Time-delayed laser scattering in a multi-level atom with Raman resonance

A general theory of time-delayed coherent scattering in an atomic medium is presented. Two short laser pulses are incident on the atom initially, followed by a third laser at a later time. Detailed time dependent expressions for the atomic coherence and the third order dipole matrix elements are obtained. We have included the effects of excited level population, phase matching, single and two-photon resonances, and atomic relaxation and dephasing. Detailed discussions are given for the case where the first two lasers are in a Raman resonance withthe atomic system. Some useful features of this type of scattering, for example, background elimination, are also pointed out.