Resonance fluorescence in intense laser fields

We consider the resonance fluorescence of a two-level atom in a vacuum with a high intensity driving field, such that the Rabi frequency of the field is non-negligible up to frequencies comparable to the transition frequency of the atom. At these high intensities, the conventional rotating wave appr oximation cannot be applied to the atom-laser Hamiltonian and the modal den sities of the vacuum at the dressed transition frequencies differ significa ntly from each other. On treating the counter-rotating part of the Hamilton ian as a perturbation and carrying out the Weisskopf-Wigner approximation i n the dressed states basis, we find that the high driving intensity leads t o significant deviations from the traditional Mellow resonance fluorescence spectrum. In particular we find unequally intense Mollow side-bands and th at the generation of higher order triplets and harmonics is substantially e nhanced by the high vacuum modal density at the corresponding high resonanc e frequencies.