TY - CONF A1 - Puthiyaveettil, N. A1 - Krishna, S. A1 - Kidangan, R. A1 - Unnikrishnakurup, Sreedhar A1 - Krishnamurthy, C. V. A1 - Ziegler, Mathias A1 - Myrach, Philipp A1 - Balasubramaniam, Krishnan T1 - In-line laser thermography for crack detection at elevated temperature: A Numerical modeling study N2 - The detection and characterization of cracks prior to damage is a technologically and economically highly significant task and is of very importance when it comes to safety-relevant structures. The evaluation of a components life is closely related to the presence of cracks in it. Laser thermography has already high capability for the detection of surface cracks and for the characterization of the geometry of artificial surface flaws in metallic samples. Crack detection in metallic samples at high temperature is highly significant in present manufacturing scenario. During the casting process of billets, surface cracks form, due to the suboptimal cooling rates. These cracks reduce value of the billet and must be removed using machining process after cooling. This secondary process increases cost of manufacturing. In this work we developed a heat transfer model for laser thermography to study the thermal contrast variation with increase in surface temperature using finite element method (FEM). Here we are mainly concentrating the capability of the scanning laser thermography in crack detection which are in elevated temperature and numerical modeling study of thermal contrast variation of crack with respect increase in metal surface temperature. This study is important to prove the capability of laser thermography for crack detection in elevated temperature. Since we are using High power CW Laser to local heating of the metal surface which can give relatively high thermal contrast even at elevated temperature compare to other heating source. Here we are modeled and simulated 2D laser scanning across a surface breaking crack and developed an algorithm to produce the vicinity of crack. The algorithm we developed applied for various surface temperature data. And validated the credibility of the algorithm with experimental data. T2 - 13th Quantitative Infrared Thermography Conference 2016 CY - Gdansk, Poland DA - 04.07.2016 KW - Thermal contrast KW - Laser thermography KW - Thermography KW - Surface cracks KW - Elevated temperatures KW - FEM PY - 2016 UR - http://www.ndt.net/article/qirt2016/papers/092.pdf DO - https://doi.org/10.21611/qirt.2016.092 VL - 2016 SP - 588 EP - 596 PB - QIRT 2016 Proceedings AN - OPUS4-39105 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Thiel, Erik A1 - Kreutzbruck, M. A1 - Ziegler, Mathias T1 - Laser-projected photothermal thermography using thermal wave field interference for subsurface defect characterization N2 - The coherent superposition of two anti-phased thermal wave fields creates a zone of destructive interference which is extremely sensitive to the presence of defects without any reference measurements. Combining a high power laser with a spatial light modulator allows modulating phase and amplitude of an illuminated surface that induces spatially and temporally controlled thermal wave fields. The position and depth of defects are reconstructed from analysis of the Amplitude and Phase of the resulting photothermal signal. The proposed concept is experimentally validated and supported by numerical modeling. KW - Thermal waves KW - Active thermography KW - DMD KW - Spatial light modulator KW - Subsurface defects PY - 2016 UR - http://scitation.aip.org/search?value1=laser+projected+photothermal&option1=all&option912=resultCategory&value912=ResearchPublicationContent&operator8=AND&option8=pub_serialIdent&value8=aip%2Fjournal%2Fapl&qs=true DO - https://doi.org/10.1063/1.4963139 SN - 0003-6951 VL - 109 IS - 12 SP - 123504-1 EP - 123504-4 PB - AIP Publishing CY - Melville, New York AN - OPUS4-37590 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ziegler, Mathias A1 - Myrach, Philipp A1 - Neding, Benjamin ED - J. Grosch, ED - E.J. Mittemeijer, T1 - Wärmebehandlung und zerstörungsfreie Prüfung: