Optical crystals with moisture-proof per-fluorinated polymer film - on sodium chloride or caesium iodide, for optical windows

摘要

Optical crystals of NaCl or CsI have a thin coating, deposited in situ, of a perfluorinated polymer, pref. a polymer of C4F8, C2F4, C2Cl2F2, C3F6 or C2ClF3. The coating pref. is ca. 1.0 mu thick and is formed by in situ polymerisation of the corresp. monomer in an electric plasma discharge. The crystals are used for optical windows used in IR spectroscopy. The film protects the windows from moisture. Thus a NaCl crystal coated on both sides with PCTFE can withstand 88.8% R.H. for 63.5 h whilst an uncoated crystal is attacked so that it is useless afater 2 min.