Theoretical Studies of Materials for High-Power Infrared Coatings
Abstract
Results and recommendations based on a survey of the coatings literature, on discussions with a number of investigators in the field, and on very simple analyses include the following. High-packing-density films should be vapor deposited using ultraclean deposition conditions including thorough baking of the entire system before deposition, high-purity single-crystal starting materials, special care in evaporation, state-of-the-art substrate preparation, and ultrahigh vacuum. Values of film absorptance A(f) per surface of A(f) = . 0001 or absorption coefficient Beta(f) = 0.5/cm roughly, are desired. A major problem is that the values of Beta(f) usually are much greater than the corresponding bulk values beta(b). Material-selection guidelines, including a bulk absorption coefficient less than 0.5 and a value of the index of refraction in the required range, are developed and used to select the following 10.6 micrometer candidate materials: ThF4, NaF, BaF2, SrF2, NaCl, KCl, KGaF4, As2S3, As2Se3, ZnS, ZnSe, and TlI. A method of distinguishing between surface and bulk absorption in coatings by utilizing the fact that the electric field is zero on the surfaces of certain types of coatings and nonzero on others is proposed.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 31, 1975
- Accession Number
- ADA031948
Entities
People
- M. Sparks