Enhanced harmonic generation and wave-mixing via two-color multiphoton   excitation of atoms/molecules
  We consider harmonics generation and wave-mixing by two-color multi photon resonant excitation of three-level atoms/molecules in strong laser fields. The coherent part of the spectra corresponding to multicolor harmonics generation is investigated. The obtained analytical results on the basis of generalized rotating wave approximation are in a good agreement with numerical calculations. The results applied to the hydrogen atom and homonuclear diatomic molecular ion show that one can achieve efficient generation of moderately high multicolor harmonics via multiphoton resonant excitation by appropriate laser pulses. 
H. K. Avetissian, B. R. Avchyan, G. F. Mkrtchian
physics.atom-ph