Femtosecond stimulated Raman spectroscopy modeled with a delta probe pulse: application to rhodamine 6G

Femtosecond stimulated Raman spectroscopy (FSRS) typically uses a picosecond Raman pump and a similar to 10 fs probe pulse. Such an ultrashort probe pulse is akin to a delta function (supercontinuum) pulse and the expressions for the third-order polarization simplifies with a reduction in the four-time correlation function to a three-time correlation function. Assuming multimode harmonic potentials for the ground and excited states of the molecule, we obtain analytic expressions for the three-time correlation functions which facilitate the computation of the third-order polarizations for resonance Raman scattering, hot luminescence, and inverse Raman scattering terms, which contribute to the FSRS spectra from the ground vibrational state. The effects of Raman pump pulse temporal width, the vibrational dephasing time, the homogeneous damping constant, and the inhomogeneous damping constant on the Raman Stokes spectrum are also more readily studied. The resonance FSRS spectra of rhodamine 6G from the ground vibrational state with various resonance excitation wavelengths were calculated using a delta probe and shown to account well for the recent experimental results of Frontiera et al., J. Chem. Phys. 2008; 129: 064507 for both the Stokes and anti-Stokes bands, as well as of Shim et al., ChemPhysChem. 2008; 9:697. Copyright (C) c 2010 John Wiley & Sons, Ltd.