Günther Wernicke

Parameter-optimized digital holographic microscope for high-resolution living-cell analysis

A parameter-optimized off-axis setup for digital holographic microscopy is presented for simultaneous, high-resolution, full-field quantitative amplitude and quantitative phase-contrast microscopy and the detection of changes in optical path length in transparent objects, such as undyed living cells. Numerical reconstruction with the described nondiffractive reconstruction method, which suppresses the zero order and the twin image, requires a mathematical model of the phase-difference distribution between the object wave and the reference wave in the hologram plane. Therefore an automated algorithm is explained that determines the parameters of the mathematical model by carrying out the discrete Fresnel transform. Furthermore the relationship between the axial position of the object and the reconstruction distance, which is required for optimization of the lateral resolution of the holographic images, is derived. The lateral and the axial resolutions of the system are discussed and quantified by application to technical objects and to living cells.

Binary diffractive beam splitters with arbitrary diffraction angles.

Diffractive optical beam splitters designed with iterative Fourier transform type algorithms can produce only certain diffraction angles given by the spatial frequencies used for the computations, which are multiples of a certain base spatial frequency. We have developed a design algorithm that overcomes this limitation and can be used to compute binary diffractive elements with arbitrary diffraction angles. The simulated and experimentally measured properties of optical elements producing beam arrays in circular arrangements are presented and discussed.

Influence of flatness distortion on the output of a liquid-crystal-television-based joint transform correlator system.

The use of liquid-crystal panels from a commercially available Sanyo video projector as spatial light modulators in a standard joint transform correlator system is investigated. It is found that the flatness distortion of the panels disturbs the output correlation signal in general. Since the reported solutions for the flatness corrections are either expensive (liquid gates) or suffer from low light efficiency (holographic techniques), we have investigated a possibility to minimize the influence of these distortions on the correlation output without flatness correction. First, we quantify optical flatness across the transparent panel area, and then we measure the effects of flatness distortion by changing the display location of the input objects and the resulting joint power spectrum. It is found that the correlation peak is 1 order of magnitude more sensitive to phase distortions of the input scene than to the same distortions of the joint power spectrum. Choosing the flattest location on the panel allows the utilization of the panels to be demonstrated through recognition of cuneiform inscription signs.

Holography and holographic pattern recognition for preservation and evaluation of cultural-historic sources

In the study of ancient cultures, a major difficulty is the fact that available remains of historic and cultural value are often in the possession of different institutions and, therefore, are not directly accessible simultaneously. Even fragments of such objects are often stored at different places, which creates an additional obstacle to the task of their recombination. Moreover, they are endangered by natural or man-made destruction, and many of them are already in such a state, that information regarding the surface structure is hardly interpretable. Thus, techniques for high-resolution 3-D documentation and fine-structure analysis as well as feature enhancement and extraction are indispensable. Documentation by two-dimensional photography gives only a restricted impression of the threedimensional appearance of these objects and is insufficient for a detailed analysis of the spatial fine structure of the surface relief. Plaster casts from molds display the three-dimensional geometry of the object, but show restricted spatial resolution, besides the risk of destruction of fine structures during the molding process. In order to overcome these obstacles holographic techniques can be used because of

Holographic Techniques Application in Analysing Cuneiform Inscriptions

Abstract For the investigation of ancient cuneiform inscriptions, an optoelectronic device with several functions was used and various spatial filtering experiments were performed. By applying twofold amplitude filtering, spatial frequency features of different cuneiform elements have been enhanced, extracted, and analysed. The correlation experiments were performed by applying complex matched filtering. Input data were significantly reduced during the filtering procedures. The results presented demonstrate the possibility of obtaining information such as similarity measures between different objects in the cluttered scene analysis problem.

Some Investigations in Holographic Microscopic Interferometry with Respect to the Estimation of Stress and Strain in Micro-Opto-Electro-Mechanical Systems (MOEMS)

Holographic microscopy with conjugate reconstruction for the interferometric determination of three-dimensional displacement was used for the investigation of the mechanical behaviour of micromechanic and microelectronic components. An experimental set-up for the exposure of the holographic interferograms is described for the application of the spatial heterodyne technique, for the application of phase shifting, and for electro-optic holography. Three holograms for different illumination directions recorded on one holographic plate were reconstructed conjugately, and spatial-heterodyne technique as well as phase-shift technique were used to evaluate the interferograms. Only by conjugated reconstruction, it is possible to obtain a perfectly optimised interferometer for the static evaluation method. The evaluation of interferograms, which are strongly disturbed by speckle noise, can be performed successfully. A comparison of the results of the application of these techniques is given. The influence of the speckle effect on the resolution was investigated.

