Pulse-length dependence of absorptance and degradation rate of fused silica at 248 nm

Eric Eva; Klaus R. Mann; Stephan Thomas

doi:10.1117/12.274232

13 May 1997 Pulse-length dependence of absorptance and degradation rate of fused silica at 248 nm

Eric Eva, Klaus R. Mann, Stephan Thomas

Proceedings Volume 2966, Laser-Induced Damage in Optical Materials: 1996; (1997) https://doi.org/10.1117/12.274232
Event: Laser-Induced Damage in Optical Materials: 1996, 1996, Boulder, CO, United States

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.

Citation Download Citation

Eric Eva, Klaus R. Mann, and Stephan Thomas "Pulse-length dependence of absorptance and degradation rate of fused silica at 248 nm", Proc. SPIE 2966, Laser-Induced Damage in Optical Materials: 1996, (13 May 1997); https://doi.org/10.1117/12.274232

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