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Physical Review Letters

Experimental Demonstration of Laser Oscillation without Population Inversion via Quantum Interference in Rb

Alexander S. Zibrov, Mikhail D. Lukin, Dmitri E. Nikonov, Leo W. Hollberg, Marlan O. Scully, Vladimir L Velichansky, H. G. Robinson

Published Aug 21, 1995• 538 citations
Publisher

Abstract

Laser oscillation without population inversion is demonstrated experimentally in a V-type atomic configuration within the ${D}_{1}\mathrm{and}{D}_{2}$ lines of Rb vapor. It is shown that the effect is due to the atomic interference. The experimental results, as first predicted by careful theoretical analysis, are in a good agreement with detailed calculations.

DOI
10.1103/physrevlett.75.1499

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Laser oscillation without population inversion is demonstrated experimentally in a V-type atomic configuration within the D1andD2{D}_{1}\mathrm{and}{D}_{2}D1​andD2​ lines of Rb vapor. It is shown that the effect is due to the atomic interference. The experimental results, as first predicted by careful theoretical analysis, are in a good agreement with detailed calculations.
Continuous wave (cw) amplification and laser oscillation without population inversion have been observed for the first time in a $\ensuremath{\Lambda}$ scheme within the sodium D1{D}_{1}D1​ line. This is also the first demonstration in which the lasing medium was an atomic beam; this is an approach which, in addition to elucidating the physics, lays a foundation for extensions into the ultraviolet. Calculations using realistic atomic structure were critical to the choice of experimental approach. Observations agree with full density-matrix calculations and clearly show there was no population inversion.
Summary form only given. Intensive theoretical work, carried out in the past decade, has indicated that optical properties of matter can be dramatically affected by atomic coherence and interference effects. In particular, atomic coherence and interference was shown to lead to such intriguing phenomena as electromagnetically induced transparency, lasing without population inversion (LWI), and resonant enhancement of refractive index accompanied by vanishing absorption. In the present paper we report the first experimental observation of LWI oscillation and the first demonstration of index enhancement.
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Continuous-wave (cw) optical gain of $1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2} {\mathrm{cm}}^{\ensuremath{-}1}$ is obtained on a probe transition in a driven, three-level, V-type atomic system. The atoms exhibit no population inversion between the probe excited state and the dressed ground states of the combined atom-drive Hamiltonian. This gain without population inversion is interpreted as direct evidence of quantum interference, arising from coherences established in the atom by the applied optical fields. Agreement with a simple four-level theoretical model is excellent.