The polarization of two-level atom in the polychromatic weak field
  The numerical solution for polarization for two-level atom in polyharmonic field has been made. The analytical solution for partial case of symmetrical position of carrier frequency relative to transition frequency is possible. The results showed that the nonlinear features in polarization spectrum take place even for small amplitudes of comb-components for small frequency distance between them. It means that it is necessary to take into account nonlinear effects for interpretation of spectra in comb spectroscopy. 
S.A.Pulkin, A.G.Antipov, A.Kalinichev, A.S.Sumarokov, S.V.Uvarova
physics.optics