ABSORPTION AND DISPERSION BY A DRIVEN ATOM IN A CAVITY

We investigate the absorption and dispersion of a probe field by a two -level atom driven by a strong external field and coupled to a single cavity mode. For moderate atom-field coupling the absorption spectrum contains ultrasharp lines, and the real part of the linear susceptibil ity changes rapidly at the Mellow sideband frequencies. For large coup ling the absorption and dispersion spectra split into multiplets whose structures depend on the photon-number distribution of the cavity fie ld. A large index of refraction accompanied by vanishing absorption is predicted.