A gradient-index antireflection coating spanning the 0.6–12.6-μm wavelength range for a ZnSe substrate was designed, fabricated, and tested. The index profile used was a fifth-order polynominal that smoothly matches the substrate. The coating was fabricated using a discrete layer approximation for the gradient-index design using ZnSe and CaF2 deposited by laser-assisted evaporation. Total thickness of the coating was 3 μm. Transmission measurements show good agreement with calculated performance. Reflectivity per surface is <3% (compared with 17% for uncoated ZnSe) in the wavelength band encompassing 4.5 octaves from 0.6 to 12.6 μm.
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