A metal plate (126) has a plurality of openings (127) extending through it, and is cleaned using a wet hydrogen process (157). Glass windows (106) are then placed in the openings, and are each fused to the metal plate by heat (231) in a manner so that each window projects outwardly on each side of the plate. Both sides of each window are then simultaneously ground and polished (232). Exposed surfaces of the metal plate are electroplated with nickel and gold (236). One or more coatings (41, 46, 47) are applied to one or both sides of each window. Several sections are then cut from the assembly, each of which can serve as a lid (17) for an optical apparatus (10).