Transverse mode instability (TMI) is still the most limiting effect for the further average-power scaling of fiber lasers and amplifiers with excellent beam quality . For the modal energy transfer to happen, a phase shift between the thermally-induced refractive index grating and the modal interference pattern in the fiber is essential . In former experimental and theoretical studies it has been shown that such a phase shift can be induced by changes of the pump power [3,4]. Thus, the investigation of the influence of pump-power noise on the TMI threshold is of high relevance since this noise could act as the main trigger for TMI.
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