Browsing by Author "Osten, Wolfgang"

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    Evaluation of a time-gated-single-pixel-camera as a promising sensor for autonomous vehicles in harsh weather conditions
    (2023) Bett, Claudia Monika; Daiber-Huppert, Max; Frenner, Karsten; Osten, Wolfgang
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    Opposed-view dark-field digital holographic microscopy
    (2014) Faridian, Ahmad; Pedrini, Giancarlo; Osten, Wolfgang
    Scattering and absorption belong to the major problems in imaging the internal layers of a biological specimen. Due to the structural inhomogeneity of the specimen, the distribution of the structures in the upper layers of a given internal structure of interest is different from the lower layers that may result in different interception of scattered light, falling into the angular aperture of the microscope objective, from the object in each imaging view. Therefore, different spatial frequencies of the scattered light can be acquired from different (top and bottom) views. We have arranged an opposed-view dark-field digital holographic microscope (DHM) to collect the scattered light concurrently from both views with the aim to increase the contrast of internal structures and improve the signal-to-noise ratio. Implementing a DHM system gives the possibility to implement digital refocusing process and obtain multilayer images from each side without a depth scan of the object. The method is explained and the results are presented exemplary for a Drosophila embryo.
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    Optische Messtechnik an den Grenzen zwischen Makro und Nano
    (2005) Osten, Wolfgang; Kerwien, Norbert
    Schaut man in der Geschichte zurück, so ist in den unterschiedlichsten Bereichen der Wissenschaft der Erkenntnisgewinn vielfach erst durch optische Techniken möglich geworden. Dies mag damit zusammenhängen, dass die visuelle Wahrnehmung für den Menschen im Kontext aller Sinne von herausragender Bedeutung ist. „I see!“ Diese zwei Worte machen deutlich, dass sich das „Sehen“ auch über den angelsächsischen Bereich hinaus nicht nur auf die visuelle Wahrnehmung beschränkt, sondern eng mit dem Verständnis und Begreifen von Zusammenhängen verknüpft ist. Es ist daher auch nicht verwunderlich, dass die großen Meilensteine in der Entwicklung der Wissenschaft eng mit den Erfolgen auf dem Gebiet der Optik verknüpft sind. Das Einsteinjahr 2005 erinnert uns vor allem daran, dass Einstein im Jahr 1905 mehrere bahnbrechende Erkenntnisse veröffentlicht hat, von denen einige wie die spezielle Relativitätstheorie und die Erklärung des lichtelektrischen Effekts aufs engste mit der Optik verknüpft sind. Weniger bekannt ist, dass er gerade für die letztgenannte Arbeit 1921 den Nobelpreis für Physik erhalten hat. Weitere anschauliche Beispiele bieten die Astronomie und der Bereich der Biologie und Medizin. Während bei der einen die Optik die technische Grundlage für den Blick in die Tiefen des Alls lieferte, richtete sich in der Biologie und Medizin das Interesse auf die Mikrowelt mit stetig kleiner werdenden Strukturen. Durch die Entwicklung immer leistungsfähigerer Teleskope und Mikroskope wurden jedoch auch die physikalischen Grenzen, denen die optischen Technologien unterliegen, deutlich.
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    Phase errors in high line density CGH used for aspheric testing : beyond scalar approximation
    (2013) Peterhänsel, Sandy; Pruss, Christof; Osten, Wolfgang
    One common way to measure asphere and freeform surfaces is the interferometric Null test, where a computer generated hologram (CGH) is placed in the object path of the interferometer. If undetected phase errors are present in the CGH, the measurement will show systematic errors. Therefore the absolute phase of this element has to be known. This phase is often calculated using scalar diffraction theory. In this paper we discuss the limitations of this theory for the prediction of the absolute phase generated by different implementations of CGH. Furthermore, for regions where scalar approximation is no longer valid, rigorous simulations are performed to identify phase sensitive structure parameters and evaluate fabrication tolerances for typical gratings.
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    Polarization scramblers with plasmonic meander-type metamaterials
    (2012) Schau, Philipp; Fu, Liwei; Frenner, Karsten; Schäferling, Martin; Schweizer, Heinz; Giessen, Harald; Gaspar Venancio, Luis Miguel; Osten, Wolfgang
    Due to plasmonic excitations, metallic meander structures exhibit an extraordinarily high transmission within a well-defined pass band. Within this frequency range, they behave like almost ideal linear polarizers, can induce large phase retardation between s- and p-polarized light and show a high polarization conversion efficiency. Due to these properties, meander structures can interact very effectively with polarized light. In this report, we suggest a novel polarization scrambler design using spatially distributed metallic meander structures with random angular orientations. The whole device has an optical response averaged over all pixel orientations within the incident beam diameter. We characterize the depolarizing properties of the suggested polarization scrambler with the Mueller matrix and investigate both single layer and stacked meander structures at different frequencies. The presented polarization scrambler can be flexibly designed to work at any wavelength in the visible range with a bandwidth of up to 100 THz. With our preliminary design, we achieve depolarization rates larger than 50% for arbitrarily polarized monochromatic and narrow-band light. Circularly polarized light could be depolarized by up to 95% at 600 THz.
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    Remote laboratory for digital holographic metrology
    (2011) Wilke, Marc; Situ, Guohai; Aleksenko, Igor; Riedel, Margarita; Pedrini, Giancarlo; Jeschke, Sabina; Osten, Wolfgang
    Advances in information technology open up the potential of combining optical systems with net based infrastructures, allowing for remote inspection and virtual metrology. In this paper, we report our recent work on building a remote laboratory for digital holographic metrology. We describe the architecture and the techniques involved in setting up the remote controlling metrology system. Further consideration will be given to the integration into an advanced infrastructure for remote experimentation, data storage and publication. Some other important issues such as information security will not be addressed.
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    Scatter-plate microscopy with spatially coherent illumination and temporal scatter modulation
    (2021) Ludwig, Stephan; Ruchka, Pavel; Pedrini, Giancarlo; Peng, Xiang; Osten, Wolfgang
    Scatter-plate microscopy (SPM) is a lensless imaging technique for high-resolution imaging through scattering media. So far, the method was demonstrated for spatially incoherent illumination and static scattering media. In this publication, we demonstrate that these restrictions are not necessary. We realized imaging with spatially coherent and spatially incoherent illumination. We further demonstrate that SPM is still a valid imaging method for scatter-plates, which change their scattering behaviour (i.e. the phase-shift) at each position on the plate continuously but independently from other positions. Especially we realized imaging through rotating ground glass diffusers.