30 December 2008 Optimization of laser-damage resistance of evaporated hafnia films at 351nm
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Abstract
A systematic study was undertaken to improve the laser-damage resistance of multilayer high-reflector coatings for use at 351 nm on the OMEGA EP Laser System. A series of hafnium dioxide monolayer films deposited by electron-beam evaporation with varying deposition rates and oxygen backfill pressures were studied using transmission electron microscopy (TEM), x-ray diffraction (XRD), and refractive index modeling. These exhibit microstructural changes for sufficiently slow deposition rates and high oxygen backfill pressures, resulting in an absence of crystalline inclusions and a lower refractive index. Hafnia monolayers exhibited laser-damage resistance as high as 12 J/cm2 at 351 nm with a 0.5-ns pulse. This process was utilized in the fabrication of reduced electric-field-type multilayer high-reflector coatings. Measured laser-damage thresholds as high as 16.63 J/cm2 were achieved under identical test conditions, an exceptional improvement relative to historical damage thresholds of the order of 3 to 5 J/cm2.
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J. B. Oliver, S. Papernov, A. W. Schmid, J. C. Lambropoulos, "Optimization of laser-damage resistance of evaporated hafnia films at 351nm", Proc. SPIE 7132, Laser-Induced Damage in Optical Materials: 2008, 71320J (30 December 2008); doi: 10.1117/12.805383; https://doi.org/10.1117/12.805383
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