Oberflächenrisse mit der Laser-Thermografie finden N2 - Die Thermografie als zerstörungsfreies Prüfverfahren erlaubt das Erkennen einer Vielzahl von Defekten in unterschiedlichsten Werkstoffen. Hierzu ist zum einen eine Energiequelle erforderlich, welche einen Wärmestrom im Werkstück erzeugt, und zum anderen eine Infrarot-Kamera, welche den orts- und zeitabhängigen Temperaturverlauf der Werkstückoberfläche analysiert. Neue Ansätze unter Verwendung von Lasern ermöglichen nun auch die Prüfung auf winzige Oberflächenrisse. Die aktuelle Grenze der Nachweisempfindlichkeit für mittels klassischer Thermografie nur schwer prüfbare hochreflektierende Metalloberflächen liegt mit Rissbreiten und -tiefen bis hinunter in den Sub-Mikrometerbereich und damit im Bereich der fluoreszierenden Magnetpulver- und Eindringprüfung. Dabei sind jedoch weder Verbrauchsmittel, noch eine Oberflächenpräparation notwendig und eine Prüfung kann berührungslos und automatisiert über Entfernungen bis in den Meter-Bereich erfolgen. Bei der Wärmebehandlung und insbesondere beim Randschichthärten mittels Laserstrahlung stehen ebenfalls hochleistungsfähige Energiequellen zur Erzeugung intensiver dynamischer Temperaturgradienten zur Verfügung. Damit eröffnet sich unmittelbar die Möglichkeit der Integration der thermografischen Prüfung in die Fertigung. Der Beitrag stellt die neuesten Entwicklungen der vielversprechenden Laser-Thermografie-Technik vor und zeigt, warum deren Einsatz potentiell die Standardprüfverfahren Magnetpulver- bzw. Eindringprüfung für eine Reihe von Prüfproblemen beerben könnte. KW - Zerstörungsfreie Prüfung KW - Thermografie KW - Infrarot-Sensor KW - Rissprüfung KW - Lasertechnik KW - Nondestructive testing KW - Thermography KW - Thermal infrared sensor KW - Crack inspection KW - Laser techniques PY - 2015 DO - https://doi.org/10.3139/105.110264 SN - 0341-101x SN - 1867-2493 VL - 70 IS - 4 SP - 190 EP - 195 PB - Hanser CY - München AN - OPUS4-34189 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ziegler, Mathias T1 - Locating subsurface defects with structured heating using high-power VCSEL-laser arrays N2 - Among the photothermal methods, full-field thermal imaging is used to characterize materials, to determine thicknesses of layers, or to find inhomogeneities such as voids or cracks. The use of classical light sources such as flash lamps (impulse heating) or halogen lamps (modulated heating) led to a variety of nondestructive testing methods, in particular lock-in and flash-thermography. In vertical cavity surface emitting lasers (VCSELs), laser light is emitted perpendicular to the surface with a symmetrical beam profile. Due to the vertical structure, they can be arranged in large arrays of many thousands of individual lasers, which allows power scaling into the kilowatt range. Recently, a high-power yet very compact version of such a VCSEL-array became available that offers both the fast timing behavior of a laser as well as the large illumination area of a lamp. Moreover, it allows a spatial and temporal control of the heating because individual parts of the array can be controlled arbitrarily in frequency, amplitude, and phase. In conjunction with a fast infrared camera, such structured heating opens up a field of novel thermal imaging and testing methods. As a first demonstration of this ansatz, we chose a testing problem very challenging to conventional thermal infrared testing: The detection of very thin subsurface defects perpendicularly oriented to the surface of metallic samples. First, we generate destructively interfering thermal wave fields which are then affected by the presence of defects within their reach. It turned out that this technique allows highly sensitive detection of subsurface defects down to depths in excess of the usual thermographic rule of thumb, with no need for a reference or surface preparation. T2 - 19th International Conference on Photoacoustic and Photothermal Phenomena CY - Bilbao, Spain DA - 16.07.2017 KW - Thermografie KW - Laser KW - Zerstörungsfreie Prüfung KW - Thermography KW - Non-destructive