Negative dispersion without absorption

Summary form only given. We study the optical properties of negative dispersive but nevertheless transparent media. Such medium can be generated using atomic phase coherence. Theoretical studies have shown that strongly driven two level systems may exhibit the desired optical properties, that is negative dispersion of a well defined amount at a point of vanishing absorption. When this medium is placed inside an optical resonator the linewidth is increased without sacrificing its build up. We present the experimental setup which is used to realize a negative dispersive non-absorbing medium. To obtain a strongly driven two level system a calcium atomic beam is pumped at the transition 4s/sup 21/S/sub 0//spl rarr/4s4p/sup 1/P/sub 1/. The optical properties of the beam are studied.