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Diffraction based multispectral imaging is a method for obtaining snapshot multispectral image information by using a structured diffraction grating or computer-generated hologram in an intermediate image plane of an imaging system. Without the need of complicated filter manufacturing it becomes possible to realize application specific spatio-spectral sampling of an image. The spectral resolution is coupled with the spatial resolution because the central stop of the imaging system serves also as the main spectral filtering component. By using two image sensors and the zeroth order of the computer-generated holograms it becomes possible to obtain high resolution spatial information as well as spectral information on a coarser sampling grid.

In this article we present the simulation and experimental implementation of a camera-based sensor with low object-space numerical aperture that is capable of measuring the distance of multiple object points with an accuracy of 8.51 µm over a range of 20 mm. The overall measurement volume is 70 mm × 50 mm × 20 mm. The lens of the camera is upgraded with a diffractive optical element (DOE) which fulfills two tasks: replication of the single object point to a predefined pattern of K spots in the image plane and adding a vortex point spread function (PSF), whose shape and rotation is sensitive to defocus. We analyze the parameters of the spiral phase mask and discuss the depth reconstruction approach. By applying the depth reconstruction to each of the K replications and averaging the results, we experimentally show that the accuracy of the reconstructed depth signal can be improved by a factor of up to 3 by the replication approach. This replication method (also called multipoint method) not only improves accuracy of depth reconstruction but also of lateral position measurement. Therefore, the presented concept can be used as a single camera 3D position sensor for multiple points with high lateral as well as depth resolution.

We demonstrate single-shot digital holographic imaging and two-wavelengths shape measurement through fog.

In this paper, we demonstrate digital holographic imaging through a 27-m-long fog tube filled with ultrasonically generated fog. Its high sensitivity makes holography a powerful technology for imaging through scattering media. With our large-scale experiments, we investigate the potential of holographic imaging for road traffic applications, where autonomous driving vehicles require reliable environmental perception in all weather conditions. We compare single-shot off-axis digital holography to conventional imaging (with coherent illumination) and show that holographic imaging requires 30 times less illumination power for the same imaging range. Our work includes signal-to-noise ratio considerations, a simulation model, and quantitative statements on the influence of various physical parameters on the imaging range.

A camera-based single-image sensor is presented, that is able to measure the distance of one or multiple object points (light emitters). The sensor consists of a camera, whose lens is upgraded with a diffractive optical element (DOE). It fulfils two tasks: adding a vortex point spread function (PSF) and replication of the vortex PSFs to a predefined pattern of K spots. Both, shape and rotation of the vortex PSF is sensitive to defocus. The sensor concept is presented and its capabilities evaluated both on axis and off-axis. The achieved standard deviation of the error ranges between 8.5 μm (on-axis) and 3.5 μm (off-axis) within a measurement range of 20 mm. However, as soon as calibration and measurement position no longer match, the accuracy is limited. An analysis of the effects responsible for this are also part of the publication.

Interferometric detection enables the acquisition of the amplitude and phase of the optical field. By making use of the synthetic wavelength as a computational construct arising from digital processing of two off-axis digital holograms, it is possible to identify the shape of an object obscured by fog and further increase the imaging range due to the increased sensitivity in coherent detection. Experiments have been conducted inside a 27 m long fog tube filled with ultrasonically generated fog. We show the improved capabilities of synthetic phase imaging through fog and compare this technique with conventional active laser illumination imaging.

