An optical coating is a stack of thin films with different refractive indices. The coatings made are anti-reflection coatings, reflectors, band pass filters, short wave pass, long wave pass, beam splitters etc.

For designing these filters the TFCalc program is used. The output of the program is a simulation of the filter and a recipe for making it. 

The coatings are made with sputter deposition of for instant alternating SiO₂ and Ta₂O₅ layers. Layer thickness is controlled with in situ reflection measurement. Thickness uniformity is 1.5 % over 100 mm. Only flat substrates can be coated. Some other materials that can be used are: Al₂O3, TiO₂ and Si₃N₄. 
On request e-gun evaporation can be used. 

Optical measurements are done with a Perkin Elmer Lambda 9 spectrometer. 

In the figures a calculated and measured short wave pass is shown. The coating consists of nine layers of SiO₂ and Ta₂O₅.