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Zusammenfassung Mit einem Multi-Punkt-Positionsmesssystem ist es möglich, Positionen und Orientierungen mit sehr hoher Genauigkeit bildbasiert zu messen. Das Messsystem besteht aus einem einfachen Kamerasystem, das um ein diffraktives optisches Element (DOE) erweitert wird. Durch die Multi-Punkt-Methode (MPM) werden Messunsicherheiten von deutlich unter 1/100 Pixel erzielt. Um dies in der Praxis anwenden zu können, ist eine entsprechend hochgenaue Kalibrierung nötig. In diesem Beitrag werden verschiedene Kalibrierverfahren und -funktionen vorgestellt und untersucht. Die Auswertung zeigt, dass sich zur Kalibrierung ein allgemeiner Polynomansatz zusammen mit der Nanomess- und Positioniermaschine NPMM-200 am besten eignet. Es werden Standardabweichungen des Restfehlers von 0,31 µm im Objektraum (etwa 6/1000 Pixel im Bildraum) auf einer Fläche von etwa 87 mm × 49 mm 87\hspace{0.1667em}\text{mm}\times 49\hspace{0.1667em}\text{mm} erreicht (Polynomgrad = 9).

The modal holographic wavefront sensor enables fast measurement of individual aberration modes without the need for time-consuming calculations. However, the measurement accuracy suffers greatly from intermodal crosstalk, caused when the wavefront contains more aberrations than the one to be measured. In this paper, we present sensor optimization to minimize this effect and show the improvement when using Karhunen–Lòeve instead of Zernike modes as the basis. Finally, we show in simulation that an open-loop adaptive optics system based on the optimized sensor can be used to correct the effect of realistic, dynamic atmospheric turbulence on a wavefront and increase its Strehl ratio significantly.

Digitization and digital transition are frequently used terms in modern communication. Facts as the transition of the classical Data-Internet to the Internet of Things IoT, and Industrial Internet, respectively, are more and more influencing all technologies and thus it is quite appropriate to think about the future of metrology in such a changing environment. In this paper we discuss the state of the art, the challenges, and the perspectives of optical metrology in times of digital transition.

The surface polarization scattering is investigated in terms of the coherence matrix for the electric field scattered from a birefringent material with a random interface between its surface and air. The relationship between the statistical properties of the scattered light at the scattering surface and the micro-structure of the anisotropic media has been explored for the first time to understand the underlying mechanism of the surface scattering phenomena for the electric field with random states of polarization.

Exploiting the optical memory effect and the equivalency between the spatial and the ensemble cross-correlation of speckle patterns, we developed a new single-pixel camera concept. It allows lensless microscopic spectrally and depth resolved imaging with spatial light modulators displaying pseudorandom scattering arrays. Since the image retrieval is based on correlation calculations, the concept proves to be quite robust to noise.

We present an optically addressed non-pixelated spatial light modulator. The system is based on reversible photoalignment of a LC cell using a red light sensitive novel azobenzene photoalignment layer. It is an electrode-free device that manipulates the liquid crystal orientation and consequently the polarization via light without artifacts caused by electrodes. The capability to miniaturize the spatial light modulator allows the integration into a microscope objective. This includes a miniaturized 200 channel optical addressing system based on a VCSEL array and hybrid refractive-diffractive beam shapers. As an application example, the utilization as a microscope objective integrated analog phase contrast modulator is shown. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement, Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe, 1001

Microlens array-based light-field imaging has been one of the most commonly used and effective technologies to record high-dimensional optical signals for developing various potential high-performance applications in many fields. However, the use of a microlens array generally suffers from an intrinsic trade-off between the spatial and angular resolutions. In this paper, we concentrate on exploiting a diffuser to explore a novel modality for light-field imaging. We demonstrate that the diffuser can efficiently angularly couple incident light rays into a detected image without needing any lens. To characterize and analyse this phenomenon, we establish a diffuser-encoding light-field transmission model, in which four-dimensional light fields are mapped into two-dimensional images via a transmission matrix describing the light propagation through the diffuser. Correspondingly, a calibration strategy is designed to flexibly determine the transmission matrix, so that light rays can be computationally decoupled from a detected image with adjustable spatio-angular resolutions, which are unshackled from the resolution limitation of the sensor. The proof-of-concept approach indicates the possibility of using scattering media for lensless four-dimensional light-field recording and processing, not just for two- or three-dimensional imaging., Imaging: Lensless light-field imaging lays foundations for new applications By replacing lenses with a diffuser in light-field imaging, scientists could expand its use in applications ranging from light-field microscopy and synthetic aperture imaging to visual odometry. Microlens array-based light-field imaging is one of the most commonly used technologies to record high-dimensional optical images. However, they suffer from a trade-off between the spatial and angular resolutions. Xiaoli Liu and colleagues from Shenzhen University in China, in collaboration with researchers from the University of Stuttgart in Germany, have now developed a novel technique that uses a diffuser to angularly couple incident light rays into a detected image without the need for a lens. The diffuser allows each sub-beam emitted by a point source to form a distinguishable sub-image covering a region on the sensor and could lead to lensless four-dimensional light-field imaging.

