Conversion between electromagnetically induced transparency and absorption in a three-level lambda system

EPL (Europhysics Letters) (Impact Factor: 2.1). 02/2011; 98(4). DOI: 10.1209/0295-5075/98/44009
Source: arXiv


We show that it is possible to change from a {\it subnatural}
electromagnetically induced transparency (EIT) feature to a {\it subnatural}
electromagnetically induced absorption (EIA) feature in a (degenerate)
three-level $\Lambda$ system. The change is effected by turning on a second
control beam counter-propagating with respect to the first beam. We observe
this change in the $D_2$ line of Rb in a room-temperature vapor cell. The
observations are supported by density-matrix analysis of the complete sublevel
structure including the effect of Doppler averaging, but can be understood
qualitatively as arising due to the formation of $N$-type systems with the two
control beams. Since many of the applications of EIT and EIA rely on the
anomalous dispersion near the resonances, this introduces a new ability to
control the sign of the dispersion.

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