Theoretical and experimental studies on intermodal nonlinear effects of a high-power near-single-mode CW Yb-doped...

An intermodal-nonlinearity-induced time-frequency evolution model of high-power near-single-mode continuous-wave fiber lasers (NSM-CWHPFLs) was proposed to simulate the evolution of spectral characteristics and beam quality under the combined action of intermodal and intramodal nonlinear effects. The influence of fiber laser parameters on intermodal nonlinearities was analyzed, and a suppression method involving fiber coiling and seed mode characteristic optimization was proposed. Verification experiments were conducted with 20/400, 25/400, and 30/600 fiber-based NSM-CWHPFLs. The results demonstrate the accuracy of the theoretical model, clarify the physical mechanisms of nonlinear spectral sidebands, and demonstrate the comprehensive optimization of intermodal-nonlinearity-induced spectral distortion and mode degradation.