Nanometer resolution metrology is a significant topic in the development and production of complex shaped high precision optics. The Nanopositioning and Nanomeasuring Machine NPMM-200 at ITO is built for nanometer scale positioning in a large scale measurement volume of 200 mm x 200 mm x 25 mm. The concept of the machine is based on a high precision interferometrically controlled stage in a stable metrological frame made of glass-ceramic. In this frame, different types of sensors can be attached for measurement of surface topographies. In this contribution, we present the use of optical sensors, such as a fixed focus probe, for measuring of high precision aspheric and freeform optics with this new machine.

This Letter reports an approach to single-shot three-dimensional (3D) imaging that is combining structured illumination and light-field imaging. The sinusoidal distribution of the radiance in the structured-light field can be processed and transformed to compute the angular variance of the local radiance difference. The angular variance across the depth range exhibits a single-peak distribution trend that can be used to obtain the unambiguous depth. The phase computation that generally requires the acquisition of multi-frame phase-shifting images is no longer mandatory, thus enabling single-shot structured-light-field 3D imaging. The proposed approach was experimentally demonstrated through a dynamic scene.

We previously proposed a three-dimensional microscopic imaging system for objects hidden behind scattering media using in-line phase-shift digital holography, which simultaneously captures amplitude and phase information. However, as the thickness of the scattering medium increases, the influence of scattering is enhanced, and the reconstructed image of the object behind the scattering medium deteriorates. In this paper, we report the evaluation of this image using a near-infrared light source with a wavelength of 780 nm that is capable of deep tissue penetration. A favorable microscopic image of the object behind the rat-skin sample of 912 μm-thickness was successfully reconstructed.

For the active control of large-scale structures, especially high-rise buildings and bridges, fast and accurate measurement of local deformations is required. We present a highly accurate and fast vision-based measurement technique and, to the best of our knowledge, first experimental results for the control of an adaptive-structures prototype frame, equipped with hydraulic actuators. Deformations are detected at multiple discrete points, based on a photogrammetric approach with additional holographic spot replication. The replication leads to effective averaging of most error contributions, especially discretization and photon noise. Measurements over a distance of 11.4 m result in a measurement uncertainty of 0.0077 pixel (corresponding to 0.055 mm in object space).

In this contribution we introduce an imaging based measurement setup, that is able to very accurately measure 3D relative positions between moving light sources. The system consists of two highspeed cameras, one equipped with a telecentric, the other with an endocentric lens. To improve accuracy of image based position detection, each lens is upgraded with a computer-generated-hologram (CGH) to replicate a single object point into a predefined pattern of spots on image plane. By averaging the centers of all replications, noise and other error contributions can be reduced. We will show how to apply image processing using two different approaches. The first approach is based on a tracking algorithm running on CPU reaching 330 fps. The second is a FPGA implementation to process whole images with a speed of 390 fps. Furthermore, we will demonstrate how threedimensional calibration can be done using the Nanomeasurement and Nanopositioning Machine NPMM-200. For the calibration, a three-dimensional multivariate polynomial is used. The standard deviations of residual error in object space for a calibration in a volume of 100 mm × 100 mm × 24 mm are σx = 0.367 μm, σy = 0.373 μm and σz = 0.437 μm (polynomial order = 9).

With the ever increasing demand for higher transistor density and improved functionality, the nanostructures on modern semiconductor chips become more and more complex and their modeling requires a multitude of parameters. As a result, the performance of scatterometry as state-of-the-art optical inspection tool is limited by insufficient sensitivities towards certain parameters and high cross-correlations between them. In order to improve the model-based reconstruction, it is essential to generate as many uncorrelated datasets as possible. In this paper, we propose to combine conventional Fourier scatterometry with Mueller polarimetry and white-light interferometry to measure both angle- and wavelength-resolved Mueller matrices. This approach takes advantage simultaneously of the most relevant information channels of the light field: intensity, wavelength, phase, propagation angle, and polarization. We validate the performance improvement in case of multi-parameter problems by means of a comprehensive simulation study. In general, both the measurement uncertainties and the cross-correlations are reduced in comparison to other scatterometric configurations. Furthermore, our approach facilitatesthe reconstruction of target asymmetries, such as asymmetric sidewall angles, or the analysis of isolated line gratings at low technology nodes. Aiming at an experimental validation as well, we finally show results from first proof-of-principle measurements performed during the ongoing setup implementation.

The demand for fast automated inspection of all manufactured components in industrial production is rising due to increasing quality demands and high-speed machining technologies. Modern surface metrology sensors are capable of implementing these tasks if they can be embedded in fast and accurate measuring machines. However, the common approach to achieve high positioning accuracy in such machines is abiding by very conservative limits in acceleration, and thus, velocity. We propose an active control system including a model-based compensation system for dynamic errors to increase acceleration and velocity. A novel optical sensor permitting the direct measurement of the actual tool-center-point (TCP) position is used for system identification of the required dynamic model. The position of a LED point source is detected with high subpixel precision by replicating the spot several times on the camera chip and averaging over the center of gravities of all spots. A model for the largest dynamic error component of a small multiaxis measuring machine is derived and the sensor is used to identify the model parameters. A model-based feedforward and feedback control system reducing the dynamic tracking error is designed. This control systems allows machine motions with both high accuracy and large velocity. The achieved performance is evaluated using TCP tracking error measurements obtained with the novel optical sensor. This model-based compensation system can also be applied to machine tools.

