Dichroic materials |
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Dichroic crystals absorb one polarization (direction of electric vector) more than the perpendicular polarization. As unpolarized light passes through the crystal it becomes partly polarized. Polarizing materials can be made by embedding oriented dichroic crystals in a plastic base. Polaroid film is made dichroic by stressing the plastic in one direction during manufacture. Polaroid was invented by Edwin Land - (a creative genius). It is used widely for sunglasses that selectively remove the reflections of sunlight from horizontal surfaces. The Sun-stones of the Vikings Natural dichroic crystals that are found as translucent pebbles on the beaches of Norway were used by the Vikings to find the position of the Sun on overcast days. They were able to navigate at sea, because of the partial polarization of sky light. The Vikings showed remarkable prowess as a sea-faring nation, reaching Greenland, the Americas and Istanbul. [There is 9th Century Viking graffiti in Hagia Sofia, Istanbul, with the name Halvarg still readable.] |