This is a seminal, well-written, very complete text studying in-depth many aspects of resonance fluorescence (here from a single molecule). The Authors claim this is the first time in the solid state but A. Muller et al.[1] beat them on the line as far as resonance fluorescence is concerned, although with a much less thorough analysis. They, however, measure the first Mollow triplet:
They use a solid-immersion lens to reduce the focus area close to the diffraction limit.
They provide an almost complete transition from the Heitler (top row is not the lowest intensity of the power series) to the other as seen from the photoluminescence spectrum (left) and the two-photon correlation function $g^{(2)}$ (right):
The description is articulated around the concept of extinction:
There are mentions of experiments admixing signal and driving beam, that appear particularly relevant to this work:[2][3]
Recently, two reports have shown that it is possible to detect single molecules coherently via interference between the excitation laser beam and the light scattered by the molecule6,7
see also 17.[4] The scheme was used by this group to later implement a proof-of-principle single-molecule transistor.[5]