Quasi-trapping of Gaussian beams in two-level systems

Abstract

Large scale quasi-trapping of Gaussian beams in a two-level-atom medium is displayed. The well-known ray theory provides a condition for the possibility of quasi-straight ray paths only in the case of a strongly saturated medium. For weak saturation, the ray paths can never be quasi-straight lines; the beam necessarily undergoes reshaping, as emphasized by Wagner et al. [ Phys. Rev.175, 256 ( 1968)]. Nevertheless, the moment theory displays a quasi-constant mean-radius condition that gives rise to fairly good trapping. These conditions are supported by numerical simulations. Quasi-trappings are displayed over many tens of Rayleigh lengths. Experiments, such as conical emission, that might involve trapping are discussed.