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Proceedings Paper

Residual stress and damage-induced critical fracture on CO2 laser treated fused silica
Author(s): M. J. Matthews; J. S. Stolken; R. M. Vignes; M. A. Norton; S. Yang; J. D. Cooke; G. M. Guss; J. J. Adams
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Paper Abstract

Localized damage repair and polishing of silica-based optics using mid- and far-IR CO2 lasers has been shown to be an effective method for increasing optical damage threshold in the UV. However, it is known that CO2 laser heating of silicate surfaces can lead to a level of residual stress capable of causing critical fracture either during or after laser treatment. Sufficient control of the surface temperature as a function of time and position is therefore required to limit this residual stress to an acceptable level to avoid critical fracture. In this work we present the results of 351 nm, 3ns Gaussian damage growth experiments within regions of varying residual stress caused by prior CO2 laser exposures. Thermally stressed regions were non-destructively characterized using polarimetry and confocal Raman microscopy to measure the stress induced birefringence and fictive temperature respectively. For 1~40s square pulse CO2 laser exposures created over 0.5-1.25kW/cm2 with a 1-3mm 1/e2 diameter beam (Tmax~1500-3000K), the critical damage site size leading to fracture increases weakly with peak temperature, but shows a stronger dependence on cooling rate, as predicted by finite element hydrodynamics simulations. Confocal micro-Raman was used to probe structural changes to the glass over different thermal histories and indicated a maximum fictive temperature of 1900K for Tmax≥2000K. The effect of cooling rate on fictive temperature caused by CO2 laser heating are consistent with finite element calculations based on a Tool-Narayanaswamy relaxation model.

Paper Details

Date Published: 31 December 2009
PDF: 12 pages
Proc. SPIE 7504, Laser-Induced Damage in Optical Materials: 2009, 750410 (31 December 2009); doi: 10.1117/12.836904
Show Author Affiliations
M. J. Matthews, Lawrence Livermore National Lab. (United States)
J. S. Stolken, Lawrence Livermore National Lab. (United States)
R. M. Vignes, Lawrence Livermore National Lab. (United States)
M. A. Norton, Lawrence Livermore National Lab. (United States)
S. Yang, Lawrence Livermore National Lab. (United States)
J. D. Cooke, Lawrence Livermore National Lab. (United States)
G. M. Guss, Lawrence Livermore National Lab. (United States)
J. J. Adams, Lawrence Livermore National Lab. (United States)


Published in SPIE Proceedings Vol. 7504:
Laser-Induced Damage in Optical Materials: 2009
Gregory J. Exarhos; Vitaly E. Gruzdev; Detlev Ristau; M. J. Soileau; Christopher J. Stolz, Editor(s)

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