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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Analysis of amplification without inversion by Monte-Carlo simulations

Yuri V. Rostovtsev

Published May 10, 1996• 0 citations
Publisher

Abstract

We derive the generation condition of amplification without inversion in three-level atoms driven by the microwave coherent pumping. Analyzing this condition we show the restriction and the possibility of observing the amplification without inversion under initial thermodynamics equilibrium between atoms and thermal radiation field.
DOI
10.1117/12.239476

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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 present a quantitative study of radiation amplification without population inversion based on models recently proposed by Harris [Phys. Rev. Lett. 62, 1033 (1989)]. We discuss both two-level and three-level arrangements in terms of the density matrix. Our calculations, which are fully time dependent, incorporate an incoherent pumping mechanism that is essential for amplification. We discuss in detail the range of and conditions on atomic parameters for which amplification is possible. Its feasibility is demonstrated through the direct calculation of the change of the intensity of a probe beam interacting with the atom.
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We analyze transient properties of light amplification without population inversion (LWI) in a closed three-level @sV -type system and study the system evolution from transient LWI into steady-state LWI. From the time evolution of the atomic coherence and population distribution with and without an incoherent pump field, we elucidate the light amplification mechanism and derive the conditions under which the @sV system exhibits LWI in any state basis. We derive analytical solution for the steady-state LWI and discuss other mechanisms of light amplification such as stimulated Raman scattering and population inversion in the dressed states. \textcopyright{} 1996 The American Physical Society.
We analyze the physical origin of the inversionless amplification in four-level atoms driven by a Raman field and identify the existence of two different mechanisms for the predicted gain. The first mechanism is connected with the appearance of a population inversion between the atomic states dressed by the coherent pump, while the second is linked to the buildup of coherence among these states. Proper selection of the relaxation parameters can make either the first or the second mechanism dominant over the other although usually both coexist.