Polarization of Light

PolarizationPolarization is a property of waves that can oscillate with more than one orientation.

Electromagnetic waves such as light exhibit polarization, as do some other types of wave, such as gravitational waves.

Sound waves in a gas or liquid do not exhibit polarization, since the oscillation is always in the direction the wave travels.

Light as an Electromagnetic Wave

Electromagnetic WaveLight is an electromagnetic wave.It consists of vibrations of electric field and magnetic field.The electric field and magnetic field are perpendicular to each other and in phase.EM wave is a transverse wave.The speed of EM wave is 3 x 108 ms-1.

Electric Field Vector

Polarized LightPolarized Light: Vibrations lie on one single plane only.

Unpolarized Light: Superposition of many beams, in the same direction of propagation, but each with random polarization.

UnpolarizedPolarized

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It is possible to transform unpolarized light into polarized light. Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming unpolarized light into polarized light is known as polarization. There are a variety of methods of polarizing light. The four methods discussed on this page are:

Polarization by TransmissionPolarization by ReflectionPolarization by RefractionPolarization by Scattering

Methods of Polarizing Light

Polarization by Reflection

Polarization byTransmission

Polarization by Refraction

Polarization by Scattering When light strikes the atoms of a material, it will often set the electrons of those atoms into vibration. The vibrating electrons then produce their own electromagnetic wave that is radiated outward in all directions. These vibrating electrons produce another electromagnetic wave. This scattered light is partially polarized.

Polarizing MaterialA Polarizing material will only allow the passage of that component of the electric field parallel to the polarization direction of the material

I = I0 cos2q

Polarization In Everyday Situations

This photograph should be compared with the one above. In this photo, the reflected glare that was seen on the water's surface (previous photo) has been removed by the use of a Polaroid filter. It is much easier to see the sidewalk below the water surface.

This photograph should be compared with the one above. The reflected glare seen on the glass panels of the lab cabinet has been removed by the use of a Polaroid filter. It is much easier to see what is present inside of the lab cabinets. This set of two photos provides another example of how a Polaroid filter can block the annoying glare that is caused when light becomes polarized upon reflection.

Action of Polaroid Sunglass

Unwanted glares are usually horizontally polarized light

Vertically Polarized Light from Objects

Light reflected from surfaces like a flat road or smooth water is generally horizontally polarized. This horizontally polarized light is blocked by the vertically oriented polarizers in the lenses.

Polarized light is often used in the stress analysis of molded plastics. Polarized light passing through molded plastics will reveal stress marks and stress patterns that would not otherwise be apparent to the naked eye. The plane of polarization of polarized light is rotated by these molded plastics at any location where the plastic is stressed. The amount of rotation depends upon the wavelength of light. White light consists of various wavelengths, each associated with a distinct color. Using a Polaroid filter and rotating it will reveal stress patterns in various colors at various angles of rotation.

Stress Analysis

Polarization is often implemented in the production and viewing of 3D films. When watching a 3D movie, there are actually two images being projected onto the screen at once. The two images were filmed with two separate cameras from two slightly offset locations. These two images are projected onto the screen through Polaroid filters. The molecules of one of the filters is aligned vertically, the other is aligned horizontally. The audience is given 3D glasses that have one lens aligned horizontally and the other aligned vertically. Thus, one eye sees one image and the other eye sees the other image. The brain receives both signals and perceives depth on a flat screen.

Polarization in 3D Movies

Seven-Segment LCD

Aerial

In a vertical transmitting aerial, vertical electron oscillation results in a vertical polarized radio wave.

Maximum electron oscillation in the receiving aerial is achieved when the aerial is aligned to be parallel to the wave’s electric field.

The sky is blue because . . . • The tiny particles in the atmosphere (dust, clumps of air

molecules, microscopic water droplets) are better at scattering shorter wavelength blue light than the longer wavelength red light.

• As sunlight passes through the atmosphere, the scattered blue light give the atmosphere an overall blue glow.

The sunset is red because . . . • At sunrise and sunset, sunlight enters our atmosphere at

a shallow angle and travels a long distance before reaching our eyes.

• During this long passage, most of the blue light is scattered away and virtually all that we see coming to us from the sun is its red and orange wavelengths.

• http://micro.magnet.fsu.edu/optics/lightandcolor/polarization.html

• http://dpfwiw.com/polarizer.htm#unwanted• Blue Skies and Red Sunsets

http://science.howstuffworks.com/framed.htm?parent=question39.htm&url=http://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l2f.html

• Easy fun page with Applets, on polarizing filters http://www.colorado.edu/physics/2000/polarization/polarizationI.html

• Polarization short course http://www.glenbrook.k12.il.us/gbssci/phys/Class/light/u12l1e.html

Reference Links