testing PY - 2017 AN - OPUS4-41829 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ziegler, Mathias T1 - Das VCSEL-Laser Array – Durch strukturierte Erwärmung mit einer neuartigen Hochleistungslichtquelle verdeckte Defekte thermografisch detektieren N2 - Vertical Cavity Surface Emitting Lasers (VCSELs) sind Diodenlaser, welche Laserstrahlung mit gutem Strahlprofil senkrecht zur Chipoberfläche emittieren. Aufgrund dieser vertikalen Bauweise können sie in großen Arrays zu vielen tausenden einzelnen Lasern zusammengefasst werden. Solch ein VCSEL-Array vereint das schnelle zeitliche Verhalten eines Diodenlasers mit der hohen optischen Bestrahlungsstärke und dem großen Beleuchtungsbereich von Blitzlampen oder LEDs und kann damit potentiell alle herkömmlichen Lichtquellen der Thermografie ersetzen. Darüber hinaus kann der Prüfkörper mithilfe dieser Lichtquelle strukturiert erwärmt werden, da einzelne Bereiche des VCSEL-Arrays unabhängig voneinander angesteuert werden können. Dieser neue Freiheitsgrad ermöglicht die Entwicklung neuer thermografischer ZfP-Verfahren. Wir demonstrieren diesen Ansatz anhand eines für die konventionelle Thermografie nur sehr bedingt lösbaren Prüfproblems, der Detektion vertikal zur Oberfläche ausgerichteter, sehr dünner, verdeckter Defekte in metallischen Werkstoffen. Wir erzeugen hierzu destruktiv interferierende thermische Wellenfelder. Defekte im Einflußbereich dieser thermischen Wellenfelder stören die destruktive Interferenz und erlauben eine hochsensible Detektion bis in Tiefen jenseits der üblichen thermografischen Faustformel, ohne Referenz und ohne Oberflächenbehandlung. T2 - DGZfP-Jahrestagung 2017 CY - Koblenz, Germany DA - 22.05.2017 KW - Thermografie KW - Laser KW - Zerstörungsfreie Prüfung PY - 2017 AN - OPUS4-41834 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hempel, M. A1 - Ziegler, Mathias A1 - Tomm, J.W. A1 - Elsaesser, T. A1 - Michel, N. A1 - Krakowski, M. T1 - Time-resolved analysis of catastrophic optical damage in 975 nm emitting diode lasers N2 - Catastrophic optical damage (COD) is analyzed during single current pulse excitation of 975 nm emitting diode lasers. Power transients and thermal images are monitored during each pulse. The COD process is unambiguously related to the occurrence of a “thermal flash” of Planck’s radiation. We observe COD to ignite multiple times in subsequent pulses. Thermography allows for tracing a spatial motion of the COD site on the front facet of the devices. The time constant of power decay after the onset of COD has values from 400 to 2000 ns, i.e., an order of magnitude longer than observed for shorter-wavelength devices. KW - Semiconductor laser KW - Thermography KW - Catastrophic optical damage KW - High-power diode lasers PY - 2010 DO - https://doi.org/10.1063/1.3456388 SN - 0003-6951 SN - 1077-3118 VL - 96 IS - 251105 SP - 1 EP - 3 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21672 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ziegler, Mathias A1 - Hempel, M. A1 - Larsen, H. E. A1 - Tomm, J. W. A1 - Andersen, P. E. A1 - Clausen, S. A1 - Elliott, S. N. A1 - Elsaesser, T. T1 - Physical limits of semiconductor laser operation: A time-resolved analysis of catastrophic optical damage N2 - The early stages of catastrophic optical damage (COD) in 808 nm emitting diode lasers are mapped by simultaneously monitoring the optical emission with a 1 ns time resolution and deriving the device temperature from thermal images. COD occurs in highly localized damage regions on a 30 to 400 ns time scale which is determined by the accumulation of excess energy absorbed from the optical output. We identify regimes in which COD is avoided by the proper choice of operation parameters. KW - Semiconductor laser KW - Thermography KW - Catastrophic optical damage KW - High-power diode lasers PY - 2010 DO - https://doi.org/10.1063/1.3463039 SN - 0003-6951 SN - 1077-3118 VL - 97 IS - 021110 SP - 1 EP - 3 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21741 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hempel, M. A1 - Tomm, J.W. A1 - Ziegler, Mathias A1 - Elsaesser, T. A1 - Michel, N. A1 - Krakowski, M. T1 - Catastrophic optical damage at front and rear facets of diode lasers N2 - Single-pulse tests of the catastrophic optical damage (COD) are performed for three batches of diode lasers with different gain-regions. The tests involve in situ inspection of front, rear, and side of the devices by a thermocamera. Devices with an Al-containing gain-region show COD at the front facet, as expected for strong facet heating via surface recombination and reabsorption of laser light. In contrast, Al-free devices with low surface recombination rates tend to fail at the rear facet, pointing to a different heating scenario. The high carrier density at the rear facet favors heating and COD via Auger recombination processes. KW - Thermography KW - Catastrophic optical damage KW - High power diode lasers KW - Destructive testing KW - Non-destructive testing KW - Auger effect KW - Carrier density KW - Heating KW - Laser beam effects KW - Optical testing KW - Semiconductor lasers KW - Surface recombination PY - 2010 DO - https://doi.org/10.1063/1.3524235 SN - 0003-6951 SN - 1077-3118 VL - 97 IS - 23 SP - 231101-1 - 231101-3 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-22763 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Tomm, J.W. A1 - Ziegler, Mathias A1 - Hempel, M. A1 - Elsaesser, T. T1 - Mechanisms and fast kinetics of the catastrophic optical damage (COD) in GaAs-based diode lasers N2 - COD diagram determined for a batch of broad-area AlGaAs diode lasers. The time to COD within a single current pulse is plotted versus the actual average optical power in the moment when the COD takes place. Full circles stand for clearly identified COD events (right ordinate), whereas open circles (left ordinate) represent the pulse duration in experiments, where no COD has been detected. A borderline (gray) exists between two regions, i. e., parameter sets, of presence (orange) and absence of COD (blue). This borderline is somewhat blurred because of the randomness in filamentation of the laser nearfield and scatter in properties of the involved individual devices. KW - Semiconductor laser KW - Thermography KW - Catastrophic optical damage KW - High-power diode lasers KW - Destructive testing KW - Non-destructive testing PY - 2011 DO - https://doi.org/10.1002/lpor.201000023 SN - 1863-8880 VL - 5 IS - 3 SP - 422 EP - 441 PB - Wiley-VCH CY - Weinheim AN - OPUS4-23624 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pagano, R. A1 - Ziegler, Mathias A1 - Tomm, J.W. A1 - Esquivias, I. A1 - Tijero, J.M.G. A1 - O'Callaghan, J.R. A1 - Michel, N. A1 - Krakowski, M. A1 - Corbett, B. T1 - Two-dimensional carrier density distribution inside a high power tapered laser diode N2 - The spontaneous emission of a GaAs-based tapered laser diode emitting at λ = 1060 nm was measured through a window in the transparent substrate in order to study the carrier density distribution inside the device. It is shown that the tapered geometry is responsible for nonuniform amplification of the spontaneous/stimulated emission which in turn influences the spatial distribution of the carriers starting from below threshold. The carrier density does not clamp at the lasing threshold and above it the device shows lateral spatial hole-burning caused by high stimulated emission along the cavity center. KW - Carrier density KW - Gallium arsenide KW - III-V semiconductors KW - Indium compounds KW - Laser cavity resonators KW - Optical hole burning KW - Quantum well lasers KW - Stimulated emission KW - Superradiance PY - 2011 DO - https://doi.org/10.1063/1.3596445 SN - 0003-6951 SN - 1077-3118 VL - 98 SP - 221110-1 EP - 221110-3 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-23873 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Ziegler, Mathias T1 - Catastrophic optical damage at front and rear facets of 975 nm emitting diode lasers T2 - CLEO, Conference on Lasers and Electro-Optics CY - Baltimore, MD, USA DA - 2011-05-03 PY - 2011 AN - OPUS4-23785 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -