M5L24g.txt

#
# File:   content-mit-8-421-5x-subtitles/M5L24g.txt
#
# Captions for 8.421x module
#
# This file has 63 caption lines.
#
# Do not add or delete any lines.
#
#----------------------------------------

So this is sort of the framework.
I want to sort of show you examples of a probe absorption
spectra.
It's more a little bit of show-and-tell.
I want to show you the result if you would work that out.
It's pretty interesting.
So first, I want to discuss the case where the coupling
laser is really in resonance.
So we are near the one-photon resonance.

So let me assume first that the Rabi frequency of the coupling
laser is much, much larger than gamma.

Then, if you look at the probe transmission,
we have this situation that we know
when we are right here in the middle we
have a window of transparency.
But if we detune the Rabi frequency over 2,
we hit the bright state 1.
And if we detune in the opposite,
we hit the bright state 2.
And the splitting in this situation, delta bar,
is nothing else than the Rabi frequency omega 2.
So what we have is we have that detuning in between.
And we know already here is our special point.
And that's what we have discussed
for long electromagnetically-induced
transparency.
The two brights states are at plus and minus 1/2
the Rabi frequency of the coupling laser.
We know that we have very strong absorption here.
And what you get is sort of broad feature.
But this was the situation when we
drive the system very strongly.

I now want to discuss the case that the coupling laser is
much weaker than gamma.
Then the splitting between the two bright states
was the Rabi frequency.
But the [INAUDIBLE] gamma, so then the two bright states
pretty much merge into one continuum feature
of [INAUDIBLE] gamma.
For that situation, we have a broad feature of absorption,
which is on the order of gamma.
Or if you are an opaque medium, of course,
you put the absorption coefficient
into the exponent of an exponential function,
and you get a [INAUDIBLE] which is wider than gamma.
But then we have our phenomenon of EIT.
But the width of this feature is now much smaller than gamma.
So what we have here in those two situations
where the lasers are close to resonance with the excited
level, we have this situation that this strong absorption
feature due to the bright states.
Either one strong feature of [INAUDIBLE] gamma,
or two features here.
Those broad single-photon absorption features,
they really overlap with our window of transparency.
And what I find very insightful is now to discuss a situation
where we separate the two.
And I want to show you what happens.
And it gives a very interesting profile.