Holography is a diffraction-based coherent imaging technique in which a complex threedimensional object can be reproduced from a flat, two-dimensional screen with a complex transparency representing amplitude and phase values. It is commonly agreed that real-time holography is the ne plus ultra art and science of visualizing fast temporally changing 3-D scenes. The integration of the real-time or electro-holographic principle into display technology is one of the most promising but also challenging developments for the future consumer display and TV market. Only holography allows the reconstruction of naturallooking 3-D scenes, and therefore provides observers with a completely comfortable viewing experience. But to date several challenges have prevented the technology from becoming commercialized. But those obstacles are now starting to be overcome. Recently, we have developed a novel approach to real-time display holography by combining an overlapping sub-hologram technique with a tracked viewing-window technology (Schwerdtner, Leister & Haussler, 2007; Schwerdtner, Haussler & Leister, 2007). For the first time, this enables solutions for large screen interactive holographic displays (Stolle & Haussler, 2008; Reichelt et al., 2008). This chapter presents these novel solutions for large real-time holographic 3-D displays in the context of previous and current approaches to electro-holography. The holographic display developed by us combines a tailored holographic recording scheme with active tracking of the observer. This unique approach dramatically reduces the demand for the space-bandwidth product of the hologram and thus allows the use of state-of-the-art spatial light modulators and enables real-time calculation. The fundamentals and challenges of the holographic display technology are described, its implementation in prototypes is demonstrated, and the bright prospects for the 3-D display market are discussed.

In this article a camera-based single-image sensor is presented, that is able to measure the distance of multiple object points. The experimental results show an accuracy of 8,51 μm within a depth range of 20 mm. The sensor consists of a camera, whose lens is upgraded with a diffractive optical element (DOE). It fulfils two tasks: adding a vortex point spread function (PSF) and replication of the vortex PSFs to a predefined pattern of K spots. Both, shape and rotation of the vortex PSF is sensitive to defocus. By applying the depth reconstruction to each of the K replications and averaging the results, we experimentally show, that the reconstruction of the depth signal can be improved by a factor of up to 3.

Obwohl walzplattierte Werkstoffe in der allgemeinen Offentlichkeit nur wenig beachtet und behandelt werden, besitzen sie bereits heute eine hohe Bedeutung, um unterschiedliche Guter des taglichen Bedarfs realisieren und produzieren zu konnen. Durch eine hohe Produktivitat und ein umfangreiches technologisches Wissen lassen sich bereits heute sehr anspruchsvolle und aufwandige Funktionswerkstoffe mittels Plattierverfahren herstellen, die masgeschneiderte Produkteigenschaften fur viele Halbzeuge und Fertigprodukte garantieren. Bedingt durch die konstruktiven Trends im Bereich von Automotive, Luft- und Raumfahrt sowie dem allgemeinen konstruktiven und materiellem Leichtbau ist davon auszugehen, dass die Bedeutung masgeschneiderter Funktionswerkstoffe fur spezifische Anwendungsfelder in naher Zukunft weiter wachsen und die Bedeutung einzelner Plattierverfahren fur eine wirtschaftliche Produktionskette verschiedener Produkte wachsen wird.

Composite sheet of Twin Roll Cast (TRC) AZ31-Mg alloy and industrial pure Al-1050 was fabricated as Al/Mg/Al with a hot roll bonding process. As the diffusion zone at the interface between the layers plays a crucial role in the formation of bonding strength and formability of clad sheets. It is important to describe the processes of inter-diffusion layer generation in order to assess the abilities of the laminate composites for further processing. Thus, the aim of this study was to investigate the development of the bonding strength, microstructure and mechanical properties of the bonding interface directly after roll bonding and additionally post-annealing processes. Microstructure characterization techniques such as optical and scanning electron microscopy including energy dispersive X-ray analysis (EDX) were applied to investigate the bonding area. No inter-metallic phases were present directly after the roll bonding process. The creation and growth of Al2Mg3 and Al12Mg17 phases were apparent after annealing at temperatures of 250 to 400 °C at different times ranging from five to 120 minutes. The results prove that the growth rate of inter-metallic phases increases considerably with an increase in the annealing temperature. The micro-hardness of the interface-area was also investigated. It was observed that the two inter-metallic phases were significantly harder than the substrate Mg and Al. In order to examine the influence of the inter-metallic phases on the resulting bonding strength after the annealing process, the shear bonding strength test has been conducted for different samples that were annealed at different heat treatment conditions. The results indicate that the optimum annealing temperature is 200 °C leading to a maximum bonding strength. Moreover, the mechanical properties of the composite after roll bonding and post annealing were determined by means of room temperature tensile test. The fracture mechanism after tensile test was also discussed.Keywords:Rollbonding,Al/Mghotrollbonding,TwinrollcastAZ31,bondingstrength

