A study of the energy source for photon echoes

Summary form only given. There are several conflicting descriptions of the stimulated photon echo (SPE) process. The SPE is often described as a phased array of classical dipole radiators in which the atoms´ spontaneous emission during the time of the echo radiates constructively in the direction of the echo and destructively in all other directions. A second description is that the SPE arises as a linear scattering event. In this paper we numerically and experimentally show that the SPE arises from a macroscopic polarization of the medium at a time /spl tau//sub 21/ after the third pulse and its energy is extracted from the atomic excited-state population. The energy extracted from the system manifests itself as a permanent drop in the population of excited-state atoms at the time of the echo. Such a permanent drop is not consistent with first two descriptions of the SPE process.