Bichromatic electromagnetically induced transparency in cold rubidium atoms

In a three-level atomic system coupled by two equal-amplitude laser fields with a frequency separation 2delta, a weak probe field exhibits a multiple-peaked absorption spectrum with a constant peak separation delta. The corresponding probe dispersion exhibits steep normal dispersion near the minimum absorption between the multiple absorption peaks, which leads to simultaneous slow group velocities for probe photons at multiple frequencies separated by delta. We report an experimental study in such a bichromatically coupled three-level Lambda system in cold Rb-87 atoms. The multiple-peaked probe absorption spectra under various experimental conditions have been observed and compared with the theoretical calculations. (C) 2003 American Institute of Physics.