The dependence of different brushing parameters during surface preparation on the resulting bonding strength for the roll-bonding of Mg-Mg composites was investigated. A parameter study with different brushing parameters was used to analyze the effect on surface roughness as pre-step for roll-bonding trials with different roughness ratio. Furthermore, the influence of different Mg alloys and of a roll-bonded Al-Mg-Al sandwich composite on the obtained bonding strength was investigated.

In this work the influence of accumulative roll bonding (ARB) process on the microstructure and the mechanical characteristic is investigated. Therefore, AZ31 magnesium sheets were successfully deformed through ARB for a maximum of three passes. Twin roll cast sheets and twin roll cast sheets with subsequent heat treatment (480 °C, 1 h) were used as initial materials. After one ARB pass, the highest microstructure changes were measured. Electron backscattered diffraction (EBSD) reveals a bimodal microstructure with an average grain size of ~1µm. In comparison to the initial material a strong basal texture was measured. The significant refinement of grain size after severe plastic deformation cause an increase of tensile and compressive strength, e.g. rising yield stress and ultimate tensile strength of 42% and 15%, respectively. However, the maximum formability remains nearly at the same level. Further ARB passes do not improve the mechanical characteristics further.

Electrical steels with lower thickness become more and more important to realize electrical machines with high nominal frequency due to high number of the poles and to provide higher power at a given volume of the electrical machine. For application at higher frequencies the dynamic magnetization processes have to be analyzed. In the paper the experimental data for frequency dependence of the magnetization curves, the coercive force, the permeability, and of the magnetic losses for nonoriented electrical steels with thicknesses in the range of 0.10 mm up to 0.50 mm will be reported. For thin electrical steels a different character of the dynamic magnetization behavior at increasing frequency of the applied external field compared to thicker materials is observed. This is attributed to differences in the number of moving walls.

The constantly increasing complexity of vehicle functions creates a need for virtual integration of individual vehicle functions at the early stages of the development process — even before the ECUs are available. This report by Audi Electronics Venture GmbH together with dSpace describes how such a prototype workflow was made possible by using the tools “EXAM” and “SystemDesk”. Results of the empirical study are also given.

Die weiter steigende Komplexitat der Fahrzeugfunktionen schafft den Bedarf nach einer virtuellen Integration einzelner Fahrzeugfunktionen bereits in zeitlich fruhen Phasen eines Entwicklungsprojektes — noch bevor die Steuergerate zur Verfugung stehen. Dieser Erfahrungsbericht der Audi Electronics Venture GmbH gemeinsam mit dSpace schildert, wie und mit welchen Ergebnissen ein solcher Workflow mit Hilfe der Werkzeuge „EXAM“ und „SystemDesk“ prototypisch im Rahmen einer Studie realisiert und evaluiert worden ist.

The first analytical method for simultaneous speciation analysis of five of the most important gadolinium-based magnetic resonance imaging (MRI) contrast agents in blood plasma samples was developed. Gd-DTPA (Magnevist), Gd-BT-DO3A (Gadovist), Gd-DOTA (Dotarem), Gd-DTPA-BMA (Omniscan), and Gd-BOPTA (Multihance) were separated by hydrophilic interaction liquid chromatography (HILIC) and detected with electrospray mass spectrometry (ESI-MS). Spiking experiments of blank plasma with Magnevist and Gadovist were performed to determine the analytical figures of merit and the recovery rates. The limits of detection ranged from 1 x 10 (-7) to 1 x 10 (-6) mol/L depending on the ionization properties of the individual compounds, and limits of quantification ranged from 5 x 10 (-7) to 5 x 10 (-6) mol/L. The linear concentration range comprised 2 orders of magnitude. With application of this method, blood plasma samples of 10 healthy volunteers, with Magnevist or Gadovist medication, were analyzed for Gd-DTPA and Gd-BT-DO3A, respectively. The obtained results were successfully validated with inductively coupled plasma-optical emission spectroscopy (ICP-OES).

