different materials have been analyzed; in this presentation a sample of low soft carbon steel with the chemical composition of C 0.2%, Mn 1.15%, S 0.04%, P 0.05 % and Fe for the rest has been considered. An in-house developed Swept Source (SS) OCT system has been used, and height profiles have been generated for the sample surface. This profile allowed for concluding that the carbon steel sample was subjected to a ductile fracture. A validation of the OCT images obtained with a 10 microns resolution has been made with SEM images obtained with a 4 nm resolution. Although the OCT resolution is much lower than the one of SEM, we thus demonstrate that it is sufficient in order to obtain clear images of the grains of the metallic materials and thus to distinguish between ductile and brittle fractures. This study analysis opens avenues for a range of applications, including: (i) to determine the causes that have generated pipe ruptures, or structural failures of metallic bridges and buildings, as well as damages of machinery parts; (ii) to optimize the design of various machinery; (iii) to obtain data regarding the structure of metallic alloys); (iv) to improve the manufacturing technologies of metallic parts.

The optical surface profiler offers fast non-contact and high-precision 3D metrology for complex surface features, which are widely used in the field of precision machining manufacturing. The optical surface profiler traditionally adopts the white light interference (WLI) technique which mainly includes optical interference system and high-precision displacement stage. The accuracy of the displacement table determines the longitudinal resolution of the instrument. In this paper, a novel WLI technique is proposed, i.e. full-field heterodyne WLI, which combines common displacement stage, low differential-frequency heterodyne system and optical interferometry system. The low differential-frequency heterodyne system generates heterodyne signal in the range of laser coherence length. By using the digital phase shift in substitution for the mechanical phase shift, the vertical resolution increases from the sub-nanometer level to the sub-angstrom level. Due to the low difference frequency technique, the common area array detector acquisition is available. A fixed displacement stage position obtains a set of three-dimensional data cubes. Through Fourier-Transform process of the time series data, the initial phase of each pixel at a specific heterodyne frequency is calculated and transformed into surface height information. By using phase unwrapping, the object surface profile can be restored within the laser coherence length. Through digital phase-shifting, phase extraction technology replaces the intensity extraction technology, the moving distance of the displacement can be calibrated with high precision. Thus it can achieve a large range of high-precision contour measurement and reduce the cost of the instrument.

Fiber Bragg grating (FBG) strain sensors are powerful tools for structural health monitoring applications. However, FBG sensor fabrication and packaging processes can lead to a non-linear behavior, that affects the accuracy of the strain measurements. Here we present a novel nondestructive calibration technique for FBG strain sensors that use a mechanical nanomotion transducer. A customized calibration setup was designed based on dovetail-type slideways that were mechanized using a stepping motor. The performance of the FBG strain sensor was investigated through analysis of experimental data, and the calibration curves for the FBG strain sensor are presented.

The evaluation of non-circular test regions poses an unusual but tricky problem to interferometric testing since typical polynomial decompositions of the measured wavefront like Zernikes are only valid in a circular region. Despite the fact that of course non-circular polynomial decompositions exist they still rely on regular regions like ellipses or rectangles. For irregular shapes of test regions no widely accepted general decomposition exists.
Unfortunately it is necessary in some cases to test completely irregularly shaped test regions. May it because the optics simply is of this shape and needs to be tested in this state or because the used area is irregular and it is undesired to extend the test region to a larger, but regular shape.
We present a simple method that not only provides a possibility to evaluate any arbitrary shaped test region but also to have a tolerance model that gives reasonable and uses worldwide accepted specification standards.
Certain interferometer software may be suited for an appropriate data analysis. An overview over some commercially available interferometer software is given with respect to the requirement of the presented method.

