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Angle resolved scattering: A method for investigations of laser induced damage

: Schröder, S.; Duparre, A.


Exarhos, G.J. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
Laser-induced damage in optical materials 2009. 41st Annual Laser Damage Symposium. Proceedings : 21 - 23 September 2009, Boulder, Colorado; Papers presented at the 41st Annual Symposium on Optical Materials for High-Power Lasers
Bellingham, WA: SPIE, 2009 (Proceedings of SPIE 7504)
ISBN: 978-0-8194-7882-5
Paper 75041H
Annual Laser Damage Symposium <41, 2009, Boulder/Colo.>
Annual Symposium on Optical Materials for High-Power Lasers <41, 2009, Boulder/Colo.>
Fraunhofer IOF ()

Light scattering from interface imperfections or defects is a topic of persistent interest. On the one hand, light scattering can be a critical issue that limits throughput and imaging quality of optical components even if high-end polishing and coating techniques are employed. This in particular holds for multilayer coatings and for short wavelengths of application. On the other hand, scattered light also carries valuable information about its origins, such as the structural properties of multilayer coatings. A large variety of instruments for scatter measurements in the visible, ultraviolet, infrared spectral ranges has been developed at the Fraunhofer IOF in Jena during the past years. In addition, software tools have been developed based on existing scattering theories which enable an advanced analysis of the observed scattering properties. For the rather complicated scattering of thin film coatings, a simplified model was developed recently which introduces two simple parameters to describe the roughness evolution from interface to interface and optical thickness deviations. An iterative solution of the inverse scattering problem yields information about alterations of the structural and optical properties inside multilayer coatings based on angle resolved scatter measurements. Experimental results will be presented for highly reflective metal fluoride coatings for 193 nm as well as for a Rugate filter after laser damage tests. It will be discussed how the procedure could be implemented in a laser damage test environment to enable the damage behavior to be characterized in-situ during irradiation. This can provide valuable information about the fundamental damage processes even prior to the ultimate damage events.