Sub-natural width of transparency window in 85Rb vapor with D2 transition,

We study 85Rb atomic vapor for electromagnetically induced transparency (EIT) and obtain sub-natural EIT spectra at optical power higher than saturation intensity. It is shown that spectral width of transmission and intensity of EIT signal increases with intensity of optical field, which is one of the desirable features for slow light and quantum information processing. A details analysis has been done on such an atomic system.