Remote sensing of ranged-resolved profiles of atmospheric turbulence is necessary and important for many applications in astronomical and adaptive optics communities. In order to obtain turbulence profiles in atmospheric boundary layer, a device is developed and experiments has been carried out. In the experiments, laser guide stars are formed at several successive altitudes by projecting pulsed laser, returned signals are received by two receiving telescopes and the images of the returned signals are formed by a imaging device. Variance of centroids′ distance is derived from the images with two spots at the same altitude and ranged-resolved profile of the variance is obtained. So, based on a inversion algorithm, atmospheric turbulence profiles are retrieved from differential image motion variance of distance of centroids at various altitudes. The structure constants of refractive index of atmosphere range from 10^-14m^-2/3 at lower altitudes to 10^-16m^-2/3 at higher altitudes are remote sensed experimentally. The results show it is a effective method that combined laser guide stars with differential image motion method and could sense atmospheric turbulence profiles remotely in real time.

Laser-line scanners have become ubiquitous in many forms of automation and measurement systems. Despite this fact, these systems are still susceptible to speckle or interference on rough scattering surfaces. Many scanning systems must be calibrated to the material being analyzed to obtain their full potential. In general, post-processing algorithms are used in most modern line-scanning devices in order to smooth out speckle and enhance the resolution through sub-pixel interpolation. However, these post-processing techniques come at a cost of increased CPU time and a subsequent decrease in bandwidth and resolution. in this paper, a low-cost, high-resolution solution to generating speckle-free sharply focused laser lines is presented. The key to this technique relies on only removing the spatial coherence in one dimension using a 1-D cylindrical lens array as a beam homogenizer. This beam homogenizer is then wrapped around and rotated about a central axis in order to remove the temporal component on the laser's coherence. Since the plane-wave-like behavior is maintained along one dimension, this beam can still be sharply focused to a line. however, the spatial coherence and temporal coherence are reduced to the point that speckle is minimally visible.

The rapid progress of light emitting diode (LED) technology has recently resulted in the availability of high power devices with unprecedented light emission intensities comparable to those of visible laser light sources. On this basis two versatile devices have been developed, constructed and tested.

The first one is a high-power, single-LED illuminator equipped with exchangeable projection lenses providing a homogenous light spot of defined diameter. The second device is a multi-LED illuminator array consisting of a number of high-power LEDs, each integrated with a separate collimating lens. These devices can emit R, G, CG, B, UV or white light and can be operated in pulsed or continuous wave (CW) mode. Using an external trigger signal they can be easily synchronized with cameras or other devices. The mode of operation and all parameters can be controlled by software. Various experiments have shown that these devices have become a versatile and competitive alternative to laser and xenon lamp based light sources.

The principle, design, achieved performances and application examples are given in this paper.

The work is devoted to ellipsometric investigation of the structured reflecting surface of a matrix sensor. By the generalized scheme of ellipsometry, the optical and geometric parameters of the layers of the matrix receiver can be determined. These parameters include the thickness and refractive index. Ellipsometric angles were determined using the ellipsometer. They are used as input data in the inverse ellipsometry problem. After determining the thickness and refractive indices of the sensor layers, it is possible to calculate its transmittance.When this indicator is known ,the sensitivity of the receiver can be calculated at the certain point. In this work the algorithm of the calculation of the sensitivity of a matrix receiver of optical radiation is described ,the input data in this algorithm are considered to be the ellipsometric angles.

The instrumentation plan for the E-ELT foresees a High Resolution Spectrograph (HIRES). Among its main goals are the detection of atmospheres of exoplanets and the determination of fundamental physical constants. For this, high radial velocity precision and accuracy are required. HIRES will be designed for maximum intrinsic stability. Systematic errors from effects like intrapixel variations or random errors like fiber noise need to be calibrated. Based on the main requirements for the calibration of HIRES, we discuss different potential calibration sources and how they can be applied. We outline the frequency calibration concept for HIRES using these sources.

