Optically transparent heat mirror films, reflective in the infrared, have been produced based on a dielectric - metal - dielectric design using zinc sulfide and silver coatings. Filters exhibit 87% peak transmission in the visible region, while reflecting 80%. in the infrared. Thermal testing indicated the that the layer filters were unstable to treatments above 300 F. Incorporation of thin barrier coatings of magnesium fluoride between the silver and zinc sulfide lavers produced filters with thermal stability to 700 F while retaining optical characteristics of the three laver svstem. These optical and thermal properties offer possible application for the heat mirror films in tungsten source efficiency improvement applications
