Realization of negative dispersion without absorption

Summary form only given. We report on the experimental realization of negative-dispersion in nevertheless nonabsorbing media. Such media are relevant for various reasons. They may be used, for example, inside a cavity to increase its bandwidth without sacrificing its buildup (white light cavity). This could be a promising application for gravitational wave detectors. Furthermore, white-light cavities are real distance measurement devices, because residual frequency noise of the laser used to measure the cavity length does not effect the measurement.