RESONANCE FLUORESCENCE IN A TAILORED VACUUM

We consider the resonance fluorescence of a two-level atom with an emphasis on the dependence of this phenomenon on the modal density of the environment. We use an approach of the Weisskopf-Wigner type to investigate the interaction of the dressed states of the atom-driving field system to the surrounding environment, and calculate the linewidth of the resonance fluorescence spectrum in terms of the decay rate of the dressed coherences. Unlike the conventional theory, we deal first with the exact interaction of the atom with the driving laser field, and then consider the coupling of this combined system to the modes of the environment within the Weisskopf-Wigner approximation. This modification of the traditional sequence in which the interactions are handled leads to a sensitive dependence of the fluorescence spectrum on the density of modes and suggests that a driven atom placed in a suitable environment, such as for example a high-e resonator, even if Markovian, might behave quite differently from an identical system in free space. The significance of this effect is shown explicitly for the case of a strongly driven two level atom in an environment with a modal density which is substantially frequency dependent on the scale of the Rabi frequency of the driving laser field.