 |
|
| |
250 W single crystal fiber Yb:YAG laser
|
 |
More than 250 W of output power out of an Yb:YAG single crystal fiber at an optical efficiency of 44% have been demonstrated at the IFSW in collaboration with the LCFIO and Fibercryst. The power in cw operation exceeds previously reported results by more than a factor of 4. These results confirm the applicability of single crystal fibers for highly efficient power amplifiers.
- X. Délen, S. Piehler, J. Didierjean, A. Voss, M. Abdou Ahmed, Th. Graf, F. Balembois, and P. Georges, “250W single crystal fiber Yb:YAG laser” post deadline paper ASSP 2012
March 2012
Contact person: Dr. Marwan Abdou Ahmed
|
| |
Narrow line width thin-disk laser with high polarization purity
|
 |
A resonant waveguide grating composed of a single high-index layer and a sub-wavelength structure was used to select the polarization and the spectral linewidth of an Yb:YAG thin-disk laser. In fundamental mode (M² ≈ 1.1) up to 70 W with a spectral linewidth of 20 pm (FWHM) were extracted whereas in multimode operation (M² ≈ 6) up to 123 W of output power with a spectral line width of 0.5 nm (4 times lower as compared to the operation with a standard HR mirror) were achieved. The degree of linear polarization (DOLP) exceeded 99% in both fundamental and multimode operation.
- M. Vogel, M. Rumpel, B. Weichelt, M. Haefner, C. Pruss, A. Voss, W. Osten, M. Abdou Ahmed, and Th. Graf, “Single-layer resonant-waveguide grating for polarization and wavelength selection in Yb:YAG thin-disk lasers,” Opt- Exp. 20, 4024-4031 (2012).
March 2012
Contact person: Dr. Marwan Abdou Ahmed
|
| |
New Gratings for Intra-Cavity Generation of Azimuthal Polarisation
|
 |
Two different circular grating-mirror concepts were investigated for the intra-cavity polarization selection in an Yb:YAG thin-disk laser. Up to 103 W of output power were generated in an azimuthally polarized mode with M² ≈ 2.2. The polarizing effect of the developed devices is based on the so-called resonant reflection in one case and on the introduction of loss for the supressed modes in the other approach.
- M. Rumpel, M. Haefner, Th. Schoder, C. Pruss, A. Voss, W. Osten, M. Abdou Ahmed, and Th. Graf, “Circular grating-waveguide-structures for intra-cavity generation of azimuthal polarization in a thin-disk laser”, accepted for publication in Optics Letters, opticsinfobase.org
March 2012
Contact person: Dr. Marwan Abdou Ahmed
|
| |
First Demonstration of a Yb:Sc2SiO5 Thin-Disk Laser
|
 |
In cooperation with the Key Laboratory of Transparent and Opto-Functional Inorganic Materials in Shanghai the first Yb:Sc2SiO5 (Yb:SSO) thin-disk laser was demonstrated recently at the IFSW [1]. The laser crystal with a thickness of only 150 μm was pumped with a broadband diode-laser centered at a wavelength of 976 nm. In fundamental-mode operation an optical efficiency of 25.4% was measured at an output power of 9.4 W. These first experiments confirmed the excellent thermo-mechanical properties of Yb:SSO and the high potential of this material also for fundamental mode operation. The current efforts to improve the crystal growth will soon lead to further increased efficiencies and allow higher output powers. Due to its spectral emission bandwith the Yb:SSO ist particularly suitable for the generation of ultra-short pulses.
- K.S. Wentsch, B. Weichelt, L. Zheng, J. Xu, M. Abdou Ahmed, Th. Graf, “Continuous-wave Yb doped Sc2SiO5 thin-disk laser,” Opt. Letters 1, 37-39 (2012).
