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Polarization Property of Light

 

 

Polarization is the property that indicates the direction of the vibrations of transverse waves. Transverse waves are waves that oscillate in the direction perpendicular to the propagation. Examples of transverse waves are electromagnetic waves, transverse sounds, and earthquake waves. Longitudinal waves oscillate in the same direction as the propagation. We can observe it in transverse waves as its polarization is perpendicular to the propagation.

We actually experience this phenomenon with light every day. As you know, light is an electromagnetic wave. It consists of electricity and magnetism. When we talk about the polarization of light, we have to look at the electric field waves, not the magnetic field.

There are three kinds of polarization.

1) Linear Polarization

 Linear polarization waves propagate toward the observed plane. The sum of the electric field E components reaches the observer, provided that it is perpendicular to the progression.

 


 2) Circular Polarization

In this type of polarization, the magnitude of the electric field is constant. However, we perceive it as a circular motion as it rotates at a constant speed in a plane perpendicular to the direction of the wave. A wave that rotates clockwise with a resultant electric field angular frequency w is called a right circular polarization, and counterclockwise rotation is called a left circular polarization.

3) Elliptical Polarization 

E waves traveling in an elliptical direction are formed by both rotation and change in magnitude. Here, too, the phase difference between the E components is ± pi/2.


Is every light that comes into our eyes polarized? The answer is no. For example, the rays coming from the Sun, our source of life, or the lights coming out of incandescent lamps are not polarized, that is, they do not have a certain geometric direction, they emit light in all directions, that is, we cannot say that they are polarized at a certain angle. However, we can polarize the light emanating from these light sources to have the direction we want by using the methods of Selective Absorption Polarization, Reflection Polarization, and Birefringence and Polarization.

Polarization with Selective Absorption: With the help of polarizers, it can be ensured that unpolarized light is transmitted by electromagnetic light in a certain direction, and unwanted directions are prevented.

Polarization by Reflection: The electric field of the light incident on the transparent surface accelerates the electrons on the surface and causes these electrons to radiate. Thus, two waves are formed, reflected, and refracted. If we examine the wave parallel to the plane of reflection, we observe that the electrons accelerated by this component of the incident light beam move perpendicular to the reflected wave. A very small part of the incident wave is absorbed by the electrons, so the reflection of this component of the incident wave is quite strong. Since the electrons accelerated by the second component move parallel to the reflected wave, the electrons absorb most of the incident wave and the reflection is weak. In polarization by reflection, if an unpolarized light beam is parallel or perpendicular to the plane of reflection, the reflected light is unpolarized. If the incident wave has other angles of incidence, I mean not perpendicular or parallel, the reflected and refracted light beams are partially polarized, that is, the electric field vectors have two components. But if the angle between the reflected and refracted light is 90 degrees, the reflected light has only the component of the electric field vector parallel to the plane of reflection. This component creates a strong reflection. The angle of incidence of light in this case has a special name and is called the Brewster angle(​θB).

 

Polarization with Birefringence: The last method is to create polarization with the help of crystal. Crystals are to make light into two beams, that is, they have birefringent properties. Both parts of the split light become polarized. A ray polarized perpendicular to the plane of incidence is called a normal ray, and a ray polarized parallel to a parallel is called an extra-normal ray. Thin sheets of tourmaline crystal absorb one of these rays and pass the other. Thus, a polarized beam is obtained. In birefringent crystals, there is a direction where the two beams meet, and this is called the "optical axis".




Reference

https://acikders.ankara.edu.tr/pluginfile.php/98722/mod_resource/content/1/week-6.pdf

P. M. Fishbane, et al. Temel Fizik. Yayınevi: Arkadaş Yayınevi.

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