Strong electromagnetically induced transparency in atomic media with   large residual Doppler broadening
  Electromagnetically induced transparency and coherent population trapping were observed in a hot (1000 K) calcium vapor embedded into an electrical gas discharge. Unexpectedly large transparencies (of up to 70%) were observed under very unfavorable conditions: probe wavelength shorter than the coupling wavelength, and coupling Rabi frequency significantly smaller than the residual Doppler linewidth of the two photon transition. We developed a theoretical model that shows that the observed results are due to the combined effects of a strong probe beam and a small open character of the atomic system. Coherent population trapping also manifests itself as a change in the impedance of the gas discharge, and the phenomenon can be probed with high sensitivity via the optogalvanic effect. 
Luis E. E. de Araujo, Silvania A. Carvalho, Luciano S. Soares, Antonio   A. Soares, Armando Mirage, Daniel Pereira, and Flav...