We present a tunable output-frequency filter (TOF) algorithm to reconstruct the object from noisy experimental data under low-power partially coherent illumination, such as LED, when imaging through scattering media. In the iterative algorithm, we employ Gaussian functions with different filter windows at different stages of iteration process to reduce corruption from experimental noise to search for a global minimum in the reconstruction. In comparison with the conventional iterative phase retrieval algorithm, we demonstrate that the proposed TOF algorithm achieves consistent and reliable reconstruction in the presence of experimental noise. Moreover, the spatial resolution and distinctive features are retained in the reconstruction since the filter is applied only to the region outside the object. The feasibility of the proposed method is proved by experimental results.

Zusammenfassung Bei der Messung technischer Oberflächen treten insbesondere im Umfeld flexibler Fertigung unterschiedlichste Anforderungen auf. Häufig ist eine schnelle hochgenaue Topographie-Messung erwünscht. Durch die Kombination des chromatisch-konfokalen Verfahrens mit der spektralen Interferometrie (Chromatisch-Konfokale Spektral-Interferometrie) ist es möglich, single-shot Messungen mit einem weiten Messbereich und gleichzeitig geringer Unsicherheit zu erzielen. Dabei können ebenso die den beiden einzelnen Verfahren inhärenten Probleme umgangen und so der Einsatzbereich erweitert werden. Mit demselben optischen Aufbau ist es auch möglich, gleichzeitig Brechungsindex und Dicke von Mehrschichtproben mit hoher Auflösung zu vermessen (Chromatisch-Konfokale Kohärenz-Tomographie). Dies ist etwa von Vorteil, wenn das Messobjekt mit funktionalen Schichten versehen ist oder beispielsweise durch eine Ölschicht gemessen werden muss.

The papers in this special section focus on the technology of digital holography and presents industrial applications for its use. Optical holography is a technique developed in the 1960s for recording a three-dimensional (3-D) scene on photographic film which is commonly referred to as hologram. Being different from classic photography that captures the intensity information from a single view point, a hologram is capable of recording the entire optical waves that are scattered from a 3-D object. Theoretically, when a hologram is illuminated by a coherent beam, the 3-D image it records will be reconstructed to the observer with complete depth and disparity information. It has been anticipated by many researchers of the 3-D technology that holography is likely to be the ultimate solution for the realization of 3-D display systems. Before the emergence of high-speed computers, optical holography has also been successfully applied in various kinds of tedious signal processing tasks. Notably, it has been demonstrated that computation intensive problems like Fourier transform and correlation can be obtained instantly through an optical system of lenses with coherent illumination. Despite these encouraging factors, it turns out that the practical applications of optical holography are rather restricted. The barricade could be attributed to the high complexity of the optical system and the strict demands on the environmental conditions that are required in setting up a holographic system.

Lack of training data is one of the main problems when realizing optical surface inspection systems. In the best case, provision of enough representative training samples is difficult and most of the time expensive. In some cases, it is not possible at all. Here we present an alternative method where the surface defects are simulated. Thereby, we focus on metal surfaces in the microscale where diffraction phenomena start to play a major role. Ray tracing and scalar diffraction approximation methods are applied and compared.

Measurement systems based on laser spot triangulation are widely used in many fields of distance-, surface and 3D measurements. Currently, strong interest in applications like laser-range detection (LIDAR) in automotive driving and robotics also promote further research in improving the technique. Laser-based ranging and triangulation techniques suffer from the great advantage of one of the lasers properties - its coherence. A coherent laser light ray allows projecting a spatially small spot onto an object compared to a broadly illuminating LED or bulb. A detector, e.g. camera or photodiode, detects the reflected measurement spot precisely with its position on the object. The downside of the coherence appears in combination with a rough reflecting surface as speckles. Speckle is the noise of the spot due to the rough object surface and the resulting random phases. In some measurement settings, the speckle noise has a large negative effect and influence on the measurement uncertainty to determine the precise center-of-gravity of the measurement-spot's position. In this contribution, we investigate a method introduced by us in an experiment to reduce the speckle noise and therefore improve the measurement uncertainty in triangulation. The proposed multi-spot-scanning method decorrelates speckle noise patterns through dynamical holography of the laser-spot by varying the position microscopically. For the dynamical scanning of the spot, we use a spatial light modulator (SLM) being addressed with digital holograms. SLMs are part of many measurement systems and other optical applications, especially projection-based systems. The holograms, illuminated by the laser, microscopically translate the measurement spot position in the object plane. These so-called "miicro-variations" are in fact translations of the first diffraction order using a grating on the SLM with additional overlaid Zernike-polynomials. The grating has a carrier frequency calculated according to the SLM's pixel size. Due to the micro-variations, the speckle noise patterns vary and decorrelate. Integrating or averaging over many patterns on the camera then allows predicting the spot's position with higher certainty through its better uniformity. Additionally, we examined how well the speckle decorrelation affects the uncertainty reduction especially in a triangulation sensor setup. Our experiments, utilizing the multi-spot-scanning method, showed promising first results. The microvariations in our experiments corresponded well to the simulations. Using different Zernike-coefficients, we are able to control the spot position to roughly a couple of micrometers while having a maximum field size for micro-variation of up to 16 mm in diameter. The best micro-variation-spot radius was between 75 μm and 85 μm considering a spot size of FWHM = 53 μm. We also found out, that with the method we could decorrelate speckle patterns to a certain degree. This degree can reduce the noise while averaging by a factor of around 40% compared to the original noise. Overall, the statistical measurement uncertainty improved by the reduction ratio of approximately R = 3 in axial direction. Further investigations on more spot-variations (7-42 spots) lead to solely slight improvements, because the denser the spots are, more overlap is present and less microvariation and decorrelation is possible. Furthermore, we have investigated different Zernike-polynomials (coma, defocus and astigmatism) and their influence on combined variations. In conclusion, we describe a method for laser-triangulation sensor systems to reduce laser speckle noise and improve measurement uncertainty. With this method, we can increase the axial resolution of the triangulation with the disadvantage of losing a small amount of lateral resolution due to the averaging and variation of the spot. We hope to be able to also expand our findings to other scenarios and setups as well as improve the findings with further research.

