On the shape of cross resonances in counterpropagating wave spectroscopy

Physical processes that generate cross resonances are studied. It is revealed that not only populational, but also coherent, effects can make a contribution to formation of cross resonances. The effects of coherent processes, lifetimes of levels, the parameter of radiation branching from the upper level, and light fields’ characteristics are shown to be qualitatively different for the Λ-, V -, and J = 1 − J = 1 types of transition. Conditions for the change in the sign of cross resonances are found and a situation wherein the cross resonance has a purely coherent nature is shown.