Optical windows or filters are made of optically transparent materials with parallel polished sides, ground edges and chamfers. The only difference between windows and filters is degree of attenuation of the optical spectrum.
The optical windows are usually intended to have maximum possible transmission for given material. In the case of filters the degree of transmission is tailored through the use of specific filter material and/or through use of specific coatings. The AR coatings are often applied on the polished sides of both optical windows and filters to improve their transmission characteristics.
Windows are often used as protective elements. However, they may have additional filter or beamsplitter function.
We can produce custom windows/filters on request.