Doorway-window description of sequential three-pulse photon echo signals

The doorway-window (DW) approach is extended to the description of the three-pulse photon echo (3PPE) signals, provided we can neglect the transient terms decaying as ∼Ei(T) (Ei(T) are the envelopes of the pulses involved and T is the interpulse delay time during which the material system is in its electronic population state). A simplified version of the DW approach is also developed, which is valid if we can additionally drop the transient terms decaying as ∼Ei(τ), τ being the interpulse delay time during which the material system is in its electronic coherent state. The proof-of-the-principle calculations of the 3PPE signal for the displaced harmonic oscillator model demonstrate that the simplified DW approach performs well, sometimes even beyond its expected domain of validity.