Observation of lasing without inversion in a hot rubidium vapor under electromagnetically-induced transparency conditions

TL;DR

This paper reports the experimental observation of lasing without inversion in hot rubidium vapor under EIT conditions, supported by a theoretical model explaining the gain mechanism involving collisional coupling.

Contribution

First demonstration of lasing without inversion in hot rubidium vapor under EIT, combining experimental results with a theoretical model.

Findings

Lasing without inversion observed in hot rubidium vapor.

Threshold behavior depends on atomic density and coupling beam strength.

Theoretical model suggests gain mechanism involves collisional coupling of ground states.

Abstract

We have observed CW lasing without inversion in a gas of hot rubidium atoms in an optical cavity under conditions of electromagnetically-induced transparency (EIT). The medium is pumped coherently and resonantly by a single ``coupling'' beam which also produces EIT in the lasing transition. The steady-state intensity exhibits thresholds as a function of the atomic density and the strength of the coupling beam. A theoretical model for an effective three-level lambda system indicates that gain without inversion is possible in this system if the two ground states are coupled by depolarizing collisions, and if the decay branching ratios meet certain conditions.