Mechatronische Systeme im Kraftfahrzeug zeigen vielfach charakteristische Eigenschaften vernetzter Regelungen. So sind typischerweise Sensoren, Steuergerate und Aktoren ortlich im Fahrzeug verteilt, und Messwerte sowie Stellgrosen werden uber Bussysteme ubertragen. Im Rahmen einer gemeinsamen Untersuchung der Audi AG, der Berufsakademie Ravensburg und dem Institut fur Kraftfahrwesen der RWTH Aachen wurden Aspekte vernetzter Regelungen und deren Anwendungen im Fahrwerk betrachtet.

Mechatronic systems in motor vehicles often show features which are characteristic for networked control systems. Typically, the sensors, ECUs, and actuators are locally distributed in the vehicle, and sensor data including control signals are transmitted via communication networks. In a joint investigation between Audi AG, “Berufsakademie Ravensburg“ (University of Cooperative Education) and the “Institut fur Kraftfahrwesen“ (Automotive Research Institute) at RWTH Aachen University (Germany), different aspects of networked control systems and their applications in car chassis systems are examined.

Flächenhafte interferometrische Prüfverfahren sind zur Qualitätsbeurteilung optischer Bauteile prädestiniert. Die Prüfung von asphärischen optischen Flächen oder Systemen erfordert jedoch fast immer spezielle Nullkompensatoren. Für diese Aufgabe werden häufig computergenerierte Hologramme (CGHs) eingesetzt. Sie zeichnen sich dadurch aus, dass mit einer einzigen diffraktiv wirkenden Funktionsfläche eine einfallende Wellenfront nahezu beliebig manipuliert werden kann. Die speziellen Anforderungen an die Asphärenprüfung mit computergenerierten Hologrammen werden entlang des gesamten Zyklus behandelt, beginnend von der Auslegung des Prüfaufbaus über Design und Herstellung der CGHs bis hin zur Anwendung und Kalibrierung der Hologramme.

A novel technique for absolute calibration the wavefront reconstructed by computer generated holograms (CGHs) is presented. It requires a specially designed multiplexed CGH (Twin-CGH), which reconstructs two wavefronts with the same symmetry. One of those is used for calibration of the CGH by means of known absolute interferometric methods. The patterns of both phase functions are simultaneously structured. The aberrations of the calibration wavefront can be transferred to those of the second wavefront. The testing method is explained and two different encoding methods are discussed. For different encoded Twin-Fresnel zone plates we experimentally demonstrate this novel calibration method.

Computer-generated holograms (CGHs) were fabricated by a polar coordinate laser plotter. The wavefront aberrations of these CGHs caused by fabrication inaccuracies were measured interferometrically. We tested Fresnel zone plates as typical examples of CGHs with focal ratios of ƒ/10 and ƒ/5 with a Fizeau interferometer. The tests comprised both binary phase holograms and binary amplitude holograms. The wavefront aberrations of the CGHs had an rms variation of about λ /50. Two types of aberrations were identified and could be referred to certain writing errors. Their size was deduced from the interferograms.

An absolute interferometric test of two-level binary Fresnel zone plates (FZPs) is presented. Five measurements with a wavefront testing interferometer are required to fully separate interferometer errors from those of the FZP. The method provides both errors, pattern errors and surface figure errors of the zone plate absolutely. The test method is suitable for zone mirrors and zone lenses. Test setups are explained, equations are derived and experimental results are presented. Further, applications of the absolute diffractive test method are described. For the estimation of the accuracy of the diffractive calibration method a comparison with the classical three-position test was carried out.

