Quantum beat in the pump-probe signal of a molecular system

In a pump-probe experiment, the probe signal shows a quantum beat structure which is a modulated exponential decay with the delay time. We have theoretically analysed the factors which affect the depth of these modulations, namely the initial preparation condition of the pump state, correlation of the lifetimes of the vibrational states of the first excited state due to coupling with a quasi-continuum, and lastly the curvatures and displacement of the two excited electronic states. The effects of these factors are studied in the multimode case where the interplay of vibrational frequencies is shown to display the modification of the quantum beat structure.