Influence of Gain Saturation Effect on Transverse Mode Instability Considering Four-Wave Mixing

Transverse mode instability (TMI) has been recognized as onse of the primary limiting factors for the average power scaling of high-brightness fiber lasers. In this work, a static model of the TMI effect based on stimulated thermal Rayleigh scattering (STRS) is established while considering the four-wave mixing (FWM) effect. The focus of the model is to theoretically investigate the TMI phenomenon and threshold power dominated by FWM. The gain saturation effect and fiber laser system parameters, such as seed power, pumping direction, and core numerical aperture, which have not been considered in the previous perturbation theory model, are also investigated. This work will enrich the perturbation theory model and extend its application scope in TMI mitigation strategies, providing guidance for understanding and suppressing TMI.