Hydrogen evolution, identified by dissolved gas analysis (DGA), is commonly used for fault detection in oil immersed electrical power equipment. Palladium (Pd) is often used as a sensing material due to its high hydrogen absorption capacity and related change in physical properties. Hydrogen is absorbed by Pd causing an expansion of the lattice. The solubility, and therefore lattice expansion, increases with increasing partial pressure of hydrogen and decreasing temperature. As long as a phase change is avoided the expansion is reversible and can be utilized to transfer strain into a sensing element. Fiber Bragg gratings (FBG) are a well-established optical fiber sensor (OFS), mainly used for temperature and strain sensing. A safe, inexpensive, reliable and precise hydrogen sensor can be constructed using an FBG strain sensor to transduce the volumetric expansion of Pd due to hydrogen absorption. This paper reports on the development, and evaluation, of an FBG gas sensing OFS and long term measurements of dissolved hydrogen in transformer mineral oil. We investigate the effects of Pd foil cross-section and strain transfer between foil and fiber on the sensitivity of the OFS. Two types of Pd metal sensors were manufactured using modified Pd foil with 20 and 100 μm thickness. The sensors were tested in transformer oil at 90°C and a hydrogen concentration range from 20- 3200 ppm.

A spectral-domain Optical Coherence Tomography (OCT) surface profilometry prototype has been developed for the purpose of surface metrology of optical elements. The prototype consists of a light source, spectral interferometer, sample fixture and software currently running on Microsoft® Windows platforms. In this system, a broadband light emitting diode beam is focused into a Michelson interferometer with a plane mirror as its sample fixture. At the interferometer output, spectral interferograms of broadband sources were measured using a Czerny-Turner mount monochromator with a 2048-element complementary metal oxide semiconductor linear array as the detector. The software performs importation and interpolation of interferometer spectra to pre-condition the data for image computation. One dimensional axial OCT images were computed by Fourier transformation of the measured spectra. A first reflection surface profilometry (FRSP) algorithm was then formulated to perform imaging of step-function-surfaced samples. The algorithm re-constructs two dimensional colour-scaled slice images by concatenation of 21 and 13 axial scans to form a 10 mm and 3.0 mm slice respectively. Measured spectral interferograms, computed interference fringe signals and depth reflectivity profiles were comparable to simulations and correlated to displacements of a single reflector linearly translated about the arm null-mismatch point. Surface profile images of a double-step-function-surfaced sample, embedded with inclination and crack detail were plotted with an axial resolution of 11 μm. The surface shape, defects and misalignment relative to the incident beam were detected to the order of a micron, confirming high resolution of the developed system as compared to electro-mechanical surface profilometry techniques.

In the confined, enclosed environment of a spacecraft, the air quality must be monitored continuously in order to safeguard the crew's health. For this reason, OHB builds the ANITA2 (Analysing Interferometer for Ambient Air) technology demonstrator for trace gas monitoring onboard the International Space Station (ISS). The measurement principle of ANITA2 is based on the Fourier Transform Infrared (FTIR) technology with dedicated gas analysis software from the Norwegian partner SINTEF. This combination proved to provide high sensitivity, accuracy and precision for parallel measurements of 33 trace gases simultaneously onboard ISS by the precursor instrument ANITA1. The paper gives a technical overview about the opto-mechanical components of ANITA2, such as the interferometer, the reference Laser, the infrared source and the gas cell design and a quick overview about the gas analysis. ANITA2 is very well suited for measuring gas concentrations specifically but not limited to usage onboard spacecraft, as no consumables are required and measurements are performed autonomously. ANITA2 is a programme under the contract of the European Space Agency, and the air quality monitoring system is a stepping stone into the future, as a precursor system for manned exploration missions.

We describe a setup for precise multi-angular measurements of light scattered by mm- to μm-sized samples. We present a calibration procedure that ensures accurate measurements. Calibration is done using a spherical sample (d = 5 mm, n = 1.517) fixed on a static holder. The ultimate goal of the project is to allow accurate multi-wavelength measurements (the full Mueller matrix) of single-particle samples which are levitated ultrasonically.

