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PROFESSOR: In this
experiment, we're

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going to illustrate how
sodium atoms exhibit

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very strong absorption
when excited

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by light at the resonance
frequency of sodium.

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We're going to use a
dye laser over here

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and a vapor cell
of atomic sodium.

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We're going to tune the laser
to 5890 angstroms or so,

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which is the resonance
frequency for four sodium.

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And we're going to observe the
sodium resonance fluorescence.

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So when we come back, we'll
have it set up for you

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so that you can
observe for yourself

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this tremendous absorption
exhibited by sodium when

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excited by dye laser radiation
at the sodium resonance.

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The sodium is in a cell--

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in a heated cell--

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on the right.

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And what you can see
right now, inside, you

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see the resonance scattering
by sodium at 5890 angstrom.

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Now, all I have to do is I
tune the dye laser waveform

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resonance, and
there's fluorescence.

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[? Onto ?] the
resonance, here we

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are, plenty of scattered light.

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And I go the other
side of resonance,

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and there's no absorption.

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So here we are again, on
resonance and off resonance.

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On resonance and off resonance.

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CREW: How was that?

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PROFESSOR: Great.