Femtosecond photon echo in semiconductors. Diagrammatic approach

Within the framework of the time ordered diagram technique a brief derivation of density matrix equations for the case of a two-band semiconductor is given. A diagram technique for the echo phenomenon is developed. The difference between single--atom dipole band (Yeh and Eberly model) and excitonic spectrum of semiconductors is discussed. A mechanism responsible for the observed very short times of the echo decay (of the order of a few femtoseconds) in semiconductors is investigated. Previous results of Gurevich ct. al. concerning the femtosecond echo decay law are confirmed within the framework of the eikonal approximation.