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Controlling mode instabilities at 628 W average output power in an Yb-doped rod-type fiber amplifier by active modulation of the pump power

: Stihler, C.; Jauregui, C.; Otto, H.-J.; Limpert, J.; Tünnermann, A.


Robin, C.A. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Fiber Lasers XIV. Technology and Systems : 30 January - 2 February 2017, San Francisco, California, United States
Bellingham, WA: SPIE, 2017 (Proceedings of SPIE 10083)
ISBN: 978-1-5106-0607-4
ISBN: 978-1-5106-0608-1
Paper 100830P
Conference "Fiber Lasers - Technology and Systems" <14, 2017, San Francisco/Calif.>
Fraunhofer IOF ()

The phenomenon of transverse mode instabilities (TMI) is currently the most limiting effect for the scaling of the average output power of fiber laser systems with nearly diffraction-limited beam quality. Thus, it is of high interest to develop efficient mitigation strategies to further enhance the performance of fiber laser systems. By actively modulating the pump power of an Yb-doped rod-type fiber amplifier, it was possible to weaken the thermally-induced refractive index grating along the fiber and, thus, to mitigate TMI to a large extent. A significant advantage of this approach is that it can be easily integrated in any existing fiber-laser system since no further optical components are needed. A function generator connected to the pump diode driver was used to achieve the modulation. With this setup we were able to extract a fully stabilized beam at ∼ 1.5 times above the TMI threshold. Furthermore, a stabilization of the beam was still feasible at an average output power of 628 W, which is more than three times higher than the free-running TMI threshold of that particular fiber under identical conditions (e.g. seed power). This is the highest average output power reported from a single-channel rod-type fiber amplifier with a high-quality stabilized beam, to the best of our knowledge.