Harnessing Self-Phase Modulation for Active Suppression of Transverse Mode Instability in High-Power Fiber Lasers

Transverse mode instability (TMI) critically limits the power scaling of high-brightness fiber l asers.W hile recent experiments have empirically demonstrated that the TMI threshold can be significantly e nhanced b y temporal modulation, the fundamental physical mechanism governing this stabilization remains unknown, preventing the rational design of high-power systems.Here, we present a comprehensive numerical framework that incorporates nonlinear optical effects into the analysis of TMI dynamics under temporal modulation.We identify self-phase modulation (SPM) as the dominant stabilizing mechanism, which generates a chaotic thermal grating to suppress resonant energy transfer between the fundamental and higher-order modes, thereby disrupting the TMI process.Building upon this insight, we derive a quantitative, predictive model that directly links modulation parameters and fiber properties to the TMI threshold.This work provides the missing physical foundation for understanding nonlinear TMI suppression and offers a powerful, predictive design tool for overcoming the power-scaling bottleneck in next-generation fiber laser systems.