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Physical Review A

Lasing without inversion and coherence in dressed states

Zhenfei Luo, Zhizhan Xu

Published Jun 1, 1992• 18 citations
Publisher

Abstract

The V and \ensuremath{\Xi} types of closed lifetime-broadened systems with lower-level-dressed-state preparation by a strong electromagnetic field are analyzed. It is found that the coherence in dressed states enhances the gain in the former system but reduces gain in the latter. However, we show that, since the dressed states are prepared in lower levels, both systems can lase without population inversion in steady state.

DOI
10.1103/physreva.45.8292

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Physical Review A•May 1, 1992•126 citations
The V and \ensuremath{\Xi} types of closed lifetime-broadened systems with lower-level-dressed-state preparation by a strong electromagnetic field are analyzed. It is found that the coherence in dressed states enhances the gain in the former system but reduces gain in the latter. However, we show that, since the dressed states are prepared in lower levels, both systems can lase without population inversion in steady state.
Light-induced absorption with population inversion and amplification without population inversion in a coherently prepared closed three level V-type system are investigated. This study is performed from the point of view of a two color dressed-state basis. Both of these processes are possible due to atomic coherence and quantum interference contrary to simple intuitive predictions. Merely on a physical basis, one would expect a complementary process to the amplification without inversion. We believe that absorption in the presence of population inversion found in the dressed-state picture utilized in this study, constitutes such a process. We derive approximate analytic time-dependent solutions, for coherences and populations that are compared with full numerical solutions exhibiting good agreement. Steady-state quantities are also calculated, and the conditions under which the system exhibits absorption and gain with and without inversion, in the dressed-state representation are derived. It is found that for weak input probe-laser field absorption with inversion and amplification without inversion may occur, for a range of system parameters. These take place at resonance and the generalized Rabi ac Stark-shifted frequencies, in agreement with exprimental investigations, and at beat frequencies, depending on the relevant parameters.
Light amplification without population inversion and absorption with inversion driven by quantum coherent interferences in a closed three level V-type system is studied from the point of view of two color dressed state basis. Approximate analytic time dependent solutions, for coherences and population distribution are derived, and compared with full numerical solutions. Steady state quantities are also calculated, and the conditions under which the system exhibits gain with and without inversion, in the dressed state representation are derived. It is found that for a weak probe laser field light amplification without inversion may occur, for a range of system parameters, in both the bare and the dressed state representations.
We show that a closed four-level system can exhibit lasing without population inversion in any state basis. The same system can be also made to exhibit lasing without population inversion in the bare-state basis but with population inversion in the dressed-state basis. We derive the conditions of lasing without inversion and examine the dependence of the gain on various system parameters. The lasing threshold and the steady-state photon numbers are calculated. Comparison with a ssV-type, three-level model is presented.