Phase relations, quasicontinuous spectra and subfemtosecond pulses in high-order stimulated Raman scattering with short-pulse excitation

High-order stimulated Raman scattering for pumping by ps and sub-ps pulses is studied in the frame of a time-domain approach without the slowly varying envelope approximation. Formation of pulse trains with sub-fs durations in the ps-pump regime is demonstrated using external phase compensation. For sub-ps excitation a novel broadening mechanism of Raman lines is predicted that leads to a quasicontinuous spectrum and permits one to generate single sub-fs pulses. We predict also essential shortening of a delayed fs-probe pulse by the Raman oscillations without phase control.