1 November 1990 Damage assessment and possible damage mechanisms to 1-meter diameter nova turning mirrors
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A major concern in the operation of the LLNL 120 kJ Nova laser system is damage to the nominal 1-meter diameter mirrors (i.e. HR coatings). The damage appears to originate from microscopic defects that vary in size up to approximately 30 pm in diameter. These defects produce damage sites up to 250 pm and, in some cases, covering 20% or more of the mirror surface. Defects due to particulates that are in or under the coating are highly unlikely due to the fact that coating thickness is only 5 pm thick and particles up to 30 pm would produce surface roughness that could be easily detected. Consequently, the defects must be plate-like (i.e. "2-D") in nature. A by-product of the damage is a haze left on the surface of the mirror. This haze is analyzed and shown to be blown-off particles of Zr02/Si02 coating material. The particle morphology suggests nucleation from a vapor phase which implies localized heating in the coating to temperatures on the order of 3000°K. Some possible damage mechanisms are also explored.
© (1990) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
G. Edwards, G. Edwards, } "Damage assessment and possible damage mechanisms to 1-meter diameter nova turning mirrors", Proc. SPIE 1438, Laser-Induced Damage in Optical Materials 1989, 14380T (1 November 1990); doi: 10.1117/12.2294438; https://doi.org/10.1117/12.2294438

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