Broadband multilayer anti-reflection coating for mid-infrared range from 7 μm to 12 μm.

We describe a design concept for broadband anti-reflection coatings for the mid-infrared that allows thinner film thickness and characterize its properties in the mid-infrared range from 7 μm to 12 μm. Two demonstrator coatings comprising zinc sulfide, yttrium fluoride, and germanium, all of which are deposited by electron beam evaporation on indium phosphide substrates, are optimized for the 7-12 μm and the 10-12 μm ranges. They exhibit less than 1.0% reflection over the target wavelength ranges with notably thin coating thickness.