Thin-film 2.8-microm and 3.8-microm absorption in single-layer films

A systematic study was made of thin-film absorption at 2.8microm and 3.8 microm for a wide variety of transparent coating materials. The extinction and absorption coefficients were measured using HF/DF chemical laser calorimetry in single-layer films of PbF(2), LiF, YbF(3), NaF, ThF(4), As(2),S(3), As(2),Se(3), Si, MgO, ZnSe, and Al(2),O(3), on CaF(2), substrates. The lowest absorbing film materials were the As glasses, ZnSe, and some fluorides. In these cases, high-purity starting material led to the lowest loss films.