Effects of non-Markovian relaxation in the femtosecond differential absorption spectra Original Research Article

Spectral diffusion effects to femtosecond four-wave mixing spectroscopy occurring from the bath–quantum system interactions are investigated theoretically by means of nonperturbative approach to the field–matter interaction. The stochastic model with coloured fluctuations of the excitation energy in a quantum (two-level) system was used when calculating the induced absorption differences. Our treatment displays time (delay) dependent shift of the transient differential absorption spectra originated from the non-Markovian relaxation of excitations in the quantum system under investigation.