Temporally resolved build-up and decay of mode instabilities in high power fiber amplifiers

State-of-the-art high power Yb-doped large mode area fibers have been developed to a performance level able to reach the so-called mode instability threshold. In this contribution we will discuss the experimaental results regarding the temporal evolution (build-up and decay) of this effect to come closer to a comprehensive understanding of its driving mechanisms. With a pulsed pump source emitting pulses in the ms range, we investigated the temporal behavior of the build-up and degradation time for mode instability in a high power fiber amplifier. To the best of our knowledge these are the first systematic, time resolved investigations on that topic.