Design and fabrication of multi-layers infrared antireflection coating consisting of ZnS and Ge on ZnS substrate

• Design and fabrication of 4-layers antireflection coating on ZnS substrate, suitable for the infrared range of 8–12 μm.
• Achieving an average transmittance of 96% in the wavelength range of 8.5–10.5 μm.
• Hardness improvement by deposition a bilayer of Y2O3/carbon.

We have designed, fabricated and characterized a multi-layers antireflection coating on multispectral ZnS substrate, suitable for the infrared range of 8–12 μm. The 4-layers coating (Ge/ZnS/Ge/ZnS) with optimized thicknesses was fabricated by PVD technique and studied by FTIR, nanoindentation and AFM. From FTIR spectroscopy it was found that, in the wavelength range of 8–12 μm, the average transmittance of the double-side coated sample increases by about 26% and its maximum reaches about 98%. To improve the mechanical hardness, a bilayer of Y2O3/carbon was deposited on the coating. Nanoindentation test shows that the coating enhances the mechanical properties. The final coating have successfully passed durability and environmental tests.