Observation of an electromagnetically induced grating in cold sodium atoms

We have observed diffraction signals by a grating originating from electromagnetically induced transparency (EIT) in a three-level {Λ} system of cold sodium atoms. Theoretical and experimental analyses of this phenomenon, called the electromagnetically induced grating (EIG), have revealed that EIG spectra exhibit background-free, Lorentzian signal profiles regardless of the pump frequencies, making a clear contrast to the case of ordinary EIT spectra.