Open AccessExperimental investigations of seeding mechanisms of TMI in rod fiber amplifier using spatially and temporally resolved imaging
Author(s) -
Simon Christensen,
Mette Marie Johansen,
Mattia Michieletto,
Marco Triches,
Martin D. Maack,
Jesper Lægsgaard
Publication year - 2020
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.400520
Subject(s) - optics , physics , amplifier , seeding , instability , perturbation (astronomy) , noise (video) , exponential function , coupling (piping) , spectral density , materials science , mechanics , optoelectronics , telecommunications , mathematical analysis , mathematics , cmos , quantum mechanics , artificial intelligence , computer science , metallurgy , image (mathematics) , thermodynamics
In this work we investigate transverse mode instability (TMI) in the presence of pump intensity noise and a controlled perturbation of the input coupling for a rod-type fiber amplifier using spatially and temporally resolved imaging (ST). We show that inherent pump intensity noise from the power supply can define significant peaks in the resulting TMI spectrum. ST measurements show that the TMI in the transition region consists of different orientations of LP 11 . This finding indicates that the simple picture of TMI being seeded by the combination of a static initial fraction of LP 11 and pump or signal intensity noise is not valid for our measurements. Furthermore we present seeding of TMI by perturbing the input coupling dynamically. ST measurements of the resulting TMI as a function of perturbation frequency provides quantitative information regarding the frequency response of the non-linear coupling coefficient. Finally, ST measurements of the resulting TMI as a function of signal power shows that the TMI experiences an exponential gain long before visible beam fluctuations appear.