Gain-induced Kerr beam cleaning in a femtosecond fiber amplifier

Kerr beam cleaning is a nonlinear phenomenon in graded-index multimode fiber where power flows toward the fundamental mode, generating bell-shaped output beams. Here we study beam cleaning of femtosecond pulses accompanied by gain in a multimode fiber amplifier. Mode-resolved energy measurements and numerical simulations showed that the amplifier generates beams with high fundamental mode content (greater than 30% of the overall pulse energy) for a wide range of amplification levels. Control experiments using stretched pulses that evolve without strong Kerr nonlinear effects showed a degrading beam profile, in contrast to nonlinear beam cleaning. Temporal measurements showed that seed pulse parameters have a strong effect on the amplified pulse quality. These results may influence the design of future high-performance fiber lasers and amplifiers. (c) 2023 Optica Publishing Group

Automated summary

Kerr beam cleaning is a nonlinear phenomenon that redirects power towards the fundamental mode, resulting in bell-shaped output beams. This study focuses on beam cleaning of femtosecond pulses with gain using a multimode fiber amplifier. Experimental measurements and simulations demonstrate that the amplifier generates beams with a significant amount of fundamental mode content, regardless of the amplification levels. Control experiments without strong Kerr nonlinear effects show degraded beam profiles, contrasting with nonlinear beam cleaning. Temporal measurements reveal that the quality of amplified pulses is strongly influenced by the seed pulse parameters. These findings hold implications for the design of future high-performance fiber lasers and amplifiers.