SWITCHING BETWEEN RAYLEIGH-LIKE AND LORENTZIAN LINESHAPES OF THE DISPERSION IN DRIVEN 2-LEVEL ATOMS

We investigate the structure of the dispersion and absorption lineshap es for driven two-level systems against a weak probing laser field. It is shown that the shape of both curves depends critically on the detu ning of the driving laser to the atomic resonance frequency and can be transformed continuously and oppositely between Rayleigh (or 'dispers ion-like') and Lorentzian (or 'absorption-like') lineshapes. An analys is in the dressed state basis explains these features via the differen t influences of coherences and populations of the corresponding dresse d states.