Spectrally resolved fs-CARS as a probe of the vibrational dynamics of a large polyatomic molecule: magnesium octaethylporphyrin

We report on the investigation of the electronic ground state vibrational dynamics of a large, biologically relevant molecule (magnesium octaethylporphyrin) using femtosecond time-resolved coherent anti-Stokes Raman scattering (CARS). By detecting the spectrum of the coherent anti-Stokes signal as a function of the delay time in a pump- and probe-type experiment, a detailed mapping of the dynamics of the vibrational coherence in the spectral region of the modes of the porphyrin macro-cycle is achieved. The method is capable to simultaneously give insight on the dephasing timescales and to provide spectral information on the vibrational mode structure.