???BK7, Float Glass
BK7 is a ubiquitous moderate-refractive-index glass. The designation "BK7" originates with Schott AG: B indicates a borosilicate glass, while K comes from the German krone (= crown) as this is also referred to as a crown glass. Borosilicate glasses are produced from alkali-lime silicates containing approximately 10% boric oxide. Because BK7 has been available for years, its refractive indices, index dispersion, Abbe number, and other properties have been well-characterized. While it does have many desirable properties, it is typically replaced by fused silica when transparency below 320nm is desired.
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Refractive Index Reference - From transmittance spectrum of 200 micron thick sample
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