Coherent amplitude modulation of continuous-wave light in cesium vapor

Abstract

We report on observations of coherent, sustained oscillations in the absorption of continuous-wave light at 388 nm that excites the 6S1/2 → 8P3/2 transition in cesium (Cs) vapor. The oscillation frequency is close to the spacing of hyperfine levels of the 8P3/2 level that are excited simultaneously by the 388 nm field. We observe a threshold behavior of the oscillation amplitude with pump power and suggest that the effect is associated with infrared directional emission due to amplified spontaneous emission (ASE) from the 8P3/2 → 8S1/2 transition that is assisted by retro-reflections from cell windows. The effect may be used to probe a lasing process in an atomic vapor, by checking the temporal properties of the pump field transmitted through the vapor.