Low scattering filter coatings made by plasma-assisted reactive magnetron sputtering

Scattering in thin-film filters is mainly driven by the substrate roughness and the deposition technology but also by the coating design as well as by the filter orientation. A high-energy, low-loss coating technology (plasma-assisted reactive magnetron sputtering, PARMS) was used to deposit an advanced thin-film filter design on substrates with low micro roughness. This approach resulted in a significantly reduced level of scattered light as well as an excellent spectral performance of the produced filters. Compared to coatings deposited by ion-assisted evaporation (IAD), the level of out-of-band scattering could be reduced by more than 2 orders of magnitude to about 0.001%.