Impact of particle shape on the laser-contaminant interaction induced damage on the protective capping layer of 1high reflector mirror coatings

S. R. Qiu; M. A. Norton; J. Honig; A. M. Rubenchik; C. D. Boley; A. Rigatti; C. J. Stolz; M. J. Matthews

doi:10.1117/12.2195517

14 December 2015 Impact of particle shape on the laser-contaminant interaction induced damage on the protective capping layer of 1ω high reflector mirror coatings

S. R. Qiu, M. A. Norton, J. Honig, A. M. Rubenchik, C. D. Boley, A. Rigatti, C. J. Stolz, M. J. Matthews

Author Affiliations +

Proceedings Volume 9632, Laser-Induced Damage in Optical Materials: 2015; 963208 (2015) https://doi.org/10.1117/12.2195517
Event: SPIE Laser Damage, 2015, Boulder, Colorado, United States

Abstract

We report an investigation on the response to laser exposure of a protective capping layer of 1ω (1053 nm) high-reflector mirror coatings, in the presence of differently shaped Ti particles. We consider two candidate capping layer materials, namely SiO₂ and Al₂O₃. They are coated over multiple silica-hafnia multilayer coatings. Each sample is exposed to a single oblique (45°) shot of a 1053 nm laser beam (p polarization, fluence ~ 10 J/cm², pulse length 14 ns), in the presence of spherically or irregularly shaped Ti particles on the surface. We observe that the two capping layers show markedly different responses. For spherically shaped particles, the Al₂O₃ cap layer exhibits severe damage, with the capping layer becoming completely delaminated at the particle locations. In contrast, the SiO₂ capping layer is only mildly modified by a shallow depression, likely due to plasma erosion. For irregularly shaped Ti filings, the Al₂O₃ capping layer displays minimal to no damage while the SiO₂ capping layer is significantly damaged. In the case of the spherical particles, we attribute the different response of the capping layer to the large difference in thermal expansion coefficient of the materials, with that of the Al₂O₃ about 15 times greater than that of the SiO₂ layer. For the irregularly shaped filings, we attribute the difference in damage response to the large difference in mechanical toughness between the two materials, with that of the Al₂O₃ being about 10 times stronger than that of the SiO₂.

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S. R. Qiu, M. A. Norton, J. Honig, A. M. Rubenchik, C. D. Boley, A. Rigatti, C. J. Stolz, and M. J. Matthews "Impact of particle shape on the laser-contaminant interaction induced damage on the protective capping layer of 1ω high reflector mirror coatings", Proc. SPIE 9632, Laser-Induced Damage in Optical Materials: 2015, 963208 (14 December 2015); https://doi.org/10.1117/12.2195517

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