Meller Optics Inc.'s Viewport Optics Preparation Service offers a two-step process: It provides a ground window blank -- usually fused silica or sapphire -- for customers to metallize, and it performs the final polishing. The result is a uniform window for assembly into viewports. The window's outside diameter can be from 1/4 to 3 in. and the thickness, from 2 to 10 mm in stepped- or straight-wall configurations. Surface finishes from 10 wavelengths to λ/10 and 60-40 scratch/dig are typical. The company also can work with ZnSe, ZnS, CaF2, MgF2 or other materials.