FLUORIDE COMPOUNDS FOR IR COATINGS

The optical properties of evaporated films of some fluoride compounds have been determined for the visible to IR spectral region, thus extending the wavelength database. The parameters for the deposition of films of the fluorides of aluminum, cerium, dysprosium, hafnium, lanthanum, neodymium, yttrium, and zirconium are presented. Each compound is discussed in terms of its optical and mechanical suitability for optical thin film deposition. An intercomparison is made of water incorporation in the film layers as evidenced by IR absorption band depths, AlF3, IRX (invented by E. Colton; patent applied for), YF3, and HfF4 exhibit low absorption in the 8-12-mu-m band, and therefore are potential candidates for replacing ThF4.