Polarization of light, linear and circular (video) | Khan Academy
What if we have a superposition of left and right circularly polarized light of equal amplitude? Phase difference between - and -components. • Algebra: = cos −. Circularly polarized light consists of two perpendicular electromagnetic plane waves of equal amplitude and 90° difference in phase. The light illustrated is right -. Lecture Polarization of a transverse Electro Magnetic Wave may or may not have same amplitude but let us assume that the phase difference The circular polarization can be divided into Left-circular and Right-circular polarization.
So because the floor is horizontal, when this light ray hits the ground and reflects, that reflected light gets partially polarized.
This horizontal component of the electric field is going to be more present than the other components. Sometimes it could be. It could be completely polarized, but often it's just partially polarized. But that's pretty cool, because now you know what we can do.
I know how to block this. We should get some sunglasses. We put some sunglasses on and we make our glasses so that these are polarized. And how do we want these polarized? I want to get rid of the glare. So what I do is, I make sure my sunglasses only let through vertically polarized light. That way, a lot of this glare gets blocked because it does not have a vertical orientation, it has a horizontal orientation. And then we can block it. So that's one good thing that polarization does for us, and understanding it, we can get rid of glare.
Also, fishermen like it because, if you're trying to look in the water at fish, you want to see in through the water, you want to see this light from the fish getting to you. You don't want to see the glare off of the sun getting to you.
So polarized sunglasses are useful. Also, we can play a trick on our eye, if we really wanted to. You could take one of these, make one eye have a vertical orientation for the polarization, have the other eye with a horizontal Well, the reason our eyes see 3D is because they're spaced a little bit apart.
They each get a different, slightly different image. That makes us see in 3D. We can play the same trick on our eye if we have the polarization like this. If light, if some of the light from the movie theater screen is coming in with one polarization, and the other light's coming in with the other polarization, we can send two different images to our eyes at the same time. If you took these off, it'd look like garbage because you'd be getting both of these slightly different images, it'd look all blurry.
If you take off your 3D glasses and look at a 3D movie, looks terrible, because now both eyes are getting both images. But if you put your glasses back on, now this eye only gets the orientation that it's supposed to get, and this eye only gets the orientation that it's supposed to get, and you get a 3D image.
So it's useful in many ways. Let me show you one more thing here. Let's come back here.
Right handed vs Left handed circular polarization | Physics Forums
This light was polarized vertically. So that's called linear polarization.
These are all linear polarization because, just up and down, one linear direction, just diagonal. This is also linear. All of these are linear. You can get circular polarized light. So if we come back to here, we've got our electric field pointing up, like that. Now let's say we sent in another light ray, another light ray that also had a polarization, but not in this direction.
Let's say our other light ray had polarization in this direction, so it looks like this, kind of like what our magnetic field would have looked like. But this is a completely different light ray with its own polarization and its own magnetic field. So we send this in. Well, at this point, you'd have a electric field that points this way. At this point, you'd have a electric field that points that way.
What would your eye see if you were over here?
Circular polarization - Wikipedia
If I draw our axis here. All right, when this point right here gets to your eye, what am I going to see? Well, I'm going to have a light ray that's one part of a light ray. One component points up. That's this electric field. One component points left.
So the total, my total electric field, would point this way. I could to the Pythagorean theorem if I wanted to figure out the size of it, but I just want to know the direction for now. And then it gets to here, and look at it: This light ray has zero electric field, this one has zero electric fields.
So then it'd just be at zero. Now what happens over here? Well, I've got light. This one points to the right at that point, this pink one, and then this red one would be pointing down. So what would I have at that point? I'd have light that went this way, and it would just be doing this over and over.
It would just be I'd just have diagonally polarized light. This isn't giving me anything new. You might think this is dumb. Why send in two different waves to just get diagonally polarized light?
- Right handed vs Left handed circular polarization
- Classification of Polarization
I could have just sent in one wave that was diagonally polarized and got the same thing. The reason is, if you shift this purple wave, this pink wave, by 90 degrees of phase, by pi over two in phase, something magical happens. Let me show you what happens here, if we move this to here.
