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Description of particle induced damage on protected silver coatings

: Schwinde, Stefan; Schürmann, Mark; Jobst, Paul Johannes; Kaiser, Norbert; Tünnermann, Andreas


Applied optics 54 (2015), No.16, pp.4966-4971
ISSN: 0003-6935
ISSN: 1539-4522
ISSN: 1559-128X
Journal Article
Fraunhofer IOF ()

In the visible to infrared spectral range, highly-reflective silver mirrors are applied in the manufacture of optical instruments such as telescopes. However, it is still difficult to combine high reflectivity and long-term stability of the protected silver coating. We show that the deposition of impervious protective layers is necessary but often not sufficient for long-term environmental stability. Hygroscopic air borne particles absorbed by the protections surface attract water molecules and form a solution. This solution first damages the protection, subsequently permeates the protection and finally damages the silver whereby the reflectivity is reduced. We demonstrate this particular damage mechanism with different experiments and describe this mechanism in detail.