Fluorescence quenching and spectral narrowing from a two-level atom drivenby a weak, narrowband, light field

We consider a single two-level atom driven by the output from a degenerate optical parametric oscillator. For squeezing bandwidths of the order of the natural atomic width and smaller, we report remarkable spectral profiles f or the scattered light, including the existence of a narrow hole at line-ce ntre. Under appropriate conditions, the spectrum may be both subnatural and narrower than the spectrum of the incident field, a phenomenon which does not depend upon strong coupling. To explain the role of the classical or no nclassical nature of the driving field plays, we consider an alternative sy stem which enables the atom to be driven by an arbitrary bandwidth light fi eld with arbitrary two-photon correlations. Both numerical and analytic sol utions are employed to provide physical insight. Surprisingly, spectral nar rowing does not require squeezing: narrowed spectra appear for driving with a blackbody field. Then the atomic fluorescence can be expressed as the pr oduct of the atomic response with the incident spectrum. The resulting narr owing is maximized for incident bandwidths of the order of the natural widt h. However, the narrow hole at line-centre does require a non-classical dri ving field. For ideal squeezing, the fluorescence at line-centre vanishes. We test how robust the effects are to changes in experimentally pertinent f actors such as the solid angle of coupling.