  The Mollow spectrum for the light scattered by a driven two-level atom is
derived in the resolvent operator formalism. The derivation is based on the
construction of a master equation from the resolvent operator of the atom-field
system. We show that the natural linewidth of the excited atomic level remains
essentially unmodified, to a very good level of approximation, even in the
strong-field regime, where Rabi flopping becomes relevant inside the
self-energy loop that yields the linewidth. This ensures that the obtained
master equation and the spectrum derived matches that of Mollow.
