Calcite (CaCO?), a trigonal negative uniaxial crystal with extreme birefringence and broad transmission (200 nm–2300nm), is the premier material for visible-near infrared polarizing optics despite its softness (Mohs 3) and hygroscopicity. It enables Glan–Taylor/Thompson polarizers with extinction ratios >10?:1, beam displacers, and UV wave plates, outperforming synthetic crystals like YVO? in the ultraviolet range but requiring AR coatings and humidity control.
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