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Proceedings Paper

Pulse-length dependence of absorptance and degradation rate of fused silica at 248 nm
Author(s): Eric Eva; Klaus R. Mann; Stephan Thomas
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Paper Abstract

Optical components for industrial excimer laser applications such as semiconductor lithography steppers have to withstand more than 1010 laser pulses without suffering from significant cumulative absorption increase due to color center formation. Lithography lasers are now approaching pulse durations of 10 ns and repetition rates of 1000 Hz, a domain unexplored in previous degradation studies. With the aid of an optical pulse-extension unit and a modified laser resonator, we measured absorptance and absorption changes in Suprasil 312 UV-grade fused silica calorimetrically at pulse lengths of 7-73 ns. At 100 mJ/cm2, no degradation was detectable even after 500,000 pulses, but there was slight evidence of an absorption decrease due to laser cleaning. At 400 mJ/cm2, both absorptance and degradation rate increased towards shorter pulses and hence higher intensities, but even over the full pulse-length range, the changes remained moderate. Furthermore, degradation at 300 Hz was lower than at 150 Hz, indicating that a simultaneous bleaching effect might be involved which favors future high- repetition rate applications.

Paper Details

Date Published: 13 May 1997
PDF: 8 pages
Proc. SPIE 2966, Laser-Induced Damage in Optical Materials: 1996, (13 May 1997); doi: 10.1117/12.274232
Show Author Affiliations
Eric Eva, Laser-Lab. Goettingen e.V. (Germany)
Klaus R. Mann, Laser-Lab. Goettingen e.V. (Germany)
Stephan Thomas, Heraeus Quarzglas GmbH (Germany)

Published in SPIE Proceedings Vol. 2966:
Laser-Induced Damage in Optical Materials: 1996
Harold E. Bennett; Arthur H. Guenther; Mark R. Kozlowski; Brian Emerson Newnam; M. J. Soileau, Editor(s)

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