January 2012
Contact person: Dr. Marwan Abdou Ahmed
|
| |
Yb:Lu2O3 thin-disk laser with an output power of 670 W
|
 |
An output power of 670 W from an Yb:Lu2O3 thin-disk laser in multimode operation was demonstrated at the IFSW [1]. This is the highest output power reported to date. The 250 μm thin laser crystal was pumped at its zero-phonon absorption band at a wevelength of 976 nm with high-power diode-laser stack which was stabilized by a volume Bragg grating and showed a high potential for further power scaling into the kilowatt regime. This will just require larger crystals with laser quality. Further investigations also on mode-locked operation are under progress and will be reported on at a later date.
- B. Weichelt, K. Wentsch, A. Voss, M. Abdou Ahmed, and Th. Graf, "A 670 W Yb:Lu2O3 thin-disk laser", accepted for publication in Laser Physics Letters
September 2011
Contact person: Dr. Marwan Abdou Ahmed
|
| |
Eleven presentations of the IFSW at the LiM 2011 in Munich
|
 |
At the WLT conference “Lasers in Manufacturing” (LiM), part of the WORLD of PHOTONICS Congress in Munich, the latest research results of the IFSW on laser material processing were presented on 23rd - 26th May 2011 with 11 talks – one of which invited. In addition to the traditional main topics on the fundamentals and the quality improvement of laser welding and on process diagnostics, the application of radially and tangentially polarized beams as well as the processing of CFRP were further highlights presented by the scientist of the IFSW:
R. Weber, A. Michalowski, P. Berger, M. Abdou-Ahmed, V. Onuseit, V. Rominger, M. Kraus, T. Graf, “Effects of Radial and Tangential Polarization in Laser Material Processing” (invited paper) V. Onuseit, M. Abdou Ahmed, R. Weber, T. Graf, “Space-Resolved Spectrometric Measurement of the Cutting Front” P. Berger, H. Hügel, T. Graf, “Understanding Pore Formation in Laser Beam Welding” A. Hess, R. Schuster, A. Heider, R. Weber, T. Graf, “Continuous Wave Laser Welding of Copper with Combined Beams at Wavelengths of 1030 nm and of 515 nm” A. Heider, P. Stritt, A. Hess, R. Weber, T. Graf, “Process Stabilization at Welding Copper by Laser Power Modulation” P. Stritt, R. Weber, T. Graf, S. Müller, C. Ebert, “Utilizing Laser Power Modulation to Investigate the Transition from Heat-Conduction to Deep-Penetration Welding” P. Berger, H. Hügel, R. Weber, T. Graf, “Understanding of Humping Based on Conservation of Volume Flow” F. Abt, A. Heider, R. Weber, T. Graf, A. Blug, D. Carl, H. Höfler, L. Nicolosi, R. Tetzlaff, “Camera Based Closed Loop Control for Partial Penetration Welding of Overlap Joints” F. Abt, R. Weber, T. Graf, G. Popko, S. Nau, “Novel X-Ray System for In-Situ Diagnostics of Laser Based Processes – First Experimental Results” J .Weberpals, T. Hermann, P. Berger, H. Singpiel, “Utilisation of Thermal Radiation for Process Monitoring” R. Weber, M. Hafner, A. Michalowski, T. Graf, “Minimum Damage in CFRP Laser Processing”
Contact: Dr. Rudolf Weber and Akad. Oberrat Peter Berger
|
| |
Fastest In-Situ X-Ray Video of a Laser Welding Process
|
 |
On 10th November 2010 a new x-ray video facility was put into operation at the IFSW. With this equipment it is possible to visualize laser processes in real time with x-ray video technology for the first time in Europe.
X-ray video sequences with a frame rate beyond 1000 fps were recorded for the first time on 23rd November 2010. A laser deep-penetration welding process in 6 mm thick Aluminum was recorded with 5000 fps at a resolution of 512 x 512 pixel. The recording time was more than one second. This is a world-wide unprecedented performance and will open up significant new insights into the fundamentals of laser material processing.
Contact persons: Dipl.-Ing. Felix Abt and Dr. Rudolf Weber
|
| |
How small is the proton?
|
 |
A thin-disk laser system developed at the Institut für Strahlwerkzeuge (IFSW) of Universität Stuttgart contributes to a major discovery: The proton – one of the universal building-blocks of all matter – is even smaller than had previously been assumed. This is the result obtained at the Paul- Scherrer-Institut (PSI) in Villigen (Switzerland) by an international research team, including scientists from the Max Planck Institute of Quantum Optics (MPQ) in Garching (Germany) and the IFSW.
