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Proceedings Paper

Mitigation of transverse mode instability with travelling waves in high-power fiber amplifiers
Author(s): Cesar Jauregui; Christoph Stihler; Yiming Tu; Sobhy Kholaif; Jens Limpert
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Paper Abstract

In this work we present a novel way to mitigate the effect of transverse mode instability in high-power fiber amplifiers. In this technique a travelling wave is induced in the modal interference pattern by seeding the amplifier with two modes that have slightly different frequencies. The interference pattern thus formed will travel up- or downstream the fiber (depending on the sign of the frequency difference between the modes) with a certain speed (that depends on the absolute value of the frequency difference). If the travelling speed is chosen properly, the thermally-induced index grating will follow the travelling modal interference pattern creating a constant phase shift between these two elements. Such a constant controllable phase shift allows for a stable energy transfer from the higher-order modes to the fundamental mode or viceversa. Thus, this technique can be adjusted in such a way that, at the output of the fiber almost all the energy is concentrated in the fundamental mode, regardless of the excitation conditions. Moreover, this technique represents one of the first examples of the new family of mitigation strategies acting upon the phase shift between the modal interference pattern and the refractive index grating. Additionally, it even exploits the effect of transverse mode instability for gaining control over the beam profile at the output of the amplifier. Therefore, by adjusting the frequency difference between the seed modes, it is possible to force that the beam at the output acquires the shape of the fundamental mode or that of a higher order mode.

Paper Details

Date Published: 21 February 2020
PDF: 6 pages
Proc. SPIE 11260, Fiber Lasers XVII: Technology and Systems, 112601A (21 February 2020); doi: 10.1117/12.2543383
Show Author Affiliations
Cesar Jauregui, Friedrich-Schiller-Univ. Jena (Germany)
Christoph Stihler, Friedrich-Schiller-Univ. Jena (Germany)
Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)
Yiming Tu, Friedrich-Schiller-Univ. Jena (Germany)
Sobhy Kholaif, Friedrich-Schiller-Univ. Jena (Germany)
Helmholtz-Institute Jena (Germany)
Jens Limpert, Friedrich-Schiller-Univ. Jena (Germany)
Helmholtz-Institute Jena (Germany)
Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)

Published in SPIE Proceedings Vol. 11260:
Fiber Lasers XVII: Technology and Systems
Liang Dong, Editor(s)

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