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SHAOUL EZEKIEL: In this
next demonstration,

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we're going to look at
the spectrum of the light

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from an argon laser.

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We know that an argon laser
lases in several wavelengths

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simultaneously.

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So, what we're
going to do, we're

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going to take the light
from the argon laser,

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and we're going to look at it
using a simple grating to see

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if, indeed, there are
several wavelengths that

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are oscillating simultaneously.

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Now we've turned the
discharge tube on,

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and the laser is lasing.

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The output of the lasers
coming out from this end

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were reflected by this
mirror mount and this mirror

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over here.

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And let me show you.

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Let me show you
then the laser beam.

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Here's the laser beam coming
out from the argon laser.

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What we're going to
do is reflect it again

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by another mirror over
here onto this screen.

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Now the argon laser lases
at several wavelengths

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at the same time.

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So, in order to
demonstrate this,

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I'm going to take
this grating here,

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and I'm going to put it
in the way of the beam,

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and it will disperse
the various colors.

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Now what you see
on the screen right

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now are the various
orders of the grating,

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but it's difficult to see the
various colors from this angle.

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So, what we'll do,
we'll take a close look

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at the various orders and see
how many lines are lasing.

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So let me again repeat
this again here.

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With the grating out, we only
have one spot on the screen.

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Then, when the grating is in,
we see the various orders.

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So now we'll zoom in and
look at these various orders.

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So here we have a close up
of the output of the grating

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and see the various orders.

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Here's the zero
order on the grading.

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Here's the first order.

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Now, in the second,
we are already

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beginning to see the
dispersion, see several colors.

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And I think, in the third
order, you're already

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beginning to see, between
the third and the fourth,

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that there are indeed several
laser lines that are lasing.

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So,

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If we can then zoom
in on these orders--

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in this case, this
is the fourth--

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we can see that we have blue,
light blue, and another weaker

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one in between and
then the green,

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which is at 5,145 angstroms.

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So, indeed, the laser is lasing
at least at three to four lines

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simultaneously.