Optics: Fraunhofer and Fresnel Diffraction
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LaserVideoOpticsDiffractionThin filmWireGround stationMaterialQuality (business)
00:20
LaserDiffractionWireThin filmFiberCamera lens
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WireLaserScreen printingPhotodissoziationDiffractionKopfstützePattern (sewing)SizingLaserWavelengthIntensity (physics)ButtonMarker penCosmic distance ladderFender (vehicle)LightSeparation processComputer animation
Transcript: English(auto-generated)
00:00
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00:22
Now we're ready to look at diffraction by thin fibers or wires opposite to slits. The setup is essentially very simple. We even took out the lens that we had here. So the laser beam can go directly onto these wires.
00:44
So if we take a close look at what we have here, we have just four wires that I can just put in the way of the laser beam. And then on the screen, we can see the associated diffraction pattern.
01:01
So let's start with the thickest wire. So here is, as you can see on the screen, here is the diffraction pattern associated with this wire. And what you can see, well, first of all, let me remind you that we have the little circles there, which are the 5-centimeter markers so you
01:21
get a feel for the spacing. Again, the distance between the wire and the screen is 200 centimeters. And the wavelength of the laser is 6328 angstroms. I'm not going to tell you the diameter of the wire, because I'm going to let you work that out for yourself.
01:42
But first, you want to look at the diffraction pattern. When you can see, it looks very similar to the single slit diffraction pattern, except for the blob in the center. And the blob in the center is a little complicated, but I can attenuate the laser beam.
02:00
And you can see that it is pretty bright, because essentially, it is the laser beam. And so it's very difficult to get information from it. The information is hidden in the lobes on the sides and the spacing between them, because that will be then
02:20
related to the diameter of the wire. So then for the thickest wire, we see this kind of pattern, this kind of spacing. Now let me move on to wire number two, which is thinner. Here's wire number two. And we can see that, first of all,
02:43
there's less light in the wings, because the wire is thinner. So we don't see as many side lobes. And then again, you'll see this blob in the ugly blob in the center, but the information is in the lobes on the side.
03:01
And you can see them very clearly, and you can see their spacing very clearly. Now let me go on to wire number three, which is again thinner still. And maybe here we can zoom in a little bit so that we can see it a little bit better.
03:23
And again, you can see the central spot is a little messy, but the information, as I said before, is in the fringes on the side. Now here again, if I reduce the laser intensity,
03:42
see what the central fringe looks like. And as I bring it up, we'll see the rest of the fringes. Now finally, I'm going to go to my thinnest wire, which is over here. And now we may have to zoom out a little bit
04:03
so that we can see the spacing. And maybe we can increase the sensitivity a little bit because it isn't all that much light. So we can see good. Now we can see the separation between the fringes in the wings.
04:20
So I hope you've been watching carefully the spacing between the fringes so that you can come up with the diameter of the individual wires. Now this is bringing me to the end of the one-dimensional Fraunhofer diffraction patterns.
04:43
Next, what we're going to do is look at two-dimensional Fraunhofer diffraction patterns. And I assure you, they're even more fun than the one-dimension.