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Publisher Summary Diamond is essentially classified into four types depending on its optical and electrical properties. Common to each type is an absorption band in the 2 to 6 μm infrared region, which is because of a multiphonon absorption. Most natural diamonds are of type Ia. The ultraviolet absorption edge of type Ia diamonds is at about 291 nm. Synthetic diamonds are type Ib and contain nitrogen as an impurity in a dispersed form. Type IIa diamonds are effectively free of nitrogen and exhibit only the intrinsic 2 to 6 μm absorption. The ultraviolet absorption edge is at about 222 nm. Therefore, type IIa diamonds exhibit the optical properties best suited for infrared optical components. Optical components with flat surfaces can be produced to specification from diamond. It is also possible to produce diamond Fresnel lenses, diffraction gratings, and other components with flat surface patterns. The index of refraction of diamond sensitively depends on the properties of the crystal. The crystal internal structure, defects, impurities, and mechanical inclusions can also alter the index. |
