Evolution of the stimulated photon echo in optically dense media

A numerical investigation is reported of the characteristics of the stimulated photon echo (SPE) excited by a sequence of 2n (n ≥ 2) paired pulses in an extended medium. The evolution of these pulses during propagation is taken into account. The SPE is shown to have a threshold governed by the total initial area of the excitation pulses. Stable SPE amplification is observed when this total area exceeds the threshold value, which is π. The optimal conditions for the SPE are identical for optically thin and dense media. This is a cumulative effect. The existence of a threshold affects also the cumulative effect: the nature of the dependence of the SPE amplitude on the number of the excitation pulse pairs varies with their total initial area. The cumulative effect is observed also when the pulse areas are no longer small. The linear part of the dependence of the SPE signal on n becomes narrower when the dimensions of a sample are increased, which is a consequence of the nonlinear nature of the evolution of pulse pairs in extended media.