Double-double electromagnetically induced transparency with amplification.

We show that an alkali-metal atom with a tripod electronic structure can yield rich electromagnetically-induced-transparency phenomena even at room temperature. In particular we introduce double-double electromagnetically induced transparency wherein signal and probe fields each have two transparency windows. Their group velocities can be matched in either the first or second pair of transparency windows. Moreover, signal and probe fields can each experience coherent gain in the second transparency windows. We explain using a semiclassical dressed picture to connect the tripod electronic structure to a double-A scheme. [ABSTRACT FROM AUTHOR]