Material selection for mid-infrared thin-film coatings and windows

We summarized the room-temperature optical properties for infrared-transparent materials, defining transparency windows for two different applications: thin-film coatings (absorption coefficient $\alpha < 10 cm^{-1}$) and windows ($\alpha < 1 cm^{-1}$). The transparency requirements for thin films are substantially less stringent, enabling the use of many more optical materials for a given wavelength range. To make an easy-to-use reference, we categorized materials by chemical group, crystallinity, and typical deposition technique, and discussed practical pros and cons such as chemical and thermal stability, mechanical hardness, and cost. The datasets and plotting scripts are provided so that users can regenerate transparency-window maps for different applications. If you do optical design at infrared wavelengths, we recommend that you print out the figures and stick them on your wall.