The system comprises a tunable multimode Argon-krypton laser, with 12 wavelengths ranging from 465 to 676 nm, a linear polarizer, a reference photomultiplier tube (PMT) monitoring beam intensity, and several PMT:s mounted radially towards the sample at an adjustable radius. The current 150 mm radius allows measuring all azimuthal angles except for ±4° around the backward scattering direction. The measurement angle is controlled by a motor-driven rotational stage with an accuracy of 15’.

In the manufacturing process of Tailored Forming components, the inline inspection of the joining zone directly after each single process step can yield advantages - such as early error detection and real-time process control. Since measuring times need to be synchronized with the production chain, there is no time to cool down the components in between two hot forming processes. On the one hand, the chosen measurement technique needs to be non-tactile due to the heat of the measurement object. On the other hand, the object's areal surface texture needs to be captured rapidly to realize a fast inline inspection. These requirements are only matched by optical 3d measurement systems. Additional challenges arise due to the high temperature of the Tailored Forming components: the ambient air is heated up and the air's temperature increase results in an inhomogeneous refractive index field surrounding the hot workpiece, effecting the light's path emitted by the illumination unit of the optical sensor. We present a simple measurement setup based on the laser light section method to visualize the measurement accuracy loss induced by the convectional heat flow from a hot cylindrical measurement object. To attain a direct validation of the measurement results, the measurements are performed with and with reduced influence of the inhomogeneous refractive index field induced by the hot object.

Digital holographic techniques to investigate drying processes of both paint films and ink dot is presented. The proposed technique based on digital holographic interferometry can achieve both visualization of variations and analysis of dryness of paint films in the drying process by using phase changes between two subsequent reconstructed complex amplitudes of the reflected light from the film. To follow the drying processes, holograms are recorded at a constant time interval. Phase-shifting digital holography has been applied to analyze the dryness of commercial paints applied on the metal plate. For analysis of an ink dot having diameter of a few hundred micrometers, digital holographic microscopy is applied to evaluating the time history of dryness of ink dot in the drying process. This paper describes these holographic techniques applied to the commercially available paint and ink and presents some experimental results.

The construction features of autocollimation systems for measurement the large-sized and extended objects deformations at industry, power and scientific instrument making are considered. The conditions of increase of a distance of measurement are analyzed in comparison with the serial autocollimation devices. The error of measurement by the restriction of a working beam is investigated. The structure of algorithm for reduces the systematic error of the measurement which based on received analytical expression of function of an error is determined.

Holographic tomography (HT) allows noninvasive, quantitative, 3D imaging of transparent microobjects, such as living biological cells and fiber optics elements. The technique is based on acquisition of multiple scattered fields for various sample perspectives using digital holographic microscopy. Then, the captured data is processed with one of the tomographic reconstruction algorithms, which enables 3D reconstruction of refractive index distribution.

In our recent works we addressed the issue of spatially variant accuracy of the HT reconstructions, which results from the insufficient model of diffraction that is applied in the widely-used tomographic reconstruction algorithms basing on the Rytov approximation. In the present study, we continue investigating the spatially variant properties of the HT imaging, however, we are now focusing on the limited spatial size of holograms as a source of this problem. Using the Wigner distribution representation and the Ewald sphere approach, we show that the limited size of the holograms results in a decreased quality of tomographic imaging in off-center regions of the HT reconstructions. This is because the finite detector extent becomes a limiting aperture that prohibits acquisition of full information about diffracted fields coming from the out-of-focus structures of a sample. The incompleteness of the data results in an effective truncation of the tomographic transfer function for the out-of-center regions of the tomographic image. In this paper, the described effect is quantitatively characterized for three types of the tomographic systems: the configuration with 1) object rotation, 2) scanning of the illumination direction, 3) the hybrid HT solution combing both previous approaches.

For high resolution imaging, X-rays and electron beams are being used. However, for such a short wavelength, imaging with lenses becomes difficult as lenses absorb a part of radiation and lenses with very low aberrations must be used. Ptychography is a lens-less imaging technique which uses intensity information of the multiple diffraction patterns in the far field. These multiple far field diffraction patterns are generated by an unknown object which is scanned by a localized illuminated spot (probe).

