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Journal of Modern Optics

Correlated emission lasing in a four-level atomic system in the double-Λ configuration

Nadeem A. Ansari

Published Jun 1, 1996• 0 citations
Publisher

Abstract

Quantum mechanical theory of a non-degenerate correlated emission laser in a four-level atomic system in the double-Λ configuration is presented. It is shown that the mode coupling gains in this model have a phase-sensitive nature so that the spontaneous emission events in the two modes are highly correlated in such a way that the relative phase diffusion coefficient can vanish under certain conditions. Also, because of mode coupling and for a certain range of atomic population in the upper atomic levels, lasing without inversion and correlated emission take place simultaneously. Stability conditions and the steady-state modal ratio are derived and it is shown that this ratio remains stable and for this stationary value of the modal ratio both the modes amplify with equal gains.

DOI
10.1080/09500349608232797

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Quantum mechanical theory of a non-degenerate correlated emission laser in a four-level atomic system in the double-Λ configuration is presented. It is shown that the mode coupling gains in this model have a phase-sensitive nature so that the spontaneous emission events in the two modes are highly correlated in such a way that the relative phase diffusion coefficient can vanish under certain conditions. Also, because of mode coupling and for a certain range of atomic population in the upper atomic levels, lasing without inversion and correlated emission take place simultaneously. Stability conditions and the steady-state modal ratio are derived and it is shown that this ratio remains stable and for this stationary value of the modal ratio both the modes amplify with equal gains.
Noninversion lasing is investigated in \ensuremath{\Lambda}-type three-level atomic systems that are coupled to two modes of the electromagnetic field. As a result of an external field driving the transition between the lower two closely spaced levels, laser action can be achieved in both modes simultaneously at arbitrarily small initial upper-level population (lasing without inversion) provided the pumping rate exceeds a certain threshold. The relative phase of the two modes is locked to a particular value controlled by the phase of the external field. In addition, new regimes of the laser operation arise when initial coherences between various atomic levels are also injected into the resonator. Firstly, laser action can be achieved in both modes at arbitrarily small pumping (no threshold). Secondly, the injected atomic coherence can control competition between the modes, and result in a variety of multistable steady-state behavior illustrating the very sensitive dynamics of the system.
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.
We study a four-level double-$\ensuremath{\Lambda}$ atomic configuration working as a two photon linear amplifier where two atomic transitions independently interact with cavity mode, while the other transitions are driven by a strong pump field. It is found that our system always works as a phase sensitive linear amplifier with no window for a phase insensitive linear amplifier. We also investigate that the system behaves as a two-photon correlated-emission laser under certain conditions.
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.
We develop a quantum theory of a correlated-emission laser (CEL) with injected atomic coherence for arbitrary initial atomic conditions and arbitrary atomic decay rates. The effect of initial atomic coherence on the CEL is studied. It is shown that, with a proper form of the initial atomic coherence and equal atomic decay rates between the two upper levels of V-type three-level lasing atoms, the diffusion coefficients for the relative phase and the relative amplitude of two laser modes can vanish under certain conditions. These conditions, plus equal cavity-loss rates, lead to the vanishing of the normally ordered variances (quantum-noise quenching) of Hermitian operators corresponding to the relative phase and the relative amplitude.
We present a dressed-atom theory of a four-level, double-\ensuremath{\Lambda} atomic configruation interacting with a strong laser light which induces a superposition of two lower states. The presence of the cavity and of damping is fully taken into account and the conditions and characteristics of a possible lasing without inversion between the unperturbed states are determined analytically. The special case of the Zeeman-degenerate J=1 lower state is found to be particularly attractive for a possible practical realization.