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Light Polarization

Etienne Malus (1775 - 1812) discovered and coined the term Polarization while experimenting with a strange type of refraction in Iceland spar crystal or calcite. Until that time, scientists doubted that light could be a transverse wave traveling in ether, as they did not believe a fluid could propagate transverse waves, only solids. Sound waves, which are longitudinal waves, are not able to be polarized.

Again, Thomas Young (1773 - 1829) and Augustine Fresnel (1788 - 1827) would play a vital role in proving that light traveled in a transverse wave, but neither could adequately explain how.

Eventually, Maxwell's investigations proved the existence of electromagnetic waves which, to no ones surprise, were transverse waves.

Transverse Wave

In a transverse wave, the particles are displaced perpendicularly to the direction of travel. A wave on a lake is a transverse wave, as the actual water droplets are moved vertically, while the wave travels horizontally along the waves surface.

Polarization

Unlike water waves, which are always polarized or displacing in the same direction up and down, light can polarize in any direction. In other words, the energy of light can displace the energy in any direction, up, down, left, right, or any angle between.

Light from the sun or a flame is inherently unpolarized.

Reflection

Malus discovered in 1808 that reflection of light from a non-metallic surface produce at least partial polarization.

Sir David Brewster (1781 - 1868) discovered that the degree of polarization varied with the degree of incidence, and that all of the reflected light would be polarized at one particular angle of incidence, called Brewster's angle. This angle, as it turns out, occurs when the Reflected ray and Refracted ray are at right angles to one-another.

This tendency for reflected waves to be polarized explains why polarized sunglasses are able to noticeably reduce glare.

Dichroic Crystals

Dichroic crystals, such as tourmaline, absorb light of one polarization, while passing the other.

Polaroid Corporation

The young American scientist, Edwin Land (1909 - 1991), discovered he could make plastic into a polarizing material by staining a certain plastic material with iodine. Later, Edwin Land developed techniques to help see color in photography.