Hannover 2013 – wissenschaftliches Programm
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Q: Fachverband Quantenoptik und Photonik
Q 44: Laser development: Solid state lasers II
Q 44.2: Vortrag
Donnerstag, 21. März 2013, 11:15–11:30, F 128
Mode instabilities in high-power fiber lasers and amplifiers — •Hans-Jürgen Otto1, Florian Janse1, Fabian Stutzki1, Cesar Jauregui1, Jens Limpert1,2, and Andreas Tünnermann1,2,3 — 1Friedrich-Schiller-Universität Jena, Institute of Applied Physics, Albert-Einstein-Str. 15, 07745 Jena, Germany — 2Helmholtz-Institute Jena, Fröbelstieg 3, 07743 Jena, Germany — 3Fraunhofer Institute for Applied Optics and Precision Engineering, Albert-Einstein-Str. 7, 07745 Jena, Germany
Currently, the onset of so-called mode instabilities (MI) in state-of-the-art high power fiber lasers and amplifiers is the most limiting effect for further output power scaling. A former stable Gaussian-like beam profile becomes temporally instable and simultaneously the beam quality reduces when a certain power threshold is reached. These phenomena can be observed in all types of fiber lasers and amplifiers. Hence, the investigation of MI is of fundamental importance for the high power fiber lasers and amplifiers of tomorrow. We will present our recent experimental results by showing slow motion videos of MI measured by a high speed camera (> 20.000 images per second). It can be seen that MI are related to a fluctuation of the intermodal phase and amplitude of several involved modes. Moreover we give a theoretical explanation of the effect. MI are caused by a mostly thermally induced long period grating due to the beating of fiber modes. Finally, we show a novel active stabilization scheme to tremendously increase quality and stability of the MI affected beam at output power levels more than three times the typical power threshold of the laser system.