<title>Scale symmetry breaking in a coherently excited cascade amplifier</title>

Abstract

We analyse the temporal development of a seed signal propagating in an ensemble of three-level atoms initially pumped by a two-photon excitation pulse. In an incoherently prepared system, the medium acts as a two-level system. Such a system is scale-invariant and therefore its dynamics is uniquely determined by the value of aL. On the other hand, a coherently prepared system is not scale invariant leading to more complicated dynamics. We show that, at low optical gain, the amplification is reduced when the pumping is coherent. We further show that at high inversion there is an exponential increase in the radiation emitted from the lower transition in an initially prepared coherent system.