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Deposition of rugate filters by magnetron sputtering technology

: Rickers, C.; Polenzky, C.; Vergöhl, M.

Aegerter, M.A.; Kirchhoff, V. ; Fraunhofer-Institut für Elektronenstrahl- und Plasmatechnik -FEP-, Dresden:
Advanced Coatings for Large-Area or High-Volume Products. Proceedings of the 6th International Conference on Coatings on Glass and Plastics : June 18-22, 2006, Dresden, Germany
Dresden, 2006
International Conference on Coatings on Glass and Plastics (ICCG) <6, 2006, Dresden>
Conference Paper
Fraunhofer IST ()

Magnetron sputtering is a promising tool for the future production of precision optical coatings. Advantages are the high film quality, high throughput and the possibility for up scaling and automation of the process. Current applications of sputtered filters are Laser mirrors or coatings for optoelectronic devices.
A relatively new type of optical filters are Rugate filters. Complementary to classical multilayer filters, Rugate filters are based on a periodically and continuously varying refractive index profile. In spite of the fact that Rugate filters need to be slightly thicker than classical filters, some important advantages can be obtained such are: Better spectral performance, improved angular range or improved thermal and Laser stability.
However, the production of Rugate filters is crucial since they need to be produced in a continuously process with two depositon sources running simultaneously. Therefore, process stability as well as process control is important.
In the present paper, we report about the deposition of Rugate filters by radio frequency magnetron sputtering. The films were deposited using two different targets materials. An optical monitor based on broad band transmission measurements was implemented. We report on the possibilities to improve process control by an optical monitor.