Accurate knowledge of initial parameters is important for a good reconstruction of the object. Robustness of the Ptychography Iterative Engine (PIE) has already been studied for inaccurately known initial parameters, where the success of the algorithm was found to be sensitive to the accuracy of the estimate of lateral positions of the probe.
:; We present here a new method to correct the lateral position of the probe with respect to the object. This method is more straightforward to implement than other existing algorithms while comparable accuracy for the lateral position is achieved. Being able to correct the probe positions has positive implication in experiments, in particular at the short wavelength cases. It relaxes the requirement for the experimental set-up.

New application of photo-thermo-refractive glass (PTR) named “holographic prism” is presented. In the holographic prism angles between directions are set by the holograms which create “fan” of signal beams. This kind of prism creates several signal beams which are equal to the reflections from facets of the conventional silica prism. Implementation of PTR glass as a holographic medium for this device brought us several advantages and new features. First it leads to decrease in overall size of the prism that positively affects the identification process of the beam's crosspoint. Thus, it increases sensitivity and accuracy of the measure. Second, greater value of the refractive index change in PTR glass in comparison with calcium fluoride crystal allows us to increase quantity of the recorded reference beams for the measure which leads to sensitivity increase. During this work, we established recording schedule for the PTR glass in case of the superimposed gratings recording. Was found that exposure for each grating should be equal to the 1/N fraction of the optimal exposure where N is the number of multiplexed gratings. We proved that in this case the total value of the refractive index modulation amplitude is equal to that for the single grating with optimal exposure. Considering obtained data we successfully performed recording of the holographic prism of the second modification with 14 channels.

Due to the high demand of LED light sources, the need to modify their radiation pattern to meet specific application requirements has also increased. This is mostly achieved by using molded secondary optics, which are composed of a combination of several aspherical and freeform surfaces. Unfortunately, the manufacturers of these secondary optics only provide output information at system level, making impossible to independently characterize the secondary optic in order to determine the sources of erroneous results. For this reason, it is necessary to perform a component-level verification leading to the validation of the correctness of the produced secondary optic independently of the light source. To understand why traditional inspection methods fail, it is necessary to take into account that not only errors due to irregularities on the lens surface like pores, glass indentations or scratches affect the performance of the lens, but also differences in refractive index appear after the compression during fabrication process. These internal alterations are generally produced during the cooling stage and their effect over the performance of the lens are not possible to be measured using tactile techniques. Additionally, the small size of the lens and the freeform characteristics of its surface introduce additional difficulties to perform its validation. In this work, the component-level test is done by obtaining the ray mapping function (RMF) which describes the deflection of the light beam as a function of the input angle. To obtain the RMF, firstly a collimated light source is held fix and the lens is rotated. Thus, a virtual point source is created and subsequently by using experimental ray tracing it is possible to determine the ray slopes, which are used to the retrieve the RMF. Under the assumption that the optical system under analysis is lossless and considering the principle of energy conservation, it is possible under specific conditions to use this new approach to obtain the output of the complete set, composed of light source plus secondary optic. Thus, for different LED models, combining their radiation pattern with the RMF allow us to obtain the resultant modified radiation pattern. By following this procedure, the correct functionality of the secondary optic is verified independently of the light source. This method brings the opportunity to the final product manufacturer of defining fail regions over the desired resultant output radiation pattern as a combination of different LED sources and then verify if the secondary optic fulfill the requirements.

