Background The performance of high-power fiber amplifiers operating in radiation environments is severely degraded by the radiation-induced mode instability (R-TMI) effect. A deep understanding of its degradation and self-recovery mechanism is therefore crucial for practical applications.

Purpose This study aims to investigate the influence of γ-ray radiation on the mode instability threshold of a high-power fiber amplifier and to elucidate the underlying self-recovery mechanism of the R-TMI effect.

Methods Experimental investigations were conducted on a fiber amplifier subjected to γ-ray radiation. The output power characteristics and the frequency-domain signals of the output laser were monitored and analyzed under varying pump current conditions to study the dynamics of the R-TMI effect.

Results The experimental results reveal that the onset of the R-TMI effect induces significant fluctuations in the output power. As the pump current is gradually increased, the output power consistently evolves through four distinct stages over time: rapid decline, slow decline, slow rise, and finally a metastable state. At each specific pump current level, the power fluctuation range, defined as the difference between the maximum and minimum output power, remains stable within 29.7% to 39.1% of the pre-radiation output power. Furthermore, frequency-domain analysis of the output laser signal provided evidence supporting the existence of a self-recovery effect in R-TMI.

Conclusions The study characterizes the variation of the TMI threshold and the subsequent power dynamics under radiation. The self-recovery behavior offers valuable theoretical and experimental references for the design and mitigation of R-TMI effects in high-power fiber lasers intended for use in radiation environments.