Spectrally resolved two-colour three-pulse photon echo studies of vibrational dynamics of molecules

Spectrally resolved two-colour three-pulse photon echoes (PE) have been investigated on a femtosecond time scale for Rhodamine B in Methanol. The time evolution of the spectra of the PE signals and their dependence on the wavelength of the excitation pulses are analysed. New spectral features are observed which differ from the spectral profile of the probe pulse and which decay with a range of time constants. The influence of vibrational-electronic coupling on the PE spectra is discussed. The vibrational relaxation times (80–200 fs), which depend on the levels selected in the vibrational manifold, and the optical dephasing time (∼400 fs) can be determined directly from the spectrally resolved PE measurements.