Within this work an alternative approach to precision surface profilometry based on a low-coherence interferometer is presented. Special emphasis is placed on the characterization of edge effects, which influence the measurement result on sharp edges and steep slopes. In contrast to other works, this examination focuses on the comparison of very broadband light sources such as a supercontinuum white-light source (SC; 380 - 1100 nm) and a laser-driven plasma light source (LDP; 200 - 1100 nm) and their influence on the formation of these effects. The interferometer is equipped with one of these broadband light sources and a defined dispersion over a given spectral range. The spectral width of the light sources in combination with the dispersive element defines the possible measurement range and resolution. Instead of detecting the signals only in a one-dimensional manner, an imaging spectrometer on the basis of a high resolution CMOS-camera is set-up. Through the introduction of a defined dispersion, a controlled phase variation in the spectral domain is created. This phase variation is dependent on the optical path difference between both arms and can therefore be used as a measure for the height of a structure which is present in one arm.
The results of measurements on a 100 nm height standard with both selected light sources have been compared. Under consideration of the coherence length of both light sources of 1.58 μm for the SC source and 1.81 m for the LDP source differences could be recorded. Especially at sharp edges, the LDP light source could record height changes with slopes twice as steep as the SC source. Furthermore, it became obvious, that measurements with the SC source tend to show edge effects like batwings due to diffraction. Additional effects on the measured roughness and the flatness of the profile were investigated and discussed.

Contemporary production systems of mechanical precision parts show challenges as increased complexity, tolerances shrinking to sub-microns and yield losses that must be mastered to the extreme. More advanced automation and process control is required to accomplish this task. Often a solution based on feedforward/feedback control is chosen requiring innovative and more advanced in line metrology. This article concentrates first on the context of in line metrology for process control and then on the development of a specific in line height profiling sensor. The novel sensor technology is based on full field time domain white light interferometry which is well know from the quality lab. The novel metrology system is to be mounted close to the production equipment, as required to minimize time delay in the control loop, and is thereby fully exposed to vibrations. This sensor is innovated to perform in line with an orders of magnitude faster throughput than laboratory instruments; it’s robust to withstand the rigors of workshops and has a height resolution that is in the nanometer range.

LIBS-technology holds the potential for on-site real-time measurements of steel products. However for a mobile and robust LIBS measurement system, an adequate small and ruggedized laser source is a key-requirement. In this contribution, we present tests with our novel compact high power laser source, which, initially, was developed for ignition applications. The CTR HiPoLas® laser is a robust diode pumped solid state laser with a passive Q-switch with dimensions of less than 10 cm³. The laser generates 2.5 ns-pulses with 30 mJ at a maximum continuous repetition rate of about 30 Hz. Feasibility of LIBS experiments with the laser source was experimentally verified with steel samples. The results show that the laser with its current optical output parameters is very well suited for LIBS measurements. We believe that the miniaturized laser presented here will enable very compact and robust portable high-performance LIBS systems.

Measurement of small force in biological applications could be helpful especially in the field of diagnostic and prognostic procedure. For this purpose, a Hybrid Fabry Perot fiber optic Micro Cavity is proposed based on Micro Silica Sphere Cavity integrated on the capillary tube, and is bound to the single mode fiber with PDMS layer. Since PDMS acts as an elastic material, under small loads the cavity length was affected. To study this mechanical behavior, the sensor structure was simulated with Finite element method. The force measurement was studied experimentally with analyzing wavelength shifts of sensor. Consequently, the force sensitivity was equal to -3pm/mN. The force resolution of our sensor was equal to 340 μN in the range of 0 to 950 mN.

The submicron-aperture fiber point-diffraction interferometer (SFPDI) can be applied to realize the measurement of three-dimensional absolute displacement within large range, in which the performance of point-diffraction wavefront and numerical iterative algorithm for displacement reconstruction determines the achievable measurement accuracy, reliability and efficiency of the system. A method based on fast searching particle swarm optimization (FS-PSO) algorithm is proposed to realize the rapid measurement of three-dimensional absolute displacement. Based on the SFPDI with two submicron-aperture fiber pairs, FS-PSO method and the corresponding model of the SFPDI, the measurement accuracy, reliability and efficiency of the SFPDI system are significantly improved, making it more feasible for practical application. The effect of point-diffraction wavefront error on the measurement is analyzed. The error of pointdiffraction wavefront obtained in the experiment is in the order of 1×10^-4λ (the wavelength λ is 532 nm), and the corresponding displacement measurement error is smaller than 0.03 μm. Both the numerical simulation and comparison experiments have been carried out to demonstrate the accuracy and feasibility of the proposed SFPDI system, high measurement accuracy in the order of 0.1 μm, convergence rate (~90.0%) and efficiency have been realized with the proposed method, providing a feasible way to measure three-dimensional absolute displacement in the case of no guide rail.

