Effect of multiorder harmonics in a double-Raman pumped gain medium for a superluminal laser

Use of a double-Raman pump applied to a three-level system is a convenient method for generating negative dispersion. When the gain at the center is high enough, such a system can be used to realize a superluminal laser, which in turn can be used to enhance the sensitivity of rotation sensors. For this condition, it is often necessary to apply strong pumps that are closely spaced in frequency. Accurate modeling of this system thus requires taking into account interference between the two pumps. We present such an analysis where we allow for an arbitrary number of harmonics that result from this interference, and investigate the behavior of the gain profile under a wide range of conditions. We also describe an experimental study of double-Raman gain in a Rb vapor cell, and find close agreement between the experimental result and the theoretical model. The technique reported here can be used in developing a quantitative model of a superluminal laser under wide-ranging conditions.