Resonance Fluorescence Spectrum by Two-Level System Without the Rotating Wave Approximation

In this paper the theory of resonance fluorescence spectrum by two-level system is presented without the assumption of rotating wave approximation. However, in this case, the application of quantum fluctuation-regression theorem to evaluate the resonance fluorescence spectrum takes a more complicated form. The prominent features of the spectrum calculated are the double splitting on the central and side bands and the emergence of harmonics in the asymmetric spectra.