Superluminal motions.
Light pulse can propagate in some media at speed exceeding the speed of
light in vacuum.
- What we have to do to observe the superluminality? Use media with dispersion.
- Can we send a bit of info with superluminal speed? - No!
In two arms of optical chain on the picture below
nonlinear gain provides compensation of linear delay.
In examples, shown below,
The two indetical fiber rings are included in optical arms.
The upper path is longer, hence in the absence of gain in the upper
loop the pulse moving along bootom path arrives to detector before the
pulse moving along upper path. Look oscilloscope traces and
animation.
Another situation is shown on the next picture.
The upper fiber loop is resonantly pumped by two VCSEL diode lasers.
Thus, the superlminal propagation is possible.
As a consequence, the upper pulse arrives faster than lower.
Why?
Look oscilloscope traces and
animation.
This effect had been explained by V.S.Letokhov in 1965.
You may also read some other pages on superluminality.
