Subfemtosecond pulses in the multicascade stimulated Raman scattering

We explore recently predicted multifrequency 2π solitons in multicascade stimulated Raman scattering (SRS) that was mode locked by the dynamics of population at a Raman quantum transition; we show that these solitons are eigensolitons of a general solitary-wave solution. Soliton components at each frequency are bright pulses of the same (Lorentzian) shape, in contrast to the familiar bright–dark soliton pair in regular SRS and to 1/cosh regular 2π solitons. Coherent interference of these components gives rise to a train of well-resolved subfemtosecond pulses. From an observation viewpoint the simplest SRS 2π solitons are so-called bright–bright solitons in noncascade SRS with either two (laser + Stokes) or three (e.g., laser + Stokes + anti-Stokes) components.