Abstract

We propose two ways of generating high- intensity subfemtosecond (~10⁻¹⁷-s) pulses and solitons of very high repetition rate. One approach¹ is based on multifrequency cascade Raman stimulated scattering (CSRS). We predict that a pump-laser wave with frequency ω_L and many cascade-excited Stokes and anti-Stokes components with frequencies ω_i = ω_L + jω₀, j = ±1, ±2, ±3, …, can be mode locked to each other through a fast full-swing 2π nutation of population at the Raman transition with frequency ω₀ ≪ ω_L. Similar to bright–bright 2-π solitons in CSRS with two² and three³ components, these solitons have a new, very simple Lorentzian intensity profile. Because of the engagement of many mode- locked components, however, their total electromagnetic field in the time domain consists of a train of ultrashort, of the order of the pump cycle 2π/ω_L or even shorter, pulses separated by the interval 2π/ω₀. The major feature of the proposed effect is that all the frequency components of the new soliton are so-called bright solitons, in contrast to the well-known bright-dark soliton combination in SRS.⁴ The high-order CSRS required to observe the proposed effect was first observed experimentally in Ref. 5 and later in many other experiments, with the total number of components as high as 10–15.

© 1995 Optical Society of America