Characterization of the cuneiform signs by the use of a multifunctional optoelectronic device

The cuneiform-inscription (CI) signs recorded on the original clay tablet known as HS 158b from Nippur (1329 B.C.) have been characterized by the use of a multifunctional optoelectronic device. Properties such as features in object and Fourier space or similarity measures between the CI sign samples were investigated by the application of various numerical and experimental procedures. An overall algorithm of the experimental work is given, and the corresponding particular steps are described. For describing the objects from the CI font numerically, a mathematical model is introduced. To decrease the sensitivity between different samples of a sign (in-class objects) and to increase the discrimination of other signs (out-of-class objects), we designed and implemented, besides digital techniques, a coherent optical technique for averaging a training set of in-class objects. The preliminary correlation experiments conducted on several CI signs illustrate the usefulness of the proposed approach.

Recognition of cuneiform inscription signs by use of a hybrid-optoelectronic correlator device

A hybrid-optoelectronic correlator device and an algorithm are proposed for recognizing cuneiform inscription signs. The device is based on the extended correlator architecture with three liquid-crystal display(s) (LCD)s and three light detectors: one CCD camera for capturing the input image, oneLCD for displaying the input image, two LCDs for the complex correlation filter (amplitude and phase parts), and two detectors for measuring the total and peak intensities of the output correlation information. The recognition algorithm is designed to allow automatic as well as real-time processing. The recognition results are given for the cuneiform signs impressed on an original clay tablet. The investigated tablet (VAT 12890 of the Pergamon Museum, Berlin, Germany) was found in Bogazköy (Hattusha) and dates from the 14th century B.C. It is a fragment of the Epic of Gilgamesh in the Akkadian language with a large number of the sign samples.

High resolution optical reconstruction of digital holograms

High resolution spatial light modulators provide a new technology option for adaptive optics, which can be used for the realization of dynamic diffractive devices. In this work, we have used the possibilities of modern SLM technology for the optical reconstruction of digital holograms. By this method it is possible to reconstruct an optical wave field and to manipulate it practically in real time. Further investigations will evaluate applications in the field of optical metrology.

Optische Zeichenerkennung an Keilschriften mit Hilfe holographischer Filterung

Cuneiform inscriptions in clay tablets are historic remainders of one of the first human civilizations on earth. About 500000 of these are stored in different museums all over the world. One aim of historians is to recognize damaged signs and to recombine tablet fragments. For that purpose methods of optical pattern recognition and optoelectronic image processing could be a helpful tool and had to be tested. The application of an extended optoelectronic correlator system to single wedges and models of cuneiform signs is described. The results show that classical matched spatial filters of averaged signs provide low sensitivity for signs that are of the same kind and high-level discrimination capacity for signs not in the same class. D ie Techniken der Holographie werden in vielen Gebieten der optischen Bildverarbeitung zur paralMen Datenverdichtung und Mustererkennung eingesetzt. Bei der Klassifizierung und Dokumentation von arch~ologischen Objekten, insbesondere dreidimensionaler Schrifttrfiger wie Keilschrifttafeln, sowie zu ihrer Archivierung wurden sie bisher jedoch noch nicht verwendet. Anwendungen der Holographie auf diesem Gebiet beschrfinkten sich auf die Gestaltung von Ausstellungen mit Displayhologrammen. Im folgenden soll ein Aspekt der Anwendung holographischer Techniken behandelt werden, der ft~r die LOsung einiger Teilprobleme in der Archfiologie vielversprechende Ansfitze ermOglicht. Archfiologische Fundstt~cke sind der wissenschaftlichen Forschung besonders dann schwer zug~nglich, wenn sie nur in Form von Bruchstt~cken vorliegen, die Oberfl~chen durch Erosion oder Korrosion beeintrfichtigt wurden oder Risse, Kratzer, Verunreinigungen usw. die enthaltenen Informationen nahezu unauswertbar machen. Ft~r die Rekonstruktion von arch~iologischen Fundstacken anhand von Merkmalen, z.B. Konturen und Kanten von Scherben, Strukturierungen auf der Oberffiche sowie Formen, Kr~immungen usw., werden zwar Bildverarbeitungsverfahren angewandt, diese gestatten jedoch lediglich das Zusammenft~gen von Bruchstt~cken, die sich am gleichen Ort befinden [1]. In der Altorientalistik sind hfiufig historische Fundstt~cke, insbesondere Tontafeln mit Keilinschriften bzw. Bruchstt~cke von diesen, an verschiedenen Stellen der Erde gelagert. Sie sind daher nur in wenigen Ffillen der direkten Bearbeitung durch den Epigraphisten zug~nglich. (Eine Einfahrung zu Keilschriften, ihre Struktur und Bedeutung ist zu finden bei Walker [2].) Bei Transporten besteht durch Umwelteinflt~sse, z.B. Feuchtigkeitsfinderungen der Umgebung, die Gefahr, dab die in den Keilschriften enthaltenen Informationen, die Zeugnis aber mehrere Jahrtausende Menschheitsgeschichte ablegen, zerstOrt werden und damit far immer verlorengehen.