Distinct sublevel coherence mechanisms in nearly resonant four-wave mixing

Abstract

Two different sublevel coherence effects may be distinguished in phase conjugation through backward, nearly-resonant four-wave mixing in optically thin three-level gas media, subject to optical pumping between ground sublevels: (i) unilateral coherent population trapping mechanisms producing light-shift unsensitive level-crossing emission resonances, (ii) two-photon resonances originating lateral power shifted emission lines. Narrow backward pump induced antiresonances are predicted, while the backward to forward pump intensity ratio is shown to play a decisive role in the incidence of distinct generation mechanisms.