Experimental Constraints of Using Slow-Light in Sodium Vapor for   Light-Drag Enhanced Relative Rotation Sensing
  We report on experimental observation of electromagnetically induced transparency and slow-light (vg ~ c/607) in atomic sodium vapor, as a potential medium for a recently proposed experiment on slow-light enhanced relative rotation sensing [11]. We have performed an interferometric measurement of the index variation associated with a two-photon resonance to estimate the dispersion characteristics of the medium that is relevant to the slow-light based rotation sensing scheme. We also show that the presence of counter-propagating pump beams in an optical Sagnac loop produces a backward optical phase conjugation beam that can generate spurious signals, which may complicate the measurement of small rotations in the slow-light enhanced gyroscope. We identify techniques for overcoming this constraint. 
Renu Tripathi, G.S. Pati, M. Messall, K. Salit and M.S. Shahriar