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Proceedings Paper

Long term tests of resonator optics in ArF excimer lasers
Author(s): Nils Beermann; Holger Blaschke; Henrik Ehlers; Detlev Ristau; Dirk Wulff-Molder; Sigrid Jukresch; Ansgar Matern; Martin Bischoff; Dieter Gäbler; Norbert Kaiser
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Paper Abstract

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.

Paper Details

Date Published: 21 April 2009
PDF: 5 pages
Proc. SPIE 7131, XVII International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers, 713117 (21 April 2009); doi: 10.1117/12.816706
Show Author Affiliations
Nils Beermann, Laser Zentrum Hannover e.V. (Germany)
Holger Blaschke, Laser Zentrum Hannover e.V. (Germany)
Henrik Ehlers, Laser Zentrum Hannover e.V. (Germany)
Detlev Ristau, Laser Zentrum Hannover e.V. (Germany)
Dirk Wulff-Molder, Korth Kristalle GmbH (Germany)
Sigrid Jukresch, Coherent GmbH (Germany)
Ansgar Matern, Coherent GmbH (Germany)
Martin Bischoff, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)
Dieter Gäbler, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)
Norbert Kaiser, Fraunhofer-Institut für Angewandte Optik und Feinmechanik (Germany)

Published in SPIE Proceedings Vol. 7131:
XVII International Symposium on Gas Flow, Chemical Lasers, and High-Power Lasers
Rui Vilar; Olinda Conde; Marta Fajardo; Luís O. Silva; Margarida Pires; Andrei Utkin, Editor(s)

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