Polarization of light, linear and circular
Now we don't just get diagonally linear polarized light. What we're going to get is Let me get rid of this. Okay, so we start off with red, right? The red electric field points up, and then this pink wave's electric field is zero at that point. So this is all I have. My total electric field would just be up. I'm going to draw it right here. The green'll be the total. Now I come over to here, and at this point, there's some red electric field that points up, but there's some of this other electric field that points this way.
So I'd have a total electric field that would point that way. And then I get over to here, and I'd have all of the electric field from the pink one, none from the red one. It would point all left then. The polarization of this light, if I shift this, if I'm sitting here, looking with my eye, as my eye receives this light, I'm going to see this light rotate its polarization. The polarization I'm going to notice swings around in a circular pattern. And because of this, we call this circular polarization.
So this is another type of polarization, where the actual angle of polarization rotates smoothly as this light ray enters your eye. And you know what? All right, actually, I sent you to receive this one first.
That makes no sense. You're going to receive the ones closes to you first in this light ray going this way. So you'd actually receive this one first, then that one, then this one, then this one.
The vertical component and its corresponding plane are illustrated in blue while the horizontal component and its corresponding plane are illustrated in green. Notice that the rightward relative to the direction of travel horizontal component leads the vertical component by one quarter of a wavelength.
It is this quadrature phase relationship which creates the helix and causes the points of maximum magnitude of the vertical component to correspond with the points of zero magnitude of the horizontal component, and vice versa. The result of this alignment is that there are select vectors, corresponding to the helix, which exactly match the maxima of the vertical and horizontal components.
To minimize visual clutter these are the only helix vectors displayed. To appreciate how this quadrature phase shift corresponds to an electric field that rotates while maintaining a constant magnitude, imagine a dot traveling clockwise in a circle.
Consider how the vertical and horizontal displacements of the dot, relative to the center of the circle, vary sinusoidally in time and are out of phase by one quarter of a cycle. The displacements are said to be out of phase by one quarter of a cycle because the horizontal maximum displacement toward the left is reached one quarter of a cycle before the vertical maximum displacement is reached.
Now referring again to the illustration, imagine the center of the circle just described, traveling along the axis from the front to the back. The circling dot will trace out a helix with the displacement toward our viewing left, leading the vertical displacement.
Just as the horizontal and vertical displacements of the rotating dot are out of phase by one quarter of a cycle in time, the magnitude of the horizontal and vertical components of the electric field are out of phase by one quarter of a wavelength. The next pair of illustrations is that of left-handed, counter-clockwise circularly polarized light when viewed by the receiver.
Because it is left-handed, the rightward relative to the direction of travel horizontal component is now lagging the vertical component by one quarter of a wavelength rather than leading it. Reversal of handedness by phase shift[ edit ] To convert a given handedness of polarized light to the other handedness one can use a half- waveplate.
A half-waveplate shifts a given component of light one half of a wavelength relative to the component to which it is orthogonal. Reversal of handedness by reflection[ edit ] The handedness of polarized light is also reversed when it is reflected off a surface at normal incidence. Upon such reflection, the rotation of the plane of polarization of the reflected light is identical to that of the incident field.
However, with propagation now in the opposite direction, the same rotation direction that would be described as "right handed" for the incident beam, is "left-handed" for propagation in the reverse direction, and vice versa. Aside from the reversal of handedness, the ellipticity of polarization is also preserved except in cases of reflection by a birefringent surface. Note that this principle only holds strictly for light reflected at normal incidence.
For instance, right circularly polarized light reflected from a dielectric surface at grazing incidence an angle beyond the Brewster angle will still emerge as right handed, but elliptically, polarized. Light reflected by a metal at non-normal incidence will generally have its ellipticity changed as well.
Such situations may be solved by decomposing the incident circular or other polarization into components of linear polarization parallel and perpendicular to the plane of incidencecommonly denoted p and s respectively.