Three-state model for femtosecond broadband stimulated Raman scattering

Stimulated Raman scattering (SRS) is analyzed with a three-state model. Using a diagrammatic density-matrix formalism, SRS by a pair of Raman pump and probe pulses, with observation along the probe direction, is described principally by eight terms. The eight terms can be grouped into four sets, which are labeled as SRS or IRS (inverse Raman scattering): SRS(I), SRS(ID, IRS(I), and IRS(II). Specializing to the case of femtosecond SRS (FSRS) by a picosecond (ps) Raman pump pulse and a femtosecond (fs) probe pulse, the spectra for the four sets of terms under off-resonance and resonance conditions were calculated. The results obtained can explain the FSRS experimental observations from a (decaying) stationary vibrational state, such as (1) high wavenumber resolution (determined by the narrow bandwidth Raman pump pulse) and high time resolution (deter-mined by the fs probe pulse), (2) Stokes gain vs anti-Stokes loss in off-resonance FSRS, and (3) dispersive lineshapes in resonance FSRS. Copyright (C) 2008 John Wiley & Sons, Ltd.