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Optical Engineering

Thermal annealing of laser damage precursors on fused silica surfaces
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Paper Abstract

Previous studies have identified two significant precursors of laser damage on fused silica surfaces at fluences <35  J/cm2: photoactive impurities from polishing and surface fractures. We evaluate isothermal heating as a means of remediating the defect structure associated with surface fractures. Vickers indentations are applied to silica surfaces at loads between 0.5 and 10 N, creating fracture networks. The indentations are characterized before and following thermal annealing under various time and temperature conditions using confocal time-resolved photo-luminescence (CTP) imaging, and R/1 damage testing with 3-ns, 355-nm laser pulses. Improvements in the damage thresholds with reductions in CTP intensity are observed at temperatures well below the glass transition temperature (Tg). The damage threshold on 0.5-N indentations improves from <8 to >35  J/cm2 after annealing at approximately 750°C. Larger fracture networks require longer or higher temperature treatment to achieve similar results. At an annealing temperature >1100°C, optical microscopy indicates morphological changes in some of the fractures surrounding the indentations, although remnants of the original fractures are still observed. We demonstrate the potential of using isothermal annealing to improve the laser damage resistance of silica optics, and provide a means of further understanding the physics of optical damage and mitigation.

Paper Details

Date Published: 10 October 2012
PDF: 5 pages
Opt. Eng. 51(12) 121817 doi: 10.1117/1.OE.51.12.121817
Published in: Optical Engineering Volume 51, Issue 12
Show Author Affiliations
Nan Shen, Lawrence Livermore National Lab. (United States)
Philip E. Miller, Lawrence Livermore National Lab. (United States)
Jeffrey D. Bude, Lawrence Livermore National Lab. (United States)
Ted A. Laurence, Lawrence Livermore National Lab. (United States)
Tayyab I. Suratwala, Lawrence Livermore National Lab. (United States)
William A. Steele, Lawrence Livermore National Lab. (United States)
Michael D. Feit, Lawrence Livermore National Lab. (United States)
Lana L. Wong, Lawrence Livermore National Lab. (United States)

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