Autocollimators are widely used for angular measurements in instrument-making and the manufacture of elements of optical systems (wedges, prisms, plane-parallel plates) to check their shape parameters (rectilinearity, parallelism and planarity) and retrieve their optical parameters (curvature radii, measure and test their flange focusing). Autocollimator efficiency is due to the high sensitivity of the autocollimation method to minor rotations of the reflecting control element or the controlled surface itself. We consider using quaternions to optimize reflector parameters during autocollimation measurements as compared to the matrix technique. Mathematical model studies have demonstrated that the orthogonal positioning of the two basic unchanged directions of the tetrahedral reflector of the autocollimator is optimal by the criterion of reducing measurement errors where the axis of actual rotation is in a bisecting position towards them. Computer results are presented of running quaternion models that yielded conditions for diminishing measurement errors provided apriori information is available on the position of rotation axis.

A practical technique is considered for synthesizing the parameters of the tetrahedral reflector that employs the newly-retrieved relationships. Following the relationships found between the angles of the tetrahedral reflector and the angles of the parameters of its initial orientation, an applied technique was developed to synthesize the control element for autocollimation measurements in case apriori information is available on the axis of actual rotation during monitoring measurements of shaft or pipeline deformation.

Optical systems have increased in quality and capability and are today widely used in many fields of applications. An important step forward was the introduction of aspheres and freeform surfaces. For manufacturing these surfaces in high quality, the accurate measurement of them is highly important. A reliable measurement requires traceability. The concept of traceability is presented, uncertainty sources are itemized and the steps towards traceability for an asphere interferometer are discussed.

The paper is about field and special methods of radiation terrain mapping with the identification of their distinctive features, advantages and disadvantages of each of them. The applicability of methods in various situations of radiation contamination is shown. An analysis of sources of radioactive radiation and of the situation of radiation contamination in Russia has been carried out. Different detectors of ionizing radiation are compared. It is proved that SiPM combines high performance and operational characteristics most effectively, making it possible to use it in a gamma spectrometer for any type of radiation mapping.

The wind-blown dust emissions frequently occur in the open storage yards of steel-making companies. Tracking the dust source and monitoring their dispersion are rather difficult. This type of open-air storage yards poses many environmental hazards. The 3-D scanning lidar system is effective in environmental monitoring (e.g., dust) with high temporal and spatial resolution, which is lacking in traditional ground-based measurement. The objective of this paper is to make an attempt for the flux estimation of dust concentration by using lidar system. Further, we investigate the dynamical process of dust and their relationship with local air quality monitoring data.

The results show that the material storage erosion by wind (~ 3.6 m/s) could cause dust to elevate up to 20m height above the material storage, and produces the flux of dust around 674 mg/s. The flux of dust is proportional to the dust mass concentration (PM₁₀) measured by commercial ambient particular monitors.

The article is based on some research which is considering the three-axis angle measuring autocollimator with one channel capable of measuring three angular coordinates simultaneously. In order to measure angular displacements around the three main coordinate axes (OX, ОY, and ОZ), special control elements are used. The use of a special control element generally improves the characteristics of the device, but it creates a problem of autocollimation mark overlapping. This issue creates a zone of inoperability of the device and makes measurement and control impossible. The ways of solving this problem are not considered in this paper. The prototype of an optoelectronic joined-channel autocollimator with a tetrahedral control element is developed. The developed prototype passed functional testing, calibration was conducted with using a flat mirror. The paper also shows the results of the research device accuracy in the measurement of different angles.

