The impressive progress in experimental femtosecond spectroscopy stimulates rapid development of accurate (especially, ab initio) methods of simulations of spectroscopic signals, see, for example, the original works and recent reviews . The signals are usually calculated by using the nonlinear response-function (NRF) approach, in which interactions of molecules with laser fields are assumed to be weak and treated in the lowest order of perturbation theory. However, a direct computation of the NRFs is tedious, especially for complex multidimensional molecular systems. The doorway-window (DW) approximation provides a practical alternative which substantially alleviates the computational costs . The DW representation of TA PP signals hinges on two assumptions: (1) the pump and probe pulses are well separated in the time domain;