New protective antireflecting coating for multispectral ZnS

With the advent of common aperture systems comes a requirement for substrates and coatings that are transparent in both the visible and IR bands. While there are many suitable bulk materials there are surprisingly few coatings available that offer both antireflecting properties and substrate protection. Materials that need little environmental protection tend to be costly to fabricate and machine while others are far too soft to be of any great use. It is for this reason that particular attention has been given to multispectral zinc sulfide which is a relatively cheap material and has good transparency both in the visible and the IR up to -13micrometers . Although it is a soft material (~150kg.mm -2 ) it may be protected by a range of coatings. This paper will look at two main materials, ZrN deposited by RF reactive sputtering and YF 3 by ion assisted deposition (IAD) which when used in conjunction offer both increased durability to the substrate and good tri-color transmittance for practical window applications.