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Optics: Polarization of Light and Polarization Manipulation

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Optics: Polarization of Light and Polarization Manipulation
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Quarter-wave plate
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49
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CC Attribution - NonCommercial - ShareAlike 4.0 International:
You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal and non-commercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this
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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.
LaserVideoOpticsLightPolarization (waves)Photographic plateMaterialGround stationQuality (business)
Wind waveLecture/Conference
Wind wavePolarization (waves)PlatingLightPlane (tool)Angeregter ZustandLecture/ConferenceMeeting/Interview
LaserGaussian beamNeon lampLecture/Conference
Rear-view mirrorScreen printingGaussian beamLinearpolarisation
LinearpolarisationTransmission (mechanics)WhiteTypesettingAvro Canada CF-105 Arrow
LinearpolarisationTransmission (mechanics)Avro Canada CF-105 ArrowLightTypesettingAngeregter ZustandLecture/Conference
Intensity (physics)Plane (tool)Wind waveLightTransmission (mechanics)Screen printingLinearpolarisationPlatingLecture/Conference
PlatingWind waveLecture/Conference
Crystal structureGlassWind waveLightAvro Canada CF-105 ArrowPlatingWhiteLinearpolarisation
Plane (tool)LightLinearpolarisationLecture/ConferenceMeeting/Interview
Crystal structureFACTS (newspaper)GameLinearpolarisationPlane (tool)Transmission (mechanics)Avro Canada CF-105 ArrowLightLecture/Conference
Plane (tool)Crystal structurePlatingAngeregter ZustandLightIntensity (physics)Angle of attackWind waveLinearpolarisationCartridge (firearms)Screen printingAlcohol proofWatch
Transmission (mechanics)Intensity (physics)Lecture/Conference
Screen printingLightIntensity (physics)Lecture/Conference
PlatingWind wavePlane (tool)Polarization (waves)Alcohol proofLinearpolarisationAngeregter ZustandLightMeeting/Interview
Transcript: English(auto-generated)
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In this demo, we're going to illustrate the basic use of a quarter wave plate. And as we know, a quarter wave plate is used to change the state of polarization of light from plane polarized, for example, to elliptical
and under certain conditions to circular polarized light. So we'd like to do that using this setup. We have a laser, a helium neon laser. And here's the beam from the laser. We're going to reflect it through this mirror and then reflect it again through a second mirror.
Then we pass it through this polarizer. And the beam coming through the polarizer then hits the screen. This polarizer, the transmission axis of which is shown by the white arrow,
sets the state of polarization of the light here in this region. No matter what the state of polarization is before the light reaches the polarizer, the polarizer then will clean it up and set it according to the transmission axis. And right now, the transmission axis is along the vertical as shown by the white arrow.
But just to check this, we will use the analyzer, which is another polarizer. And we place it over here. The white arrow is along the vertical direction
and labels the transmission axis of this polarizer. So let's see, indeed, whether the light here is plane polarized. So I'm going to rotate the analyzer and see if I can extinguish the light. Now, what I would like to do is
look at this extinguishing of the light more closely in the bottom left-hand corner, which is a close-up of what you see on the screen. And here, you can see that the extinguishing is pretty complete, which shows that, indeed,
the light in this region is plane polarized. So let me set the analyzer back so that we are transmitting the maximum intensity, which means the transmission axis is lined up with the transmission axis of this polarizer. Now, we're ready to bring in the quarter wave plate.
Here's the quarter wave plate. I'm going to place it in this position, secure it. Now, this quarter wave plate has, as we know, has two principal axes. One of them is labeled by the white arrow here. And again, we know that when this light is propagated
along the principal axis of the quarter wave plate, there is no change in the polarization, just like a piece of glass. Let's check that. So we take the analyzer again, and we rotate the analyzer to see, indeed, whether the light is plane polarized. And as you can see, maybe I didn't get the labeling here,
but as you can see, the light is pretty close to plane polarized. Now, we know that there are two principal axes, so let's turn the arrow to 90 degrees
and show the fact that when light propagates along the other principal axis, the light here is again plane polarized, which means it cannot get past this polarizer when the transmission axis is orthogonal to the initial polarization set
by this polarizer. So now, we've established that indeed, when we propagate along principal axes of the quarter wave plate, nothing happens to the light. It just stays plane polarized. Now, we're going to demonstrate the actual use of a quarter wave plate, which changes, for example, in this case, changes the state of polarization
from plane polarized light to elliptical depending on the angular position that we set, the quarter wave plate at. So let's start with a very small angle away from the principal axis. And now, we want to look at the intensity on the screen
and also in the insert to see whether the light, first of all, whether the light gets extinguished. And also, watch the intensity as I rotate my analyzer. Now, you can see the minimum is around here.
It's not 0. And the maximum is around here, which shows that the light is elliptically polarized, certainly not plane polarized as it was before. Now, if you want circular polarization, we have to rotate the quarter wave plate to about 45 degrees
from one of the principal axes. And if the light is indeed circularly polarized, then we wouldn't see any change in intensity as we rotate the transmission axis of the analyzer. And let's see if we got this close. Now, you can see as I'm rotating the analyzer,
you can see that the intensity on the screen doesn't change all that much, which shows that the light is circularly polarized. In summary, we've shown that a quarter wave plate can change the state of polarization of light.
In particular, we've demonstrated that if plane polarized light is incident on the quarter wave plate and the quarter wave plate is oriented appropriately, we can get elliptically polarized light. If the quarter wave plate is oriented at 45 degrees with respect to the state of polarization
of the light, then we can get circularly polarized light.