The need for protective coatings on critical optical surfaces, such as halide crystal windows or lenses used in spectroscopy, has long been recognized. Many widely used halide materials are extremely moisture sensitive, such as sodium chloride and cesium iodide, and a number of approaches have been taken to protect such optics. These approaches, often crude, have not always been reliable or particularly convenient. It has been demonstrated that thin, one micron, organic coatings produced by polymerization of flourinated monomers in low temperature gas discharge (plasma) exhibit very high degrees of moisture resistence, e.g., hundreds of hours protection for cesium iodide vs. minutes before degradation sets in for untreated surfaces. Moreover, the index of refraction of these coatings is intermediate between that of the halide substrate and air, a condition for anti-reflection, another desirable property of optical coatings. Thus, the organic coatings not only offer protection, but improved transmittance as well. Further, the polymer coating is non-absorbing over the range 0.4 to 40 μ with an exception at 8.0 μ, the expected absorption for C-F bonds.