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Effects of structural defects on laser-induced damage of 355-nm high-reflective coatings sputtered on etched substrates.

Authors :
Guo, Kesheng
Wang, Yanzhi
Chen, Ruiyi
Zhu, Meiping
Yi, Kui
He, Hongbo
Shao, Jianda
Source :
Optical Materials. Mar2019, Vol. 89, p173-177. 5p.
Publication Year :
2019

Abstract

Abstract Laser-induced damage of ultraviolet (UV) coatings poses a great challenge and restricts its application in space. Coatings prepared by ion beam sputtering are dense and possess high laser-induced damage threshold (LIDT), which are absence of structural nodule defects. Subsurface damage defects easily exposed by etching are inevitable under substrate grinding and polishing processes, which are usually ignored in electron-beam evaporation coatings. In our experiments, we find that LIDT of 355-nm high-reflection (HR) coatings sputtered on etched substrates declines dramatically, meanwhile defect density increases. Pits are found on the surface of the substrates and the coatings, and the pits that induce laser damage are very small (submicron-scale). Laser damage morphologies reveal that damage sites are prone to occur around the pits caused by acid etching. Finite element analysis shows consistent results, enhancement of electric field and rise of temperature are obvious, and the most significant part is around the pits, which is prone to induce damage. To conclude, small structural defects are sensitive to laser-induced damage of HR coatings prepared by dual ion beam sputtering (DIBS). This work contributes to finding new ways of improving the LIDT of sputtering coatings. Highlights • The structural defects on substrates are relatively small and shallow, the depth and the diameter of the pits are in the range of ∼50–120 nm and ∼400–600 nm, respectively. • The diameters of the pits on the surface of the coatings (DIBS) are larger than the substrate, which is different from the EBE coatings and indicates different growth process. • The LIDTs of our samples are sharply declined by the presence of the pits, the damage morphologies show thermal ablation. • High electric field and temperature by a FEA method are found at the edge of the pits on the surface of the coatings, which agrees with the experimental result. • The pits strongly enhance the thermal effect, which increases the possibility of damage of 355 nm IBS coatings. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
09253467
Volume :
89
Database :
Academic Search Index
Journal :
Optical Materials
Publication Type :
Academic Journal
Accession number :
135491885
Full Text :
https://doi.org/10.1016/j.optmat.2018.12.024