Dichroism is exhibited by several minerals and by some
organic compounds. The best known of the mineral crystals is tourmaline. When the
ordinary light is sent through a thin slab of tourmaline crystal, the
transmitted light is polarized. We take two crystals T1 and
T2 which are parallel to each
other. The light transmitted by the first crystal is also transmitted by the
second crystal. But suppose we rotate the second crystal through 900, no
light is transmitted. Because the absorption by tourmaline of all light rays
vibrating in one particular plane, not all planes.
Attempts to produce polarizing crystals of large aperture
were made by Herapath in 1852. He was successful in producing small crystals of
the organic compound quinine iodo sulfate now it is known as herapathite. In 1932 Land invented the Polaroid which has been used in many different kinds of
optical instruments. (Land was a scientist who invented Polaroid) Land and Rogers found further that when an oriented transparent
film of polyvinyl alcohol is heated in the presence of an active dehydrating
catalyst such as hydrogen chloride, the film darkens slightly and becomes
strongly dichroic.
Nowadays polarizing films have more usage. Polarizing films
are usually mounted between two thin plates of optical glass. These polarizing
films are used to increase the wavelength of light rays in some other light-transmitted systems. Like a car headlight, we add polarized films that
will help to increase the wavelength of light rays.
Polarization by dichroic crystals
Reviewed by knowledge people creators
on
May 12, 2019
Rating:
Reviewed by knowledge people creators
on
May 12, 2019
Rating:
