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Proceedings Paper

Laser pre-exposure to mitigate damage on microparticle-contaminated fused silica surface in high power laser systems
Author(s): Rajesh N. Raman; David Cross; Mary A. Norton; Jeff D. Bude; Raminder Garcha; Tylisia N. Wallace; C. Wren Carr
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Paper Abstract

Current fused silica surface processing, aimed at reducing known absorbing precursor concentration, has brought laboratory-tested ultraviolet laser-induced damage rates to nearly nil at fluences up to 10 J/cm2 . Yet this damage rate reduction has not been fully realized in large facility operation. A recently discovered source of damage in the facility is from particles ejected from damage of a neighboring optic under laser exposure and deposited onto the substrate surface. This state was observed to provide a means to couple energy from a subsequent laser pulse into the contaminated substrate and cause damage characterized by fracture. In this work, we explore the rate at which particles are removed from the surface and the rate at which particles lead to damage as a function of laser fluence and particle characteristics. This analysis allows for a derivation of an optimal pre-exposure fluence of a contaminated optic which maximizes particle removal probability while minimizing surface damage probability. For fluences up to 9.5 J/cm2 (351 nm, 5 ns square pulse), both particle removal and damage probabilities generally increased with particle size and laser fluence, with damage threshold around 6.5 J/cm2 . Two possible mechanisms that facilitate particle-induced damage on the substrate surface from laser-generated and deposited ejecta will be discussed, namely i) enhanced thermal contact from molten or partially molten ejecta and ii) fracture generated upon impact of solid ejecta with high kinetic energy.

Paper Details

Date Published: 23 February 2018
PDF: 7 pages
Proc. SPIE 10520, Laser-based Micro- and Nanoprocessing XII, 105201T (23 February 2018); doi: 10.1117/12.2293034
Show Author Affiliations
Rajesh N. Raman, Lawrence Livermore National Lab. (United States)
David Cross, Lawrence Livermore National Lab. (United States)
Mary A. Norton, Lawrence Livermore National Lab. (United States)
Jeff D. Bude, Lawrence Livermore National Lab. (United States)
Raminder Garcha, Lawrence Livermore National Lab. (United States)
Tylisia N. Wallace, Norfolk State Univ. (United States)
C. Wren Carr, Lawrence Livermore National Lab. (United States)

Published in SPIE Proceedings Vol. 10520:
Laser-based Micro- and Nanoprocessing XII
Udo Klotzbach; Kunihiko Washio; Rainer Kling, Editor(s)

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