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

Lasing without inversion: a dream come true

Dmitri E. Nikonov, Marlan O. Scully, Mikhail D. Lukin, Edward S. Fry, Leo W. Hollberg, G. G. Padmbandu, George R. Welch, Alexander S. Zibrov

Published May 10, 1996• 4 citations
Publisher

Abstract

Two experiments in which laser oscillation without population inversion was obtained for the first time are reported. Analytical solutions are presented to elucidate the principles of the experiments. Numerical simulations and experimental results in a Rb vapor cell and a Na atomic beam for the gain profile are compared.
DOI
10.1117/12.239492

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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.
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.
Mirrorless lasing has been a topic of particular interest for about a decade due to promising new horizons for quantum science and applications. In this work, we review first-principles theory that describes this phenomenon, and discuss degenerate mirrorless lasing in a vapor of Rb atoms, the mechanisms of amplification of light generated in the medium with population inversion between magnetic sublevels within the D2{{D}_{2}}D2​ line, and challenges associated with experimental realization.
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.
The most commonly used lasers operate with population inversion. This requires an incoherent pumping power (from lamps, electrical discharges, etc.) that rapidly scales with the frequency of the generated laser radiation. In practice, this is the main obstacle for the operation in the continuous-wave regime of short-wavelength lasers in the UV, X-rays, etc. But lasers can also operate without population inversion using atomic coherences excited in the laser medium by coherent pumping with another laser. We present in this paper a short review of the field of lasing without inversion (LWI). In particular, we summarize the basic physics of LWI in the framework of both semiclassical theory and quantumjump formalism to describe light-matter interaction. We also review the experimental state-of-the-art in LWI. Most proof-of-principle demonstrations of LWI have used atomic vapours, so far. But recently gain without inversion (a pre-requisite for lasing) has been observed also in a technologically relevant medium: semiconductor nanostructures that can be tailored to have “artificial atom” electron states.