Simultaneous observation of excited-state Raman scattering and resonance-enhanced three-photon scattering

Abstract
New resonances have been observed in the fluorescence spectrum of atomic sodium, near the D lines, for both resonant and nonresonant laser excitation. The resonances are interpreted as arising from the interaction of the strong driving laser field and the three-level atom. Specifically, two simultaneously acting mechanisms are identified: resonantly enhanced three-photon scattering and excited-state Raman scattering.