Beam self-cleaning of femtosecond pulses in the anomalous dispersion regime

Wu, H. Pourbeyram, D. N. Christodoulides, and F. W. Wise, “Weak beam self-cleaning of femtosecond pulses in the anomalous dispersion regime,” Opt. Lett. 46, 3312–3315 (2021).

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, beam-cleaning is observed experimentally.  Beyond the spatial dynamics, with the increase of input pulse energy, there is a strong temporal self-compression of the pulse from 500 fs down to around 30 fs (a factor of 17). Numerical simulations exhibit the qualitative trends of the experiments. Our study provides a way to enhance beam quality and temporal peak power at the same time in graded-index multimode fiber and the anomalous dispersion regime.