Original publication: Randolf Pohl et al. "The size of the proton", Nature 466 (7303), 213-216, 8. July 2010, DOI: 10.1038/nature09250.
Contact person: Prof. Dr. Thomas Graf
|
| |
How small is the proton?
|
 |
Three out of four papers on our latest achievements in laser development submitted to Photonics Europe (12.-16. April 2010 in Brussels) were upgraded to invited talks by the program committee. The talks present the IFSW′s latest progress on fiber and thin-disk lasers. The contribution on the thin-disk laser was additionally selected as a newsroom article.
Contact person: Dr.-Ing. Andreas Voß
|
| |
A single-mode multi-core fiber consisting of 19 hexagonally arranged cores is presented
by Moritz Vogel and Dr. Marwan Abdou Ahmed
|
 |
A single-mode multi-core fiber consisting of 19 hexagonally arranged cores is presented.
Theoretical and experimental results show a fundamental mode with an effective area of 450 µm2.
A beam propagation factor M2 better than 1.03 was measured for different conditions.
The picture shows the measured nearfield distribution of the fiber end face transmitting laser radiation with a wavelength of 1 µm.
Moritz M. Vogel, Marwan Abdou-Ahmed, Andreas Voss and Thomas Graf,
"Very-large-mode-area, single-mode multicore fiber", Opt. Lett. 34, 2876-2878 (2009), doi:10.1364/OL.34.002876
http://www.opticsinfobase.org/abstract.cfm?URI=ol-34-18-2876
Contact person: Dr. -Ing. Andreas Voß
|
| |
International Workshop of the IFSW on the Process Stability of Laser Welding and Cutting
|
 |
For the 11th time the IFSW organized the traditional scientific workshop on the process dynamics in laser-based manufacturing. An exclusive group of international experts from science and industry were invited to join the event in the beautiful Kleinwalsertal. The challenges and findings especially related to the new generation of laser sources with high brilliance were analyzed in numerous talks and discussions. Thanks to the excellent atmosphere the fruitful intensive debates continued until late into the nights.
The behaviour of the absorption of the laser radiation in the welding key-hole was a special focus of the event this year (Figure). Another exciting topic was the strong similarity of some melt-dynamic processes in cutting and welding. Several promising approaches were discussed that could help to overcome some of the known process instabilities.
Contact person: Dr. Rudolf Weber
and Peter Berger
|
| |
ACES – Analog Image Processing with Cellular Neural Networks (CNN) for Closed Loop Control of Laser based Welding Processes
by Felix Abt
|
 |
For further improvements on productivity and quality of laser based welding processes, it is – in most cases - necessary to implement closed loop control systems on the process. Due to the complex and high dynamic processes, a closed loop control system has to be based on ultra fast optical image processing. By intelligent neuronal connections, CNN-Cameras are able to reduce the amount of image data and perform image elaboration with frame rates in the multi-kilohertz range. In the project ACES the FGSW and the Fraunhofer IPM developed a technology for a fast camera based closed loop control system. This technology enables a closed loop control of laser welding processes to ensure the full penetration state independent of the material thickness, the feeding rate and other influences by adjusting the laser power with a control frequency of up to 13 kHz.
Contact person: Dr. Rudolf Weber
|
| |
Inauguration of the Fibre Manufacturing Facility at the IFSW
|
 |
After several months of assembling and testing the IFSW has started the regular operation of its new fibre drawing tower. The complete facility which will enable research on novel optical fibres for laser technologies was inaugurated on March 3rd in an opening event of the Stuttgart Laser Technology Forum SLT 2008.
 Press Release - IFSW 03.03.2008 and at Optics.org
Contact person: Dr.-Ing. Andreas Voß |
|
|
webmaster) | © Universität
Stuttgart | Impressum