The concept of white light cavities using atomic phase coherence

We describe a concept to realize a broadband high finesse optical cavity (white light cavity) using low-loss negative dispersive media. Two atomic systems are discussed, which allow transparency and lambda-compensation, i.e. the dispersion of the medium compensates the frequency dependence of the vacuum wavelength. These atomic systems are (i) the driven two-level system and (ii) two closely spaced gain lines. We explain why the second scheme should provide better performance in terms of the realization of a white light cavity.