Study of Surface Finishing and Coating of DF Laser Windows.

Research was conducted into the minimization of optical absorption in low-loss window and coating materials for use in high-power DF chemical lasers. Candidate coating materials that were investigated as single-layer, half-wave thick films at 3.8 micron include PbF2, ThF4, ZnSe, Si, MgO, Al2O3, LiF, and NaF on CaF2 substrates. Of these, the fluorides have the lowest absorption losses and the Si and oxide films have the largest. A thorough study of extrinsic absorptions in ThF4 and ZnSe films on CaF2 was performed in conjunction with NRL using attenuated total reflection spectroscopy. ZnSe films showed considerably less OH(-) absorption than did the ThF4 films. (Author)