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Journal of Modern Optics

Quantum theory of non-degenerate inversionless laser: Effects of initial partial coherence

Nadeem A. Ansari, A. H. Toor

Published Dec 1, 1996• 8 citations
Publisher

Abstract

In this paper, we have included the effects of initial partial coherence in the quantum theory of a non-degenerate inversionless laser. A three-level atomic system in open A-configuration is considered. The atoms are initially prepared in the partial coherent superposition of the lower two atomic levels with some incoherent population in the excited state. The master equation for the cavity field modes is derived and converted into a Fokker-Planck equation to determine the phase locking and stability conditions. The effects of initial partial coherence on the gain of two modes are studied under these conditions. The range of values of the initial partial coherence for which the action of lasing without inversion can take place are shown. Our results show that under certain conditions the two modes can amplify with equal gain below threshold.

DOI
10.1080/09500349608230671

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We analyze a laser system consisting of N closed three-level atoms confined in a single-mode cavity and derive the conditions for the onset of lasing without inversion or with inversion. We calculate the steady-state gain and lasing in the system and show that far above the lasing threshold, depending on the pumping and decay rates, the inversionless laser may operate in three different regimes, where the intensity of the laser depends linearly on N, is proportional to \ensuremath{\surd}N , or independent of N.
In this paper, a quantum theory of an inversionless laser is presented. The gain medium is considered to consist of three-level atoms in a closed \ensuremath{\Lambda} configuration, with a lower-level microwave coupling. By deriving an equation of motion for the reduced density matrix for the two modes of the field, gain and diffusion are studied. In particular, two mechanisms through which inversionless amplification takes place in the context of this model, namely, the suppression of absorption and mode coupling, are discussed. Stable conditions for inversionless amplification and the attendant phase diffusion are discussed and a comparison is made with conventional, inversion-based lasers. It is shown that lasing without inversion does not necessarily result in a reduced linewidth compared to a conventional laser.