A study of the energy source for photon echoes

Abstract

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.