Femtosecond coherent anti-Stokes Raman beats between vibration modes in PVA film

We have performed femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) to study the vibrational dynamics of Polyvinyl alcohol (PVA) film. We observed CARS signal beats between vibrational modes in PVA and measured the coherent vibrational relaxation rates of CH and OH stretch modes. We found that the coherent vibrational relaxation of anti-symmetric CH stretch mode in PVA is much faster than that of symmetric mode, probably due to faster resonant vibrational energy transfer to adjacent CH groups in a polymer chain.