Methods for measuring and compensating the nonlinear electro-optical effect of transmissive, parallel-aligned liquid crystal (LC)-based spatial light modulators (SLMs) are presented. Particularly, the analysis is focused on the spatial nonuniformity of the voltage versus phase modulation characteristics for an active-matrix-driven, electrically controlled birefringence type LC-SLM. A high-quality reconstruction from phase-only modulating SLMs requires a well-calibrated phase addressing across the entire SLM panel. I discuss how the commonly inherent phase-response inhomogeneity of LC-SLM is characterized by purposeful localized measurement techniques. This phase-response inhomogeneity is efficiently compensated by utilizing a Legendre polynomial representation in combination with a remapping of an 8 bit gray level addressing. The calibration procedure is corroborated by measurement data. The LC-SLM's experimental demonstration finally verifies the resultant improvement in holographic imaging.

Over the last decade, various technologies for visualizing three-dimensional (3D) scenes on displays have been technologically demonstrated and refined, among them such of stereoscopic, multi-view, integral imaging, volumetric, or holographic type. Most of the current approaches utilize the conventional stereoscopic principle. But they all lack of their inherent conflict between vergence and accommodation since scene depth cannot be physically realized but only feigned by displaying two views of different perspective on a flat screen and delivering them to the corresponding left and right eye. This mismatch requires the viewer to override the physiologically coupled oculomotor processes of vergence and eye focus that may cause visual discomfort and fatigue. This paper discusses the depth cues in the human visual perception for both image quality and visual comfort of direct-view 3D displays. We concentrate our analysis especially on near-range depth cues, compare visual performance and depth-range capabilities of stereoscopic and holographic displays, and evaluate potential depth limitations of 3D displays from a physiological point of view.

A design method for correcting chromatic as well as spherical aberrations of variable-focus, multi-chamber liquid lenses is described. By combining suitable optical liquids with appropriate radii of the liquid's interfaces, liquid lenses with superior, diffraction-limited resolution over a wide focal tuning range are possible. For an infinite object distance, the analytic thin-lens approximation of an achromatic positive/negative varifocal liquid lens is derived and the obtained results are compared with ray-traced optimized designs which consider finite thicknesses and rigid cover glasses. As a design example, the optical performance of a 4mm-diameter positive/negative f /3.6 achromatic liquid lens is given in detail.

Large real-time holographic displays with full color are feasible with SeeReal's new approach to holography and today's technology. The display provides the information about the 3D scene in a viewing window at each observer eye. A tracking system always locates the viewing windows at the observer eyes. This combination of diffractive and refractive optics leads to a significant reduction of required display resolution and computation effort and enables holographic displays for wide-spread consumer applications. We tested our approach with two 20 inch prototypes that use two alternatives to achieve full color. One prototype uses color filters and interlaced holograms to generate the colors simultaneously. The other prototype generates the colors sequentially. In this paper we review our technology briefly, explain the two alternatives to full color and discuss the next steps toward a consumer product.

Novel solutions for large real-time holographic 3D displays are presented. The holographic display combines a tailored holographic recording scheme with active tracking of the observer. This approach dramatically reduces the demand for the space-bandwidth product of the hologram and thus allows the use of state-of-the-art spatial light modulators and enables real-time calculation. The fundamentals and challenges of the holographic display technology are described, its implementation in prototypes is demonstrated, and the bright prospects for the 3D display market are discussed.

A long-term implantable photoplethysmographic sensor system is proposed. The system employs an elastic cuff which is directly wrapped around an arterial blood vessel. The optically transparent cuff is equipped with light emitting diodes and a photo transistor including the technology of pulse oximetry. The sensor will permit real-time, continuous monitoring of important vital parameters such as arterial blood oxygen saturation and pulse rate over a long-term period in vivo. We emphasize on the specific requirements for design and instrumentation of the implantable sensor and discuss first in vitro data acquired with that new photonics-based sensor.