In this paper, we propose a method for the structured-light field (SLF) 3D measurement, involving ray calibration and phase mapping. The ray calibration is carried out to determine each light ray with metric spatio-angular parameters. Base on the ray parametric equation, the phase mapping in the SLF is developed so that spatial coordinates could be directly mapped from phase-encoding information. Then, a calibration strategy is designed to determine the mapping coefficients for each light ray, achieving high-efficiency SLF 3D reconstruction.

Most of the neural networks proposed so far for computational imaging (CI) in optics employ a supervised training strategy, and thus need a large training set to optimize their weights and biases. Setting aside the requirements of environmental and system stability during many hours of data acquisition, in many practical applications, it is unlikely to be possible to obtain sufficient numbers of ground-truth images for training. Here, we propose to overcome this limitation by incorporating into a conventional deep neural network a complete physical model that represents the process of image formation. The most significant advantage of the resulting physics-enhanced deep neural network (PhysenNet) is that it can be used without training beforehand, thus eliminating the need for tens of thousands of labeled data. We take single-beam phase imaging as an example for demonstration. We experimentally show that one needs only to feed PhysenNet a single diffraction pattern of a phase object, and it can automatically optimize the network and eventually produce the object phase through the interplay between the neural network and the physical model. This opens up a new paradigm of neural network design, in which the concept of incorporating a physical model into a neural network can be generalized to solve many other CI problems.

For unfocused plenoptic imaging systems, metric calibration is generally mandatory to achieve high-quality imaging and metrology. In this paper, we present an explicit derivation of an unfocused plenoptic metric model associating a measured light field in the object space with a recorded light field in the image space to conform physically to the imaging properties of unfocused plenoptic cameras. In addition, the impact of unfocused plenoptic imaging distortion on depth computation was experimentally explored, revealing that radial distortion parameters contain depth-dependent common factors, which were then modeled as depth distortions. Consequently, a complete unfocused plenoptic metric model was established by combining the explicit metric model with the imaging distortion model. A three-step unfocused plenoptic metric calibration strategy, in which the Levenberg-Marquardt algorithm is used for parameter optimization, is correspondingly proposed to determine 12 internal parameters for each microlens unit. Based on the proposed modeling and calibration, the depth measurement precision can be increased to 0.25 mm in a depth range of 300 mm, ensuring the potential applicability of consumer unfocused plenoptic cameras in high-accuracy three-dimensional measurement.

Digitalization and digital transition are frequently used terms in modern communication. We are far from underrating these global phenomenons that are strongly connected with the worldwide networking between all domains of the public, private, commercial, and industrial life. Facts as the transition of the classical Data-Internet to the Internet of Things IoT, and Industrial Internet, respectively, are more and more influencing all technologies and thus it is quite appropriate to think about the future of metrology in such a changing environment. But it should be noticed that at least since the widespread introduction of computer technology in the 80ths and 90th, optical imaging and metrology have already implemented the transition to digital technologies. Methods such as digital image processing, digital holography, digital microscopy, and digital image correlation are state of the art by now. Manifold worldwide installations like digital/virtual/remote labs and robotic telescopes/microscopes support the position, that not only the simple transition from analog to digital but even more the total networking between complex physical entities and a new quality of data acquisition, processing and evaluation are characteristic for the new quality of imaging and metrology. In this paper we discuss the state of the art, the challenges, and the perspectives of optical metrology in times of digital transition.

In this contribution, an approach for the characterization of various fiber-based slit homogenizer devices in the NIR and SWIR is shown. The devices are to be tested for use in a satellite-based spectrometer for spatial monitoring of anthropogenic greenhouse gases. This leads to the characterization requirement for temporal coherence and spatial incoherence. Speckle noise has to be reduced to a very low level, which is achieved using a fixed diffusor in combination with a rotating diffusor and a tunable (wavelength) laser as well as temporal averaging. Remaining variations due to unwanted interferences at the imager are removed by controlled movement of the sensor with an automated micro positioning stage in combination with image processing. The design, realization and characterization of the measurement breadboard as well as near field homogenization results for different input scenes and polarizations are shown. Additionally, the geometric characteristics and the depolarization effect of the fibers are investigated for a homogeneous input scene. Furthermore, a setup and measurement results concerning the focal ratio degradation of the fibers are presented.

