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PROFESSOR: Now, I would
like to demonstrate to you

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a very widely tunable laser.

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In this gates it's a dye laser.

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The dye being rhodamine 6G.

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When pumped with an argon
laser, the dye laser

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can be tuned from light
green, to yellow, to orange,

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red, and even deep red,
using just that one dye.

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So in this demonstration
then, what we're going to do

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is fire up the dye
laser, and then tune it

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so that you can see all these
colors right on your screen.

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Again, you have to be
careful and make sure

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that your monitor is
is adjusted so that you

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can see these colors.

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Now, the dye laser is
right here behind me.

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And when we come back,
we'll have it all set up,

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ready to show you those
beautiful colors that

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come out from this dye laser.

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Now, on the left you
see the argon laser

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pump that pumps that dye jet.

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Now, as we zoom out, we see
the entire ring dye laser.

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So let's look at the dye
laser in more of a close-up.

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Here's the pump coming
in into the dye laser.

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Here it is.

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Here's the argon laser pump.

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And the pump gets focused
into the dye jet over here.

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The fluorescence
from the dye jet

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then is picked up by
mirrors close to the dye jet

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and then sent around
this ring cavity.

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There's one mirror here,
here's the laser beam,

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and here's the other
mirror here, and then

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the other two on
either side of the jet.

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So here's the output
of the dye laser.

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What we're going to
do with it, we're

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going to pass it through
a diffuser to dramatize

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the display of the color.

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Here's the output
of the diffuser.

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And I'm going to let it fall
onto the screen over there.

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Now, right now, the dye
laser is putting out

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an orangish sort of color,
as you can see on the screen.

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So, now, I'm ready to tune
the dye laser so that we can

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observe this huge tuning range.

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And in order to
tune the laser, we

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have inserted a birefringent
element over here.

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And just by simply adjusting
the angle using a micrometer,

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we can tune the
wavelength of the laser.

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But first let me remind you
that the colors you're seeing

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depend on the setting
of your monitor.

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Right now you should
be seeing orange.

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Now, I'm going to tune
either side of orange.

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Now, I have yellow and going
towards greenish-yellow.

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Here we are.

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On the screen, I see
light green color,

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and I hope you see that also.

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So here we are from light green.

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Now I'm going to
turn towards the red.

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That's becoming yellow, now
orange, and now even a stronger

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orange, is becoming reddish.

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Now it's nice and red, and
we're getting, in fact,

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deep red over here.

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Again, I hope your monitor
is going to show you

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this huge, huge turning range.

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Now, we'll go back
again to red and orange.

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Now we have yellow
and then light green.

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All right.

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Now, let me just also remind
you that the tuning range

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that you've seen is
about 10 to the 14 hertz.

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That's a huge,
huge tuning range.