(2) durations of both pulses are much shorter than the time scale of the system evolution. Under the DW approximation, evaluation of the TA PP signal is decomposed into three steps: evaluation of the doorway operator which describes interaction of the system with the pump pulse, field-free propagation of the doorway wavepacket, convolution of the doorway wavepacket with the window operator which describes interaction of the system with the probe pulse. In other words, calculation of TA PP signals is reduced to the propagation of the electronic ground-state and excited-state wavepackets.