Tilted Wave Interferometry has been invented and developed over the last years as a flexible and very fast method to test precision aspheres and freeform surfaces . It measures surface deviations full field, with high lateral resolution, without any null compensator like CGH and without moving the tested part while measuring. The test of non-spherical optical components is a topic of high relevance for optics industry, as current optic designs rely heavily on those elements, since the small form factors and high performance of actual designs would be impossible with traditional spherical optics designs. As all precision components, aspheres and freeform surfaces need accurate testing for their production. Ideally, testing of components is closely integrated into the fabrication chain. Due to the high flexibility and measurement speed of the TWI of typically less than 30 sec it is well suited for this purpose. Due to the special illumination scheme, the first implementations of this new interferometer have been of Mach Zehnder type. In this contribution we demonstrate, how the tilted wave interferometer principle can be implemented in a Fizeau configuration. The benefit of this configuration against the Mach Zehnder configuration is the common path feature. Here, the reference beam and the measurement beam follow the same optical track inside the interferometer, making the interferometer much more robust against temporal environmental influences such as vibrations and air turbulences. At the same time, form tolerances of the interferometer components in the common path area can be relaxed. These advantages of Fizeau are well known. The multiple source illumination of the tilted wave interferometer however leads to the generation of multiple reference wavefronts that can be disturbing. We therefore present a new TWI implementation that avoids these problems. It relies on a new illumination design with four sets of illumination patterns that each generate their own reference wave. The new approach has been implemented in a lab setup and shows in first measurements the expected improvements in stability. We tested the system in extensive Monte Carlo simulations. The common path approach showed a reconstruction error of the test specimen of up to an order of magnitude lower compared the Mach-Zehnder configuration.

High-resolution optical inspection techniques typically require expensive imaging systems. One possible approach for reducing the overall cost of such systems is to combine optics of limited performance with digital image restoration techniques. In this contribution, we introduce a new hybrid system based on the combination of a field-programmablegate-array (FPGA), a large telecentric lens with strong field dependent chromatic aberrations and different types of object-adapted projections for 2D and 3D inspection tasks. The optical design tries to minimize cost and weight by replacing the – typically very large – first refractive group of the object-sided telecentric lens by one thin diffractive optical element. This approach can correct the field-dependent aberrations very well. Unfortunately, strong chromatic aberrations are unavoidable. For restoration, we use digital image processing by means of advanced deconvolution algorithms. The necessary number of operations for the strong fielddependent aberrations is extremely high. We combine algorithmic approaches (convolutions using singular-value decomposition) and parallelization directly on the FPGA to achieve live restoration (15 Hz) for a custom-built image sensor with three megapixels. The power consumption is low and a compact processing unit is realized. This hybrid (digital-optical) imaging system is used for 2D- and 3D inspection based on adaptive triangulation. One approach is based on inverse fringe projection. Ray-tracing based on the sensor setup and a reference CAD-model of the part to be tested is used for computing a fringe mask. This mask is inscribed on a spatial light modulator, which then projects the fringes towards the object. If the object under test is without faults, high-frequency equidistant straight-line fringes will result on the image sensor and low height measurement uncertainties at low lateral resolutions, even for non-cooperative objects, are achievable. The importance of a large depth-of-field and constant image-scale along the optical axis for the inverse fringe projection lead to the decision of a telecentric objective.

This letter reports a novel method for light field three-dimensional measurement by using unfocused plenoptic cameras. A light field metric model, based on which nonmetric depths in the image space can be mapped to metric dimensions in the object space, was established. Furthermore, with the aid of a three-dimensional measurement system, light field metric calibration was carried out by determining light rays with spatio-angular parameters and set up the depth relationship between the object and image spaces in accordance with the light field image properties.

Within the past decade, a variety of scientific groups have demonstrated the potential of radially and azimuthally polarized laser beams in many applications [1–3]. Experimental investigations in high-power operation indicate additional beneficial properties for material processing, such as drilling and deep-penetration-welding, which have been demonstrated to lead to an increase of the process efficiency by using such a polarization state. Cutting of metal sheets with radially polarized beams at 1 micron wavelength have been reported recently to increase the process efficiency [4].

Passive light field imaging generally uses depth cues that depend on the image structure to perform depth estimation, causing robustness and accuracy problems in complex scenes. In this study, the commonly used depth cues, defocus and correspondence, were analyzed by using phase encoding instead of the image structure. The defocus cue obtained by spatial variance is insensitive to the global spatial monotonicity of the phase-encoded field. In contrast, the correspondence cue is sensitive to the angular variance of the phase-encoded field, and the correspondence responses across the depth range have single-peak distributions. Based on this analysis, a novel active light field depth estimation method is proposed by directly using the correspondence cue in the structured light field to search for non-ambiguous depths, and thus no optimization is required. Furthermore, the angular variance can be weighted to reduce the depth estimation uncertainty according to the phase encoding information. The depth estimation of an experimental scene with rich colors demonstrated that the proposed method could distinguish different depth regions in each color segment more clearly, and was substantially improved in terms of phase consistency compared to the passive method, thus verifying its robustness and accuracy.

