Beckert, Erik

Bruchmann, Claudia

Eberhardt, Ramona

Peschel, Thomas

Tünnermann, Andreas

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PROCEEDINGS            Faculty of Mechanical Engineering   ..........................................................................................  PROSPECTS IN MECHANICAL ENGINEERING  8 - 12 September 2008            www.tu-ilmenau.de     Home / Index: http://www.db-thueringen.de/servlets/DocumentServlet?id=17534 53. IWKInternationales Wissenschaftliches KolloquiumInternational Scientific ColloquiumPublished by Impressum  Publisher Der Rektor der Technischen Universität Ilmenau Herausgeber Univ.-Prof. Dr. rer. nat. habil. Dr. h. c. Prof. h. c. Peter Scharff  Editor Referat Marketing und Studentische Angelegenheiten Redaktion Andrea Schneider    Fakultät für Maschinenbau Univ.-Prof. Dr.-Ing. habil. Peter Kurz, Univ.-Prof. Dr.-Ing. habil. Rainer Grünwald, Univ.-Prof. Dr.-Ing. habil. Prof. h. c. Dr. h. c. mult. Gerd Jäger, Dr.-Ing Beate Schlütter, Dipl.-Ing. Silke Stauche  Editorial Deadline  17. August 2008 Redaktionsschluss  Publishing House Verlag ISLE, Betriebsstätte des ISLE e.V. Verlag Werner-von-Siemens-Str. 16, 98693 llmenau   CD-ROM-Version:  Implementation  Technische Universität Ilmenau Realisierung Christian Weigel, Helge Drumm  Production CDA Datenträger Albrechts GmbH, 98529 Suhl/Albrechts Herstellung  ISBN: 978-3-938843-40-6 (CD-ROM-Version)   Online-Version:  Implementation Universitätsbibliothek Ilmenau Realisierung  Postfach 10 05 65  98684 Ilmenau       © Technische Universität Ilmenau (Thür.) 2008  The content of the CD-ROM and online-documents are copyright protected by law. Der Inhalt der CD-ROM und die Online-Dokumente sind urheberrechtlich geschützt.   Home / Index: http://www.db-thueringen.de/servlets/DocumentServlet?id=17534  Figure 1: Product of deflection and force depending on relative height a and strength c 53rd Internationales Wissenschaftliches Kolloquium Technische Universität Ilmenau  08 – 12 September 2008  C. Bruchmann / T. Peschel / R. Eberhardt / E. Beckert / A. Tünnermann   Concept and Dimensioning of Thin Ceramic High Power Mirrors Introduction  High power laser processing of sheet metal including cutting, welding and drilling has gained much in importance in recent years. A significant increase of system power and beam quality has enabled the progress in e.g. cutting of thick plates. The beam shaping inside the laser is made either with lenses of large diameters and an optional cooling or massive mirrors that can also be cooled. This work develops a new design for laser beam profile shaping mirrors that is based on thin ceramic wafers with a reflecting sur-face and integrated piezoelectric zirconat titanat (PZT) actuators. The present work dis-cusses various concepts for thin high power adaptive mirrors and their dimensioning. Material Selection  The further progress in laser processing will depend heavily on a further increase and tuneability of the system power and on an enhanced beam quality. Laser profiles for material machining are typically shaped as flattop, whereas profiles inside the laser are Gaussian. This leads to an increasing need for high power shaping devices. Such high power adaptive mirrors are constructed by applying piezoelectric layers on the backside of the mirror. The set-up with a single layer piezoelectric material on a passive substrate is already known as monomorph and extensively described analytically [1].  The relative strength c and height a of the substrate to the PZT thick film determines the product of deflection and force of the monomorph (Fig. 1). Thin substrates with a high elastic modulus lead to the highest product of deflection and force. To keep the manufacturing effort low, a screen printing process for the application of a PZT thick film was chosen. Films with a thickness of 80-130 µm were applied on the microelectronic substrates alumina (Al2O3), zircon oxide (ZrO2), low Figure 2 starting design of adaptive LTCC mirror; 2 bottom: new design concept temperature co-fired ceramics (LTCC) and silicon (Si) [2].  The material selection for conventional high power mirrors results basically either in a low thermal expansion material (e.g., ULE) or a high thermal conductive material (e.g., copper). In contrast to the established solutions, a thin multilayer material system is pro-posed and not a massive design. Hence requires more sophisticated material selecting tools.  Multilayer System Concepts for Reducing Thermal Influences on Mirrors  Adaptive mirror systems under a thermal load and based on LTCC substrates were in-vestigated. LTCC was chosen as substrate material because it allows for easy integra-tion of metallizations and thermal vias. A piezoelectric layer with a bottom electrode (15 µm thickness) and a top gold electrode is applied on the back. A metallization as a reflecting surface is applied on the substrates front. The modeled mirror has a diameter of 100 mm and a thickness between 200 and 300 µm, depending on the number of LTCC layers.  Studies on the performance of different reflecting surface metallization materials (copper, nickel- phosphorous, silver) under high thermal laser load (laser beam diameter 30 mm, Gaussian profile,1 W material absorption) were carried out with FEA. It is shown that copper and silver lead to low thermal induced deformation. Three layers of LTCC lead to less deformation compared to two layers of LTCC. An additional inner metallization between two LTCC layers lowers the thermal induced deformation once more. Starting from FEA-Simulations and experimental validations new concepts of LTCC-based high power adaptive mirrors are presented.     References:  [1] Ellis, Edric M.: Low-cost Bimorph Mirrors in Adaptive Optics, Diss., Imperial College of Science, London, 1999 [2] Gebhardt S., Schönecker A., Bruchmann C., u.a.: Active Optical Structures by Use of PZT Thick Films, to be published on CICMT 2008  Authors:    Claudia Bruchmann1 / Thomas Peschel2 / Ramona Eberhardt2/ Erik Beckert2 / Andreas Tünnermann1,2  1Friedrich Schiller University Jena               2Fraunhofer Institut für Optik und Institute of Applied Physics      Feinmechanik Albert-Einstein-Straße 15     Albert-Einstein-Str. 7 07745 Jena, Germany      07745 Jena, Germany  Phone: +49(0)3641-807343 Fax: +49(0)3641-807604 E-mail: claudia.bruchmann@iof.fraunhofer.de 

Concept and dimensioning of thin ceramic high power mirrors

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Concept and dimensioning of thin ceramic high power mirrors

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