Simple antireflection overcoat for opaque coatings in the submillimeter region

An antireflection overcoat for opaque baffle coatings in the far-IR/submillimeter region has been made from a simple Teflon spray-on lubricant. The Teflon overcoat reduced the specular reflectance of four different opaque coatings by nearly a factor or 2. Analysis, based on the interference term of a reflecting-layer model, indicates that in the submillimeter region the reduced reflectance depends primarily on the refractive index of the overcoat and very little on its thickness.