Large depth of field (DOF) is a longstanding goal in optical imaging field. In this paper we presented a simple but efficient method to extend the DOF of a diffraction-limited imaging system using a thin scattering diffuser. The DOF characteristic of the imaging system with random phase modulation was analyzed based on the analytical model of ambiguity function as a polar display of the optical transfer function (OTF). The results of numerical simulation showed that more high-frequency components existed in the defocused OTF curve when the exit pupil of the imaging system exhibited a random phase modulation. It proved the important role of the scattering diffuser in extending the DOF of imaging systems. For the reconstruction, a stack of point spread functions (PSFs) corresponding to different axial locations within a measurement range were superimposed to construct the stacked PSF. Then the large DOF image was recovered from a speckle pattern by deconvolution. In this proof-of-concept, we experimentally demonstrated the single-shot imaging with larger DOF using a thin glass scattering diffuser in both a single-lens imaging system and a microscopic imaging system.

We demonstrate microscopic three-dimensional imaging of an object hidden behind a diffuser by using in-line phase-shift digital holography. A spatial resolution of 2.9 μm was achieved, and highly accurate quantitative phase imaging and three-dimensional imaging were realized.

We investigated the capabilities of deconvolution for image enhancement in scatter-plate microscopy. This lensless imaging technique enables the investigation of microstructures through scattering media by cross-correlating the scattered light intensity with a previously recorded point spread function (PSF) of the scattering medium. The autocorrelation function of the PSF appears as the transfer function of the imaging process. Deconvolution methods use the knowledge of this transfer function to enhance the image quality by reducing the blur and strengthening the contrast with the objective to achieve diffraction-limited resolution. We obtained significant image enhancement both with means of inverse filtering and by applying iterative deconvolution algorithms.

Scatter-plate microscopy is a lensless imaging method using a simple groundglass diffuser instead of a microscope objective. In this paper we describe further application of deconvolution improving both contrast and resolution of the acquired images.

Based on the optical memory effect of scattered light, we developed a new single-pixel camera concept. The retrieved images contain both 3D and spectral information about the sample. A spatial light modulator (SLM) generates a random intensity modulation. The signal recorded by the single-pixel detector is cross correlated by the calculated point spread function (PSF) signals of the SLM to retrieve the image. In this publication, both simulations and experimental results are presented.

The experimental approach of a highly accurate imaging based stereo measurement setup with a total measurement volume of 140 mm × 100 mm × 50 mm is presented. The system can detect the position of multiple target points (LEDs) in a calibrated volume of 100 mm × 75 mm × 24 mm with an accuracy of σ x = 0 . 367 μ m, σ y = 0 . 373 μ m and σ z = 0 . 437 μ m. This high accuracy is reached by holographically replicating each point light source to a predefined pattern (cluster) of spots on the camera sensor and averaging the center positions of all spots. We present a detailed description of the principle, the process and results of calibration including deformation compensation and stability measurements, as well as the results of two- and three-dimensional trajectory measurements. To validate the performance and accuracy of the measurement setup, interferometers are employed as reference sensors. The residual error of a two-dimensional trajectory of distance D = 277 μ m is σ d = 0 . 242 μ m and for a three-dimensional trajectory of distance D = 57 . 2 mm it is σ d = 0.674 μ m.

Three dimensional (3D) imaging of objects requires the retrieval of both phase and amplitude of the object wavefront. Two beam techniques such as digital holography can reconstruct the whole field from the interference pattern, resulting from the superposition of the object wavefront and a known reference wavefront using light sources with sufficient coherence length. The diffraction field originating from the interaction of the probe wavefront with the object contains the spatial frequency information about the object. By studying the variation in the diffraction field with axial position, the phase of the object wavefront can be determined by iterative use of the scalar diffraction integral. Based on this approach, the development of a lensless whole field imaging technique using a low temporally coherent source (LED) in combination with axially arranged sensors is presented. Since the developed technique uses a single beam approach, less complex instrumentation compared to interferometric (two-beam) techniques is required. The technique was tested on technical as well as biological specimen to reconstruct and display their intensity and phase distributions. Since the developed microscope is lensless in nature with unit magnification, larger field of views become possible.

Techniques of unconventional holography, called holographic correloscopy, for imaging a three-dimensional (3-D) object through an opaque diffuser or via a scattering wall are reviewed. This paper is not intended to be a general overview. Instead, it will focus and shed light on less-known techniques termed coherence holography, photon-correlation holography, remote imaging digital holography, and dual-reference holography. This paper will introduce how they perform 3-D imaging through a diffuser or via a scattering wall with a thin but strongly scattering layer.

Measuring systems for production quality control face increasing demands in both measurement velocity and accuracy The undesired dynamic effects of measuring machines pose more stringent limits to the measurement velocity than modern optical sensors for surface metrology for example chromatic confocal point sensors. These dynamics are investigated at an exemplary coordinate measuring machine and their negative effects on the measured values are described. A compensation system for the reduction of the induced errors based on internal deviation sensors is proposed and investigated. Subsequently a dynamic model for the machine’s dominant dynamic effects is identified in order to transfer the compensation system to machines without internal deviation sensors.

