Fast Light, Slow Light, and Optical Precursors in Cold Atoms
Abstract
We report experimental observations of optical precursors generated from a square-modulated probe laser pulse, with finite rise and fall time, propagating through a cold atomic ensemble, in either a two-level Lorentz absorber or a three-level system with electromagnetically induced transparency (EIT). Because of the finite rise (fall) time, the precursor signal decreases as we increase the optical depth (α0 L). We find that the absorption of the precursor peak magnitude can be controlled by varying the rise (fall) time. At α0 L =42, we increase the precursor peak transmission from 8% to 27% by shortening the rise (fall) time from 7 ns to 3 ns. Meanwhile, we observe no violation to Einstein's causality in both slow and fast light mediums. In the EIT system at a high OD, the main field propagates with a slow group velocity and is separated from the precursor. In the two-level system, we confirm the negative group velocity in the anomalous dispersion regime, but no advancement to the rising edge.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2010
- Bibcode:
- 2010APS..MARZ31001C