Abstract

Germanium is the most important raw material used in the fabrication of optical elements for the second atmospheric window in the infra red. Due to its high index of refraction germanium requires AR coating for the relevant wavelengths. Current applications in numerous devices limit the average maximum reflectance to 0.3% in the 8.0-11.5μm region and to a maximum of 1.0% (or less), in the peripheral regions down to 7.5μm and up to 12.5μm. A number of commercial coating companies offer such a product, without revealing the coating design⁽¹⁾. A few publications describe AR coatings for Ge in this region, but with inferior performances^(2-3).

© 1988 Optical Society of America