Mode instability in fiber lasers and amplifiers represents the temporal variations of mode content with typical bandwidth of few kHz. This detrimental phenomenon leads to the degradation of М2 and to substantial growth of intensity noise observed after spatial filtering. The modal instability thus prevents the scaling of output power with high beam quality. The basic mechanism behind this instability originates from the mode coupling in the periodic grating in a fiber core formed owing to intermodal interference. Among the techniques proposed for instability suppression, it should primarily be mentioned an efficient thermal management of the gain fiber combined with dynamic modulation of excitation [1].

© 2015 IEEE

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