Electromagnetically-induced transparency has become an important tool tocontrol the optical properties of dense media. However, in a broad class ofsystems, the interplay between inhomogeneous broadening and the existence ofseveral excited levels may lead to a vanishing transparency. Here, byidentifying the underlying physical mechanisms resulting in this effect, weshow that transparency can be strongly enhanced. We thereby demonstrate a5-fold enhancement in a room-temperature vapor of alkali-metal atoms via aspecific shaping of the atomic velocity distribution.
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