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Physical Review A

Inversionless amplification in a multilevel system

Paul Mandel, Olga A. Kocharovskaya

Published Jun 1, 1993• 25 citations
Publisher

Abstract

We prove that the amplification condition for a multifrequency field in an atomic system with multiple splitting of the operating levels implies a population inversion between the eigenstates of the density matrix. This explains the possibility of amplification without population inversion when a coherent superposition state of sublevels is prepared.

DOI
10.1103/physreva.47.5003

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Amplification of a weak circularly polarized light signal in a multilevel atomic medium

E. A. Gazazyan, G. G. Grigoryan, A. Papoyan

Amplification of a weak circularly polarized light signal in a multilevel atomic medium excited by a strong linearly polarized resonant radiation is studied. A strong optical pumping may lead to the population inversion between magnetic sublevels of hyperfine components of the ground and excited states. Solution to the self-consistent system of density matrix equations and Maxwell equations for propagation of the weak signal allows analyzing optimum conditions of amplification.

Journal of Contemporary Physics (Armenian Academy of Sciences)•Jul 7, 2011•3 citations
We prove that the amplification condition for a multifrequency field in an atomic system with multiple splitting of the operating levels implies a population inversion between the eigenstates of the density matrix. This explains the possibility of amplification without population inversion when a coherent superposition state of sublevels is prepared.
In a two-level medium, the condition for amplification is population inversion. The simplest scheme in which inversionless amplification occurs is a three-level medium. It was shown recently that a trichromatic field can be amplified by a three-level medium without population inversion if the low-frequency (LF) coherence exceeds some critical value.1 The question that we address here is how to generalize the two-level amplification condition when one or both levels are split into a number of sublevels.
We consider the problem of amplification without inversion in a three-level atomic system. When atoms are driven by a field reservoir and a low-frequency coherent field, amplification of a high-frequency probe field may occur even when there is no population inversion on any atomic transition. We prove that, depending on the ratio of the probe and coherent drive field frequencies, which we term the frequency up-conversion factor, this process may or may not require hidden inversion in the field reservoir. In the special case of a frequency up-conversion factor less than 2, we demonstrate that amplification is possible even if the field reservoir is in complete thermal equilibrium: this represents a new kind of coherent radiation source, distinct from both conventional lasers and lasers without inversion.
We consider a three-level medium with low-frequency separation between the two upper levels. The medium interacts with an external field that induces a coherence between the two upper levels. We analyze the amplification condition for the probe monochromatic optical field in a general nonresonant case. We show that amplification without population inversion arises either at line center or at the sidebands, depending on the sign of the population difference between the upper sublevels. This amplification occurs in a limited range of the coherent pump intensity.