Visible light is an electromagnetic wave, which is composed of an electric field and a magnetic field.
All electromagnetic waves are transverse waves. When it travels through space, its electric field and magnetic field are perpendicular to each other.
A traveling electromagnetic wave with the electric field and magnetic field perpendicular to each other.
The general plane electromagnetic wave has an electric field and a magnetic field perpendicular to each other, and is also perpendicular to the traveling direction of the light.
The polarized light of the light refers to the direction of the electric field, and the direction of the polar phase is also Often referred to as the direction of polarization.
Lights with different polarization directions often have different reflection characteristics on the reflective surface.
Photographers often use various polarizers to filter unwanted reflected light and take photos of various environmental light sources.
The polarization technology of light used in liquid crystal flat panel displays and 3D movies.
A polarizer is a device which allows a specific polarization of light waves to pass through and blocks other polarization.
Two common types of polarizers are linear polarizer
and circular polarizer
Polarizers are used in research labs, the optical industry and equipment at homes.
Available polarizers made by different materials such as glass, crystals or plastics.
Plastic polarizers are not expensive and used in LCD (liquid crystal display).
Such as screens of calculators or computer monitors, sunglasses, and 3D movie glasses.
Electromagnetic waves may be unpolarized, partially polarized or completely polarized depending on the electric field vectors associated with the traveling waves.
For example, visible light given by an incandescent light bulb unpolarized.
When an unpolarized light travel, the electric field vectors are in all directions in a plane which is perpendicular to the direction of the wave travels.
The electric field vectors symbolize the random directions of polarization of the individual waves that comprise the light.
Linearly polarized light can be produced from unpolarized light with the aid of certain material called a polarizer.
Commonly used polarizing sheet or film consists of certain long molecules embedded in plastic.
When the sheet is manufactured, it is stretched to align the molecules in parallel rows.
When light sent through the sheet, electric field components along one direction pass through the sheet, while components perpendicular to the direction are absorbed by the molecules and disappear.
In this case, the light is linearly polarized.
Polarized light can be produced from an unpolarized light
If the electric field vectors are not completely random nor are perfectly aligned in one direction, it is called a partially polarized light.
Polarization can be achieved through other processes such as reflection, refraction and scattering.
Polarization by reflection
When unpolarized light is incident on a nonmetallic surface, the reflected ray is partially polarized.
The extent of polarization depends upon the angle of incidence and the material that the surface is made of.
Metallic surfaces reflect light with a variety of vibrational directions; such reflected light is unpolarized.
However, nonmetallic surfaces such as asphalt roadways, snowfields and water reflect light such that there is a large concentration of vibrations in a plane parallel to the reflecting surface.
This reflected ray is called s-polarized, the electric field polarized perpendicular to the plane of the incident ray and the surface normal.
A person viewing objects by means of light reflected off of nonmetallic surfaces will often perceive a glare if the extent of polarization is large.
Sunglasses with the proper polarization axis allows for blocking this polarization and reducing the glare.
Partially s-polarized light reflected from a non-metallic surface.
Polarization by Refraction
Polarization can also occur by the refraction of light.
Refraction occurs when a beam of light passes from one material into another material.
At the surface of the two materials, the path of the beam changes its direction. The refracted beam acquires some degree of polarization.
This partially polarized refraction is called p-polarized, electric field polarized in the same plane as the incident ray and the surface normal.
Refracted ray and reflected ray are partially polarized
There is one special angle of incidence at which the reflected light is completely
polarized parallel to the surface, the refracted ray being only partially polarized. This angle is called the Brewster angle.
Unpolarized light can be separated into fully s-polarized and p-polarized light by stacking many plates at Brewster's angle with respect to the incident beam.
S-polarized and P-polarized light can be produced by stacking an array of glass plates at Brewster’s angle
Polarization by scattering
Polarization also occurs when light is scattered while traveling through a medium.
Since light waves are electromagnetic waves, they will vibrate the electrons of air molecules perpendicular to the direction in which they are traveling.
The electrons then produce radiation that is polarized perpendicular to the direction of the ray.
The observed light parallel to the original ray has no polarization. The observed light perpendicular to the original ray is completely polarized.
In all other directions, the observed light scattered by air will be partially polarized.
The extent of polarization of scattering light depends on the locations of the observers.