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Long term tests of resonator optics in ArF excimer lasers

: Beermann, N.; Blaschke, H.; Ehlers, H.; Ristau, D.; Wulff-Molder, D.; Jukresch, S.; Matern, A.; Bischoff, M.; Gäbler, D.; Kaiser, N.


Vilar, R. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
XVII International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers : 15 - 19 September 2008, Lisboa, Portugal
Bellingham, WA: SPIE, 2009 (Proceedings of SPIE 7131)
ISBN: 978-0-8194-7365-3
Paper 713117
International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers (GCL-HPL) <17, 2008, Lisboa>
Conference Paper
Fraunhofer IOF ()

The aim of this work is the optimization of the resonator optics of excimer laser systems to achieve longer lifetimes and to reduce the cost of ownership. The degradation after long-term exposure to high photon fluxes (typically 80 mJ/cm2) at the ArF laser wavelength of 193 nm was analyzed. Based on the investigations, a model describing the process of the deterioration of the out-coupling partial reflector was developed. It was found that contamination of the optics by the laser's discharge electrodes leads to absorption losses on the surface facing the inside of the resonator. As a consequence, the laser irradiation causes a temperature gradient in the CaF2-substrates which leads to crystal cleavage and braking of the optics. Defects on the outward surface are the origin for the growth of Calcite crystals and organic compounds by photo induced chemical reactions of the substrate material and contaminations in the purge gas. It was demonstrated that the lifetime of the resonator optics can be substantially increased by adapted optical designs and coatings.