This paper illustrates one of the various capabilities of static diractive optical elements (DOE) benecial to realtime holographic displays. Custom kinoform-type DOE can be used as elements for illumination of the spatial light modulator, i.e. the display where the video hologram is encoded. For an RGB application of diractive optical elements, particular issues concerning the inherent wavelength-dependence have to be addressed. Multiorder DOE oer a way to compensate for chromatic as well as monochromatic aberrations. We will discuss concepts and performance of multi-order DOE, show their application in holographic displays, describe issues of fabrication and replication, and give experimental results of the multi-order DOE performance.

A fiber-optic-based, time-domain optical coherence tomography (OCT) system coupled with a pneumatically-actuated micro-lens is demonstrated. The OCT system uses a superluminescent diode emitting at a center wavelength of λ ≈ 1300 nm. Microsystem fabrication technologies employing polydimethylsiloxane (PDMS) are used to fabricate the micro-lens with an aperture of 2 mm. A B-scan is carried out while dynamically shifting the focal length of the micro-lens along the axial scan. The OCT scan results show a higher lateral resolution and higher contrast of the backscattered interference signals when using the tunable lens; hence, deeper axial scans are possible. The ability to miniaturize the dimensions of the micro-lens will allow the system to be applicable to en-face optical coherence tomography and endoscopic applications.

A miniaturized photoplethysmographic sensor system which utilizes the principle of pulse oximetry is presented. The sensor is designed to be implantable and will permit continuous monitoring of important human vital parameters such as arterial blood oxygen saturation as well as pulse rate and shape over a long-term period in vivo. The system employs light emitting diodes and a photo transistor embedded in a transparent elastic cuff which is directly wrapped around an arterial vessel. This paper highlights the specific challenges in design, instrumentation, and electronics associated with that sensor location. In vitro measurements were performed using an artificial circulation system which allows for regulation of the oxygen saturation and pulsatile pumping of whole blood through a section of a domestic pig's arterial vessel. We discuss our experimental results compared to reference CO-oximeter measurements and determine the empirical calibration curve. These results demonstrate the capabilities of the pulse oximeter implant for measurement of a wide range of oxygen saturation levels and pave the way for a continuous and mobile monitoring of high-risk cardiovascular patients.

A pneumatically-actuated micro-lens integrated in the sample arm of a time-domain optical coherence tomography (OCT) system is presented. A 50 mum thick polydimethylsiloxane (PDMS) membrane is spun onto the front side of the lens. Deep-reactive ion-etching (DRIE) is applied to create the aperture of the lens. Dynamically shifting the focal length for each A-scan step enhances the axial scan length and the contrast of the backscattered interference signal of the structures beneath the surface. The successful integration of the micro-lens with an OCT system allows its use in endoscopic in-vivo applications.

Der vorliegende Beitrag diskutiert das Nutzungspotential des deterministischen Bussystems FlexRay im Automobil. Dabei wird sowohl auf das Konzept einer zeitgesteuerten System- und Knotenarchitektur sowie deren mogliche Umsetzung naher eingegangen. In Verbindung mit dem Standard AUTOSAR und geeigneter Betriebssystemunterstutzung lasst sich ein deterministisches Zeitverhalten und dadurch eine erhebliche Verbesserung in der Qualitat von Fahrwerkregelsystemen erreichen. Erganzt wird der Artikel um praktische Erfahrungen bei der Anwendung der aktuellen Entwicklungsumgebung.

Self-calibration techniques in interferometry imply the absolute determination of the interferometer's systematic error without the need for a high-quality, precisely-known calibration standard. By taking separate measurements at different positions and under different orientations, the interferometer's error can be determined in an absolute manner even with non-perfect optical elements. This paper discusses the versatile possibilities of using diffractive optical elements as calibration tools in wavefront testing interferometry.