The paper deals with the machine learning approach to automatic tuning of extended Kalman filter in application to interferometric signals processing. The representation of interferometric signals as output of dynamic systems with varying state vector is presented. It is shown that the challenge of the extended Kalman filter application to interferometric data processing is selection of initial parameters for the filter. The complex tuning problem is described in a formal form. The machine learning approach to the automatic filter tuning is proposed. The combination of Monte Carlo optimization and the gradient descent are implemented for initial filter parameters selection. The optimization criterion in the form of sum differences between measured and estimated signal value is presented and discussed. The results of simulated and experimental interferometric signals processing are presented and analyzed. The quality of amplitude and phase estimation by the automatically tuned filter is at the same level as hand tuned filter. It is shown, that proposed approach allows to obtain robust results of experimental data processing.

The article describes a new optical scheme of noncontact sensor for measuring linear displacement - linear encoder. This sensor is an optical device in which the measurement of displacement is performed by analyzing the optical signal, which pass through two diffraction gratings, one of which is moved relative to the other. The optical signal is obtained by the diffraction of light in these diffraction gratings and subsequent interference of diffracted beams. Often this type of sensors are multi-channel devices with symmetrically positioned of detectors. This scheme is proposed to use a multisection phase mask that allows to make a small-sized sensor. Sections of this multi-section phase mask are the optical windows and they made the final interference signals to be shifted relative to each other in phase. The number of sections in the multi-section phase mask can be varied. Estimated sufficient number of sections is four or more.

One of the results of intensive development of led technology was the creation of a multi-component, managed devices and illumination/irradiation used in various fields of production (e.g., food industry analysis, food quality). The use of LEDs has become possible due to their structure determining spatial, energy, electrical, thermal and other characteristics. However, the development of the devices for illumination/irradiation require closer attention in the case if you want to provide precise illumination to the area of analysis, located at a specified distance from the radiation source. The present work is devoted to the development and modelling of a specialized source of radiation intended for solving problems of analysis of food products, medicines and water for suitability in drinking. In this work, we provided a mathematical model of spatial and spectral distribution of irridation from the source of infrared radiation ring structure. When you create this kind of source, you address factors such spectral component, the power settings, the spatial and energy components of the diodes.

The consumption of fresh-cut agricultural produce in Korea has been growing. The browning of fresh-cut vegetables that occurs during storage and foreign substances such as worms and slugs are some of the main causes of consumers’ concerns with respect to safety and hygiene. The purpose of this study is to develop an on-line system for evaluating quality of agricultural products using hyperspectral imaging technology. The online evaluation system with single visible-near infrared hyperspectral camera in the range of 400 nm to 1000 nm that can assess quality of both surfaces of agricultural products such as fresh-cut lettuce was designed. Algorithms to detect browning surface were developed for this system. The optimal wavebands for discriminating between browning and sound lettuce as well as between browning lettuce and the conveyor belt were investigated using the correlation analysis and the one-way analysis of variance method. The imaging algorithms to discriminate the browning lettuces were developed using the optimal wavebands. The ratio image (RI) algorithm of the 533 nm and 697 nm images (RI533/697) for abaxial surface lettuce and the ratio image algorithm (RI_533/697) and subtraction image (SI) algorithm (SI538-697) for adaxial surface lettuce had the highest classification accuracies. The classification accuracy of browning and sound lettuce was 100.0% and above 96.0%, respectively, for the both surfaces. The overall results show that the online hyperspectral imaging system could potentially be used to assess quality of agricultural products.

In this study, we propose a method to enhance the spatial resolution of digital holographic microscopy with speckle illuminations. In this method, speckle patterns are generated from coherence light passing through ringslit apertures instead of the most typical circular apertures, to obtain higher numerical aperture. The results show that a reconstructed image with the higher resolution is obtained using ring-slit apertures.