Karin Wiesauer

En-face scanning optical coherence tomography with ultra-high resolution for material investigation

Optical coherence tomography (OCT) is an emerging technique for cross-sectional imaging, originally developed for biological structures. When OCT is employed for material investigation, high-resolution and short measurement times are required, and for many applications, only transversal (en-face) scans yield substantial information which cannot be obtained from cross-sectional images oriented perpendicularly to the sample surface alone. In this work, we combine transversal with ultra-high resolution OCT: a broadband femto-second laser is used as a light source in combination with acousto-optic modulators for heterodyne signal generation and detection. With our setup we are able to scan areas as large as 3 x 3 mm2 with a sensitivity of 100 dB, representing areas 100 times larger compared to other high-resolution en-face OCT systems (full field). We demonstrate the benefits of en-face scanning for different applications in materials investigation.

Transversal ultrahigh-resolution polarizationsensitive optical coherence tomography for strain mapping in materials.

Optical coherence tomography (OCT) and its extension, polarization-sensitive (PS-)OCT, are techniques for contactless and nondestructive imaging of internal structures. In this work, we apply PS-OCT for material characterization. We use a transversal scanning, ultra-high resolution (UHR-)PS-OCT setup providing cross-sectional as well as inplane information about the internal microstructure, the birefringence and the orientation of the optical axis within the material. We perform structural analysis and strain-mapping for different samples: we show the necessity of UHR imaging for a highly strained elastomer sample, and we discuss the effect of large birefringence on the PS-OCT images. Furthermore, we investigate high-aspect ratio photoresist moulds for the production of microelectromechanical parts (MEMS), demonstrating that transversal UHR-PSOCT is a promising tool for non-destructive strain-mapping.

Investigation of polymer and polymer/fibre composite materials with optical coherence tomography

Optical coherence tomography (OCT), a technique originally proposed for applications in the field of biomedical diagnostics, is shown to be an efficient measurement technique for a multitude of problems posed in technical engineering and material research. Especially advanced OCT modifications, involving ultrahigh-resolution (UHR) imaging and fast Fourier-domain (FD) techniques, show promising potential, as successfully demonstrated in this paper by a variety of applications from the field of polymer materials. Thin polymer films and multilayer structures as well as polymer blends and fibre-reinforced polymer composites are successfully evaluated by means of UHR-OCT and FD-OCT performed at different wavelengths. In addition, comparative measurements have been performed with confocal microscopy and synchrotron computed tomography to show the potential and advantages of the OCT measurement technique.

Spatially Resolved Stress Measurements in Materials With Polarisation‐Sensitive Optical Coherence Tomography: Image Acquisition and Processing Aspects

:  We demonstrate that polarisation-sensitive optical coherence tomography (PS-OCT) is suitable for mapping the stress distribution within materials in a contact-free and non-destructive way. In contrast to transmission photoelasticity measurements, the samples do not have to be transparent but can be of scattering nature. Denoising and analysis of fringe patterns in single PS-OCT retardation images are demonstrated to be the bases for a quantitative whole-field evaluation of the internal stress state of samples under investigation.

Imaging of the inner structure of cave bear teeth by novel non-destructive techniques

