Supercontinuum generation by femtosecond flat-top laser pulses in fused silica

In this work we report the numerical results on the filamentation and supercontinuum (SC) generation of femtosecond flat-top pulses with different steep edges propagating in fused silica. Results show that the filamentation process is determined mainly by the self-steepening effect and ionization, and the SC generation is influenced mainly by the self-steepening effect. The filamentation onset and termination is determined by the leading edge and the tailing edge, respectively. The steeper the leading edge is, the earlier the filamentation onset is; the steeper the tailing edge is, the earlier the filamentation termination is. The cutoff wavelength in the blue-side region of the SC has no obvious difference for the pulses with different leading and tailing edges. But the spectral intensity of the blue extension is much stronger for the pulses with the steeper leading edges. The stronger spectral intensity results from the formation of more steep descending edges during filamentation. (C) 2019 Optical Society of America