Controllable Anomalous Dispersion and Group Index Nulling via   Bi-Frequency Raman Gain in Rb Vapor for application to Ultraprecision   Rotation Sensing
  We have recently proposed [9], the use of fast-light media to obtain ultrahigh precision rotation sensing capabilities. The scheme relies on producing a critically anomalous dispersion, in a suitable dispersive medium, which is introduced in the arms of a Sagnac interferometer. We present here an experimental investigation of the anomalous dispersion properties of bi-frequency Raman gain in rubidium vapor, with the goal of using this medium for producing the critically anomalous dispersion condition. A heterodyne phase measurement technique is used to measure accurately the index variation associated with the dispersion. The slope of the negative linear dispersion (or group index) is experimentally varied by more than two orders of magnitude while changing the frequency separation between pump fields, responsible for producing gain. Using this result, we have identified the experimental parameters for achieving a null value of the group index, corresponding to the critically anomalous dispersion condition necessary for enhanced rotational sensitivity. 
G.S. Pati, Renu Tripathi, M. Messall, K. Salit and M.S. Shahriar