We propose an optical sensor design for position measurements with sub-nanometer precision on small diffraction gratings with a wide pitch range from 400 nm to approximately 10 µm. The interferometric position detection is based on a self-reference introduced via 180°-rotational shearing. A lateral scan of the target generates a periodically varying intensity signal whose phase encodes the target position. The small size of the target (down to approximately 5 × 5 µm2) necessitates an even smaller illumination-spot size on the target for the scanning procedure. In our sensor, a spot diameter of only 2–3 µm is realized by illuminating large off-axis areas in the entrance pupil of a microscope objective with high numerical aperture (NA). A set of two complementary aperture stops ensures blocking of the specular reflection, thus allowing for a signal contrast close to one. Due to the large NA-extent of the illumination profile, the sensor is inherently sensitive for aberrations. We correct the resulting positioning error via additional beam monitoring in the pupil plane. A tolerance analysis in terms of a comprehensive simulation study shows that the sensor performance is robust against typical target and parameter variations. Furthermore, first proof-of-principle measurements validate the practical feasibility.

Modern industrial production requires fast and automated quality control using state-of-the-art surface metrology sensors embedded in fast high-precision measuring machines. In order to achieve both fast and precise positioning, active control systems with model-based compensation of dynamic positioning errors due to increased acceleration forces can be applied. However, these active control systems require an accurate estimate of the dynamic positioning errors of the tool-center-point (TCP) with respect to the precisely measured position of the drive axes. A novel optical camera sensor system with high subpixel precision based on multi-spot detection enables the direct measurement of the TCP position at a slower rate than the sampling time of the control system and with significant latency or dead-time. Based on a general yet simple deviation model with large model mismatch, three approaches to estimate the TCP position are presented and compared with simulation and test bench results of a modified Mahr MFU 100 measuring machine. First, a multi-rate Kalman filter with delay compensation is designed based on a simple physical modal model generalizing the applicability of the concept for different types of measuring machines and machine tools. Second, additional sensors in form of accelerometers placed at the TCP are used to obtain an indirect measurement of the TCP position at a fast sampling rate to reduce the effect of the model mismatch. Third, instead of additional sensors, an alternative concept consisting of enhanced Gaussian process modeling to improve the model accuracy with a data-based error model is incorporated in the Kalman filter framework in form of fast pseudo-measurements outperforming the other approaches.

Light-field imaging can simultaneously record spatio-angular information of light rays to carry out depth estimation via depth cues which reflect a coupling of the angular information and the scene depth. However, the unavoidable imaging distortion in a light-field imaging system has a side effect on the spatio-angular coordinate computation, leading to incorrectly estimated depth maps. Based on the previously established unfocused plenoptic metric model, this paper reports a study on the effect of the plenoptic imaging distortion on the light-field depth estimation. A method of light-field depth estimation considering the plenoptic imaging distortion is proposed. Besides, the accuracy analysis of the light-field depth estimation was performed by using standard components. Experimental results demonstrate that efficiently compensating the plenoptic imaging distortion results in a six-fold improvement in measuring accuracy and more consistency across the measuring depth range. Consequently, the proposed method is proved to be suitable for light-field depth estimation and three-dimensional measurement with high quality, enabling unfocused plenoptic cameras to be metrological tools in the potential application scenarios such as industry, biomedicine, entertainment, and many others.

Conventional confocal 3D microscopes suffer from a slow measurement speed due to its requirement of scanning in three directions. Although lateral slit scanning has been proven to perform similarly to single point scanning, a direct area confocal scanning microscope is commonly considered impossible as the system is reduced into a wide-field microscope and loses its depth discerning capability. In this article, a direct area scanning method is proposed for 3D surface profilometry based on a tilted focal field. To demonstrate the underlying principle, theoretical analysis is conducted with simulation result, showing that depth discerning capability can be maintained in area scanning when the tilting angle is specifically chosen according to the numerical aperture of the system. An adaptive experimental setup is constructed based on a programmable light source and a programmable array microscope with chromatic axial encoding. Measurement result of a test target using the proposed method is comparable to the result of conventional array scanning. Although the axial uncertainty is increased by a factor of approximately 2.5, the direct area scanning method is more than 300 times faster than the conventional array scanning mode of the same setup.

The ability to track and image a moving object hidden behind scattering medium provides a crucial advantage when it is impossible or unpractical to physically invade the obstacles. Recently, a few methods based on optical memory effect (OME), especially speckle autocorrelation technology and deconvolution-based methods, have demonstrated that it is possible to reconstruct an object hidden from view. However, these methods do not allow for the noninvasive tracking and imaging a moving object in real time. We present a noninvasive single shot technology to recover the optical transfer function (OTF) of the scattering system. As the object moves, a simple and fast optimization of the OTF is employed to overcome the limitation of the tracking range as well as the restriction of the field of view (FOV), enabling sharp reconstructed images when object travels cross over the edge of OME. Experimental demonstration is presented to verify the feasibility of proposed method.

