Power of all-fiber amplifier increasing from 1030 W to 2280 W through suppressing mode instability by increasing the seed power

In this work, we investigate suppressing mode instability in detail by varying the seed power in a large mode area all-fiber amplifier with a fiber core diameter of $25\mu m$. The transverse mode instability (TMI) thresholds are systematically measured for different seed power. Our experimental results reveal that increasing the seed power has a positive influence on enhancing the output power before the TMI effect appears, and finally the TMI threshold is approximately doubled from 1030 W to 2280 W when the seed power is increased from 27 W to 875 W. Almost 84.7% slope efficiency is reached with different seed power before the TMI threshold power. During our operation, we also find that in this type of LMA fiber the beam quality of the amplifier is degraded gradually instead of a sudden change as the pump power increases. (paper)