The potential of non-destructive imaging techniques, such as optical coherence tomography (OCT), X-ray micro-3D computed tomography (μ-CT) and terahertz (THz) imaging has been considered for structural and age diagnostic tasks in the field of paleontology. In particular OCT, a high-resolution, non-destructive and contactless technology for two and three dimensional (2D, 3D) imaging, was evaluated for the investigation of dental cementum microstructures, exemplified by cave bear teeth. OCT with a depth resolution in the micron range showed its ability to count the annual appositional lines consisting of cementum and thus to determine the age of the individual. As additional method also THz technology is presented which exhibits much larger penetration depths up to centimeters, but with a lower resolution, in contrast to OCT. Thus, THz imaging gives insight into the internal structure of the cave bear teeth on a larger scale. Furthermore, to complete the variety of considered non-destructive imaging techniques, μ-CT has been applied for analysis of the teeth structures, in comparison to OCT and THz imaging results. The combination of these complementary methods is well suited for the non-destructive characterization of teeth. Elisabeth Leiss-Holzinger. Research Center for Non-Destructive Testing GmbH, Science Park 2/2.OG, Altenberger Straße 69, 4040 Linz, Austria; elisabeth.leiss@recendt.at Karin Wiesauer. Research Center for Non-Destructive Testing GmbH, Science Park 2/2.OG, Altenberger Straße 69, 4040 Linz, Austria; wiesauer.k@gmail.com Henrike Stephani. Fraunhofer Institute for Industrial Mathematics, Fraunhofer-Platz 1, 67663 Kaiserslautern, Germany; henrike.stephani@itwm.fraunhofer.de Bettina Heise. FLLL at Johannes Kepler University Linz and CDL MS-MACH, Altenberger Strasse 69, 4040Linz, Austria; bettina.heise@jku.at and Research Center for Non-Destructive Testing GmbH, Science Park 2/2.OG, Altenberger Straße 69, 4040 Linz, Austria; bettina.heise@recendt.at David Stifter. CDL MS-MACH, Altenberger Strasse 69, 4040Linz, Austria; david.stifter@jku.at Benjamin Kriechbaumer. University of Applied Sciences Upper Austria, Linz Campus, Garnisonstraße 21, 4020 Linz, Austria; benjamin.kriechbaumer@gmail.com Stefan J. Spachinger. University of Applied Sciences Upper Austria, Wels Campus, Stelzhamerstraße 23, 4600 Wels, Austria; no email PE Article Number: 18.1.1T Copyright: Palaeontological Association February 2015 Submission: 9 May 2014. Acceptance: 21 January 2015 Leiss-Holzinger, Elisabeth, Wiesauer, Karin, Stephani, Henrike, Heise, Bettina, Stifter, David, Kriechbaumer, Benjamin, Spachinger, Stefan J., Gusenbauer, Christian, and Withalm, Gerhard. 2015. Imaging of the inner structure of cave bear teeth by novel nondestructive techniques. Palaeontologia Electronica 18.1.1T: 1-15. palaeo-electronica.org/content/2015/1058-optical-tomography-comparisons LEISS-HOLZINGER ET AL.: OPTICAL TOMOGRAPHY COMPARISONS Christian Gusenbauer. University of Applied Sciences Upper Austria, Wels Campus, Stelzhamerstraße 23, 4600 Wels, Austria; Christian.Gusenbauer@fh-wels.at Gerhard Withalm. Institute of Palaeontology, University of Vienna, Althanstraße 14, 1090 Wien, Austria; gerhard.withalm@univie.ac.at

Ultra-high resolution optical coherence tomography for material characterization and quality control

Optical coherence tomography (OCT), so far mainly used in the biomedical field, has a high potential as non-destructive and contactless technique for material characterization and analysis. For these applications, OCT systems with ultra-high resolution in the micrometer range and capable of high imaging speeds are required. In this work, we combine ultra-high resolution imaging using a femtosecond Ti:sapphire laser as light source with the concepts of transversal OCT. Based on acquisition by heterodyne detection via acousto-optic modulators (AOMs), and by using an xy-galvano scanner unit we are able to obtain en-face scans with sizes as large as 3 x 3 mm2 within a few seconds. The ultra-high resolution of our OCT system of 2.95 μm axially and 4 μm laterally, both in air, is shown to be essential for imaging of different compounds and fibre materials. We demonstrate the benefits of en-face scanning OCT for various applications in material investigation where in-plane information is of interest which can hardly be obtained by cross-sectional OCT.

