FIGURE 4. Measured pulse advancement for a light pulse traversing through the caesium vapour in the gain-assisted superluminality state.
From the following article:
Gain-assisted superluminal light propagation
L. J. Wang, A. Kuzmich and A. Dogariu
Nature 406, 277-279(20 July 2000)
doi:10.1038/35018520
A indicates a light pulse far off-resonance from the caesium D2 transitions propagating at speed c through 6 cm of vacuum. B shows the same light pulse propagating through the same caesium-cell near resonance with a negative group velocity -c/310. Insets show the front and trailing portions of the pulses. Pulses A and B are both the average of 1,000 pulses. The off-resonance pulse (A) is normalized to the magnitude of B.
