Coherent two-field spectroscopy of degenerate two-level systems - art. no.013801

Spectroscopic features revealing the coherent interaction of a degenerate t wo-level atomic system with two optical fields are examined. A model for th e numerical calculation of the response of a degenerate two-level system to the action of an arbitrarily intense resonant pump field and a weak probe in the presence of a magnetic field is presented, The model is valid for ar bitrary values of the total angular momentum of the lower and upper levels and for any choice of the polarizations of the optical waves. Closed and op en degenerate two-level systems are considered. Predictions for probe absor ption and dispersion, field generation by four-wave mixing, population modu lation, and Zeeman optical pumping are derived. On all these observables, s ubnatural-width coherence resonances are predicted and their spectroscopic features are discussed. Experimental spectra for probe absorption and excit ed-state population modulation in the D-2 line of Rb vapor are presented in good agreement with the calculations.