Optische Kohärenztomografie als neues Werkzeug für die zerstörungsfreie Werkstoffprüfung (Optical Coherence Tomography as a Novel Tool for Non-Destructive Material Characterization)

Mittels optischer Kohärenztomografie (OCT) können in kontaktfreier Weise Querschnittsbilder von semitransparenten Proben aufgenommen werden. In diesem Artikel werden instrumentelle Erweiterungen der OCT vorgestellt, welche in der zerstörungsfreien Materialcharakterisierung zur Anwendung kommen können. Messungen an diversen Materialproben, wie z. B. an Fotolackschichten für die Fabrikation von mikromechanischen Teilen, wurden mit verschiedenen OCT-Aufbauten durchgeführt, um die individuellen Vorteile der ultrahochauflösenden OCT, der schnellen Fourier-Domain-OCT und der polarisationssensitiven OCT aufzuzeigen. Optical coherence tomography (OCT) provides depth-resolved information on the internal geometry of samples in a contact-free way. We present advanced methods of OCT for applications in materials research and non-destructive sample evaluation. For comparison and demonstration, different OCT setups are used for the imaging of diverse material samples like thick photoresist moulds for the fabrication of micro-electromechanical parts: a standard resolution OCT, a high-speed and high-resolution spectral domain OCT, as well as a ultrahigh-resolution OCT with polarization detection capability.

Optische Kohärenztomografie und 3D-Röntgen-Computertomografie: Zwei Methoden zur zerstörungsfreien Materialprüfung und dimensionellen Messung

Kurzfassung In dieser Publikation wird die optische Kohärenztomografie (OCT) mit der Mikro-Röntgen-Computertomografie (μ-CT) verglichen. Optische Kohärenztomografie ist eine neue, berührungslose und zerstörungsfreie Methode, die es erlaubt, Querschnittsaufnahmen einer Probe anzufertigen. Mikro-3D-Röntgen-Computertomografie ist eine Werkstoffprüfmethode, bei der ein CT-Scanner mit einem Matrixdetektor und einer Mikrofokusröhre eine Reihe von Röntgen-Absorptionsbildern erzeugt, die benutzt werden, um ein rekonstruiertes 3D-Bild des Objektes herzustellen. Die Vor- und Nachteile und die erreichbaren Genauigkeiten von OCT und μ-CT für die Charakterisierung von verschiedenen Materialsystemen und für die Messungen von Dimensionen werden erläutert. Die untersuchten Materialsysteme sind faserverstärkte Kunststoffe, Kunststoffschäume, komplexe Kunststoffbauteile, Multischichtfolien, eine Laminatschichtstruktur sowie diverse Teststrukturen und -bauteile.

Ultrahigh-Resolution Transversal Polarization-Sensitive Optical Coherence Tomography: Structural Analysis and Strain-Mapping

Optical coherence tomography (OCT), originally developed and so far nearly exclusively used for biomedical applications (e.g., [1,2]), is a contact-free, non-destructive technique based on low-coherence interferometry to image structures within translucent and turbid materials. Commonly, cross-sectional reflectivity images with a depth-resolution determined by the coherence length of the near-infrared light source are obtained. When OCT is performed in a polarization sensitive way (PS-OCT), additional information about birefringence within a material is obtained by mapping the retardation between ordinary and extraordinary rays [3]. Because birefringence is induced when strain occurs, PS-OCT provides depth resolved information about the internal stress within a sample.

Ultra-high resolution polarization sensitive transversal optical coherence tomography for structural analysis and strain mapping

Optical coherence tomography (OCT) is a contactless and non-invasive technique nearly exclusively applied for bio-medical imaging of tissues. Besides the internal structure, additionally strains within the sample can be mapped when OCT is performed in a polarization sensitive (PS) way. In this work, we demonstrate the benefits of PS-OCT imaging for non-biological applications. We have developed the OCT technique beyond the state-of-the-art: based on transversal ultra-high resolution (UHR-)OCT, where an axial resolution below 2 μm within materials is obtained using a femtosecond laser as light source, we have modified the setup for polarization sensitive measurements (transversal UHR-PS-OCT). We perform structural analysis and strain mapping for different types of samples: for a highly strained elastomer specimen we demonstrate the necessity of UHR-imaging. Furthermore, we investigate epoxy waveguide structures, photoresist moulds for the fabrication of micro-electromechanical parts (MEMS), and the glass-fibre composite outer shell of helicopter rotor blades where cracks are present. For these examples, transversal scanning UHR-PS-OCT is shown to provide important information about the structural properties and the strain distribution within the samples.