Abstract: Optical elements, and methods for fabricating them, are described wherein each element includes a free standing (self supporting) polycrystalline continuous thin film of diamond combined with a non-hydrogenated amorphous diamond like carbon (DLC) film having a high percentage of sp.sup.3 bonding. These elements may be designed to have optically smooth surfaces, have wide optical transmission ranges (for example, be transparent across the infrared portion of the spectrum), and exhibit exceptional durability characteristics. Optical instruments that include such elements are also described, along with the derivative benefits, such as improved operating performance and lower maintenance requirements, realized using the novel optical elements. In particular, a polarization Michaelson interferometer (PMI) is taught which is operative over the entire range from far infrared into the visible portion of the spectrum without requiring the exchange of beam splitters or beam polarizers.