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Optics: Two-Beam Interference

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Optics: Two-Beam Interference
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Fringe contrast - polarization difference
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49
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CC Attribution - NonCommercial - ShareAlike 4.0 International:
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This resource contains demonstrations used to illustrate the theory and applications of lasers and optics. A detailed listing of the topics can be found below. Lasers today are being used in an ever-increasing number of applications. In fact, there is hardly a field that has not been touched by the laser. Lasers are playing key roles in the home, office, hospital, factory, outdoors, and theater, as well as in the laboratory. To learn about lasers and related optics, one usually takes a course or two, or acquires the necessary information from books and journal articles. To make this learning more vivid and more exciting, and, one hopes, more understandable, one needs to see some of the basic phenomena involved. To fill this need, Professor Ezekiel has videotaped 48 demonstrations that illustrate most of the fundamental phenomena relating to lasers and physical optics. By using split-screen inserts and a wide range of video-recording capabilities, it is possible to show real-time effects in lasers and optics with the simultaneous manipulation of the components that cause these effects. In this way, one can see effects in close up that would be difficult, if not impossible, to display in front of an audience or in the classroom. These video demonstrations are designed for: The individual student of lasers and optics who wants to observe the various phenomena covered in theoretical treatments in courses, books, and technical papers. The Instructor in lasers and optics in a company, university, college, or high school who wants to illustrate, in class, many of the fundamental phenomena in optics and lasers.
VideoLaserOpticsPolarisierte StrahlungContrast (vision)Gaussian beamInterference (wave propagation)Quality (business)MaterialGround station
Contrast (vision)
FirearmLightAM-Herculis-SternInterferometryMeeting/Interview
AM-Herculis-SternInterferometry
AM-Herculis-SternFirearmInterferometry
FirearmLightAvro Canada CF-105 ArrowDirect currentPlane (tool)InterferometryAM-Herculis-SternTransmission (mechanics)Gaussian beamScreen printingCylinder block
FirearmLightPlane (tool)AM-Herculis-SternWind wavePlatingLecture/Conference
AM-Herculis-SternPlatingWind wave
Screen printingContrast (vision)AM-Herculis-SternAlcohol proofLightAvro Canada CF-105 ArrowPlatingRotationFirearmPlane (tool)Transmission (mechanics)Effects unitWind wave
InterferometryGaussian beamScreen printingAngeregter ZustandPlane (tool)AM-Herculis-Stern
Contrast (vision)LightPlane (tool)AM-Herculis-SternInterference (wave propagation)FirearmAlcohol proofFACTS (newspaper)
LightTiefdruckgebietInterferometryFirearmAM-Herculis-SternContrast (vision)Meeting/Interview
Transcript: English(auto-generated)
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Now I'm going to show another way of reducing fringe contrast. This one has to do with the polarization of the light coming out from each arm of the interferometer. The setup is the same as we had before, except that I've added a polarizer here to clean up the polarization before we
enter the interferometer. So first, let's check on the polarization coming out of each arm of the interferometer in the present setup. And I'll do this by putting a polarizer out here.
And then I'm going to block each arm and check on the polarization. Now as we can see on the screen, when the arrow of the polarizer or the transmission
axis of the polarizer is along the horizontal, I have a lot of light. And when the arrow is vertical, I've extinguished the light, which means that the light coming out from this arm of the interferometer is plane polarized in the horizontal direction.
All right, that's for this arm. Now I'll check on the beam coming out from the other arm, from this arm here. And again, there's a lot of light when the arrow is horizontal. And it's extinguished when the arrow is vertical, which says that the polarization of the light coming out of the two arms is the same
and in the horizontal direction. Now I'm going to rotate the plane of polarization of the light coming out from this arm by using this quarter-wave plate, which I will insert in this arm.
Now as we know, light going through a quarter-wave plate twice, its polarization will be rotated, as we'll see. So now I want to show that the light from this arm going through this polarizer here onto the screen is going to have its plane of polarization changed
as I rotate the alignment of this quarter-wave plate. So with the arrow over here, we can see we have a lot of light. And as I rotate the quarter-wave plate, I see that I can extinguish the light, which
means now the polarization of the light coming out from this arm is orthogonal to the transmission axis of the polarizer. So good. So in this way then, I can rotate the plane of polarization from 0 to 90 degrees by simply rotating the quarter-wave plate.
Now I'm ready to look at the effect of polarization rotation on the fringe contrast. And what I'll do first, I will take out the polarizer. So now I have then two beams coming out from the interferometer.
One has polarization in the horizontal plane. This one here, I can change the state of polarization anywhere from horizontal to vertical. So let's look at the screen. And we see that we have good contrast in this position. Then as I rotate the plane of polarization of this arm
by 90 degrees, you can see that the fringe contrast disappears. And in fact, in this position, you don't even see any fringes at all. If I go back to the original position
and see that the contrast comes back. Let me go back again, wash out the fringes because the polarizations are orthogonal. And just to show you that indeed I'm not hiding anything,
I'm going to show that there's still light coming out from each arm, light coming out from this arm and light coming out from this arm. But when I superimpose them, there's no interference. Now let me put it back to the position where the polarization are equal.
And indeed, we get the good contrast back again. So in conclusion, we've shown that orthogonally polarized light does not interfere. And that's why we get very low contrast fringes when we try to interfere orthogonally polarized light. So then in any interferometer experiment,
you have to make sure that the polarization is the same coming out from each arm of the interferometer. The question I want to leave with you is why orthogonally polarized light does not interfere.