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© Copyright 2001, Jim Loy
On the left, we see a drawing of "optical
calcite" sitting on a surface upon which are the words "Optical
Calcite." The word "Optical" is under the crystal. And you can
see that this word is a double image. Rotate the crystal (rotation is not shown
here), and the orientation of the double image rotates. How is this possible?
Optical calcite, like many crystals, refracts differently polarized light differently. In other words, the index of refraction is different for light that is polarized up-down, from light that is polarized left-right. I will write an article on polarized light some day. In the mean time, look it up in an encyclopedia. Anyway, optical calcite was apparently used as a beam splitter in bomber sights, in WWII. You can probably find some optical calcite in a rock shop.