Fig. 3
From: Intensity noise as a driver for transverse mode instability in fiber amplifiers
Dependence of the TMI threshold on the frequency bandwidth of the pump intensity-noise. The applied noise traces range from 1 Hz up to the displayed cut-off frequencies (detailed in Fig. 2). Pump-noise frequencies between 125 Hz and 500 Hz have the strongest impact on the TMI threshold (blue shading), which corresponds to the main beam-fluctuation frequency of 241 Hz (black dashed line; measured slightly above the TMI threshold). In a more general way, it can be seen that only frequencies below 2 kHz influence the TMI threshold of the used active fiber (green shading)