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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.
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Weak beam self-cleaning of femtosecond pulses in the anomalous dispersion regime
Kerr beam cleaning in graded-index multimode fiber has been investigated in experiments with sub-nanosecond pulses and in experiments with femtosecond pulses at wavelengths where the dispersion is normal. We report a theoretical and experimental study of this effect with femtosecond pulses and anomalous dispersion. In this regime, only weak beam cleaning is observed experimentally, along with strong temporal evolution of the pulse. Numerical simulations exhibit the qualitative trends of the experiments.
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- Award ID(s):
- 1912742
- PAR ID:
- 10258385
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Letters
- Volume:
- 46
- Issue:
- 13
- ISSN:
- 0146-9592; OPLEDP
- Format(s):
- Medium: X Size: Article No. 3312
- Size(s):
- Article No. 3312
- Sponsoring Org:
- National Science Foundation
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