Spin-dependent photon echo for an ensemble of three-level systems

We consider the action of a polarized rectangular laser pulse on a three-level system as a model of the interaction of electromagnetic radiation with matter. We managed to get the analytical solution for non-resonant excitation by light of a system with degenerate excited energy states without taking relaxation into account. The found analytical expressions were applied then to model the signal of a two-pulse photon echo from an ensemble of three-level systems.