Ambiguity caused by a wrapped phase is an intrinsic problem in fringe projection-based 3D shape measurement. Among traditional methods for avoiding phase ambiguity, spatial phase unwrapping is sensitive to sensor noise and depth discontinuity, and temporal phase unwrapping requires additional encoding information that leads to an increase of image sequence acquisition time or a reduction of fringe contrast. Here, to the best of our knowledge, we report a novel method of absolute phase unwrapping based on light field imaging. In a recorded light field under structured illumination, i.e., a structured light field, a wrapped phase-encoded field can be retrieved and resampled in diverse image planes associated with several possible fringe orders in a measurement volume. Then, by leveraging phase consistency constraint in the resampled wrapped phase-encoded field, correct fringe orders can be determined to unwrap the wrapped phase without any additional encoding information. Experimental results demonstrated that the proposed method was suitable for accurate and robust absolute phase unwrapping.

Image Processing and Computer Vision for MEMS Testing Markus Huttel Introduction Classification of Tasks Image Processing and Computer Vision Components Processing and Analysis of Image Data Commercial and Noncommercial Image Processing and Computer Vision Software Image Processing Techniques for the Processing of Fringe Patterns in Optical Metrology Conclusion References Image Correlation Techniques for Microsystems Inspection Dietmar Vogel and Bernd Michel Introduction Deformation Measurement by Digital Image Correlation (DIC) Techniques Base Equipment for DIC Applications Applications of DIC Techniques to Microsystems Conclusions and Outlook References Light Scattering Techniques for the Inspection of Microcomponents and Microstructures Angela Duparre Introduction Theoretical Background of Light Scattering Measurement Equipment Standardization of Light Scattering Methods Applications for Microcomponent and Microstructure Inspection Combination of Light Scattering and Profilometric Techniques Conclusions and Outlook References Characterization and Measurement of Microcomponents with the Atomic Force Microscope (AFM) F. Michael Serry and Joanna Schmit Introduction Components of AFM and Principles of AFM Operation AFM Imaging Modes AFM Nonimaging Modes Applications of AFM for Microcomponent Inspection: A Case Study Atomic Force Profilometer (AFP) - A Combination of AFM and Stylus Profiler Optical Metrology Complementary to AFM Conclusions and Outlook References Optical Profiling Techniques for MEMS Measurement Klaus Korner, Aiko Ruprecht, and Tobias Wiesendanger Introduction Principles of Confocal Microscopy Principle of Microscopic Depth-Scanning Fringe Projection (DSFP) Conclusion References Grid and Moire Methods for Micromeasurements Anand Asundi, Bing Zhao, and Huimin Xie Introduction Grid or Grating Fabrication Methods Micro-Moire Interferometer Moire Methods Using High-Resolution Microscopy Microscopic Grid Methods Conclusions References Grating Interferometry for In-Plane Displacement and Strain Measurement of Microcomponents Leszek Salbut Introduction Principle of Grating Interferometry Waveguide Grating Interferometry Measurement System SG Technology Exemplary Applications of WGI Conclusions References Interference Microscopy Techniques for Microsystem Characterization Alain Bosseboeuf and Sylvain Petitgrand Introduction Interference Microscopes Modeling of Two-Beam Homodyne Interference Microscopes Static Measurements by Interference Microscopy Performance and Issues of Interference Microscopy Applications of Interferometric Profilometers in the MEMS Field Dynamic Measurements by Interference Microscopy Conclusion Acknowledgments References Measuring MEMS in Motion by Laser Doppler Vibrometry Christian Rembe, Georg Siegmund, Heinrich Steger, and Michael Wortge Introduction Laser Doppler Effect and Its Interferometric Detection Techniques of Laser Doppler Vibrometry Full-Field Vibrometry Measuring on Microscopic Structures Resolution and Accuracy Combination with Other Techniques Examples Conclusion and Outlook References An Interferometric Platform for Static, Quasi-Static, and Dynamic Evaluation of Out-Of-Plane Deformations of MEMS and MOEMS Christophe Gorecki, Michal Jozwik, and Patrick Delobelle Introduction Interferometric Platform Architecture and Principle of Operation Optomechanical Characterization of Membranes by "Pointwise" Deflection Method Mechanical Expertise of Scratch Drive Actuators via Interferometric Measurement of Out-of-Plane Microdisplacements Dynamic Evaluation of Active MOEMS by Interferometry Using Stroboscopic Technique General Conclusion and Outlook Acknowledgments References Optoelectronic Holography for Testing Electronic Packaging and MEMS Cosme Furlong Introduction Overview of MEMS Fabrication Processes Optoelectronic Holography Representative Applications Summary Acknowledgments References Digital Holography and Its Application in MEMS/MOEMS Inspection Wolfgang Osten and Pietro Ferraro Introduction Theory and Basic Principle of Digital Holography (DH) Digital Holographic Interferometry Digital Holographic Microscopy (DHM) The Application of DH to the Investigation of Microcomponents Conclusion References Speckle Metrology for Microsystem Inspection Roland Hofling and Petra Aswendt Introduction Basics Applications Conclusion References Spectroscopic Techniques for MEMS Inspection Ingrid De Wolf Introduction Raman Spectroscopy (RS) Spectroscopic Ellipsometry (SE) Dual-Beam Spectroscopy (DBS) X-Ray Photoelectron Spectroscopy (XPS) High-Resolution Electron Energy Loss Spectroscopy (HREELS) Auger Electron Spectroscopy (AES) Brillouin Scattering (BS) Conclusions References Index