Electromagnetically induced transparency in a molecular gas

The dynamic Stark effect on the as Q (5,4) transition of the 0 → 1 vibrational band of the ν 2 mode of ammonia 15 NH 3 was studied by the method of copropagating waves of radiation of two 13 CO 2 lasers operating at the R (18) I line. For waves with mutually orthogonal polarizations, which propagated in a waveguide cell, the intensity of the saturating radiation reached 225 W/cm 2 , and the absorption line of the probing radiation had the form of a two-hump curve with a splitting that was consistent with the Rabi frequency for the ammonia transition being investigated. At the maximum intensity of the saturating radiation, complete transparency was observed at the center of the absorption line of 15 NH 3 . When identically polarized saturating and probing waves propagating in a cell at a small angle with respect to each other were used, the splitting was more weakly manifested. The effect of a spatial inhomogeneity of the optical fields on the shape of the line of saturated absorption is discussed.